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+The Project Gutenberg EBook of Zoonomia, Vol. I, by Erasmus Darwin
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Zoonomia, Vol. I
+       Or, the Laws of Organic Life
+
+Author: Erasmus Darwin
+
+Release Date: April 25, 2005 [EBook #15707]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ZOONOMIA, VOL. I ***
+
+
+
+
+Produced by Greg Alethoup, Robert Shimmin, Keith Edkins and the
+Online Distributed Proofreading Team.
+
+
+
+
+
+ZOONOMIA;
+
+OR,
+
+THE LAWS
+
+OF
+
+ORGANIC LIFE.
+
+VOL. I.
+
+_By ERASMUS DARWIN, M.D. F.R.S._
+
+AUTHOR OF THE BOTANIC GARDEN.
+
+       *       *       *       *       *
+
+  Principiò coelum, ac terras, camposque liquentes,
+  Lucentemque globum lunæ, titaniaque astra,
+  Spiritus intùs alit, totamque infusa per artus
+  Mens agitat molem, et magno se corpore miscet.--VIRG. Æn. vi.
+
+  Earth, on whose lap a thousand nations tread,
+  And Ocean, brooding his prolific bed,
+  Night's changeful orb, blue pole, and silvery zones,
+  Where other worlds encircle other suns,
+  One Mind inhabits, one diffusive Soul
+  Wields the large limbs, and mingles with the whole.
+
+       *       *       *       *       *
+
+_THE SECOND EDITION, CORRECTED._
+
+       *       *       *       *       *
+
+LONDON:
+PRINTED FOR. J. JOHNSON, IN ST. PAUL'S CHURCH-YARD.
+1796.
+
+Entered at Stationers' Hall.
+
+       *       *       *       *       *
+
+DEDICATION.
+
+To the candid and ingenious Members of the College of Physicians, of the
+Royal Philosophical Society, of the Two Universities, and to all those, who
+study the Operations of the Mind as a Science, or who practice Medicine as
+a Profession, the subsequent Work is, with great respect, inscribed by the
+Author,
+
+DERBY, May 1, 1794.
+
+CONTENTS.
+
+            _Preface._
+  SECT. I.  _Of Motion._
+       II.  _Explanations and Definitions._
+      III.  _The Motions of the Retina demonstrated by Experiments._
+       IV.  _Laws of Animal Causation._
+        V.  _Of the four Faculties or Motions of the Sensorium._
+       VI.  _Of the four Classes of Fibrous Motions._
+      VII.  _Of Irritative Motions._
+     VIII.  _Of Sensitive Motions._
+       IX.  _Of Voluntary Motions._
+        X.  _Of Associate Motions._
+       XI.  _Additional Observations on the Sensorial Powers._
+      XII.  _Of Stimulus, Sensorial Exertion, and Fibrous Contraction._
+     XIII.  _Of Vegetable Animation._
+      XIV.  _Of the Production of Ideas._
+       XV.  _Of the Classes of Ideas._
+      XVI.  _Of Instinct._
+     XVII.  _The Catenation of Animal Motions._
+    XVIII.  _Of Sleep._
+      XIX.  _Of Reverie._
+       XX.  _Of Vertigo._
+      XXI.  _Of Drunkenness._
+     XXII.  _Of Propensity to Motion. Repetition. Imitation._
+    XXIII.  _Of the Circulatory System._
+     XXIV.  _Of the Secretion of Saliva, and of Tears. And of the
+            Lacrymal Sack._
+      XXV.  _Of the Stomach and Intestines._
+     XXVI.  _Of the Capillary Glands, and of the Membranes._
+    XXVII.  _Of Hemorrhages._
+   XXVIII.  _The Paralysis of the Lacteals._
+     XXIX.  _The Retrograde Motions of the Absorbent Vessels._
+      XXX.  _The Paralysis of the Liver._
+     XXXI.  _Of Temperaments._
+    XXXII.  _Diseases of Irritation._
+   XXXIII.  ---- _of Sensation._
+    XXXIV.  ---- _of Volition._
+     XXXV.  ---- _of Relation._
+    XXXVI.  _The Periods of Diseases._
+   XXXVII.  _Of Digestion, Secretion, Nutrition._
+  XXXVIII.  _Of the Oxygenation of the Blood in the Lungs and Placenta._
+    XXXIX.  _Of Generation._
+       XL.  _Of Ocular Spectra._
+
+       *       *       *       *       *
+
+TO
+
+ERASMUS DARWIN,
+
+ON HIS WORK INTITLED
+
+ZOONOMIA,
+
+_By DEWHURST BILSBORROW._
+
+       *       *       *       *       *
+
+  HAIL TO THE BARD! who sung, from Chaos hurl'd
+  How suns and planets form'd the whirling world;
+  How sphere on sphere Earth's hidden strata bend,
+  And caves of rock her central fires defend;
+  Where gems new-born their twinkling eyes unfold,               5
+  And young ores shoot in arborescent gold.
+    How the fair Flower, by Zephyr woo'd, unfurls
+  Its panting leaves, and waves its azure curls;
+  Or spreads in gay undress its lucid form
+  To meet the sun, and shuts it to the storm;                   10
+  While in green veins impassion'd eddies move,
+  And Beauty kindles into life and love.
+    How the first embryon-fibre, sphere, or cube,
+  Lives in new forms,--a line,--a ring,--a tube;
+  Closed in the womb with limbs unfinish'd laves,               15
+  Sips with rude mouth the salutary waves;
+  Seeks round its cell the sanguine streams, that pass,
+  And drinks with crimson gills the vital gas;
+  Weaves with soft threads the blue meandering vein,
+  The heart's red concave, and the silver brain;                20
+  Leads the long nerve, expands the impatient sense,
+  And clothes in silken skin the nascent Ens.
+    Erewhile, emerging from its liquid bed,
+  It lifts in gelid air its nodding head;
+  The lights first dawn with trembling eyelid hails,            25
+  With lungs untaught arrests the balmy gales;
+  Tries its new tongue in tones unknown, and hears
+  The strange vibrations with unpractised ears;
+  Seeks with spread hands the bosom's velvet orbs.
+  With closing lips the milky fount absorbs;                    30
+  And, as compress'd the dulcet streams distil,
+  Drinks warmth and fragrance from the living rill;--
+  Eyes with mute rapture every waving line,
+  Prints with adoring kiss the Paphian shrine,
+  And learns erelong, the perfect form confess'd,               35
+  Ideal Beauty from its mother's breast.
+    Now in strong lines, with bolder tints design'd,
+  You sketch ideas, and portray the mind;
+  Teach how fine atoms of impinging light
+  To ceaseless change the visual sense excite;                  40
+  While the bright lens collects the rays, that swerve,
+  And bends their focus on the moving nerve.
+  How thoughts to thoughts are link'd with viewless chains,
+  Tribes leading tribes, and trains pursuing trains;
+  With shadowy trident how Volition guides,                     45
+  Surge after surge, his intellectual tides;
+  Or, Queen of Sleep, Imagination roves
+  With frantic Sorrows, or delirious Loves.
+    Go on, O FRIEND! explore with eagle-eye;
+  Where wrapp'd in night retiring Causes lie:                   50
+  Trace their slight bands, their secret haunts betray,
+  And give new wonders to the beam of day;
+  Till, link by link with step aspiring trod,
+  You climb from NATURE to the throne of GOD.
+  --So saw the Patriarch with admiring eyes                     55
+  From earth to heaven a golden ladder rise;
+  Involv'd in clouds the mystic scale ascends,
+  And brutes and angels crowd the distant ends.
+
+TRIN. COL. CAMBRIDGE, _Jan._ 1, 1794.
+
+       *       *       *       *       *
+
+REFERENCES TO THE WORK.
+
+          _Botanic Garden._ Part I.
+
+  Line 1.  Canto I.  l. 105.
+  ---- 3.  ---- IV.  l. 402.
+  ---- 4.  ---- I.  l. 140.
+  ---- 5.  ---- III.  l. 401.
+  ---- 8.  ---- IV.  l. 452.
+  ---- 9.  ---- I.  l. 14.
+
+
+          _Zoonomia._
+
+  ---- 12.  Sect. XIII.
+  ---- 13.  ---- XXXIX. 4. 1.
+  ---- 18.  ---- XVI. 2. and XXXVIII.
+  ---- 26.  ---- XVI. 4.
+  ---- 30.  ---- XVI. 4.
+  ---- 36.  ---- XVI. 6.
+  ---- 38.  ---- III. and VII.
+  ---- 43.  ---- X.
+  ---- 44.  ---- XVIII. 17.
+  ---- 45.  ---- XVII. 3. 7.
+  ---- 47.  ---- XVIII. 8.
+  ---- 50.  ---- XXXIX. 4. 8.
+  ---- 51.  ---- XXXIX the Motto.
+  ---- 54.  ---- XXXIX. 8.
+
+       *       *       *       *       *
+
+PREFACE.
+
+       *       *       *       *       *
+
+The purport of the following pages is an endeavour to reduce the facts
+belonging to ANIMAL LIFE into classes, orders, genera, and species; and, by
+comparing them with each other, to unravel the theory of diseases. It
+happened, perhaps unfortunately for the inquirers into the knowledge of
+diseases, that other sciences had received improvement previous to their
+own; whence, instead of comparing the properties belonging to animated
+nature with each other, they, idly ingenious, busied themselves in
+attempting to explain the laws of life by those of mechanism and chemistry;
+they considered the body as an hydraulic machine, and the fluids as passing
+through a series of chemical changes, forgetting that animation was its
+essential characteristic.
+
+The great CREATOR of all things has infinitely diversified the works of his
+hands, but has at the same time stamped a certain similitude on the
+features of nature, that demonstrates to us, that _the whole is one family
+of one parent_. On this similitude is founded all rational analogy; which,
+so long as it is concerned in comparing the essential properties of bodies,
+leads us to many and important discoveries; but when with licentious
+activity it links together objects, otherwise discordant, by some fanciful
+similitude; it may indeed collect ornaments for wit and poetry, but
+philosophy and truth recoil from its combinations.
+
+The want of a theory, deduced from such strict analogy, to conduct the
+practice of medicine is lamented by its professors; for, as a great number
+of unconnected facts are difficult to be acquired, and to be reasoned from,
+the art of medicine is in many instances less efficacious under the
+direction of its wisest practitioners; and by that busy crowd, who either
+boldly wade in darkness, or are led into endless error by the glare of
+false theory, it is daily practised to the destruction of thousands; add to
+this the unceasing injury which accrues to the public by the perpetual
+advertisements of pretended nostrums; the minds of the indolent become
+superstitiously fearful of diseases, which they do not labour under; and
+thus become the daily prey of some crafty empyric.
+
+A theory founded upon nature, that should bind together the scattered facts
+of medical knowledge, and converge into one point of view the laws of
+organic life, would thus on many accounts contribute to the interest of
+society. It would capacitate men of moderate abilities to practise the art
+of healing with real advantage to the public; it would enable every one of
+literary acquirements to distinguish the genuine disciples of medicine from
+those of boastful effrontery, or of wily address; and would teach mankind
+in some important situations the _knowledge of themselves_.
+
+There are some modern practitioners, who declaim against medical theory in
+general, not considering that to think is to theorize; and that no one can
+direct a method of cure to a person labouring under disease without
+thinking, that is, without theorizing; and happy therefore is the patient,
+whose physician possesses the best theory.
+
+The words idea, perception, sensation, recollection, suggestion, and
+association, are each of them used in this treatise in a more limited sense
+than in the writers of metaphysic. The author was in doubt, whether he
+should rather have substituted new words instead of them; but was at length
+of opinion, that new definitions of words already in use would be less
+burthensome to the memory of the reader.
+
+A great part of this work has lain by the writer above twenty years, as
+some of his friends can testify: he had hoped by frequent revision to have
+made it more worthy the acceptance of the public; this however his other
+perpetual occupations have in part prevented, and may continue to prevent,
+as long as he may be capable of revising it; he therefore begs of the
+candid reader to accept of it in its present state, and to excuse any
+inaccuracies of expression, or of conclusion, into which the intricacy of
+his subject, the general imperfection of language, or the frailty he has in
+common with other men, may have betrayed him; and from which he has not the
+vanity to believe this treatise to be exempt.
+
+       *       *       *       *       *
+
+ZOONOMIA.
+
+       *       *       *       *       *
+
+SECT. I.
+
+OF MOTION.
+
+The whole of nature may be supposed to consist of two essences or
+substances; one of which may be termed spirit, and the other matter. The
+former of these possesses the power to commence or produce motion, and the
+latter to receive and communicate it. So that motion, considered as a
+cause, immediately precedes every effect; and, considered as an effect, it
+immediately succeeds every cause.
+
+The MOTIONS OF MATTER may be divided into two kinds, primary and secondary.
+The secondary motions are those, which are given to or received from other
+matter in motion. Their laws have been successfully investigated by
+philosophers in their treatises on mechanic powers. These motions are
+distinguished by this circumstance, that the velocity multiplied into the
+quantity of matter of the body acted upon is equal to the velocity
+multiplied into the quantity of matter of the acting body.
+
+The primary motions of matter may be divided into three classes, those
+belonging to gravitation, to chemistry, and to life; and each class has its
+peculiar laws. Though these three classes include the motions of solid,
+liquid, and aerial bodies; there is nevertheless a fourth division of
+motions; I mean those of the supposed ethereal fluids of magnetism,
+electricity, heat, and light; whose properties are not so well investigated
+as to be classed with sufficient accuracy.
+
+_1st._ The gravitating motions include the annual and diurnal rotation of
+the earth and planets, the flux and reflux of the ocean, the descent of
+heavy bodies, and other phænomena of gravitation. The unparalleled sagacity
+of the great NEWTON has deduced the laws of this class of motions from the
+simple principle of the general attraction of matter. These motions are
+distinguished by their tendency to or from the centers of the sun or
+planets.
+
+_2d._ The chemical class of motions includes all the various appearances of
+chemistry. Many of the facts, which belong to these branches of science,
+are nicely ascertained, and elegantly classed; but their laws have not yet
+been developed from such simple principles as those above-mentioned; though
+it is probable, that they depend on the specific attractions belonging to
+the particles of bodies, or to the difference of the quantity of attraction
+belonging to the sides and angles of those particles. The chemical motions
+are distinguished by their being generally attended with an evident
+decomposition or new combination of the active materials.
+
+_3d._ The third class includes all the motions of the animal and vegetable
+world; as well those of the vessels, which circulate their juices, and of
+the muscles, which perform their locomotion, as those of the organs of
+sense, which constitute their ideas.
+
+This last class of motion is the subject of the following pages; which,
+though conscious of their many imperfections, I hope may give some pleasure
+to the patient reader, and contribute something to the knowledge and to the
+cure of diseases.
+
+       *       *       *       *       *
+
+SECT. II.
+
+EXPLANATIONS AND DEFINITIONS.
+
+    I. _Outline of the animal economy._--II. 1. _Of the sensorium._ 2. _Of
+    the brain and nervous medulla._ 3. _A nerve._ 4. _A muscular fibre._ 5.
+    _The immediate organs of sense._ 6. _The external organs of sense._ 7.
+    _An idea or sensual motion._ 8. _Perception._ 9. _Sensation._ 10.
+    _Recollection and suggestion._ 11. _Habit, causation, association,
+    catenation._ 12. _Reflex ideas._ 13. _Stimulus defined._
+
+       *       *       *       *       *
+
+    As some explanations and definitions will be necessary in the
+    prosecution of the work, the reader is troubled with them in this
+    place, and is intreated to keep them in his mind as he proceeds, and to
+    take them for granted, till an apt opportunity occurs to evince their
+    truth; to which I shall premise a very short outline of the animal
+    economy.
+
+       *       *       *       *       *
+
+I.--1. The nervous system has its origin from the brain, and is distributed
+to every part of the body. Those nerves, which serve the senses,
+principally arise from that part of the brain, which is lodged in the head;
+and those, which serve the purposes of muscular motion, principally arise
+from that part of the brain, which is lodged in the neck and back, and
+which is erroneously called the spinal marrow. The ultimate fibrils of
+these nerves terminate in the immediate organs of sense and muscular
+fibres, and if a ligature be put on any part of their passage from the head
+or spine, all motion and perception cease in the parts beneath the
+ligature.
+
+2. The longitudinal muscular fibres compose the locomotive muscles, whose
+contractions move the bones of the limbs and trunk, to which their
+extremities are attached. The annular or spiral muscular fibres compose the
+vascular muscles, which constitute the intestinal canal, the arteries,
+veins, glands, and absorbent vessels.
+
+3. The immediate organs of sense, as the retina of the eye, probably
+consist of moving fibrils, with a power of contraction similar to that of
+the larger muscles above described.
+
+4. The cellular membrane consists of cells, which resemble those of a
+sponge, communicating with each other, and connecting together all the
+other parts of the body.
+
+5. The arterial system consists of the aortal and the pulmonary artery,
+which are attended through their whole course with their correspondent
+veins. The pulmonary artery receives the blood from the right chamber of
+the heart, and carries it to the minute extensive ramifications of the
+lungs, where it is exposed to the action of the air on a surface equal to
+that of the whole external skin, through the thin moist coats of those
+vessels, which are spread on the air-cells, which constitute the minute
+terminal ramifications of the wind-pipe. Here the blood changes its colour
+from a dark red to a bright scarlet. It is then collected by the branches
+of the pulmonary vein, and conveyed to the left chamber of the heart.
+
+6. The aorta is another large artery, which receives the blood from the
+left chamber of the heart, after it has been thus aerated in the lungs, and
+conveys it by ascending and descending branches to every other part of the
+system; the extremities of this artery terminate either in glands, as the
+salivary glands, lacrymal glands, &c. or in capillary vessels, which are
+probably less involuted glands; in these some fluid, as saliva, tears,
+perspiration, are separated from the blood; and the remainder of the blood
+is absorbed or drank up by branches of veins correspondent to the branches
+of the artery; which are furnished with valves to prevent its return; and
+is thus carried back, after having again changed its colour to a dark red,
+to the right chamber of the heart. The circulation of the blood in the
+liver differs from this general system; for the veins which drink up the
+refluent blood from those arteries, which are spread on the bowels and
+mesentery, unite into a trunk in the liver, and form a kind of artery,
+which is branched into the whole substance of the liver, and is called the
+vena portarum; and from which the bile is separated by the numerous hepatic
+glands, which constitute that viscus.
+
+7. The glands may be divided into three systems, the convoluted glands,
+such as those above described, which separate bile, tears, saliva, &c.
+Secondly, the glands without convolution, as the capillary vessels, which
+unite the terminations of the arteries and veins; and separate both the
+mucus, which lubricates the cellular membrane, and the perspirable matter,
+which preserves the skin moist and flexible. And thirdly, the whole
+absorbent system, consisting of the lacteals, which open their mouths into
+the stomach and intestines, and of the lymphatics, which open their mouths
+on the external surface of the body, and on the internal linings of all the
+cells of the cellular membrane, and other cavities of the body.
+
+These lacteal and lymphatic vessels are furnished with numerous valves to
+prevent the return of the fluids, which they absorb, and terminate in
+glands, called lymphatic glands, and may hence be considered as long necks
+or mouths belonging to these glands. To these they convey the chyle and
+mucus, with a part of the perspirable matter, and atmospheric moisture; all
+which, after having passed through these glands, and having suffered some
+change in them, are carried forward into the blood, and supply perpetual
+nourishment to the system, or replace its hourly waste.
+
+8. The stomach and intestinal canal have a constant vermicular motion,
+which carries forwards their contents, after the lacteals have drank up the
+chyle from them; and which is excited into action by the stimulus of the
+aliment we swallow, but which becomes occasionally inverted or retrograde,
+as in vomiting, and in the iliac passion.
+
+II. 1. The word _sensorium_ in the following pages is designed to express
+not only the medullary part of the brain, spinal marrow, nerves, organs of
+sense, and of the muscles; but also at the same time that living principle,
+or spirit of animation, which resides throughout the body, without being
+cognizable to our senses, except by its effects. The changes which
+occasionally take place in the sensorium, as during the exertions of
+volition, or the sensations of pleasure or pain, are termed _sensorial
+motions_.
+
+2. The similarity of the texture of the brain to that of the pancreas, and
+some other glands of the body, has induced the inquirers into this subject
+to believe, that a fluid, perhaps much more subtile than the electric aura,
+is separated from the blood by that organ for the purposes of motion and
+sensation. When we recollect, that the electric fluid itself is actually
+accumulated and given out voluntarily by the torpedo and the gymnotus
+electricus, that an electric shock will frequently stimulate into motion a
+paralytic limb, and lastly that it needs no perceptible tubes to convey it,
+this opinion seems not without probability; and the singular figure of the
+brain and nervous system seems well adapted to distribute it over every
+part of the body.
+
+For the medullary substance of the brain not only occupies the cavities of
+the head and spine, but passes along the innumerable ramifications of the
+nerves to the various muscles and organs of sense. In these it lays aside
+its coverings, and is intermixed with the slender fibres, which constitute
+those muscles and organs of sense. Thus all these distant ramifications of
+the sensorium are united at one of their extremities, that is, in the head
+and spine; and thus these central parts of the sensorium constitute a
+communication between all the organs of sense and muscles.
+
+3. A _nerve_ is a continuation of the medullary substance of the brain from
+the head or spine towards the other parts of the body, wrapped in its
+proper membrane.
+
+4. The _muscular fibres_ are moving organs intermixed with that medullary
+substance, which is continued along the nerves, as mentioned above. They
+are indued with the power of contraction, and are again elongated either by
+antagonist muscles, by circulating fluids, or by elastic ligaments. So the
+muscles on one side of the forearm bend the fingers by means of their
+tendons, and those on the other side of the fore-arm extend them again. The
+arteries are distended by the circulating blood; and in the necks of
+quadrupeds there is a strong elastic ligament, which assists the muscles,
+which elevate the head, to keep it in its horizontal position, and to raise
+it after it has been depressed.
+
+5. The _immediate organs of sense_ consist in like manner of moving fibres
+enveloped in the medullary substance above mentioned; and are erroneously
+supposed to be simply an expansion of the nervous medulla, as the retina of
+the eye, and the rete mucosum of the skin, which are the immediate organs
+of vision, and of touch. Hence when we speak of the contractions of the
+fibrous parts of the body, we shall mean both the contractions of the
+muscles, and those of the immediate organs of sense. These _fibrous
+motions_ are thus distinguished from the _sensorial motions_ above
+mentioned.
+
+6. The _external organs_ of sense are the coverings of the immediate organs
+of sense, and are mechanically adapted for the reception or transmission of
+peculiar bodies, or of their qualities, as the cornea and humours of the
+eye, the tympanum of the ear, the cuticle of the fingers and tongue.
+
+7. The word _idea_ has various meanings in the writers of metaphysic: it is
+here used simply for those notions of external things, which our organs of
+sense bring us acquainted with originally; and is defined a contraction, or
+motion, or configuration, of the fibres, which constitute the immediate
+organ of sense; which will be explained at large in another part of the
+work. Synonymous with the word idea, we shall sometimes use the words
+_sensual motion_ in contradistinction to _muscular motion_.
+
+8. The word _perception_ includes both the action of the organ of sense in
+consequence of the impact of external objects, and our attention to that
+action; that is, it expresses both the motion of the organ of sense, or
+idea, and the pain or pleasure that succeeds or accompanies it.
+
+9. The pleasure or pain which necessarily accompanies all those perceptions
+or ideas which we attend to, either gradually subsides, or is succeeded by
+other fibrous motions. In the latter case it is termed _sensation_, as
+explained in Sect. V. 2, and VI. 2.--The reader is intreated to keep this
+in his mind, that through all this treatise the word sensation is used to
+express pleasure or pain only in its active state, by whatever means it is
+introduced into the system, without any reference to the stimulation of
+external objects.
+
+10. The vulgar use of the word _memory_ is too unlimited for our purpose:
+those ideas which we voluntarily recall are here termed ideas of
+_recollection_, as when we will to repeat the alphabet backwards. And those
+ideas which are suggested to us by preceding ideas are here termed ideas of
+_suggestion_, as whilst we repeat the alphabet in the usual order; when by
+habits previously acquired B is suggested by A, and C by B, without any
+effort of deliberation.
+
+11. The word _association_ properly signifies a society or convention of
+things in some respects similar to each other. We never say in common
+language, that the effect is associated with the cause, though they
+necessarily accompany or succeed each other. Thus the contractions of our
+muscles and organs of sense may be said to be associated together, but
+cannot with propriety be said to be associated with irritations, or with
+volition, or with sensation; because they are caused by them, as mentioned
+in Sect. IV. When fibrous contractions succeed other fibrous contractions,
+the connection is termed _association_; when fibrous contractions succeed
+sensorial motions, the connection is termed _causation_; when fibrous and
+sensorial motions reciprocally introduce each other in progressive trains
+or tribes, it is termed _catenation_ of animal motions. All these
+connections are said to be produced by _habit_; that is, by frequent
+repetition.
+
+12. It may be proper to observe, that by the unavoidable idiom of our
+language the ideas of perception, of recollection, or of imagination, in
+the plural number signify the ideas belonging to perception, to
+recollection, or to imagination; whilst the idea of perception, of
+recollection, or of imagination, in the singular number is used for what is
+termed "a reflex idea of any of those operations of the sensorium."
+
+13. By the word _stimulus_ is not only meant the application of external
+bodies to our organs of sense and muscular fibres, which excites into
+action the sensorial power termed irritation; but also pleasure or pain,
+when they excite into action the sensorial power termed sensation; and
+desire or aversion, when they excite into action the power of volition; and
+lastly, the fibrous contractions which precede association; as is further
+explained in Sect. XII. 2. 1.
+
+       *       *       *       *       *
+
+SECT. III.
+
+THE MOTIONS OF THE RETINA DEMONSTRATED BY EXPERIMENTS.
+
+    I. _Of animal motions and of ideas._ II. _The fibrous structure of the
+    retina._ III. _The activity of the retina in vision._ 1. _Rays of light
+    have no momentum._ 2. _Objects long viewed become fainter._ 3. _Spectra
+    of black objects become luminous._ 4. _Varying spectra from gyration._
+    5. _From long inspection of various colours._ IV. _Motions of the
+    organs of sense constitute ideas._ 1. _Light from pressing the
+    eye-ball, and sound from the pulsation of the carotid artery._ 2.
+    _Ideas in sleep mistaken for perceptions._ 3. _Ideas of imagination
+    produce pain and sickness like sensations._ 4. _When the organ of sense
+    is destroyed, the ideas belonging to that sense perish._ V. _Analogy
+    between muscular motions and sensual motions, or ideas._ 1. _They are
+    both originally excited by irritations._ 2. _And associated together in
+    the same manner._ 3. _Both act in nearly the same times._ 4. _Are alike
+    strengthened or fatigued by exercise._ 5. _Are alike painful from
+    inflammation._ 6. _Are alike benumbed by compression._ 7. _Are alike
+    liable to paralysis._ 8. _To convulsion._ 9. _To the influence of old
+    age._--VI. _Objections answered._ 1. _Why we cannot invent new ideas._
+    2. _If ideas resemble external objects._ 3. _Of the imagined sensation
+    in an amputated limb._ 4. _Abstract ideas._--VII. _What are ideas, if
+    they are not animal motions?_
+
+Before the great variety of animal motions can be duly arranged into
+natural classes and orders, it is necessary to smooth the way to this yet
+unconquered field of science, by removing some obstacles which thwart our
+passage. I. To demonstrate that the retina and other immediate organs of
+sense possess a power of motion, and that these motions constitute our
+ideas, according to the fifth and seventh of the preceding assertions,
+claims our first attention.
+
+Animal motions are distinguished from the communicated motions, mentioned
+in the first section, as they have no mechanical proportion to their cause;
+for the goad of a spur on the skin of a horse shall induce him to move a
+load of hay. They differ from the gravitating motions there mentioned as
+they are exerted with equal facility in all directions, and they differ
+from the chemical class of motions, because no apparent decompositions or
+new combinations are produced in the moving materials.
+
+Hence, when we say animal motion is excited by irritation, we do not mean
+that the motion bears any proportion to the mechanical impulse of the
+stimulus; nor that it is affected by the general gravitation of the two
+bodies; nor by their chemical properties, but solely that certain animal
+fibres are excited into action by something external to the moving organ.
+
+In this sense the stimulus of the blood produces the contractions of the
+heart; and the substances we take into our stomach and bowels stimulate
+them to perform their necessary functions. The rays of light excite the
+retina into animal motion by their stimulus; at the same time that those
+rays of light themselves are physically converged to a focus by the
+inactive humours of the eye. The vibrations of the air stimulate the
+auditory nerve into animal action; while it is probable that the tympanum
+of the ear at the same time undergoes a mechanical vibration.
+
+To render this circumstance more easy to be comprehended, _motion may be
+defined to be a variation of figure_; for the whole universe may be
+considered as one thing possessing a certain figure; the motions of any of
+its parts are a variation of this figure of the whole: this definition of
+motion will be further explained in Section XIV. 2. 2. on the production of
+ideas.
+
+Now the motions of an organ of sense are a succession of configurations of
+that organ; these configurations succeed each other quicker or slower; and
+whatever configuration of this organ of sense, that is, whatever portion of
+the motion of it is, or has usually been, attended to, constitutes an idea.
+Hence the configuration is not to be considered as an effect of the motion
+of the organ, but rather as a part or temporary termination of it; and
+that, whether a pause succeeds it, or a new configuration immediately takes
+place. Thus when a succession of moving objects are presented to our view,
+the ideas of trumpets, horns, lords and ladies, trains and canopies, are
+configurations, that is, parts or links of the successive motions of the
+organ of vision.
+
+[Illustration: Plate I.]
+
+These motions or configurations of the organs of sense differ from the
+sensorial motions to be described hereafter, as they appear to be simply
+contractions of the fibrous extremities of those organs, and in that
+respect exactly resemble the motions or contractions of the larger muscles,
+as appears from the following experiment. Place a circular piece of red
+silk about an inch in diameter on a sheet of white paper in a strong light,
+as in Plate I.--look for a minute on this area, or till the eye becomes
+somewhat fatigued, and then, gently closing your eyes, and shading them
+with your hand, a circular green area of the same apparent diameter becomes
+visible in the closed eye. This green area is the colour reverse to the red
+area, which had been previously inspected, as explained in the experiments
+on ocular spectra at the end of the work, and in Botanical Garden, P. 1.
+additional note, No. 1. Hence it appears, that a part of the retina, which
+had been fatigued by contraction in one direction, relieves itself by
+exerting the antagonist fibres, and producing a contraction in an opposite
+direction, as is common in the exertions of our muscles. Thus when we are
+tired with long action of our arms in one direction, as in holding a bridle
+on a journey, we occasionally throw them into an opposite position to
+relieve the fatigued muscles.
+
+Mr. Locke has defined an idea to be "whatever is present to the mind;" but
+this would include the exertions of volition, and the sensations of
+pleasure and pain, as well as those operations of our system, which
+acquaint us with external objects; and is therefore too unlimited for our
+purpose. Mr. Lock seems to have fallen into a further error, by conceiving,
+that the mind could form a general or abstract idea by its own operation,
+which was the copy of no particular perception; as of a triangle in
+general, that was neither acute, obtuse, nor right angled. The ingenious
+Dr. Berkley and Mr. Hume have demonstrated, that such general ideas have no
+existence in nature, not even in the mind of their celebrated inventor. We
+shall therefore take for granted at present, that our recollection or
+imagination of external objects consists of a partial repetition of the
+perceptions, which were excited by those external objects, at the time we
+became acquainted with them; and that our reflex ideas of the operations of
+our minds are partial repetitions of those operations.
+
+II. The following article evinces that the organ of vision consists of a
+fibrous part as well as of the nervous medulla, like other white muscles;
+and hence, as it resembles the muscular parts of the body in its structure,
+we may conclude, that it must resemble them in possessing a power of being
+excited into animal motion.--The subsequent experiments on the optic nerve,
+and on the colours remaining in the eye, are copied from a paper on ocular
+spectra published in the seventy-sixth volume of the Philos. Trans. by Dr.
+R. Darwin of Shrewsbury; which, as I shall have frequent occasion to refer
+to, is reprinted in this work, Sect. XL. The retina of an ox's eye was
+suspended in a glass of warm water, and forcibly torn in a few places; the
+edges of these parts appeared jagged and hairy, and did not contract and
+become smooth like simple mucus, when it is distended till it breaks; which
+evinced that it consisted of fibres. This fibrous construction became still
+more distinct to the light by adding some caustic alcali to the water; as
+the adhering mucus was first eroded, and the hair-like fibres remained
+floating in the vessel. Nor does the degree of transparency of the retina
+invalidate this evidence of its fibrous structure, since Leeuwenhoek has
+shewn, that the crystalline humour itself consists of fibres. Arc. Nat. V.
+I. 70.
+
+Hence it appears, that as the muscles consist of larger fibres intermixed
+with a smaller quantity of nervous medulla, the organ of vision consists of
+a greater quantity of nervous medulla intermixed with smaller fibres. It is
+probable that the locomotive muscles of microscopic animals may have
+greater tenuity than these of the retina; and there is reason to conclude
+from analogy, that the other immediate organs of sense, as the portio
+mollis of the auditory nerve, and the rete mucosum of the skin, possess a
+similarity of structure with the retina, and a similar power of being
+excited into animal motion.
+
+III. The subsequent articles shew, that neither mechanical impressions, nor
+chemical combinations of light, but that the animal activity of the retina
+constitutes vision.
+
+1. Much has been conjectured by philosophers about the momentum of the rays
+of light; to subject this to experiment a very light horizontal balance was
+constructed by Mr. Michel, with about an inch square of thin leaf-copper
+suspended at each end of it, as described in Dr. Priestley's History of
+Light and Colours. The focus of a very large convex mirror was thrown by
+Dr. Powel, in his lectures on experimental philosophy, in my presence, on
+one wing of this delicate balance, and it receded from the light; thrown on
+the other wing, it approached towards the light, and this repeatedly; so
+that no sensible impulse could be observed, but what might well be ascribed
+to the ascent of heated air.
+
+Whence it is reasonable to conclude, that the light of the day must be much
+too weak in its dilute state to make any mechanical impression on so
+tenacious a substance as the retina of the eye.--Add to this, that as the
+retina is nearly transparent, it could therefore make less resistance to
+the mechanical impulse of light; which, according, to the observations
+related by Mr. Melvil in the Edinburgh Literary Essays, only communicates
+heat, and should therefore only communicate momentum, where it is
+obstructed, reflected, or refracted.--From whence also may be collected the
+final cause of this degree of transparency of the retina, viz. left by the
+focus of stronger lights, heat and pain should have been produced in the
+retina, instead of that stimulus which excites it into animal motion.
+
+2. On looking long on an area of scarlet silk of about an inch in diameter
+laid on white paper, as in Plate I. the scarlet colour becomes fainter,
+till at length it entirely vanishes, though the eye is kept uniformly and
+steadily upon it. Now if the change or motion of the retina was a
+mechanical impression, or a chemical tinge of coloured light, the
+perception would every minute become stronger and stronger,--whereas in
+this experiment it becomes every instant weaker and weaker. The same
+circumstance obtains in the continued application of sound, or of sapid
+bodies, or of odorous ones, or of tangible ones, to their adapted organs of
+sense.
+
+[Illustration: Plate II.]
+
+Thus when a circular coin, as a shilling, is pressed on the palm of the
+hand, the sense of touch is mechanically compressed; but it is the stimulus
+of this pressure that excites the organ of touch into animal action, which
+constitutes the perception of hardness and of figure; for in some minutes
+the perception ceases, though the mechanical pressure of the object
+remains.
+
+3. Make with ink on white paper a very black spot about half an inch in
+diameter, with a tail about an inch in length, so as to resemble a tadpole,
+as in Plate II.; look steadfastly for a minute on the center of this spot,
+and, on moving the eye a little, the figure of the tadpole will be seen on
+the white part of the paper; which figure of the tadpole will appear more
+luminous than the other part of the white paper; which can only be
+explained by supposing that a part of the retina, on which the tadpole was
+delineated, to have become more sensible to light than the other parts of
+it, which were exposed to the white paper; and not from any idea of
+mechanical impression or chemical combination of light with the retina.
+
+4. When any one turns round rapidly, till he becomes dizzy, and falls upon
+the ground, the spectra of the ambient objects continue to present
+themselves in rotation, and he seems to behold the objects still in motion.
+Now if these spectra were impressions on a passive organ, they either must
+continue as they were received last, or not continue at all.
+
+5. Place a piece of red silk about an inch in diameter on a sheet of white
+paper in a strong light, as in Plate I; look steadily upon it from the
+distance of about half a yard for a minute; then closing your eye-lids,
+cover them with your hands and handkerchief, and a green spectrum will be
+seen in your eyes resembling in form the piece of red silk. After some
+seconds of time the spectrum will disappear, and in a few more seconds will
+reappear; and thus alternately three or four times, if the experiment be
+well made, till at length it vanishes entirely.
+
+[Illustration: Plate III.]
+
+6. Place a circular piece of white paper, about four inches in diameter, in
+the sunshine, cover the center of this with a circular piece of black silk,
+about three inches in diameter; and the center of the black silk with a
+circle of pink silk, about two inches in diameter; and the center of the
+pink silk with a circle of yellow silk, about one inch in diameter; and the
+center of this with a circle of blue silk, about half an inch in diameter;
+make a small spot with ink in the center of the blue silk, as in Plate
+III.; look steadily for a minute on this central spot, and then closing
+your eyes, and applying your hand at about an inch distance before them, so
+as to prevent too much or too little light from passing through the
+eye-lids, and you will see the most beautiful circles of colours that
+imagination can conceive; which are most resembled by the colours
+occasioned by pouring a drop or two of oil on a still lake in a bright day.
+But these circular irises of colours are not only different from the
+colours of the silks above mentioned, but are at the same time perpetually
+changing as long as they exist.
+
+From all these experiments it appears, that these spectra in the eye are
+not owing to the mechanical impulse of light impressed on the retina; nor
+to its chemical combination with that organ; nor to the absorption and
+emission of light, as is supposed, perhaps erroneously, to take place in
+calcined shells and other phosphorescent bodies, after having been exposed
+to the light: for in all these cases the spectra in the eye should either
+remain of the same colour, or gradually decay, when the object is
+withdrawn; and neither their evanescence during the presence of their
+object, as in the second experiment, nor their change from dark to
+luminous, as in the third experiment, nor their rotation, as in the fourth
+experiment, nor the alternate presence and evanescence of them, as in the
+fifth experiment, nor the perpetual change of colours of them, as in the
+last experiment, could exist.
+
+IV. The subsequent articles shew, that these animal motions or
+configurations of our organs of sense constitute our ideas.
+
+1. If any one in the dark presses the ball of his eye, by applying his
+finger to the external corner of it, a luminous appearance is observed; and
+by a smart stroke on the eye great slashes of fire are perceived. (Newton's
+Optics.) So that when the arteries, that are near the auditory nerve, make
+stronger pulsations than usual, as in some fevers, an undulating sound is
+excited in the ears. Hence it is not the presence of the light and sound,
+but the motions of the organ, that are immediately necessary to constitute
+the perception or idea of light and sound.
+
+2. During the time of sleep, or in delirium, the ideas of imagination are
+mistaken for the perceptions of external objects; whence it appears, that
+these ideas of imagination, are no other than a reiteration of those
+motions of the organs of sense, which were originally excited by the
+stimulus of external objects: and in our waking hours the simple ideas,
+that we call up by recollection or by imagination, as the colour of red, or
+the smell of a rose, are exact resemblances of the same simple ideas from
+perception; and in consequence must be a repetition of those very motions.
+
+3. The disagreeable sensation called the tooth-edge is originally excited
+by the painful jarring of the teeth in biting the edge of the glass, or
+porcelain cup, in which our food was given us in our infancy, as is further
+explained in the Section XVI. 10, on Instinct.--This disagreeable sensation
+is afterwards excitable not only by a repetition of the sound, that was
+then produced, but by imagination alone, as I have myself frequently
+experienced; in this case the idea of biting a china cup, when I imagine it
+very distinctly, or when I see another person bite a cup or glass, excites
+an actual pain in the nerves of my teeth. So that this idea and pain seem
+to be nothing more than the reiterated motions of those nerves, that were
+formerly so disagreeably affected.
+
+Other ideas that are excited by imagination or recollection in many
+instances produce similar effects on the constitution, as our perceptions
+had formerly produced, and are therefore undoubtedly a repetition of the
+same motions. A story which the celebrated Baron Van Swieton relates of
+himself is to this purpose. He was present when the putrid carcase of a
+dead dog exploded with prodigious stench; and some years afterwards,
+accidentally riding along the same road, he was thrown into the same
+sickness and vomiting by the idea of the stench, as he had before
+experienced from the perception of it.
+
+4. Where the organ of sense is totally destroyed, the ideas which were
+received by that organ seem to perish along with it, as well as the power
+of perception. Of this a satisfactory instance has fallen under my
+observation. A gentleman about sixty years of age had been totally deaf for
+near thirty years: he appeared to be a man of good understanding, and
+amused himself with reading, and by conversing either by the use of the
+pen, or by signs made with his fingers, to represent letters. I observed
+that he had so far forgot the pronunciation of the language, that when he
+attempted to speak, none of his words had distinct articulation, though his
+relations could sometimes understand his meaning. But, which is much to the
+point, he assured me, that in his dreams he always imagined that people
+conversed with him by signs or writing, and never that he heard any one
+speak to him. From hence it appears, that with the perceptions of sounds he
+has also lost the ideas of them; though the organs of speech still retain
+somewhat of their usual habits of articulation.
+
+This observation may throw some light on the medical treatment of deaf
+people; as it may be learnt from their dreams whether the auditory nerve be
+paralytic, or their deafness be owing to some defect of the external organ.
+
+It rarely happens that the immediate organ of vision is perfectly
+destroyed. The most frequent causes of blindness are occasioned by defects
+of the external organ, as in cataracts and obfuscations of the cornea. But
+I have had the opportunity of conversing with two men, who had been some
+years blind; one of them had a complete gutta serena, and the other had
+lost the whole substance of his eyes. They both told me that they did not
+remember to have ever dreamt of visible objects, since the total loss of
+their sight.
+
+V. Another method of discovering that our ideas are animal motions of the
+organs of sense, is from considering the great analogy they bear to the
+motions of the larger muscles of the body. In the following articles it
+will appear that they are originally excited into action by the irritation
+of external objects like our muscles; are associated together like our
+muscular motions; act in similar time with them; are fatigued by continued
+exertion like them; and that the organs of sense are subject to
+inflammation, numbness, palsy, convulsion, and the defects of old age, in
+the same manner as the muscular fibres.
+
+1. All our perceptions or ideas of external objects are universally allowed
+to have been originally excited by the stimulus of those external objects;
+and it will be shewn in a succeeding section, that it is probable that all
+our muscular motions, as well those that are become voluntary as those of
+the heart and glandular system, were originally in like manner excited by
+the stimulus of something external to the organ of motion.
+
+2. Our ideas are also associated together after their production precisely
+in the same manner as our muscular motions; which will likewise be fully
+explained in the succeeding section.
+
+3. The time taken up in performing an idea is likewise much the same as
+that taken up in performing a muscular motion. A musician can press the
+keys of an harpsichord with his fingers in the order of a tune he has been
+accustomed to play, in as little time as he can run over those notes in his
+mind. So we many times in an hour cover our eye-balls with our eye-lids
+without perceiving that we are in the dark; hence the perception or idea of
+light is not changed for that of darkness in so small a time as the
+twinkling of an eye; so that in this case the muscular motion of the
+eye-lid is performed quicker than the perception of light can be changed
+for that of darkness.--So if a fire-stick be whirled round in the dark, a
+luminous circle appears to the observer; if it be whirled somewhat slower,
+this circle becomes interrupted in one part; and then the time taken up in
+such a revolution of the stick is the same that the observer uses in
+changing his ideas: thus the [Greek: dolikoskoton enkos] of Homer, the long
+shadow of the flying javelin, is elegantly designed to give us an idea of
+its velocity, and not of its length.
+
+4. The fatigue that follows a continued attention of the mind to one object
+is relieved by changing the subject of our thoughts; as the continued
+movement of one limb is relieved by moving another in its stead. Whereas a
+due exercise of the faculties of the mind strengthens and improves those
+faculties, whether of imagination or recollection; as the exercise of our
+limbs in dancing or fencing increases the strength and agility of the
+muscles thus employed.
+
+5. If the muscles of any limb are inflamed, they do not move without pain;
+so when the retina is inflamed, its motions also are painful. Hence light
+is as intolerable in this kind of ophthalmia, as pressure is to the finger
+in the paronychia. In this disease the patients frequently dream of having
+their eyes painfully dazzled; hence the idea of strong light is painful as
+well as the reality. The first of these facts evinces that our perceptions
+are motions of the organs of sense; and the latter, that our imaginations
+are also motions of the same organs.
+
+6. The organs of sense, like the moving muscles, are liable to become
+benumbed, or less sensible, from compression. Thus, if any person on a
+light day looks on a white wall, he may perceive the ramifications of the
+optic artery, at every pulsation of it, represented by darker branches on
+the white wall; which is evidently owing to its compressing the retina
+during the diastole of the artery. Savage Nosolog.
+
+7. The organs of sense and the moving muscles are alike liable to be
+affected with palsy, as in the gutta serena, and in some cases of deafness;
+and one side of the face has sometimes lost its power of sensation, but
+retained its power of motion; other parts of the body have lost their
+motions but retained their sensation, as in the common hemiplagia; and in
+other instances both these powers have perished together.
+
+8. In some convulsive diseases a delirium or insanity supervenes, and the
+convulsions cease; and conversely the convulsions shall supervene, and the
+delirium cease. Of this I have been a witness many times in a day in the
+paroxysms of violent epilepsies; which evinces that one kind of delirium is
+a convulsion of the organs of sense, and that our ideas are the motions of
+these organs: the subsequent cases will illustrate this observation.
+
+Miss G----, a fair young lady, with light eyes and hair, was seized with
+most violent convulsions of her limbs, with outrageous hiccough, and most
+vehement efforts to vomit: after near an hour was elapsed this tragedy
+ceased, and a calm talkative delirium supervened for about another hour;
+and these relieved each other at intervals during the greatest part of
+three or four days. After having carefully considered this disease, I
+thought the convulsions of her ideas less dangerous than those of her
+muscles; and having in vain attempted to make any opiate continue in her
+stomach, an ounce of laudanum was rubbed along the spine of her back, and a
+dram of it was used as an enema; by this medicine a kind of drunken
+delirium was continued many hours; and when it ceased the convulsions did
+not return; and the lady continued well many years, except some lighter
+relapses, which were relieved in the same manner.
+
+Miss H----, an accomplished young lady, with light eyes and hair, was
+seized with convulsions of her limbs, with hiccough, and efforts to vomit,
+more violent than words can express; these continued near an hour, and were
+succeeded with a cataleptic spasm of one arm, with the hand applied to her
+head; and after about twenty minutes these spasms ceased, and a talkative
+reverie supervened for near an other hour, from which no violence, which it
+was proper to use, could awaken her. These periods of convulsions, first of
+the muscles, and then of the ideas, returned twice a day for several weeks;
+and were at length removed by great doses of opium, after a great variety
+of other medicines and applications had been in vain experienced. This lady
+was subject to frequent relapses, once or twice a year for many years, and
+was as frequently relieved by the same method.
+
+Miss W----, an elegant young lady, with black eyes and hair, had sometimes
+a violent pain of her side, at other times a most painful strangury, which
+were every day succeeded by delirium; which gave a temporary relief to the
+painful spasms. After the vain exhibition of variety of medicines and
+applications by different physicians, for more than a twelvemonth, she was
+directed to take some doses of opium, which were gradually increased, by
+which a drunken delirium was kept up for a day or two, and the pains
+prevented from returning. A flesh diet, with a little wine or beer, instead
+of the low regimen she had previously used, in a few weeks completely
+established her health; which, except a few relapses, has continued for
+many years.
+
+9. Lastly, as we advance in life all the parts of the body become more
+rigid, and are rendered less susceptible of new habits of motion, though
+they retain those that were before established. This is sensibly observed
+by those who apply themselves late in life to music, fencing, or any of the
+mechanic arts. In the same manner many elderly people retain the ideas they
+had learned early in life, but find great difficulty in acquiring new
+trains of memory; insomuch that in extreme old age we frequently see a
+forgetfulness of the business of yesterday, and at the same time a
+circumstantial remembrance of the amusements of their youth; till at length
+the ideas of recollection and activity of the body gradually cease
+together,--such is the condition of humanity!--and nothing remains but the
+vital motions and sensations.
+
+VI. 1. In opposition to this doctrine of the production of our ideas, it
+may be asked, if some of our ideas, like other animal motions, are
+voluntary, why can we not invent new ones, that have not been received by
+perception? The answer will be better understood after having perused the
+succeeding section, where it will be explained, that the muscular motions
+likewise are originally excited by the stimulus of bodies external to the
+moving organ; and that the will has only the power of repeating the motions
+thus excited.
+
+2. Another objector may ask, Can the motion of an organ of sense resemble
+an odour or a colour? To which I can only answer, that it has not been
+demonstrated that any of our ideas resemble the objects that excite them;
+it has generally been believed that they do not; but this shall be
+discussed at large in Sect. XIV.
+
+3. There is another objection that at first view would seem less easy to
+surmount. After the amputation, of a foot or a finger, it has frequently
+happened, that an injury being offered to the stump of the amputated limb,
+whether from cold air, too great pressure, or other accidents, the patient
+has complained, of a sensation of pain in the foot or finger, that was cut
+off. Does not this evince that all our ideas are excited in the brain, and
+not in the organs of sense? This objection is answered, by observing that
+our ideas of the shape, place, and solidity of our limbs, are acquired by
+our organs of touch and of sight, which are situated in our fingers and
+eyes, and not by any sensations in the limb itself.
+
+In this case the pain or sensation, which formerly has arisen in the foot
+or toes, and been propagated along the nerves to the central part of the
+sensorium, was at the same time accompanied with a visible idea of the
+shape and place, and with a tangible idea of the solidity of the affected
+limb: now when these nerves are afterwards affected by any injury done to
+the remaining stump with a similar degree or kind of pain, the ideas of the
+shape, place, or solidity of the lost limb, return by association; as these
+ideas belong to the organs of sight and touch, on which they were first
+excited.
+
+4. If you wonder what organs of sense can be excited into motion, when you
+call up the ideas of wisdom or benevolence, which Mr. Locke has termed
+abstracted ideas; I ask you by what organs of sense you first became
+acquainted with these ideas? And the answer will be reciprocal; for it is
+certain that all our ideas were originally acquired by our organs of sense;
+for whatever excites our perception must be external to the organ that
+perceives it, and we have no other inlets to knowledge but by our
+perceptions: as will be further explained in Section XIV. and XV. on the
+Productions and Classes of Ideas.
+
+VII. If our recollection or imagination be not a repetition of animal
+movements, I ask, in my turn, What is it? You tell me it consists of images
+or pictures of things. Where is this extensive canvas hung up? or where are
+the numerous receptacles in which those are deposited? or to what else in
+the animal system have they any similitude?
+
+That pleasing picture of objects, represented in miniature on the retina of
+the eye, seems to have given rise to this illusive oratory! It was forgot
+that this representation belongs rather to the laws of light, than to those
+of life; and may with equal elegance be seen in the camera obscura as in
+the eye; and that the picture vanishes for ever, when the object is
+withdrawn.
+
+       *       *       *       *       *
+
+SECT. IV.
+
+LAWS OF ANIMAL CAUSATION.
+
+I. The fibres, which constitute the muscles and organs of sense, possess a
+power of contraction. The circumstances attending the exertion of this
+power of CONTRACTION constitute the laws of animal motion, as the
+circumstances attending the exertion of the power of ATTRACTION constitute
+the laws of motion of inanimate matter.
+
+II. The spirit of animation is the immediate cause of the contraction of
+animal fibres, it resides in the brain and nerves, and is liable to general
+or partial diminution or accumulation.
+
+III. The stimulus of bodies external to the moving organ is the remote
+cause of the original contractions of animal fibres.
+
+IV. A certain quantity of stimulus produces irritation, which is an
+exertion of the spirit of animation exciting the fibres into contraction.
+
+V. A certain quantity of contraction of animal fibres, if it be perceived
+at all, produces pleasure; a greater or less quantity of contraction, if it
+be perceived at all, produces pain; these constitute sensation.
+
+VI. A certain quantity of sensation produces desire or aversion; these
+constitute volition.
+
+VII. All animal motions which have occurred at the same time, or in
+immediate succession, become so connected, that when one of them is
+reproduced, the other has a tendency to accompany or succeed it. When
+fibrous contractions succeed or accompany other fibrous contractions, the
+connection is termed association; when fibrous contractions succeed
+sensorial motions, the connexion is termed causation; when fibrous and
+sensorial motions reciprocally introduce each other, it is termed
+catenation of animal motions. All these connections are said to be produced
+by habit, that is, by frequent repetition. These laws of animal causation
+will be evinced by numerous facts, which occur in our daily exertions; and
+will afterwards be employed to explain the more recondite phænomena of the
+production, growth, diseases, and decay of the animal system.
+
+       *       *       *       *       *
+
+SECT. V.
+
+OF THE FOUR FACULTIES OR MOTIONS OF THE SENSORIUM.
+
+    1. _Four sensorial powers._ 2. _Irritation, sensation, volition,
+    association defined._ 3. _Sensorial motions distinguished from fibrous
+    motions._
+
+1. The spirit of animation has four different modes of action, or in other
+words the animal sensorium possesses four different faculties, which are
+occasionally exerted, and cause all the contractions of the fibrous parts
+of the body. These are the faculty of causing fibrous contractions in
+consequence of the irritations excited by external bodies, in consequence
+of the sensations of pleasure or pain, in consequence of volition, and in
+consequence of the associations of fibrous contractions with other fibrous
+contractions, which precede or accompany them.
+
+These four faculties of the sensorium during their inactive state are
+termed irritability, sensibility, voluntarity, and associability; in their
+active state they are termed as above, irritation, sensation, volition,
+association.
+
+2. IRRITATION is an exertion or change of some extreme part of the
+sensorium residing in the muscles or organs of sense, in consequence of the
+appulses of external bodies.
+
+SENSATION is an exertion or change of the central parts of the sensorium,
+or of the whole of it, _beginning_ at some of those extreme parts of it,
+which reside in the muscles or organs of sense.
+
+VOLITION is an exertion or change of the central parts of the sensorium, or
+of the whole of it, _terminating_ in some of those extreme parts of it,
+which reside in the muscles or organs of sense.
+
+ASSOCIATION is an exertion or change of some extreme part of the sensorium
+residing in the muscles or organs of sense, in consequence of some
+antecedent or attendant fibrous contractions.
+
+3. These four faculties of the animal sensorium may at the time of their
+exertions be termed motions without impropriety of language; for we cannot
+pass from a state of insensibility or inaction to a state of sensibility or
+of exertion without some change of the sensorium, and every change includes
+motion. We shall therefore sometimes term the above described faculties
+_sensorial motions_ to distinguish them from _fibrous motions_; which
+latter expression includes the motions of the muscles and organs of sense.
+
+The active motions of the fibres, whether those of the muscles or organs of
+sense, are probably simple contractions; the fibres being again elongated
+by antagonist muscles, by circulating fluids, or sometimes by elastic
+ligaments, as in the necks of quadrupeds. The sensorial motions, which
+constitute the sensations of pleasure or pain, and which constitute
+volition, and which cause the fibrous contractions in consequence of
+irritation or of association, are not here supposed to be fluctuations or
+refluctuations of the spirit of animation; nor are they supposed to be
+vibrations or revibrations, nor condensations or equilibrations of it; but
+to be changes or motions of it peculiar to life.
+
+       *       *       *       *       *
+
+SECT. VI.
+
+OF THE FOUR CLASSES OF FIBROUS MOTIONS.
+
+    I. _Origin of fibrous contractions._ II. _Distribution of them into
+    four classes, irritative motions, sensitive motions, voluntary motions,
+    and associate motions, defined._
+
+I. All the fibrous contractions of animal bodies originate from the
+sensorium, and resolve themselves into four classes, correspondent with the
+four powers or motions of the sensorium above described, and from which
+they have their causation.
+
+1. These fibrous contractions were originally caused by the irritations
+excited by objects, which are external to the moving organ. As the
+pulsations of the heart are owing to the irritations excited by the
+stimulus of the blood; and the ideas of perception are owing to the
+irritations excited by external bodies.
+
+2. But as painful or pleasurable sensations frequently accompanied those
+irritations, by habit these fibrous contractions became causeable by the
+sensations, and the irritations ceased to be necessary to their production.
+As the secretion of tears in grief is caused by the sensation of pain; and
+the ideas of imagination, as in dreams or delirium, are excited by the
+pleasure or pain, with which they were formerly accompanied.
+
+3. But as the efforts of the will frequently accompanied these painful or
+pleasureable sensations, by habit the fibrous contractions became causable
+by volition; and both the irritations and sensations ceased to be necessary
+to their production. As the deliberate locomotions of the body, and the
+ideas of recollection, as when we will to repeat the alphabet backwards.
+
+4. But as many of these fibrous contractions frequently accompanied other
+fibrous contractions, by habit they became causable by their associations
+with them; and the irritations, sensations, and volition, ceased to be
+necessary to their production. As the actions of the muscles of the lower
+limbs in fencing are associated with those of the arms; and the ideas of
+suggestion are associated with other ideas, which precede or accompany
+them; as in repeating carelessly the alphabet in its usual order after
+having began it.
+
+II. We shall give the following names to these four classes of fibrous
+motions, and subjoin their definitions.
+
+1. Irritative motions. That exertion or change of the sensorium, which is
+caused by the appulses of external bodies, either simply subsides, or is
+succeeded by sensation, or it produces fibrous motions; it is termed
+irritation, and irritative motions are those contractions of the muscular
+fibres, or of the organs of sense, that are immediately consequent to this
+exertion or change of the sensorium.
+
+2. Sensitive motions. That exertion or change of the sensorium, which
+constitutes pleasure or pain, either simply subsides, or is succeeded by
+volition, or it produces fibrous motions; it is termed sensation, and the
+sensitive motions are those contractions of the muscular fibres, or of the
+organs of sense, that are immediately consequent to this exertion or change
+of the sensorium.
+
+3. Voluntary motions. That exertion or change of the sensorium, which
+constitutes desire or aversion, either simply subsides, or is succeeded by
+fibrous motions; it is then termed volition, and voluntary motions are
+those contractions of the muscular fibres, or of the organs of sense, that
+are immediately consequent to this exertion or change of the sensorium.
+
+4. Associate motions. That exertion or change of the sensorium, which
+accompanies fibrous motions, either simply subsides, or is succeeded by
+sensation or volition, or it produces other fibrous motions; it is then
+termed association, and the associate motions are those contractions of the
+muscular fibres, or of the organs of sense, that are immediately consequent
+to this exertion or change of the sensorium.
+
+       *       *       *       *       *
+
+SECT. VII.
+
+OF IRRITATIVE MOTIONS.
+
+    I. 1. _Some muscular motions are excited by perpetual irritations._ 2.
+    _Others more frequently by sensations._ 3. _Others by volition. Case of
+    involuntary stretchings in paralytic limbs._ 4. _Some sensual motions
+    are excited by perpetual irritations._ 5. _Others more frequently by
+    sensation or volition._
+
+    II. 1. _Muscular motions excited by perpetual irritations occasionally
+    become obedient sensation and to volition._ 2. _And the sensual
+    motions._
+
+    III. 1. _Other muscular motions are associated with the irritative
+    ones._ 2. _And other ideas with irritative ones. Of letters, language,
+    hieroglyphics. Irritative ideas exist without our attention to them._
+
+I. 1. Many of our muscular motions are excited by perpetual irritations, as
+those of the heart and arterial system by the circumfluent blood. Many
+other of them are excited by intermitted irritations, as those of the
+stomach and bowels by the aliment we swallow; of the bile-ducts by the
+bile; of the kidneys, pancreas, and many other glands, by the peculiar
+fluids they separate from the blood; and those of the lacteal and other
+absorbent vessels by the chyle, lymph, and moisture of the atmosphere.
+These motions are accelerated or retarded, as their correspondent
+irritations are increased or diminished, without our attention or
+consciousness, in the same manner as the various secretions of fruit, gum,
+resin, wax, and, honey, are produced in the vegetable world, and as the
+juices of the earth and the moisture of the atmosphere are absorbed by
+their roots and foliage.
+
+2. Other muscular motions, that are most frequently connected with our
+sensations, as those of the sphincters of the bladder and anus, and the
+musculi erectores penis, were originally excited into motion by irritation,
+for young children make water, and have other evacuations without attention
+to these circumstances; "et primis etiam ab incunabulis tenduntur sæpius
+puerorum penes, amore nondum expergefacto." So the nipples of young women
+are liable to become turgid by irritation, long before they are in a
+situation to be excited by the pleasure of giving milk to the lips of a
+child.
+
+3. The contractions of the larger muscles of our bodies, that are most
+frequently connected with volition, were originally excited into action by
+internal irritations: as appears from the stretching or yawning of all
+animals after long sleep. In the beginning of some fevers this irritation
+of the muscles produces perpetual stretching and yawning; in other periods
+of fever an universal restlessness arises from the same cause, the patient
+changing the attitude of his body every minute. The repeated struggles of
+the foetus in the uterus must be owing to this internal irritation: for the
+foetus can have no other inducement to move its limbs but the tædium or
+irksomeness of a continued posture.
+
+The following case evinces, that the motions of stretching the limbs after
+a continued attitude are not always owing to the power of the will. Mr.
+Dean, a mason, of Austry in Leicestershire, had the spine of the third
+vertebra of the back enlarged; in some weeks his lower extremities became
+feeble, and at length quite paralytic: neither the pain of blisters, the
+heat of fomentations, nor the utmost efforts of the will could produce the
+least motion in these limbs; yet twice or thrice a day for many months his
+feet, legs, and thighs, were affected for many minutes with forceable
+stretchings, attended with the sensation of fatigue; and he at length
+recovered the use of his limbs, though the spine continued protuberant. The
+same circumstance is frequently seen in a less degree in the common
+hemiplagia; and when this happens, I have believed repeated and strong
+shocks of electricity to have been of great advantage.
+
+4. In like manner the various organs of sense are originally excited into
+motion by various external stimuli adapted to this purpose, which motions
+are termed perceptions or ideas; and many of these motions during our
+waking hours are excited by perpetual irritation, as those of the organs of
+hearing and of touch. The former by the constant low indistinct noises that
+murmur around us, and the latter by the weight of our bodies on the parts
+which support them; and by the unceasing variations of the heat, moisture,
+and pressure of the atmosphere; and these sensual motions, precisely as the
+muscular ones above mentioned, obey their correspondent irritations without
+our attention or consciousness.
+
+5. Other classes of our ideas are more frequently excited by our sensations
+of pleasure or pain, and others by volition: but that these have all been
+originally excited by stimuli from external objects, and only vary in their
+combinations or reparations, has been fully evinced by Mr. Locke: and are
+by him termed the ideas of perception in contradistinction to those, which
+he calls the ideas of reflection.
+
+II. 1. These muscular motions, that are excited by perpetual irritation,
+are nevertheless occasionally excitable by the sensations of pleasure or
+pain, or by volition; as appears by the palpitation of the heart from fear,
+the increased secretion of saliva at the sight of agreeable food, and the
+glow on the skin of those who are ashamed. There is an instance told in the
+Philosophical Transactions of a man, who could for a time stop the motion
+of his heart when he pleased; and Mr. D. has often told me, be could so far
+increase the peristaltic motion of his bowels by voluntary efforts, as to
+produce an evacuation by stool at any time in half an hour.
+
+2. In like manner the sensual motions, or ideas, that are excited by
+perpetual irritation, are nevertheless occasionally excited by sensation or
+volition; as in the night, when we listen under the influence of fear, or
+from voluntary attention, the motions excited in the organ of hearing by
+the whispering of the air in our room, the pulsation of our own arteries,
+or the faint beating of a distant watch, become objects of perception.
+
+III. 1. Innumerable trains or tribes of other motions are associated with
+these muscular motions which are excited by irritation; as by the stimulus
+of the blood in the right chamber of the heart, the lungs are induced to
+expand themselves; and the pectoral and intercostal muscles, and the
+diaphragm, act at the same time by their associations with them. And when
+the pharinx is irritated by agreeable food, the muscles of deglutition are
+brought into action by association. Thus when a greater light falls on the
+eye, the iris is brought into action without our attention; and the ciliary
+process, when the focus is formed before or behind the retina, by their
+associations with the increased irritative motions of the organ of vision.
+Many common actions of life are produced in a similar manner. If a fly
+settle on my forehead, whilst I am intent on my present occupation, I
+dislodge it with my finger, without exciting my attention or breaking the
+train of my ideas.
+
+2. In like manner the irritative ideas suggest to us many other trains or
+tribes of ideas that are associated with them. On this kind of connection,
+language, letters, hieroglyphics, and every kind of symbol, depend. The
+symbols themselves produce irritative ideas, or sensual motions, which we
+do not attend to; and other ideas, that are succeeded by sensation, are
+excited by their association with them. And as these irritative ideas make
+up a part of the chain of our waking thoughts, introducing other ideas that
+engage our attention, though themselves are unattended to, we find it very
+difficult to investigate by what steps many of our hourly trains of ideas
+gain their admittance.
+
+It may appear paradoxical, that ideas can exist, and not be attended to;
+but all our perceptions are ideas excited by irritation, and succeeded by
+sensation. Now when these ideas excited by irritation give us neither
+pleasure nor pain, we cease to attend to them. Thus whilst I am walking
+through that grove before my window, I do not run against the trees or the
+benches, though my thoughts are strenuously exerted on some other object.
+This leads us to a distinct knowledge of irritative ideas, for the idea of
+the tree or bench, which I avoid, exists on my retina, and induces by
+association the action of certain locomotive muscles; though neither itself
+nor the actions of those muscles engage my attention.
+
+Thus whilst we are conversing on this subject, the tone, note, and
+articulation of every individual word forms its correspondent irritative
+idea on the organ of hearing; but we only attend to the associated ideas,
+that are attached by habit to these irritative ones, and are succeeded by
+sensation; thus when we read the words "PRINTING-PRESS" we do not attend to
+the shape, size, or existence of the letters which compose these words,
+though each of them excites a correspondent irritative motion of our organ
+of vision, but they introduce by association our idea of the most useful of
+modern inventions; the capacious reservoir of human knowledge, whose
+branching streams diffuse sciences, arts, and morality, through all nations
+and all ages.
+
+       *       *       *       *       *
+
+SECT. VIII.
+
+OF SENSITIVE MOTIONS.
+
+    I. 1. _Sensitive muscular motions were originally excited into action
+    by irritation._ 2. _And sensitive sensual motions, ideas of
+    imagination, dreams._ II. 1. _Sensitive muscular motions are
+    occasionally obedient to volition._ 2. _And sensitive sensual motions._
+    III. 1. _Other muscular motions are associated with the sensitive
+    ones._ 2. _And other sensual motions._
+
+I. 1. Many of the motions of our muscles, that are excited into action by
+irritation, are at the same time accompanied with painful or pleasurable
+sensations; and at length become by habit causable by the sensations. Thus
+the motions of the sphincters of the bladder and anus were originally
+excited into action by irritation; for young children give no attention to
+these evacuations; but as soon as they become sensible of the inconvenience
+of obeying these irritations, they suffer the water or excrement to
+accumulate, till it disagreeably affects them; and the action of those
+sphincters is then in consequence of this disagreeable sensation. So the
+secretion of saliva, which in young children is copiously produced by
+irritation, and drops from their mouths, is frequently attended with the
+agreeable sensation produced by the mastication of tasteful food;, till at
+length the sight of such food to a hungry person excites into action these
+salival glands; as is seen in the slavering of hungry dogs.
+
+The motions of those muscles, which are affected by lascivious ideas, and
+those which are exerted in smiling, weeping, starting from fear, and
+winking at the approach of danger to the eye, and at times the actions of
+every large muscle of the body become causable by our sensations. And all
+these motions are performed with strength and velocity in proportion to the
+energy of the sensation that excites them, and the quantity of sensorial
+power.
+
+2. Many of the motions of our organs of sense, or ideas, that were
+originally excited into action by irritation, become in like manner more
+frequently causable by our sensations of pleasure or pain. These motions
+are then termed the ideas of imagination, and make up all the scenery and
+transactions of our dreams. Thus when any painful or pleasurable sensations
+possess us, as of love, anger, fear; whether in our sleep or waking hours,
+the ideas, that have been formerly excited by the objects of these
+sensations, now vividly recur before us by their connection with these
+sensations themselves. So the fair smiling virgin, that excited your love
+by her presence, whenever that sensation recurs, rises before you in
+imagination; and that with all the pleasing circumstances, that had before
+engaged your attention. And in sleep, when you dream under the influence of
+fear, all the robbers, fires, and precipices, that you formerly have seen
+or heard of, arise before you with terrible vivacity. All these sensual
+motions, like the muscular ones above mentioned, are performed with
+strength and velocity in proportion to the energy of the sensation of
+pleasure or pain, which excites them, and the quantity of sensorial power.
+
+II. 1. Many of these muscular motions above described, that are most
+frequently excited by our sensations, are nevertheless occasionally
+causable by volition; for we can smile or frown spontaneously, can make
+water before the quantity or acrimony of the urine produces a disagreeable
+sensation, and can voluntarily masticate a nauseous drug, or swallow a
+bitter draught, though our sensation would strongly dissuade us.
+
+2. In like manner the sensual motions, or ideas, that are most frequently
+excited by our sensations, are nevertheless occasionally causeable by
+volition, as we can spontaneously call up our last night's dream before us,
+tracing it industriously step by step through all its variety of scenery
+and transaction; or can voluntarily examine or repeat the ideas, that have
+been excited by out disgust or admiration.
+
+III. 1. Innumerable trains or tribes of motions are associated with these
+sensitive muscular motions above mentioned; as when a drop of water falling
+into the wind-pipe disagreeably affects the air-vessels of the lungs, they
+are excited into violent action; and with these sensitive motions are
+associated the actions of the pectoral and intercostal muscles, and the
+diaphragm; till by their united and repeated succussions the drop is
+returned through the larinx. The same occurs when any thing disagreeably
+affects the nostrils, or the stomach, or the uterus; variety of muscles are
+excited by association into forcible action, not to be suppressed by the
+utmost efforts of the will; as in sneezing, vomiting, and parturition.
+
+2. In like manner with these sensitive sensual motions, or ideas of
+imagination, are associated many other trains or tribes of ideas, which by
+some writers of metaphysics have been classed under the terms of
+resemblance, causation, and contiguity; and will be more fully treated of
+hereafter.
+
+       *       *       *       *       *
+
+SECT. IX.
+
+OF VOLUNTARY MOTIONS.
+
+    I. 1. _Voluntary muscular motions are originally excited by
+    irritations._ 2. _And voluntary ideas. Of reason._ II. 1. _Voluntary
+    muscular motions are occasionally causable by sensations._ 2. _And
+    voluntary ideas._ III. 1. _Voluntary muscular motions are occasionally
+    obedient to irritations._ 2. _And voluntary ideas._ IV. 1. _Voluntary
+    muscular motions are associated with other muscular motions._ 2. _And
+    voluntary ideas._
+
+When pleasure or pain affect the animal system, many of its motions both
+muscular and sensual are brought into action; as was shewn in the preceding
+section, and were called sensitive motions. The general tendency of these
+motions is to arrest and to possess the pleasure, or to dislodge or avoid
+the pain: but if this cannot immediately be accomplished, desire or
+aversion are produced, and the motions in consequence of this new faculty
+of the sensorium are called voluntary.
+
+I. 1. Those muscles of the body that are attached to bones, have in general
+their principal connections with volition, as I move my pen or raise my
+body. These motions were originally excited by irritation, as was explained
+in the section on that subject, afterwards the sensations of pleasure or
+pain, that accompanied the motions thus excited, induced a repetition of
+them; and at length many of them were voluntarily practised in succession
+or in combination for the common purposes of life, as in learning to walk,
+or to speak; and are performed with strength and velocity in proportion to
+the energy of the volition, that excites them, and the quantity of
+sensorial power.
+
+2. Another great class of voluntary motions consists of the ideas of
+recollection. We will to repeat a certain train of ideas, as of the
+alphabet backwards; and if any ideas, that do not belong to this intended
+train, intrude themselves by other connections, we will to reject them, and
+voluntarily persist in the determined train. So at my approach to a house
+which I have but once visited, and that at the distance of many months, I
+will to recollect the names of the numerous family I expect to see there,
+and I do recollect them.
+
+On this voluntary recollection of ideas our faculty of reason depends, as
+it enables us to acquire an idea of the dissimilitude of any two ideas.
+Thus if you voluntarily produce the idea of a right-angled triangle, and
+then of a square; and after having excited these ideas repeatedly, you
+excite the idea of their difference, which is that of another right-angled
+triangle inverted over the former; you are said to reason upon this
+subject, or to compare your ideas.
+
+These ideas of recollection, like the muscular motions above mentioned,
+were originally excited by the irritation of external bodies, and were
+termed ideas of perception: afterwards the pleasure or pain, that
+accompanied these motions, induced a repetition of them in the absence of
+the external body, by which they were first excited; and then they were
+termed ideas of imagination. At length they become voluntarily practised in
+succession or in combination for the common purposes of life; as when we
+make ourselves masters of the history of mankind, or of the sciences they
+have investigated; and are then called ideas of recollection; and are
+performed with strength and velocity in proportion to the energy of the
+volition that excites them, and the quantity of sensorial power.
+
+II. 1. The muscular motions above described, that are most frequently
+obedient to the will are nevertheless occasionally causable by painful or
+pleasurable sensation, as in the starting from fear, and the contraction of
+the calf of the leg in the cramp.
+
+2. In like manner the sensual motions, or ideas, that are most frequently
+connected with volition, are nevertheless occasionally causable by painful
+or pleasurable sensation. As the histories of men, or the description of
+places, which we have voluntarily taken pains to remember, sometimes occur
+to us in our dreams.
+
+III. 1. The muscular motions that are generally subservient to volition,
+are also occasionally causable by irritation, as in stretching the limbs
+after sleep, and yawning. In this manner a contraction of the arm is
+produced by passing the electric fluid from the Leyden phial along its
+muscles; and that even though the limb is paralytic. The sudden motion of
+the arm produces a disagreeable sensation in the joint, but the muscles
+seem to be brought into action simply by irritation.
+
+2. The ideas, that are generally subservient to the will, are in like
+manner occasionally excited by irritation; as when we view again an object,
+we have before well studied, and often recollected.
+
+IV. 1. Innumerable trains or tribes of motions are associated with these
+voluntary muscular motions above mentioned; as when I will to extend my arm
+to a distant object, some other muscles are brought into action, and
+preserve the balance of my body. And when I wish to perform any steady
+exertion, as in threading a needle, or chopping with an ax, the pectoral
+muscles are at the same time brought into action to preserve the trunk of
+the body motionless, and we cease to respire for a time.
+
+2. In like manner the voluntary sensual motions, or ideas of recollection,
+are associated with many other trains or tribes of ideas. As when I
+voluntarily recollect a gothic window, that I saw some time ago, the whole
+front of the cathedral occurs to me at the same time.
+
+       *       *       *       *       *
+
+SECT. X.
+
+OF ASSOCIATE MOTIONS.
+
+    I. 1. _Many muscular motions excited by irritations in trains or tribes
+    become associated._ 2. _And many ideas._ II. 1. _Many sensitive
+    muscular motions become associated._ 2. _And many sensitive ideas._
+    III. 1. _Many voluntary muscular motions become associated._ 2. _And
+    then become obedient to sensation or irritation._ 3. _And many
+    voluntary ideas become associated._
+
+All the fibrous motions, whether muscular or sensual, which are frequently
+brought into action together, either in combined tribes, or in successive
+trains, become so connected by habit, that when one of them is reproduced
+the others have a tendency to succeed or accompany it.
+
+I. 1. Many of our muscular motions were originally excited in successive
+trains, as the contractions of the auricles and of the ventricles of the
+heart; and others in combined tribes, as the various divisions of the
+muscles which compose the calf of the leg, which were originally irritated
+into synchronous action by the tædium or irksomeness of a continued
+posture. By frequent repetitions these motions acquire associations, which
+continue during our lives, and even after the destruction of the greatest
+part of the sensorium; for the heart of a viper or frog will continue to
+pulsate long after it is taken from the body; and when it has entirely
+ceased to move, if any part of it is goaded with a pin, the whole heart
+will again renew its pulsations. This kind of connection we shall term
+irritative association, to distinguish it from sensitive and voluntary
+associations.
+
+2. In like manner many of our ideas are originally excited in tribes; as
+all the objects of sight, after we become so well acquainted with the laws
+of vision, as to distinguish figure and distance as well as colour; or in
+trains, as while we pass along the objects that surround us. The tribes
+thus received by irritation become associated by habit, and have been
+termed complex ideas by the writers of metaphysics, as this book, or that
+orange. The trains have received no particular name, but these are alike
+associations of ideas, and frequently continue during our lives. So the
+taste of a pine-apple, though we eat it blindfold, recalls the colour and
+shape of it; and we can scarcely think on solidity without figure.
+
+II. 1. By the various efforts of our sensations to acquire or avoid their
+objects, many muscles are daily brought into successive or synchronous
+actions; these become associated by habit, and are then excited together
+with great facility, and in many instances gain indissoluble connections.
+So the play of puppies and kittens is a representation of their mode of
+fighting or of taking their prey; and the motions of the muscles necessary
+for those purposes become associated by habit, and gain a great adroitness
+of action by these early repetitions: so the motions of the abdominal
+muscles, which were originally brought into concurrent action, with the
+protrusive motion of the rectum or bladder by sensation, become so
+conjoined with them by habit, that they not only easily obey these
+sensations occasioned by the stimulus of the excrement and urine, but are
+brought into violent and unrestrainable action in the strangury and
+tenesmus. This kind of connection we shall term sensitive association.
+
+2. So many of our ideas, that have been excited together or in succession
+by our sensations, gain synchronous or successive associations, that are
+sometimes indissoluble but with life. Hence the idea of an inhuman or
+dishonourable action perpetually calls up before us the idea of the wretch
+that was guilty of it. And hence those unconquerable antipathies are
+formed, which some people have to the sight of peculiar kinds of food, of
+which in their infancy they have eaten to excess or by constraint.
+
+III. 1. In learning any mechanic art, as music, dancing, or the use of the
+sword, we teach many of our muscles to act together or in succession by
+repeated voluntary efforts; which by habit become formed into tribes or
+trains of association, and serve all our purposes with great facility, and
+in some instances acquire an indissoluble union. These motions are
+gradually formed into a habit of acting together by a multitude of
+repetitions, whilst they are yet separately causable by the will, as is
+evident from the long time that is taken up by children in learning to walk
+and to speak; and is experienced by every one, when he first attempts to
+skate upon the ice or to swim: these we shall term voluntary associations.
+
+2. All these muscular movements, when they are thus associated into tribes
+or trains, become afterwards not only obedient to volition, but to the
+sensations and irritations; and the same movement composes a part of many
+different tribes or trains of motion. Thus a single muscle, when it acts in
+consort with its neighbours on one side, assists to move the limb in one
+direction; and in another, when, it acts with those in its neighbourhood on
+the other side; and in other directions, when it acts separately or jointly
+with those that lie immediately under or above it; and all these with equal
+facility after their associations have been well established.
+
+The facility, with which each muscle changes from one associated tribe to
+another, and that either backwards or forwards, is well observable in the
+muscles of the arm in moving the windlass of an air-pump; and the slowness
+of those muscular movements, that have not been associated by habit, may be
+experienced by any one, who shall attempt to saw the air quick
+perpendicularly with one hand, and horizontally with the other at the same
+time.
+
+3. In learning every kind of science we voluntarily associate many tribes
+and trains of ideas, which afterwards are ready for all the purposes either
+of volition, sensation, or irritation; and in some instances acquire
+indissoluble habits of acting together, so as to affect our reasoning, and
+influence our actions. Hence the necessity of a good education.
+
+These associate ideas are gradually formed into habits of acting together
+by frequent repetition, while they are yet separately obedient to the will;
+as is evident from the difficulty we experience in gaining so exact an idea
+of the front of St. Paul's church, as to be able to delineate it with
+accuracy, or in recollecting a poem of a few pages.
+
+And these ideas, thus associated into tribes, not only make up the parts of
+the trains of volition, sensation, and irritation; but the same idea
+composes a part of many different tribes and trains of ideas. So the simple
+idea of whiteness composes a part of the complex idea of snow, milk, ivory;
+and the complex idea of the letter A composes a part of the several
+associated trains of ideas that make up the variety of words, in which this
+letter enters.
+
+The numerous trains of these associated ideas are divided by Mr. Hume into
+three classes, which he has termed contiguity, causation, and resemblance.
+Nor should we wonder to find them thus connected together, since it is the
+business of our lives to dispose them into those three classes; and we
+become valuable to ourselves and our friends, as we succeed in it. Those
+who have combined an extensive class of ideas by the contiguity of time or
+place, are men learned in the history of mankind, and of the sciences they
+have cultivated. Those who have connected a great class of ideas of
+resemblances, possess the source of the ornaments of poetry and oratory,
+and of all rational analogy. While those who have connected great classes
+of ideas of causation, are furnished with the powers of producing effects.
+These are the men of active wisdom, who lead armies to victory, and
+kingdoms to prosperity; or discover and improve the sciences, which
+meliorate and adorn the condition of humanity.
+
+       *       *       *       *       *
+
+SECT. XI.
+
+ADDITIONAL OBSERVATIONS ON THE SENSORIAL POWERS.
+
+    I. _Stimulation is of various kinds adapted to the organs of sense, to
+    the muscles, to hollow membranes, and glands. Some objects irritate our
+    senses by repeated impulses._ II. 1. _Sensation and volition frequently
+    affect the whole sensorium._ 2. _Emotions, passions, appetites._ 3.
+    _Origin of desire and aversion. Criterion of voluntary actions,
+    difference of brutes and men._ 4. _Sensibility and voluntarity._ III.
+    _Associations formed before nativity, irritative motions mistaken for
+    officiated ones._
+
+_Irritation._
+
+I. The various organs of sense require various kinds of stimulation to
+excite them into action; the particles of light penetrate the cornea and
+humours of the eye, and then irritate the naked retina; rapid particles,
+dissolved or diffused in water or saliva, and odorous ones, mixed or
+combined with the air, irritate the extremities of the nerves of taste and
+smell; which either penetrate, or are expanded on the membranes of the
+tongue and nostrils; the auditory nerves are stimulated by the vibrations
+of the atmosphere communicated by means of the tympanum and of the fluid,
+whether of air or of water, behind it; and the nerves of touch by the
+hardness of surrounding bodies, though the cuticle is interposed between
+these bodies and the medulla of the nerve.
+
+As the nerves of the senses have each their appropriated objects, which
+stimulate them into activity; so the muscular fibres, which are the
+terminations of other sets of nerves, have their peculiar objects, which
+excite them into action; the longitudinal muscles are stimulated into
+contraction by extension, whence the stretching or pandiculation after a
+long continued posture, during which they have been kept in a state of
+extension; and the hollow muscles are excited into action by distention, as
+those of the rectum and bladder are induced to protrude their contents from
+their sense of the distention rather than of the acrimony of those
+contents.
+
+There are other objects adapted to stimulate the nerves, which terminate in
+variety of membranes, and those especially which form the terminations of
+canals; thus the preparations of mercury particularly affect the salivary
+glands, ipecacuanha the stomach, aloe the sphincter of the anus,
+cantharides that of the bladder, and lastly every gland of the body appears
+to be indued with a kind of taste, by which it selects or forms each its
+peculiar fluid from the blood; and by which it is irritated into activity.
+
+Many of these external properties of bodies, which stimulate our organs of
+sense, do not seem to effect this by a single impulse, but by repeated
+impulses; as the nerve of the ear is probably not excitable by a single
+vibration of air, nor the optic nerve by a single particle of light; which
+circumstance produces some analogy between those two senses, at the same
+time the solidity of bodies is perceived by a single application of a solid
+body to the nerves of touch, and that even through the cuticle; and we are
+probably possessed of a peculiar sense to distinguish the nice degrees of
+heat and cold.
+
+The senses of touch and of hearing acquaint us with the mechanical impact
+and vibration of bodies, those of smell and taste seem to acquaint us with
+some of their chemical properties, while the sense of vision and of heat
+acquaint us with the existence of their peculiar fluids.
+
+_Sensation and Volition._
+
+II. Many motions are produced by pleasure or pain, and that even in
+contradiction to the power of volition, as in laughing, or in the
+strangury; but as no name has been given to pleasure or pain, at the time
+it is exerted so as to cause fibrous motions, we have used the term
+sensation for this purpose; and mean it to bear the same analogy to
+pleasure and pain, that the word volition does to desire and aversion.
+
+1. It was mentioned in the fifth Section, that, what we have termed
+sensation is a motion of the central parts, or of the whole sensorium,
+_beginning_ at some of the extremities of it. This appears first, because
+our pains and pleasures are always caused by our ideas or muscular motions,
+which are the motions of the extremities of the sensorium. And, secondly,
+because the sensation of pleasure or pain frequently continues some time
+after the ideas or muscular motions which excited it have ceased: for we
+often feel a glow of pleasure from an agreeable reverie, for many minutes
+after the ideas, that were the subject of it, have escaped our memory; and
+frequently experience a dejection of spirits without being able to assign
+the cause of it but by much recollection.
+
+When the sensorial faculty of desire or aversion is exerted so as to cause
+fibrous motions, it is termed volition; which is said in Sect. V. to be a
+motion of the central parts, or of the whole sensorium, _terminating_ in
+some of the extremities of it. This appears, first, because our desires and
+aversions always terminate in recollecting and comparing our ideas, or in
+exerting our muscles; which are the motions of the extremities of the
+sensorium. And, secondly, because desire or aversion begins, and frequently
+continues for a time in the central parts of the sensorium, before it is
+peculiarly exerted at the extremities of it; for we sometimes feel desire
+or aversion without immediately knowing their objects, and in consequence
+without immediately exerting any of our muscular or sensual motions to
+attain them: as in the beginning of the passion of love, and perhaps of
+hunger, or in the ennui of indolent people.
+
+Though sensation and volition begin or terminate at the extremities or
+central parts of the sensorium, yet the whole of it is frequently
+influenced by the exertion of these faculties, as appears from their
+effects on the external habit: for the whole skin is reddened by shame, and
+an universal trembling is produced by fear: and every muscle of the body is
+agitated in angry people by the desire of revenge.
+
+There is another very curious circumstance, which shews that sensation and
+volition are movements of the sensorium in contrary directions; that is,
+that volition begins at the central parts of it, and proceeds to the
+extremities; and that sensation begins at the extremities, and proceeds to
+the central parts: I mean that these two sensorial faculties cannot be
+strongly exerted at the same time; for when we exert our volition strongly,
+we do not attend to pleasure or pain; and conversely, when we are strongly
+affected with the sensation of pleasure or pain, we use no volition. As
+will be further explained in Section XVIII. on sleep, and Section XXXIV. on
+volition.
+
+2. All our emotions and passions seem to arise out of the exertions of
+these two faculties of the animal sensorium. Pride, hope, joy, are the
+names of particular pleasures: shame, despair, sorrow, are the names of
+peculiar pains: and love, ambition, avarice, of particular desires: hatred,
+disgust, fear, anxiety, of particular aversions. Whilst the passion of
+anger includes the pain from a recent injury, and the aversion to the
+adversary that occasioned it. And compassion is the pain we experience at
+the sight of misery, and the desire of relieving it.
+
+There is another tribe of desires, which are commonly termed appetites, and
+are the immediate consequences of the absence of some irritative motions.
+Those, which arise from defect of internal irritations, have proper names
+conferred upon them, as hunger, thirst, lust, and the desire of air, when
+our respiration is impaired by noxious vapours; and of warmth, when we are
+exposed to too great a degree of cold. But those, whose stimuli are
+external to the body, are named from the objects, which are by nature
+constituted to excite them; these desires originate from our past
+experience of the pleasurable sensations they occasion, as the smell of an
+hyacinth, or the taste of a pine-apple.
+
+Whence it appears, that our pleasures and pains are at least as various and
+as numerous as our irritations; and that our desires and aversions must be
+as numerous as our pleasures and pains. And that as sensation is here used
+as a general term for our numerous pleasures and pains, when they produce
+the contractions of our fibres; so volition is the general name for our
+desires and aversions, when they produce fibrous contractions. Thus when a
+motion of the central parts, or of the whole sensorium, terminates in the
+exertion of our muscles, it is generally called voluntary action; when it
+terminates in the exertion of our ideas, it is termed recollection,
+reasoning, determining.
+
+3. As the sensations of pleasure and pain are originally introduced by the
+irritations of external objects: so our desires and aversions are
+originally introduced by those sensations; for when the objects of our
+pleasures or pains are at a distance, and we cannot instantaneously possess
+the one, or avoid the other, then desire or aversion is produced, and a
+voluntary exertion of our ideas or muscles succeeds.
+
+The pain of hunger excites you to look out for food, the tree, that shades
+you, presents its odoriferous fruit before your eyes, you approach, pluck,
+and eat.
+
+The various movements of walking to the tree, gathering the fruit, and
+masticating it, are associated motions introduced by their connection with
+sensation; but if from the uncommon height of the tree, the fruit be
+inaccessible, and you are prevented from quickly possessing the intended
+pleasure, desire is produced. The consequence of this desire is, first, a
+deliberation about the means to gain the object of pleasure in process of
+time, as it cannot be procured immediately; and, secondly, the muscular
+action necessary for this purpose.
+
+You voluntarily call up all your ideas of causation, that are related to
+the effect you desire, and voluntarily examine and compare them, and at
+length determine whether to ascend the tree, or to gather stones from the
+neighbouring brook, is easier to practise, or more promising of success;
+and, finally, you gather the stones, and repeatedly fling them to dislodge
+the fruit.
+
+Hence then we gain a criterion to distinguish voluntary acts or thoughts
+from those caused by sensation. As the former are always employed about the
+_means_ to acquire pleasurable objects, or the _means_ to avoid painful
+ones; while the latter are employed in the possession of those, which are
+already in our power.
+
+Hence the activity of this power of volition produces the great difference
+between the human and the brute creation. The ideas and the actions of
+brutes are almost perpetually employed about their present pleasures, or
+their present pains; and, except in the few instances which are mentioned
+in Section XVI, on instinct, they seldom busy themselves about the means of
+procuring future bliss, or of avoiding future misery; so that the acquiring
+of languages, the making of tools, and labouring for money, which are all
+only the means to procure pleasures; and the praying to the Deity, as
+another means to procure happiness, are characteristic of human nature.
+
+4. As there are many diseases produced by the quantity of the sensation of
+pain or pleasure being too great or too little; so are there diseases
+produced by the susceptibility of the constitution to motions causable by
+these sensations being too dull or too vivid. This susceptibility of the
+system to sensitive motions is termed sensibility, to distinguish it from
+sensation, which is the actual existence or exertion of pain or pleasure.
+
+Other classes of diseases are owing to the excessive promptitude, or
+sluggishness of the constitution to voluntary exertions, as well as to the
+quantity of desire or of aversion. This susceptibility of the system to
+voluntary motions is termed voluntarity, to distinguish it from volition,
+which is the exertion of desire or aversion; these diseases will be treated
+of at length in the progress of the work.
+
+_Association._
+
+III. 1. It is not easy to assign a cause, why those animal movements, that
+have once occurred in succession, or in combination, should afterwards have
+a tendency to succeed or accompany each other. It is a property of
+animation, and distinguishes this order of being from the other productions
+of nature.
+
+When a child first wrote the word man, it was distinguished in his mind
+into three letters, and those letters into many parts of letters; but by
+repeated use the word man becomes to his hand in writing it, as to his
+organs of speech in pronouncing it, but one movement without any
+deliberation, or sensation, or irritation, interposed between the parts of
+it. And as many separate motions of our muscles thus become united, and
+form, as it were, one motion; so each separate motion before such union may
+be conceived to consist of many parts or spaces moved through; and perhaps
+even the individual fibres of our muscles have thus gradually been brought
+to act in concert, which habits began to be acquired as early as the very
+formation of the moving organs, long before the nativity of the animal; as
+explained in the Section XVI. 2. on instinct.
+
+2. There are many motions of the body, belonging to the irritative class,
+which might by a hasty observer be mistaken for associated ones; as the
+peristaltic motion of the stomach and intestines, and the contractions of
+the heart and arteries, might be supposed to be associated with the
+irritative motions of their nerves of sense, rather than to be excited by
+the irritation of their muscular fibres by the distention, acrimony, or
+momentum of the blood. So the distention or elongation of muscles by
+objects external to them irritates them into contraction, though the
+cuticle or other parts may intervene between the stimulating body and the
+contracting muscle. Thus a horse voids his excrement when its weight or
+bulk irritates the rectum or sphincter ani. These muscles act from the
+irritation of distention, when he excludes his excrement, but the muscles
+of the abdomen and diaphragm are brought into motion by association with
+those of the sphincter and rectum.
+
+       *       *       *       *       *
+
+SECT. XII.
+
+OF STIMULUS, SENSORIAL EXERTION, AND FIBROUS CONTRACTION.
+
+    I. Of fibrous contraction. 1. _Two particles of a fibre cannot approach
+    without the intervention of something, as in magnetism, electricity,
+    elasticity. Spirit of life is not electric ether. Galvani's
+    experiments._ 2. _Contraction of a fibre._ 3. _Relaxation succeeds._ 4.
+    _Successive contractions, with intervals. Quick pulse from debility,
+    from paucity of blood. Weak contractions performed in less time, and
+    with shorter intervals._ 5. _Last situation of the fibres continues
+    after contraction._ 6. _Contraction greater than usual induces pleasure
+    or pain._ 7. _Mobility of the fibres uniform. Quantity of sensorial
+    power fluctuates. Constitutes excitability._ II. Of sensorial exertion.
+    1. _Animal motion includes stimulus, sensorial power, and contractile
+    fibres. The sensorial faculties act separately or conjointly. Stimulus
+    of four kinds. Strength and weakness defined. Sensorial power
+    perpetually exhausted and renewed. Weakness from defect of stimulus.
+    From defect of sensorial power, the direct and indirect debility of Dr.
+    Brown. Why we become warm in Buxton bath after a time, and see well
+    after a time in a darkish room. Fibres may act violently, or with their
+    whole force, and yet feebly. Great exertion in inflammation explained.
+    Great muscular force of some insane people._ 2. _Occasional
+    accumulation of sensorial power in muscles subject to constant
+    stimulus. In animals sleeping in winter. In eggs, seeds, schirrous
+    tumours, tendons, bones._ 3. _Great exertion introduces pleasure or
+    pain. Inflammation. Libration of the system between torpor and
+    activity. Fever-fits._ 4. _Desire and aversion introduced. Excess of
+    volition cures fevers._ III. Of repeated stimulus. 1. _A stimulus
+    repeated too frequently looses effect. As opium, wine, grief. Hence old
+    age. Opium and aloes in small doses._ 2. _A stimulus not repeated too
+    frequently does not lose effect. Perpetual movement of the vital
+    organs._ 3. _A stimulus repeated at uniform times produces greater
+    effect. Irritation combined with association._ 4. _A stimulus repeated
+    frequently and uniformly may be withdrawn, and the action of the organ
+    will continue. Hence the bark cures agues, and strengthens weak
+    constitutions._ 5. _Defect of stimulus repeated at certain intervals
+    causes fever-fits._ 6. _Stimulus long applied ceases to act a second
+    time._ 7. _If a stimulus excites sensation in an organ not usually
+    excited into sensation, inflammation is produced._ IV. Of stimulus
+    greater than natural. 1. _A stimulus greater than natural diminishes
+    the quantity of sensorial power in general._ 2. _In particular organs._
+    3. _Induces the organ into spasmodic actions._ 4. _Induces the
+    antagonist fibres into action._ 5. _Induces the organ into convulsive
+    or fixed spasms._ 6. _Produces paralysis of the organ._ V. Of stimulus
+    less than natural. 1. _Stimulus less than natural occasions
+    accumulation of sensorial power in general._ 2. _In particular organs,
+    flushing of the face in a frosty morning. In fibres subject to
+    perpetual stimulus only. Quantity of sensorial power inversely as the
+    stimulus._ 3. _Induces pain. As of cold, hunger, head-ach._ 4. _Induces
+    more feeble and frequent contraction. As in low fevers. Which are
+    frequently owing to deficiency of sensorial power rather than to
+    deficiency of stimulus._ 5. _Inverts successive trains of motion.
+    Inverts ideas._ 6. _Induces paralysis and death._ VI. Cure of increased
+    exertion. 1. _Natural cure of exhaustion of sensorial power._ 2.
+    _Decrease the irritations. Venesection. Cold. Abstinence._ 3. _Prevent
+    the previous cold fit. Opium. Bark. Warmth. Anger. Surprise._ 4.
+    _Excite some other part of the system. Opium and warm bath relieve
+    pains both from defect and from excess of stimulus._ 5. _First increase
+    the stimulus above, and then decrease it beneath the natural quantity._
+    VII. Cure of decreased exertion. 1. _Natural cure by accumulation of
+    sensorial power. Ague-fits. Syncope._ 2. _Increase the stimulation, by
+    wine, opium, given so as not to intoxicate. Cheerful ideas._ 3. _Change
+    the kinds of stimulus._ 4. _Stimulate the associated organs. Blisters
+    of use in heart-burn, and cold extremities._ 5. _Decrease the
+    stimulation for a time, cold bath._ 6. _Decrease the stimulation below
+    natural, and then increase it above natural. Bark after emetics. Opium
+    after venesection. Practice of Sydenham in chlorosis._ 7. _Prevent
+    unnecessary expenditure of sensorial power. Decumbent posture, silence,
+    darkness. Pulse quickened by rising out of bed._ 8. _To the greatest
+    degree of quiescence apply the least stimulus. Otherwise paralysis or
+    inflammation of the organ ensues. Gin, wine, blisters, destroy by too
+    great stimulation in fevers with debility. Intoxication in the
+    slightest degree succeeded by debility. Golden rule for determining the
+    best degree of stimulus in low fevers. Another golden rule for
+    determining the quantity of spirit which those, who are debilitated by
+    drinking it, may safely omit._
+
+I. _Of fibrous contraction._
+
+1. If two particles of iron lie near each other without motion, and
+afterwards approach each other; it is reasonable to conclude that something
+besides the iron particles is the cause of their approximation; this
+invisible something is termed magnetism. In the same manner, if the
+particles, which compose an animal muscle, do not touch each other in the
+relaxed state of the muscle, and are brought into contact during the
+contraction of the muscle, it is reasonable to conclude, that some other
+agent is the cause of this new approximation. For nothing can act, where it
+does not exist; for to act includes to exist; and therefore the particles
+of the muscular fibre (which in its state of relaxation are supposed not to
+touch) cannot affect each other without the influence of some intermediate
+agent; this agent is here termed the spirit of animation, or sensorial
+power, but may with equal propriety be termed the power, which causes
+contraction; or may be called by any other name, which the reader may
+choose to affix to it.
+
+The contraction of a muscular fibre may be compared to the following
+electric experiment, which is here mentioned not as a philosophical
+analogy, but as an illustration or simile to facilitate the conception of a
+difficult subject. Let twenty very small Leyden phials properly coated be
+hung in a row by fine silk threads at a small distance from each other; let
+the internal charge of one phial be positive, and of the other negative
+alternately, if a communication be made from the internal surface of the
+first to the external surface of the last in the row, they will all of them
+instantly approach each other, and thus shorten a line that might connect
+them like a muscular fibre. See Botanic Garden, p. 1. Canto I. 1. 202, note
+on Gymnotus.
+
+The attractions of electricity or of magnetism do not apply philosophically
+to the illustration of the contraction of animal fibres, since the force of
+those attractions increases in some proportion inversely as the distance,
+but in muscular motion there appears no difference in velocity or strength
+during the beginning or end of the contraction, but what may be clearly
+ascribed to the varying mechanic advantage in the approximation of one bone
+to another. Nor can muscular motion be assimilated with greater
+plausibility to the attraction of cohesion or elasticity; for in bending a
+steel spring, as a small sword, a less force is required to bend it the
+first inch than the second; and the second than the third; the particles of
+steel on the convex side of the bent spring endeavouring to restore
+themselves more powerfully the further they are drawn from each other. See
+Botanic Garden, P. I. addit. Note XVIII.
+
+I am aware that this may be explained another way, by supposing the
+elasticity of the spring to depend more on the compression of the particles
+on the concave side than on the extension of them on the convex side; and
+by supposing the elasticity of the elastic gum to depend more on the
+resistance to the lateral compression of its particles than to the
+longitudinal extension of them. Nevertheless in muscular contraction, as
+above observed, there appears no difference in the velocity or force of it
+at its commencement or at its termination; from whence we must conclude
+that animal contraction is governed by laws of its own, and not by those of
+mechanics, chemistry, magnetism, or electricity.
+
+On these accounts I do not think the experiments conclusive, which were
+lately published by Galvani, Volta, and others, to shew a similitude
+between the spirit of animation, which contracts the muscular fibres, and
+the electric fluid. Since the electric fluid may act only as a more potent
+stimulus exciting the muscular fibres into action, and not by supplying
+them with a new quantity of the spirit of life. Thus in a recent hemiplegia
+I have frequently observed, when the patient yawned and stretched himself,
+that the paralytic limbs moved also, though they were totally disobedient
+to the will. And when he was electrified by passing shocks from the
+affected hand to the affected foot, a motion of the paralytic limbs was
+also produced. Now as in the act of yawning the muscles of the paralytic
+limbs were excited into action by the stimulus of the irksomeness of a
+continued posture, and not by any additional quantity of the spirit of
+life; so we may conclude, that the passage of the electric fluid, which
+produced a similar effect, acted only as a stimulus, and not by supplying
+any addition of sensorial power.
+
+If nevertheless this theory should ever become established, a stimulus must
+be called an eductor of vital ether; which stimulus may consist of
+sensation or volition, as in the electric eel, as well as in the appulses
+of external bodies; and by drawing off the charges of vital fluid may
+occasion the contraction or motions of the muscular fibres, and organs of
+sense.
+
+2. The immediate effect of the action of the spirit of animation or
+sensorial power on the fibrous parts of the body, whether it acts in the
+mode of irritation, sensation, volition, or association, is a contraction
+of the animal fibre, according to the second law of animal causation. Sect.
+IV. Thus the stimulus of the blood induces the contraction of the heart;
+the agreeable taste of a strawberry produces the contraction of the muscles
+of deglutition; the effort of the will contracts the muscles, which move
+the limbs in walking; and by association other muscles of the trunk are
+brought into contraction to preserve the balance of the body. The fibrous
+extremities of the organs of sense have been shewn, by the ocular spectra
+in Sect. III. to suffer similar contraction by each of the above modes of
+excitation; and by their configurations to constitute our ideas.
+
+3. After animal fibres have for some time been excited into contraction, a
+relaxation succeeds, even though the exciting cause continues to act. In
+respect to the irritative motions this is exemplified in the peristaltic
+contractions of the bowels; which cease and are renewed alternately, though
+the stimulus of the aliment continues to be uniformly applied; in the
+sensitive motions, as in strangury, tenesmus, and parturition, the
+alternate contractions and relaxations of the muscles exist, though the
+stimulus is perpetual. In our voluntary exertions it is experienced, as no
+one can hang long by the hands, however vehemently he wills so to do; and
+in the associate motions the constant change of our attitudes evinces the
+necessity of relaxation to those muscles, which have been long in action.
+
+This relaxation of a muscle after its contraction, even though the stimulus
+continues to be applied, appears to arise from the expenditure or
+diminution of the spirit of animation previously resident in the muscle,
+according to the second law of animal causation in Sect. IV. In those
+constitutions, which are termed weak, the spirit of animation becomes
+sooner exhausted, and tremulous motions are produced, as in the hands of
+infirm people, when they lift a cup to their mouths. This quicker
+exhaustion of the spirit of animation is probably owing to a less quantity
+of it residing in the acting fibres, which therefore more frequently
+require a supply from the nerves, which belong to them.
+
+4. If the sensorial power continues to act, whether it acts in the mode of
+irritation, sensation, volition, or association, a new contraction of the
+animal fibre succeeds after a certain interval; which interval is of
+shorter continuance in weak people than in strong ones. This is exemplified
+in the shaking of the hands of weak people, when they attempt to write. In
+a manuscript epistle of one of my correspondents, which is written in a
+small hand, I observed from four to six zigzags in the perpendicular stroke
+of every letter, which shews that both the contractions of the fingers, and
+intervals between them, must have been performed in very short periods of
+time.
+
+The times of contraction of the muscles of enfeebled people being less, and
+the intervals between those contractions being less also, accounts for the
+quick pulse in fevers with debility, and in dying animals. The shortness of
+the intervals between one contraction and another in weak constitutions, is
+probably owing to the general deficiency of the quantity of the spirit of
+animation, and that therefore there is a less quantity of it to be received
+at each interval of the activity of the fibres. Hence in repeated motions,
+as of the fingers in performing on the harpsichord, it would at first sight
+appear, that swiftness and strength were incompatible; nevertheless the
+single contraction of a muscle is performed with greater velocity as well
+as with greater force by vigorous constitutions, as in throwing a javelin.
+
+There is however another circumstance, which may often contribute to cause
+the quickness of the pulse in nervous fevers, as in animals bleeding to
+death in the slaughter-house; which is the deficient quantity of blood;
+whence the heart is but half distended, and in consequence sooner
+contracts. See Sect. XXXII. 2. 1.
+
+For we must not confound frequency of repetition with quickness of motion,
+or the number of pulsations with the velocity, with which the fibres, which
+constitute the coats of the arteries, contract themselves. For where the
+frequency of the pulsations is but seventy-five in a minute, as in health;
+the contracting fibres, which constitute the sides of the arteries, may
+move through a greater space in a given time, than where the frequency of
+pulsation is one hundred and fifty in a minute, as in some fevers with
+great debility. For if in those fevers the arteries do not expand
+themselves in their diastole to more than half the usual diameter of their
+diastole in health, the fibres which constitute their coats, will move
+through a less space in a minute than in health, though they make two
+pulsations for one.
+
+Suppose the diameter of the artery during its systole to be one line, and
+that the diameter of the same artery during its diastole is in health is
+four lines, and in a fever with, great debility only two lines. It follows,
+that the arterial fibres contract in health from a circle of twelve lines
+in circumference to a circle of three lines in circumference, that is they
+move through a space of nine lines in length. While the arterial fibres in
+the fever with debility would twice contract from a circle of six lines to
+a circle of three lines; that is while they move through a space equal to
+six lines. Hence though the frequency of pulsation in fever be greater as
+two to one, yet the velocity of contraction in health is greater as nine to
+six, or as three to two.
+
+On the contrary in inflammatory diseases with strength, as in the pleurisy,
+the velocity of the contracting sides of the arteries is much greater than
+in health, for if we suppose the number of pulsations in a pleurisy to be
+half as much more than in health, that is as one hundred and twenty to
+eighty, (which is about what generally happens in inflammatory diseases)
+and if the diameter of the artery in diastole be one third greater than in
+health, which I believe is near the truth, the result will be, that the
+velocity of the contractile sides of the arteries will be in a pleurisy as
+two and a half to one, compared to the velocity of their contraction in a
+state of health, for if the circumference of the systole of the artery be
+three lines, and the diastole in health be twelve lines in circumference,
+and in a pleurisy eighteen lines; and secondly, if the artery pulsates
+thrice in the diseased state for twice in the healthy one, it follows, that
+the velocity of contraction in the diseased state to that in the healthy
+state will be forty-five to eighteen, or as two and a half to one.
+
+From hence it would appear, that if we had a criterion to determine the
+velocity of the arterial contractions, it would at the same time give us
+their strength, and thus be of more service in distinguishing diseases,
+than the knowledge of their frequency. As such a criterion cannot be had,
+the frequency of pulsation, the age of the patient being allowed for, will
+in some measure assist us to distinguish arterial strength from arterial
+debility, since in inflammatory diseases with strength the frequency seldom
+exceeds one hundred and eighteen or one hundred and twenty pulsations in a
+minute; unless under peculiar circumstance, as the great additional stimuli
+of wine or of external heat.
+
+5. After a muscle or organ of sense has been excited into contraction, and
+the sensorial power ceases to act, the last situation or configuration of
+it continues; unless it be disturbed by the action of some antagonist
+fibres, or other extraneous power. Thus in weak or languid people, wherever
+they throw their limbs on their bed or sofa, there they lie, till another
+exertion changes their attitude; hence one kind of ocular spectra seems to
+be produced after looking at bright objects; thus when a fire-stick is
+whirled round in the night, there appears in the eye a complete circle of
+fire; the action or configuration of one part of the retina not ceasing
+before the return of the whirling fire.
+
+Thus if any one looks at the setting sun for a short time, and then covers
+his closed eyes with his hand, he will for many seconds of time perceive
+the image of the sun on his retina. A similar image of all other bodies
+would remain some time in the eye, but is effaced by the eternal change of
+the motions of the extremity of this nerve in our attention to other
+objects. See Sect. XVIII. 5. on Sleep. Hence the dark spots, and other
+ocular spectra, are more frequently attended to, and remain longer in the
+eyes of weak people, as after violent exercise, intoxication, or want of
+sleep.
+
+6. A contraction of the fibres somewhat greater than usual introduces
+pleasurable sensation into the system, according to the fourth law of
+animal causation. Hence the pleasure in the beginning of drunkenness is
+owing to the increased action of the system from the stimulus of vinous
+spirit or of opium. If the contractions be still greater in energy or
+duration, painful sensations are introduced, as in consequence of great
+heat, or caustic applications, or fatigue.
+
+If any part of the system, which is used to perpetual activity, as the
+stomach, or heart, or the fine vessels of the skin, acts for a time with
+less energy, another kind of painful sensation ensues, which is called
+hunger, or faintness, or cold. This occurs in a less degree in the
+locomotive muscles, and is called wearysomeness. In the two former kinds of
+sensation there is an expenditure of sensorial power, in these latter there
+is an accumulation of it.
+
+7. We have used the words exertion of sensorial power as a general term to
+express either irritation, sensation, volition, or association; that is, to
+express the activity or motion of the spirit of animation, at the time it
+produces the contractions of the fibrous parts of the system. It may be
+supposed that there may exist a greater or less mobility of the fibrous
+parts of our system, or a propensity to be stimulated into contraction by
+the greater or less quantity or energy of the spirit of animation; and that
+hence if the exertion of the sensorial power be in its natural state, and
+the mobility of the fibres be increased, the same quantity of fibrous
+contraction will be caused, as if the mobility of the fibres continues in
+its natural state, and the sensorial exertion be increased.
+
+Thus it may be conceived, that in diseases accompanied with strength, as in
+inflammatory fevers with arterial strength, that the cause of greater
+fibrous contraction, may exist in the increased mobility of the fibres,
+whose contractions are thence both more forceable and more frequent. And
+that in diseases attended with debility, as in nervous fevers, where the
+fibrous contractions are weaker, and more frequent, it may be conceived
+that the cause consists in a decrease of mobility of the fibres; and that
+those weak constitutions, which are attended with cold extremities and
+large pupils of the eyes, may possess less mobility of the contractile
+fibres, as well as less quantity of exertion of the spirit of animation.
+
+In answer to this mode of reasoning it may be sufficient to observe, that
+the contractile fibres consist of inert matter, and when the sensorial
+power is withdrawn, as in death, they possess no power of motion at all,
+but remain in their last state, whether of contraction or relaxation, and
+must thence derive the whole of this property from the spirit of animation.
+At the same time it is not improbable, that the moving fibres of strong
+people may possess a capability of receiving or containing a greater
+quantity of the spirit of animation than those of weak people.
+
+In every contraction of a fibre there is an expenditure of the sensorial
+power, or spirit of animation; and where the exertion of this sensorial
+power has been for some time increased, and the muscles or organs of sense
+have in consequence acted with greater energy, its propensity to activity
+is proportionally lessened; which is to be ascribed to the exhaustion or
+diminution of its quantity. On the contrary, where there has been less
+fibrous contraction than usual for a certain time, the sensorial power or
+spirit of animation becomes accumulated in the inactive part of the system.
+Hence vigour succeeds rest, and hence the propensity to action of all our
+organs of sense and muscles is in a state of perpetual fluctuation. The
+irritability for instance of the retina, that is, its quantity of sensorial
+power, varies every moment according to the brightness or obscurity of the
+object last beheld compared with the present one. The same occurs to our
+sense of heat, and to every part of our system, which is capable of being
+excited into action.
+
+When this variation of the exertion of the sensorial power becomes much and
+permanently above or beneath the natural quantity, it becomes a disease. If
+the irritative motions be too great or too little, it shews that the
+stimulus of external things affect this sensorial power too violently or
+too inertly. If the sensitive motions be too great or too little, the cause
+arises from the deficient or exuberant quantity of sensation produced in
+consequence of the motions of the muscular fibres or organs of sense; if
+the voluntary actions are diseased the cause is to be looked for in the
+quantity of volition produced in consequence of the desire or aversion
+occasioned by the painful or pleasurable sensations above mentioned. And
+the diseases of associations probably depend on the greater or less
+quantity of the other three sensorial powers by which they were formed.
+
+From whence it appears that the propensity to action, whether it be called
+irritability, sensibility, voluntarity, or associability, is only another
+mode of expression for the quantity of sensorial power residing in the
+organ to be excited. And that on the contrary the words inirritability and
+insensibility, together with inaptitude to voluntary and associate motions,
+are synonymous with deficiency of the quantity of sensorial power, or of
+the spirit of animation, residing in the organs to be excited.
+
+II. _Of sensorial Exertion._
+
+1. There are three circumstances to be attended to in the production of
+animal motions, 1st. The stimulus. 2d. The sensorial power. 3d. The
+contractile fibre. 1st. A stimulus, external to the organ, originally
+induces into action the sensorial faculty termed irritation; this produces
+the contraction of the fibres, which, if it be perceived at all, introduces
+pleasure or pain; which in their active state are termed sensation; which
+is another sensorial faculty, and occasionally produces contraction of the
+fibres; this pleasure or pain is therefore to be considered as another
+stimulus, which may either act alone or in conjunction with the former
+faculty of the sensorium termed irritation.
+
+This new stimulus of pleasure or pain either induces into action the
+sensorial faculty termed sensation, which then produces the contraction of
+the fibres; or it introduces desire or aversion, which excite into action
+another sensorial faculty, termed volition, and may therefore be considered
+as another stimulus, which either alone or in conjunction with one or both
+of the two former faculties of the sensorium produces the contraction of
+animal fibres. There is another sensorial power, that of association, which
+perpetually, in conjunction with one or more of the above, and frequently
+singly, produces the contraction of animal fibres, and which is itself
+excited into action by the previous motions of contracting fibres.
+
+Now as the sensorial power, termed irritation, residing in any particular
+fibres, is excited into exertion by the stimulus of external bodies acting
+on those fibres; the sensorial power, termed sensation, residing in any
+particular fibres is excited into exertion by the stimulus of pleasure or
+pain acting on those fibres; the sensorial power, termed volition, residing
+in any particular fibres is excited into exertion by the stimulus of desire
+or aversion; and the sensorial power, termed association, residing in any
+particular fibres, is excited into action by the stimulus of other fibrous
+motions, which had frequently preceded them. The word stimulus may
+therefore be used without impropriety of language, for any of these four
+causes, which excite the four sensorial powers into exertion. For though
+the immediate cause of volition has generally been termed _a motive_; and
+that of irritation only has generally obtained the name of _stimulus_; yet
+as the immediate cause, which excites the sensorial powers of sensation, or
+of association into exertion, have obtained no general name, we shall use
+the word stimulus for them all.
+
+Hence the quantity of motion produced in any particular part of the animal
+system will be as the quantity of stimulus and the quantity of sensorial
+power, or spirit of animation, residing in the contracting fibres. Where
+both these quantities are great, _strength_ is produced, when that word is
+applied to the motions of animal bodies. Where either of them is deficient,
+_weakness_ is produced, as applied to the motions of animal bodies.
+
+Now as the sensorial power, or spirit of animation, is perpetually
+exhausted by the expenditure of it in fibrous contractions, and is
+perpetually renewed by the secretion or production of it in the brain and
+spinal marrow, the quantity of animal strength must be in a perpetual state
+of fluctuation on this account; and if to this be added the unceasing
+variation of all the four kinds of stimulus above described, which produce
+the exertions of the sensorial powers, the ceaseless vicissitude of animal
+strength becomes easily comprehended.
+
+If the quantity of sensorial power remains the same, and the quantity of
+stimulus be lessened, a weakness of the fibrous contractions ensues, which
+may be denominated _debility from defect of stimulus_. If the quantity of
+stimulus remains the same, and the quantity of sensorial power be lessened,
+another kind of weakness ensues, which may be termed _debility from defect
+of sensorial power_; the former of these is called by Dr. Brown, in his
+Elements of Medicine, direct debility, and the latter indirect debility.
+The coincidence of some parts of this work with correspondent deductions in
+the Brunonian Elementa Medicina, a work (with some exceptions) of great
+genius, must be considered as confirmations of the truth of the theory, as
+they were probably arrived at by different trains of reasoning.
+
+Thus in those who have been exposed to cold and hunger there is a
+deficiency of stimulus. While in nervous fever there is a deficiency of
+sensorial power. And in habitual drunkards, in a morning before their usual
+potation, there is a deficiency both of stimulus and of sensorial power.
+While, on the other hand, in the beginning of intoxication there is an
+excess of stimulus; in the hot-ach, after the hands have been immersed in
+snow, there is a redundancy of sensorial power; and in inflammatory
+diseases with arterial strength, there is an excess of both.
+
+Hence if the sensorial power be lessened, while the quantity of stimulus
+remains the same as in nervous fever, the frequency of repetition of the
+arterial contractions may continue, but their force in respect to removing
+obstacles, as in promoting the circulation of the blood, or the velocity of
+each contraction, will be diminished, that is, the animal strength will be
+lessened. And secondly, if the quantity of sensorial power be lessened, and
+the stimulus be increased to a certain degree, as in giving opium in
+nervous fevers, the arterial contractions may be performed more frequently
+than natural, yet with less strength.
+
+And thirdly, if the sensorial power continues the same in respect to
+quantity, and the stimulus be somewhat diminished, as in going into a
+darkish room, or into a coldish bath, suppose of about eighty degrees of
+heat, as Buxton-bath, a temporary weakness of the affected fibres is
+induced, till an accumulation of sensorial power gradually succeeds, and
+counterbalances the deficiency of stimulus, and then the bath ceases to
+feel cold, and the room ceases to appear dark; because the fibres of the
+subcutaneous vessels, or of the organs of sense, act with their usual
+energy.
+
+A set of muscular fibres may thus be stimulated into violent exertion, that
+is, they may act frequently, and with their whole sensorial power, but may
+nevertheless not act strongly; because the quantity of their sensorial
+power was originally small, or was previously exhausted. Hence a stimulus
+may be great, and the irritation in consequence act with its full force, as
+in the hot paroxysms of nervous fever; but if the sensorial power, termed
+irritation, be small in quantity, the force of the fibrous contractions,
+and the times of their continuance in their contracted state, will be
+proportionally small.
+
+In the same manner in the hot paroxysm of putrid fevers, which are shewn in
+Sect. XXXIII. to be inflammatory fevers with arterial debility, the
+sensorial power termed sensation is exerted with great activity, yet the
+fibrous contractions, which produce the circulation of the blood, are
+performed without strength, because the quantity of sensorial power then
+residing in that part of the system is small.
+
+Thus in irritative fever with arterial strength, that is, with excess of
+spirit of animation, the quantity of exertion during the hot part of the
+paroxysm is to be estimated from the quantity of stimulus, and the quantity
+of sensorial power. While in sensitive (or inflammatory) fever with
+arterial strength, that is, with excess of spirit of animation, the violent
+and forcible actions of the vascular system during the hot part of the
+paroxysm are induced by the exertions of two sensorial powers, which are
+excited by two kinds of stimulus. These are the sensorial power of
+irritation excited by the stimulus of bodies external to the moving fibres,
+and the sensorial power of sensation excited by the pain in consequence of
+the increased contractions of those moving fibres.
+
+And in insane people in some cases the force of their muscular actions will
+be in proportion to the quantity of sensorial power, which they possess,
+and the quantity of the stimulus of desire or aversion, which excites their
+volition into action. At the same time in other cases the stimulus of pain
+or pleasure, and the stimulus of external bodies, may excite into action
+the sensorial powers of sensation and irritation, and thus add greater
+force to their muscular actions.
+
+2. The application of the stimulus, whether that stimulus be some quality
+of external bodies, or pleasure or pain, or desire or aversion, or a link
+of association, excites the correspondent sensorial power into action, and
+this causes the contraction of the fibre. On the contraction of the fibre a
+part of the spirit of animation becomes expended, and the fibre ceases to
+contract, though the stimulus continues to be applied; till in a certain
+time the fibre having received a supply of sensorial power is ready to
+contract again, if the stimulus continues to be applied. If the stimulus on
+the contrary be withdrawn, the same quantity of quiescent sensorial power
+becomes resident in the fibre as before its contraction; as appears from
+the readiness for action of the large locomotive muscles of the body in a
+short time after common exertion.
+
+But in those muscular fibres, which are subject to constant stimulus, as
+the arteries, glands, and capillary vessels, another phenomenon occurs, if
+their accustomed stimulus be withdrawn; which is, that the sensorial power
+becomes accumulated in the contractile fibres, owing to the want of its
+being perpetually expended, or carried away, by their usual unremitted
+contractions. And on this account those muscular fibres become afterwards
+excitable into their natural actions by a much weaker stimulus; or into
+unnatural violence of action by their accustomed stimulus, as is seen in
+the hot fits of intermittent fevers, which are in consequence of the
+previous cold ones. Thus the minute vessels of the skin are constantly
+stimulated by the fluid matter of heat; if the quantity of this stimulus of
+heat be a while diminished, as in covering the hands with snow, the vessels
+cease to act, as appears from the paleness of the skin; if this cold
+application of snow be continued but a short time, the sensorial power,
+which had habitually been supplied to the fibres, becomes now accumulated
+in them, owing to the want of its being expended by their accustomed
+contractions. And thence a less stimulus of heat will now excite them into
+violent contractions.
+
+If the quiescence of fibres, which had previously been subject to perpetual
+stimulus, continues a longer time; or their accustomed stimulus be more
+completely withdrawn; the accumulation of sensorial power becomes still
+greater, as in those exposed to cold and hunger; pain is produced, and the
+organ gradually dies from the chemical changes, which take place in it; or
+it is at a great distance of time restored to action by stimulus applied
+with great caution in small quantity, as happens to some larger animals and
+to many insects, which during the winter months lie benumbed with cold, and
+are said to sleep, and to persons apparently drowned, or apparently frozen
+to death. Snails have been said to revive by throwing them into water after
+having been many years shut up in the cabinets of the curious; and eggs and
+seeds in general are restored to life after many months of torpor by the
+stimulus of warmth and moisture.
+
+The inflammation of schirrous tumours, which have long existed in a state
+of inaction, is a process of this kind; as well as the sensibility acquired
+by inflamed tendons and bones, which had at their formation a similar
+sensibility, which had so long lain dormant in their uninflamed state.
+
+3. If after long quiescence from defect of stimulus the fibres, which had
+previously been habituated to perpetual stimulus, are again exposed to but
+their usual quantity of it; as in those who have suffered the extremes of
+cold or hunger; a violent exertion of the affected organ commences, owing,
+as above explained, to the great accumulation of sensorial power. This
+violent exertion not only diminishes the accumulated spirit of animation,
+but at the same time induces pleasure or pain into the system, which,
+whether it be succeeded by inflammation or not, becomes an additional
+stimulus, and acting along with the former one, produces still greater
+exertions; and thus reduces the sensorial power in the contracting fibres
+beneath its natural quantity.
+
+When the spirit of animation is thus exhausted by useless exertions, the
+organ becomes torpid or unexcitable into action, and a second fit of
+quiescence succeeds that of abundant activity. During this second fit of
+quiescence the sensorial power becomes again accumulated, and another fit
+of exertion follows in train. These vicissitudes of exertion and inertion
+of the arterial system constitute the paroxysms of remittent fevers; or
+intermittent ones, when there is an interval of the natural action of the
+arteries between the exacerbations.
+
+In these paroxysms of fevers, which consist of the libration of the
+arterial system between the extremes of exertion and quiescence, either the
+fits become less and less violent from the contractile fibres becoming
+coming less excitable to the stimulus by habit, that is, by becoming
+accustomed to it, as explained below XII. 3. 1. or the whole sensorial
+power becomes exhausted, and the arteries cease to beat, and the patient
+dies in the cold part of the paroxysm. Or secondly, so much pain is
+introduced into the system by the violent contractions of the fibres, that
+inflammation arises, which prevents future cold fits by expending a part of
+the sensorial power in the extension of old vessels or the production of
+new ones; and thus preventing the too great accumulation or exertion of it
+in other parts of the system; or which by the great increase of stimulus
+excites into great action the whole glandular system as well as the
+arterial, and thence a greater quantity of sensorial power is produced in
+the brain, and thus its exhaustion in any peculiar part of the system
+ceases to be affected.
+
+4. Or thirdly, in consequence of the painful or pleasurable sensation above
+mentioned, desire and aversion are introduced, and inordinate volition
+succeeds; which by its own exertions expends so much of the spirit of
+animation, that the two other sensorial faculties, or irritation and
+sensation, act so much more feebly; that the paroxysms of fever, or that
+libration between the extremes of exertion and inactivity of the arterial
+system, gradually subsides. On this account a temporary insanity is a
+favourable sign in fevers, as I have had some opportunities of observing.
+
+III. _Of repeated Stimulus._
+
+1. When a stimulus is repeated more frequently than the expenditure of
+sensorial power can be renewed in the acting organ, the effect of the
+stimulus becomes gradually diminished. Thus if two grains of opium be
+swallowed by a person unused to so strong a stimulus, all the vascular
+systems in the body act with greater energy, all the secretions and the
+absorption from those secreted fluids are increased in quantity; and
+pleasure or pain are introduced into the system, which adds an additional
+stimulus to that already too great. After some hours the sensorial power
+becomes diminished in quantity, expended by the great activity of the
+system; and thence, when the stimulus of the opium is withdrawn, the fibres
+will not obey their usual degree of natural stimulus, and a consequent
+torpor or quiescence succeeds, as is experienced by drunkards, who on the
+day after a great excess of spirituous potation feel indigestion, head-ach,
+and general debility.
+
+In this fit of torpor or quiescence of a part or of the whole of the
+system, an accumulation of the sensorial power in the affected fibres is
+formed, and occasions a second paroxysm of exertion by the application only
+of the natural stimulus, and thus a libration of the sensorial exertion
+between one excess and the other continues for two or three days, where the
+stimulus was violent in degree; and for weeks in some fevers, from the
+stimulus of contagious matter.
+
+But if a second dose of opium be exhibited before the fibres have regained
+their natural quantity of sensorial power, its effect will be much less
+than the former, because the spirit of animation or sensorial power is in
+part exhausted by the previous excess of exertion. Hence all medicines
+repeated too frequently gradually lose their effect, as opium and wine.
+Many things of disagreeable taste at first cease to be disagreeable by
+frequent repetition, as tobacco; grief and pain gradually diminish, and at
+length cease altogether, and hence life itself becomes tolerable.
+
+Besides the temporary diminution of the spirit of animation or sensorial
+power, which is naturally stationary or resident in every living fibre, by
+a single exhibition of a powerful stimulus, the contractile fibres
+themselves, by the perpetual application of a new quantity of stimulus,
+before they have regained their natural quantity of sensorial power, appear
+to suffer in their capability of receiving so much as the natural quantity
+of sensorial power; and hence a permanent deficiency of spirit of animation
+takes place, however long the stimulus may have been withdrawn. On this
+cause depends the permanent debility of those, who have been addicted to
+intoxication, the general weakness of old age, and the natural debility or
+inirritability of those, who have pale skins and large pupils of their
+eyes.
+
+There is a curious phenomenon belongs to this place, which has always
+appeared difficult of solution; and that is, that opium or aloes may be
+exhibited in small doses at first, and gradually increased to very large
+ones without producing stupor or diarrhoea. In this case, though the opium
+and aloes are given in such small doses as not to produce intoxication or
+catharsis, yet they are exhibited in quantities sufficient in some degree
+to exhaust the sensorial power, and hence a stronger and a stronger dose is
+required; otherwise the medicine would soon cease to act at all.
+
+On the contrary, if the opium or aloes be exhibited in a large dose at
+first, so as to produce intoxication or diarrhoea; after a few repetitions
+the quantity of either of them may be diminished, and they will still
+produce this effect. For the more powerful stimulus dissevers the
+progressive catenations of animal motions, described in Sect. XVII. and
+introduces a new link between them; whence every repetition strengthens
+this new association or catenation, and the stimulus may be gradually
+decreased, or be nearly withdrawn, and yet the effect shall continue;
+because the sensorial power of association or catenation being united with
+the stimulus, increases in energy with every repetition of the catenated
+circle; and it is by these means that all the irritative associations of
+motions are originally produced.
+
+2. When a stimulus is repeated at such distant intervals of time, that the
+natural quantity of sensorial power becomes completely restored in the
+acting fibres, it will act with the same energy as when first applied.
+Hence those who have lately accustomed themselves to large doses of opium
+by beginning with small ones, and gradually increasing them, and repeating
+them frequently, as mentioned in the preceding paragraph; if they intermit
+the use of it for a few days only, must begin again with as small doses as
+they took at first, otherwise they will experience the inconveniences of
+intoxication.
+
+On this circumstance depend the constant unfailing effects of the various
+kinds of stimulus, which excite into action all the vascular systems in the
+body; the arterial, venous, absorbent, and glandular vessels, are brought
+into perpetual unwearied action by the fluids, which are adapted to
+stimulate them; but these have the sensorial power of association added to
+that of irritation, and even in some degree that of sensation, and even of
+volition, as will be spoken of in their places; and life itself is thus
+carried on by the production of sensorial power being equal to its waste or
+expenditure in the perpetual movement of the vascular organization.
+
+3. When a stimulus is repeated at uniform intervals of time with such
+distances between them, that the expenditure of sensorial power in the
+acting fibres becomes completely renewed, the effect is produced with
+greater facility or energy. For the sensorial power of association is
+combined with the sensorial power of irritation, or, in common language,
+the acquired habit assists the power of the stimulus.
+
+This circumstance not only obtains in the annual and diurnal catenations of
+animal motions explained in Sect. XXXVI. but in every less circle of
+actions or ideas, as in the burthen of a song, or the iterations of a
+dance; and constitutes the pleasure we receive from repetition and
+imitation; as treated of in Sect. XXII. 2.
+
+4. When a stimulus has been many times repeated at uniform intervals, so as
+to produce the complete action of the organ, it may then be gradually
+diminished, or totally withdrawn, and the action of the organ will
+continue. For the sensorial power of association becomes united with that
+of irritation, and by frequent repetition becomes at length of sufficient
+energy to carry on the new link in the circle of actions, without the
+irritation which at first introduced it.
+
+Hence, when the bark is given at stated intervals for the cure of
+intermittent fevers, if sixty grains of it be given every three hours for
+the twenty-four hours preceding the expected paroxysm, so as to stimulate
+the defective part of the system into action, and by that means to prevent
+the torpor or quiescence of the fibres, which constitutes the cold fit;
+much less than half the quantity, given before the time at which another
+paroxysm of quiescence would have taken place, will be sufficient to
+prevent it; because now the sensorial power, termed association, acts in a
+twofold manner. First, in respect to the period of the catenation in which
+the cold fit was produced, which is now dissevered by the stronger stimulus
+of the first doses of the bark; and, secondly, because each dose of bark
+being repeated at periodical times, has its effect increased by the
+sensorial faculty of association being combined with that of irritation.
+
+Now, when sixty grains of Peruvian bark are taken twice a day, suppose at
+ten o'clock and at six, for a fortnight, the irritation excited by this
+additional stimulus becomes a part of the diurnal circle of actions, and
+will at length carry on the increased action of the system without the
+assistance of the stimulus of the bark. On this theory the bitter
+medicines, chalybeates, and opiates in appropriated doses, exhibited for a
+fortnight, give permanent strength to pale feeble children, and other weak
+constitutions.
+
+5. When a defect of stimulus, as of heat, recurs at certain diurnal
+intervals, which induces some torpor or quiescence of a part of the system,
+the diurnal catenation of actions becomes disordered, and a new association
+with this link of torpid action is formed; on the next period the quantity
+of quiescence will be increased, suppose the same defect of stimulus to
+recur, because now the new association conspires with the defective
+irritation in introducing the torpid action of this part of the diurnal
+catenation. In this manner many fever-fits commence, where the patient is
+for some days indisposed at certain hours, before the cold paroxysm of
+fever is completely formed. See Sect. XVII. 3. 3. on Catenation of Animal
+Motions.
+
+6. If a stimulus, which at first excited the affected organ into so great
+exertion as to produce sensation, be continued for a certain time, it will
+cease to produce sensation both then and when repeated, though the
+irritative motions in consequence of it may continue or be re-excited.
+
+Many catenations of irritative motions were at first succeeded by
+sensation, as the apparent motions of objects when we walk past them, and
+probably the vital motions themselves in the early state of our existence.
+But as those sensations were followed by no movements of the system in
+consequence of them, they gradually ceased to be produced, not being joined
+to any succeeding link of catenation. Hence contagious matter, which has
+for some weeks stimulated the system into great and permanent sensation,
+ceases afterwards to produce general sensation, or inflammation, though it
+may still induce topical irritations. See Sect. XXXIII. 2. 8. XIX. 9.
+
+Our absorbent system then seems to receive those contagious matters, which
+it has before experienced, in the same manner as it imbibes common moisture
+or other fluids; that is, without being thrown into so violent action as to
+produce sensation; the consequence of which is an increase of daily energy
+or activity, till inflammation and its consequences succeed.
+
+7. If a stimulus excites an organ into such violent contractions as to
+produce sensation, the motions of which organ had not usually produced
+sensation, this new sensorial power, added to the irritation occasioned by
+the stimulus, increases the activity of the organ. And if this activity be
+catenated with the diurnal circle of actions, an increasing inflammation is
+produced; as in the evening paroxysms of small-pox, and other fevers with
+inflammation. And hence schirrous tumours, tendons and membranes, and
+probably the arteries themselves become inflamed, when they are strongly
+stimulated.
+
+IV. _Of Stimulus greater than natural._
+
+1. A quantity of stimulus greater than natural, producing an increased
+exertion of sensorial power, whether that exertion be in the mode of
+irritation, sensation, volition, or association, diminishes the general
+quantity of it. This fact is observable in the progress of intoxication, as
+the increased quantity or energy of the irritative motions, owing to the
+stimulus of vinous spirit, introduces much pleasurable sensation into the
+system, and much exertion of muscular or sensual motions in consequence of
+this increased sensation; the voluntary motions, and even the associate
+ones, become much impaired or diminished; and delirium and staggering
+succeed. See Sect. XXI. on Drunkenness. And hence the great prostration of
+the strength of the locomotive muscles in some fevers, is owing to the
+exhaustion of sensorial power by the increased action of the arterial
+system.
+
+In like manner a stimulus greater than natural, applied to a part of the
+system, increases the exertion of sensorial power in that part, and
+diminishes it in some other part. As in the commencement of scarlet fever,
+it is usual to see great redness and heat on the faces and breasts of
+children, while at the same time their feet are colder than natural;
+partial heats are observable in other fevers with debility, and are
+generally attended with torpor or quiescence of some other part of the
+system. But these partial exertions of sensorial power are sometimes
+attended with increased partial exertions in other parts of the system,
+which sympathize with them, as the flushing of the face after a full meal.
+Both these therefore are to be ascribed to sympathetic associations,
+explained in Sect. XXXV. and not to general exhaustion or accumulation of
+sensorial power.
+
+2. A quantity of stimulus greater than natural, producing an increased
+exertion of sensorial power in any particular organ, diminishes the
+quantity of it in that organ. This appears from the contractions of animal
+fibres being not so easily excited by a less stimulus after the organ has
+been subjected to a greater. Thus after looking at any luminous object of a
+small size, as at the setting sun, for a short time, so as not much to
+fatigue the eye, this part of the retina becomes less sensible to smaller
+quantities of light; hence when the eyes are turned on other less luminous
+parts of the sky, a dark spot is seen resembling the shape of the sun, or
+other luminous object which we last behold. See Sect. XL. No. 2.
+
+Thus we are some time before we can distinguish objects in an obscure room
+after coming from bright day-light, though the iris presently contracts
+itself. We are not able to hear weak sounds after loud ones. And the
+stomachs of those who have been much habituated to the stronger stimulus of
+fermented or spirituous liquors, are not excited into due action by weaker
+ones.
+
+3. A quantity of stimulus something greater than the last mentioned, or
+longer continued, induces the organ into spasmodic action, which ceases and
+recurs alternately. Thus on looking for a time on the setting sun, so as
+not greatly to fatigue the sight, a yellow spectrum is seen when the eyes
+are closed and covered, which continues for a time, and then disappears and
+recurs repeatedly before it entirely vanishes. See Sect. XL. No. 5. Thus
+the action of vomiting ceases and is renewed by intervals, although the
+emetic drug is thrown up with the first effort. A tenesmus continues by
+intervals some time after the exclusion of acrid excrement; and the
+pulsations of the heart of a viper are said to continue some time after it
+is cleared from its blood.
+
+In these cases the violent contractions of the fibres produce pain
+according to law 4; and this pain constitutes an additional kind or
+quantity of excitement, which again induces the fibres into contraction,
+and which painful excitement is again renewed, and again induces
+contractions of the fibres with gradually diminishing effect.
+
+4. A quantity of stimulus greater than that last mentioned, or longer
+continued, induces the antagonist muscles into spasmodic action. This is
+beautifully illustrated by the ocular spectra described in Sect. XL. No. 6.
+to which the reader is referred. From those experiments there is reason to
+conclude that the fatigued part of the retina throws itself into a contrary
+mode of action like oscitation or pandiculation, as soon as the stimulus,
+which has fatigued it, is withdrawn; but that it still remains liable to be
+excited into action by any other colours except the colour with which it
+has been fatigued. Thus the yawning and stretching the limbs after a
+continued action or attitude seems occasioned by the antagonist muscles
+being stimulated by their extension during the contractions of those in
+action, or in the situation in which that action last left them.
+
+5. A quantity of stimulus greater than the last, or longer continued,
+induces variety of convulsions or fixed spasms either of the affected organ
+or of the moving fibres in the other parts of the body. In respect to the
+spectra in the eye, this is well illustrated in No. 7 and 8, of Sect. XL.
+Epileptic convulsions, as the emprosthotonos and opisthotonos, with the
+cramp of the calf of the leg, locked jaw, and other cataleptic fits, appear
+to originate from pain, as some of these patients scream aloud before the
+convulsion takes place; which seems at first to be an effort to relieve
+painful sensation, and afterwards an effort to prevent it.
+
+In these cases the violent contractions of the fibres produce so much pain,
+as to constitute a perpetual excitement; and that in so great a degree as
+to allow but small intervals of relaxation of the contracting fibres as in
+convulsions, or no intervals at all as in fixed spasms.
+
+6. A quantity of stimulus greater than the last, or longer continued,
+produces a paralysis of the organ. In many cases this paralysis is only a
+temporary effect, as on looking long on a small area of bright red silk
+placed on a sheet of white paper on the floor in a strong light, the red
+silk gradually becomes paler, and at length disappears; which evinces that
+a part of the retina, by being violently excited, becomes for a time
+unaffected by the stimulus of that colour. Thus cathartic medicines,
+opiates, poisons, contagious matter, cease to influence our system after it
+has been habituated to the use of them, except by the exhibition of
+increased quantities of them; our fibres not only become unaffected by
+stimuli, by which they have previously been violently irritated, as by the
+matter of the small-pox or measles; but they also become unaffected by
+sensation, where the violent exertions, which disabled them, were in
+consequence of too great quantity of sensation. And lastly the fibres,
+which become disobedient to volition, are probably disabled by their too
+violent exertions in consequence of too great a quantity of volition.
+
+After every exertion of our fibres a temporary paralysis succeeds, whence
+the intervals of all muscular contractions, as mentioned in No. 3 and 4 of
+this Section; the immediate cause of these more permanent kinds of
+paralysis is probably owing in the same manner to the too great exhaustion
+of the spirit of animation in the affected part; so that a stronger
+stimulus is required, or one of a different kind from that, which
+occasioned those too violent contractions, to again excite the affected
+organ into activity; and if a stronger stimulus could be applied, it must
+again induce paralysis.
+
+For these powerful stimuli excite pain at the same time, that they produce
+irritation; and this pain not only excites fibrous motions by its stimulus,
+but it also produces volition; and thus all these stimuli acting at the
+same time, and sometimes with the addition of their associations, produce
+so great exertion as to expend the whole of the sensorial power in the
+affected fibres.
+
+V. _Of Stimulus less than natural._
+
+1. A quantity of stimulus less than natural, producing a decreased exertion
+of sensorial power, occasions an accumulation of the general quantity of
+it. This circumstance is observable in the hemiplagia, in which the
+patients are perpetually moving the muscles, which are unaffected. On this
+account we awake with greater vigour after sleep, because during so many
+hours, the great usual expenditure of sensorial power in the performance of
+voluntary actions, and in the exertions of our organs of sense, in
+consequence of the irritations occasioned by external objects had been
+suspended, and a consequent accumulation had taken place.
+
+In like manner the exertion of the sensorial power less than natural in one
+part of the system, is liable to produce an increase of the exertion of it
+in some other part. Thus by the action of vomiting, in which the natural
+exertion of the motions of the stomach are destroyed or diminished, an
+increased absorption of the pulmonary and cellular lymphatics is produced,
+as is known by the increased absorption of the fluid deposited in them in
+dropsical cases. But these partial quiescences of sensorial power are also
+sometimes attended with other partial quiescences, which sympathize with
+them, as cold and pale extremities from hunger. These therefore are to be
+ascribed to the associations of sympathy explained in Sect. XXXV. and not
+to the general accumulation of sensorial power.
+
+2. A quantity of stimulus less than natural, applied to fibres previously
+accustomed to perpetual stimulus, is succeeded by accumulation of sensorial
+power in the affected organ. The truth of this proposition is evinced,
+because a stimulus less than natural, if it be somewhat greater than that
+above mentioned, will excite the organ so circumstanced into violent
+activity. Thus on a frosty day with wind, the face of a person exposed to
+the wind is at first pale and shrunk; but on turning the face from the
+wind, it becomes soon of a glow with warmth and flushing. The glow of the
+skin in emerging from the cold-bath is owing to the same cause.
+
+It does not appear, that an accumulation of sensorial power above the
+natural quantity is acquired by those muscles, which are not subject to
+perpetual stimulus, as the locomotive muscles: these, after the greatest
+fatigue, only acquire by rest their usual aptitude to motion; whereas the
+vascular system, as the heart and arteries, after a short quiescence, are
+thrown into violent action by their natural quantity of stimulus.
+
+Nevertheless by this accumulation of sensorial power during the application
+of decreased stimulus, and by the exhaustion of it during the action of
+increased stimulus, it is wisely provided, that the actions of the vascular
+muscles and organs of sense are not much deranged by small variations of
+stimulus; as the quantity of sensorial power becomes in some measure
+inversely as the quantity of stimulus.
+
+3. A quantity of stimulus less than that mentioned above, and continued for
+some time, induces pain in the affected organ, as the pain of cold in the
+hands, when they are immersed in snow, is owing to a deficiency of the
+stimulation of heat. Hunger is a pain from the deficiency of the
+stimulation of food. Pain in the back at the commencement of ague-fits, and
+the head-achs which attend feeble people, are pains from defect of
+stimulus, and are hence relieved by opium, essential oils, spirit of wine.
+
+As the pains, which originate from defect of stimulus, only occur in those
+parts of the system, which have been previously subjected to perpetual
+stimulus; and as an accumulation of sensorial power is produced in the
+quiescent organ along with the pain, as in cold or hunger, there is reason
+to believe, that the pain is owing to the accumulation of sensorial power.
+For, in the locomotive muscles, in the retina of the eye, and other organs
+of senses, no pain occurs from the absence of stimulus, nor any great
+accumulation of sensorial power beyond their natural quantity, since these
+organs have not been used to a perpetual supply of it. There is indeed a
+greater accumulation occurs in the organ of vision after its quiescence,
+because it is subject to more constant stimulus.
+
+4. A certain quantity of stimulus less than natural induces the moving
+organ into feebler and more frequent contractions, as mentioned in No. I.
+4. of this Section. For each contraction moving through a less space, or
+with less force, that is, with less expenditure of the spirit of animation,
+is sooner relaxed, and the spirit of animation derived at each interval
+into the acting fibres being less, these intervals likewise become shorter.
+Hence the tremours of the hands of people accustomed to vinous spirit, till
+they take their usual stimulus; hence the quick pulse in fevers attended
+with debility, which is greater than in fevers attended with strength; in
+the latter the pulse seldom beats above 120 times in a minute, in the
+former it frequently exceeds 140.
+
+It must be observed, that in this and the two following articles the
+decreased action of the system is probably more frequently occasioned by
+deficiency in the quantity of sensorial power, than in the quantity of
+stimulus. Thus those feeble constitutions which have large pupils of their
+eyes, and all who labour under nervous fevers, seem to owe their want of
+natural quantity of activity in the system to the deficiency of sensorial
+power; since, as far as can be seen, they frequently possess the natural
+quantity of stimulus.
+
+5. A certain quantity of stimulus, less than that above mentioned, inverts
+the order of successive fibrous contractions; as in vomiting the vermicular
+motions of the stomach and duodenum are inverted, and their contents
+ejected, which is probably owing to the exhaustion of the spirit of
+animation in the acting muscles by a previous excessive stimulus, as by the
+root of ipecacuanha, and the consequent defect of sensorial power. The same
+retrograde motions affect the whole intestinal canal in ileus; and the
+oesophagus in globus hystericus. See this further explained in Sect. XXIX.
+No. 11. on Retrograde Motions.
+
+I must observe, also, that something similar happens in the production of
+our ideas, or sensual motions, when they are too weakly excited; when any
+one is thinking intensely about one thing, and carelessly conversing about
+another, he is liable to use the word of a contrary meaning to that which
+he designed, as cold weather for hot weather, summer for winter.
+
+6. A certain quantity of stimulus, less than that above mentioned, is
+succeeded by paralysis, first of the voluntary and sensitive motions, and
+afterwards of those of irritation, and of association, which constitutes
+death.
+
+VI. _Cure of increased Exertion._
+
+1. The cure, which nature has provided for the increased exertion of any
+part of the system, consists in the consequent expenditure of the sensorial
+power. But as a greater torpor follows this exhaustion of sensorial power,
+as explained in the next paragraph, and a greater exertion succeeds this
+torpor, the constitution frequently sinks under these increasing librations
+between exertion and quiescence; till at length complete quiescence, that
+is, death, closes the scene.
+
+For, during the great exertion of the system in the hot fit of fever, an
+increase of stimulus is produced from the greater momentum of the blood,
+the greater distention of the heart and arteries, and the increased
+production of heat, by the violent actions of the system occasioned by this
+augmentation of stimulus, the sensorial power becomes diminished in a few
+hours much beneath its natural quantity, the vessels at length cease to
+obey even these great degrees of stimulus, as shewn in Sect. XL. 9. 1. and
+a torpor of the whole or of a part of the system ensues.
+
+Now as this second cold fit commences with a greater deficiency of
+sensorial power, it is also attended with a greater deficiency of stimulus
+than in the preceding cold fit, that is, with less momentum of blood, less
+distention of the heart. On this account the second cold fit becomes more
+violent and of longer duration than the first; and as a greater
+accumulation of sensorial power must be produced before the system of
+vessels will again obey the diminished stimulus, it follows, that the
+second hot fit of fever will be more violent than the former one. And that
+unless some other causes counteract either the violent exertions in the hot
+fit, or the great torpor in the cold fit, life will at length be
+extinguished by the expenditure of the whole of the sensorial power. And
+from hence it appears, that the true means of curing fevers must be such as
+decrease the action of the system in the hot fit, and increase it in the
+cold fit; that is, such as prevent the too great diminution of sensorial
+power in the hot fit, and the too great accumulation of it in the cold one.
+
+2. Where the exertion of the sensorial powers is much increased, as in the
+hot fits of fever or inflammation, the following are the usual means of
+relieving it. Decrease the irritations by blood-letting, and other
+evacuations; by cold water taken into the stomach, or injected as an enema,
+or used externally; by cold air breathed into the lungs, and diffused over
+the skin; with food of less stimulus than the patient has been accustomed
+to.
+
+3. As a cold fit, or paroxysm of inactivity of some parts of the system,
+generally precedes the hot fit, or paroxysm of exertion, by which the
+sensorial power becomes accumulated, this cold paroxysm should be prevented
+by stimulant medicines and diet, as wine, opium, bark, warmth,
+cheerfulness, anger, surprise.
+
+4. Excite into greater action some other part of the system, by which means
+the spirit of animation may be in part expended, and thence the inordinate
+actions of the diseased part may be lessened. Hence when a part of the skin
+acts violently, as of the face in the eruption of the small-pox, if the
+feet be cold they should be covered. Hence the use of a blister applied
+near a topical inflammation. Hence opium and warm bath relieve pains both
+from excess and defect of stimulus.
+
+5. First increase the general stimulation above its natural quantity, which
+may in some degree exhaust the spirit of animation, and then decrease the
+stimulation beneath its natural quantity. Hence after sudorific medicines
+and warm air, the application of refrigerants may have greater effect, if
+they could be administered without danger of producing too great torpor of
+some part of the system; as frequently happens to people in health from
+coming out of a warm room into the cold air, by which a topical
+inflammation in consequence of torpor of the mucous membrane of the nostril
+is produced, and is termed a cold in the head.
+
+VII. _Cure of decreased Exertion._
+
+1. Where the exertion of the sensorial powers is much decreased, as in the
+cold fits of fever, a gradual accumulation of the spirit of animation takes
+place; as occurs in all cases where inactivity or torpor of a part of the
+system exists; this accumulation of sensorial power increases, till stimuli
+less than natural are sufficient to throw it into action, then the cold fit
+ceases; and from the action of the natural stimuli a hot one succeeds with
+increased activity of the whole system.
+
+So in fainting fits, or syncope, there is a temporary deficiency of
+sensorial exertion, and a consequent quiescence of a great part of the
+system. This quiescence continues, till the sensorial power becomes again
+accumulated in the torpid organs; and then the usual diurnal stimuli excite
+the revivescent parts again into action; but as this kind of quiescence
+continues but a short time compared to the cold paroxysm of an ague, and
+less affects the circulatory system, a less superabundancy of exertion
+succeeds in the organs previously torpid, and a less excess of arterial
+activity. See Sect. XXXIV. 1. 6.
+
+2. In the diseases occasioned by a defect of sensorial exertion, as in cold
+fits of ague, hysteric complaint, and nervous fever, the following means
+are those commonly used. 1. Increase the stimulation above its natural
+quantity for some weeks, till a new habit of more energetic contraction of
+the fibres is established. This is to be done by wine, opium, bark, steel,
+given at exact periods, and in appropriate quantities; for if these
+medicines be given in such quantity, as to induce the least degree of
+intoxication, a debility succeeds from the useless exhaustion of spirit of
+animation in consequence of too great exertion of the muscles or organs of
+sense. To these irritative stimuli should be added the sensitive ones of
+cheerful ideas, hope, affection.
+
+3. Change the kinds of stimulus. The habits acquired by the constitution
+depend on such nice circumstances, that when one kind of stimulus ceases to
+excite the sensorial power into the quantity of exertion necessary to
+health, it is often sufficient to change the stimulus for another
+apparently similar in quantity and quality. Thus when wine ceases to
+stimulate the constitution, opium in appropriate doses supplies the defect;
+and the contrary. This is also observed in the effects of cathartic
+medicines, when one loses its power, another, apparently less efficacious,
+will succeed. Hence a change of diet, drink, and stimulating medicines, is
+often advantageous in diseases of debility.
+
+4. Stimulate the organs, whose motions are associated with the torpid parts
+of the system. The actions of the minute vessels of the various parts of
+the external skin are not only associated with each other, but are strongly
+associated with those of some of the internal membranes, and particularly
+of the stomach. Hence when the exertion of the stomach is less than
+natural, and indigestion and heartburn succeed, nothing so certainly
+removes these symptoms as the stimulus of a blister on the back. The
+coldness of the extremities, as of the nose, ears, or fingers, are hence
+the best indication for the successful application of blisters.
+
+5. Decrease the stimulus for a time. By lessening the quantity of heat for
+a minute or two by going into the cold bath, a great accumulation of
+sensorial power is produced; for not only the minute vessels of the whole
+external skin for a time become inactive, as appears by their paleness; but
+the minute vessels of the lungs lose much of their activity also by concert
+with those of the skin, as appears from the difficulty of breathing at
+first going into cold water. On emerging from the bath the sensorial power
+is thrown into great exertion by the stimulus of the common degree of the
+warmth of the atmosphere, and a great production of animal heat is the
+consequence. The longer a person continues in the cold bath the greater
+must be the present inertion of a great part of the system, and in
+consequence a greater accumulation of sensorial power. Whence M. Pomè
+recommends some melancholy patients to be kept from two to six hours in
+spring-water, and in baths still colder.
+
+6. Decrease the stimulus for a time below the natural, and then increase it
+above natural. The effect of this process, improperly used, is seen in
+giving much food, or applying much warmth, to those who have been
+previously exposed to great hunger, or to great cold. The accumulated
+sensorial power is thrown into so violent exertion, that inflammations and
+mortifications supervene, and death closes the catastrophe. In many
+diseases this method is the most successful; hence the bark in agues
+produces more certain effect after the previous exhibition of emetics. In
+diseases attended with violent pain, opium has double the effect, if
+venesection and a cathartic have been previously used. On this seems to
+have been founded the successful practice of Sydenham, who used venesection
+and a cathartic in chlorosis before the exhibition of the bark, steel, and
+opiates.
+
+7. Prevent any unnecessary expenditure of sensorial power. Hence in fevers
+with debility, a decumbent posture is preferred, with silence, little
+light, and such a quantity of heat as may prevent any chill sensation, or
+any coldness of the extremities. The pulse of patients in fevers with
+debility increases in frequency above ten pulsations in a minute on their
+rising out of bed. For the expenditure of sensorial power to preserve an
+erect posture of the body adds to the general deficiency of it, and thus
+affects the circulation.
+
+8. The longer in time and the greater in degree the quiescence or inertion
+of an organ has been, so that it still retains life or excitability, the
+less stimulus should at first be applied to it. The quantity of stimulation
+is a matter of great nicety to determine, where the torpor or quiescence of
+the fibres has been experienced in a great degree, or for a considerable
+time, as in cold fits of the ague, in continued fevers with great debility,
+or in people famished at sea, or perishing with cold. In the two last
+cases, very minute quantities of food should be first supplied, and very
+few additional degrees of heat. In the two former cases, but little
+stimulus of wine or medicine, above what they had been lately accustomed
+to, should be exhibited, and this at frequent and stated intervals, so that
+the effect of one quantity may be observed before the exhibition of
+another.
+
+If these circumstances are not attended to, as the sensorial power becomes
+accumulated in the quiescent fibres, an inordinate exertion takes place by
+the increase of stimulus acting on the accumulated quantity of sensorial
+power, and either the paralysis, or death of the contractile fibres ensues,
+from the total expenditure of the sensorial power in the affected organ,
+owing to this increase of exertion, like the debility after intoxication.
+Or, secondly, the violent exertions above mentioned produce painful
+sensation, which becomes a new stimulus, and by thus producing
+inflammation, and increasing the activity of the fibres already too great,
+sooner exhausts the whole of the sensorial power in the acting organ, and
+mortification, that is, the death of the part, supervenes.
+
+Hence there have been many instances of people, whose limbs have been long
+benumbed by exposure to cold, who have lost them by mortification on their
+being too hastily brought to the fire; and of others, who were nearly
+famished at sea, who have died soon after having taken not more than an
+usual meal of food. I have heard of two well-attested instances of patients
+in the cold fit of ague, who have died from the exhibition of gin and
+vinegar, by the inflammation which ensued. And in many fevers attended with
+debility, the unlimited use of wine, and the wanton application of
+blisters, I believe, has destroyed numbers by the debility consequent to
+too great stimulation, that is, by the exhaustion of the sensorial power by
+its inordinate exertion.
+
+Wherever the least degree of intoxication exists, a proportional debility
+is the consequence; but there is a golden rule by which the necessary and
+useful quantity of stimulus in fevers with debility may be ascertained.
+When wine or beer are exhibited either alone or diluted with water, if the
+pulse becomes slower the stimulus is of a proper quantity; and should be
+repeated every two or three hours, or when the pulse again becomes quicker.
+
+In the chronical debility brought on by drinking spirituous or fermented
+liquors, there is another golden rule by which I have successfully directed
+the quantity of spirit which they may safely lessen, for there is no other
+means by which they can recover their health. It should be premised, that
+where the power of digestion in these patients is totally destroyed, there
+is not much reason to expect a return to healthful vigour.
+
+I have directed several of these patients to omit one fourth part of the
+quantity of vinous spirit they have been lately accustomed to, and if in a
+fortnight their appetite increases, they are advised to omit another fourth
+part; but if they perceive that their digestion becomes impaired from the
+want of this quantity of spirituous potation, they are advised to continue
+as they are, and rather bear the ills they have, than risk the encounter of
+greater. At the same time flesh-meat with or without spice is recommended,
+with Peruvian bark and steel in small quantities between their meals, and
+half a grain of opium or a grain, with five or eight grains of rhubarb at
+night.
+
+       *       *       *       *       *
+
+SECT. XIII.
+
+OF VEGETABLE ANIMATION.
+
+    I. 1. _Vegetables are irritable; mimosa, dionæa muscipula. Vegetable
+    secretions._ 2. _Vegetable buds are inferior animals, are liable to
+    greater or less irritability._ II. _Stamens and pistils of plants shew
+    marks of sensibility._ III. _Vegetables possess some degree of
+    volition._ IV. _Motions of plants are associated like those of
+    animals._ V. 1. _Vegetable structure like that of animals, their
+    anthers and stigmas are living creatures. Male-flowers of Vallisneria._
+    2. _Whether vegetables, possess ideas? They have organs of sense as of
+    touch and smell, and ideas of external things?_
+
+I. 1. The fibres of the vegetable world, as well as those of the animal,
+are excitable into a variety of motion by irritations of external objects.
+This appears particularly in the mimosa or sensitive plant, whose leaves
+contract on the slightest injury; the dionæa muscipula, which was lately
+brought over from the marshes of America, presents us with another curious
+instance of vegetable irritability; its leaves are armed with spines on
+their upper edge, and are spread on the ground around the stem; when an
+insect creeps on any of them in its passage to the flower or seed, the leaf
+shuts up like a steel rat-trap, and destroys its enemy. See Botanic Garden,
+Part II. note on Silene.
+
+The various secretions of vegetables, as of odour, fruit, gum, resin, wax,
+honey, seem brought about in the same manner as in the glands of animals;
+the tasteless moisture of the earth is converted by the hop-plant into a
+bitter juice; as by the caterpillar in the nut-shell the sweet kernel is
+converted into a bitter powder. While the power of absorption in the roots
+and barks of vegetables is excited into action by the fluids applied to
+their mouths like the lacteals and lymphatics of animals.
+
+2. The individuals of the vegetable world may be considered as inferior or
+less perfect animals; a tree is a congeries of many living buds, and in
+this respect resembles the branches of coralline, which are a congeries of
+a multitude of animals. Each of these buds of a tree has its proper leaves
+or petals for lungs, produces its viviparous or its oviparous offspring in
+buds or seeds; has its own roots, which extending down the stem of the tree
+are interwoven with the roots of the other buds, and form the bark, which
+is the only living part of the stem, is annually renewed, and is
+superinduced upon the former bark, which then dies, and with its stagnated
+juices gradually hardening into wood forms the concentric circles, which we
+see in blocks of timber.
+
+The following circumstances evince the individuality of the buds of trees.
+First, there are many trees, whose whole internal wood is perished, and yet
+the branches are vegete and healthy. Secondly, the fibres of the barks of
+trees are chiefly longitudinal, resembling roots, as is beautifully seen in
+those prepared barks, that were lately brought from Otaheita. Thirdly, in
+horizontal wounds of the bark of trees, the fibres of the upper lip are
+always elongated downwards like roots, but those of the lower lip do not
+approach to meet them. Fourthly, if you wrap wet moss round any joint of a
+vine, or cover it with moist earth, roots will shoot out from it. Fifthly,
+by the inoculation or engrafting of trees many fruits are produced from one
+stem. Sixthly, a new tree is produced from a branch plucked from an old
+one, and set in the ground. Whence it appears that the buds of deciduous
+trees are so many annual plants, that the bark is a contexture of the roots
+of each individual bud; and that the internal wood is of no other use but
+to support them in the air, and that thus they resemble the animal world in
+their individuality.
+
+The irritability of plants, like that of animals, appears liable to be
+increased or decreased by habit; for those trees or shrubs, which are
+brought from a colder climate to a warmer, put out their leaves and
+blossoms a fortnight sooner than the indigenous ones.
+
+Professor Kalm, in his Travels in New York, observes that the apple-trees
+brought from England blossom a fortnight sooner than the native ones. In
+our country the shrubs, that are brought a degree or two from the north,
+are observed to flourish better than those, which come from the south. The
+Siberian barley and cabbage are said to grow larger in this climate than
+the similar more southern vegetables. And our hoards of roots, as of
+potatoes and onions, germinate with less heat in spring, after they have
+been accustomed to the winter's cold, than in autumn after the summer's
+heat.
+
+II. The stamens and pistils of flowers shew evident marks of sensibility,
+not only from many of the stamens and some pistils approaching towards each
+other at the season of impregnation, but from many of them closing their
+petals and calyxes during the cold parts of the day. For this cannot be
+ascribed to irritation, because cold means a defect of the stimulus of
+heat; but as the want of accustomed stimuli produces pain, as in coldness,
+hunger, and thirst of animals, these motions of vegetables in closing up
+their flowers must be ascribed to the disgreeable sensation, and not to the
+irritation of cold. Others close up their leaves during darkness, which,
+like the former, cannot be owing to irritation, as the irritating material
+is withdrawn.
+
+The approach of the anthers in many flowers to the stigmas, and of the
+pistils of some flowers to the anthers, must be ascribed to the passion of
+love, and hence belongs to sensation, not to irritation.
+
+III. That the vegetable world possesses some degree of voluntary powers,
+appears from their necessity to sleep, which we have shewn in Sect. XVIII.
+to consist in the temporary abolition of voluntary power. This voluntary
+power seems to be exerted in the circular movement of the tendrils of
+vines, and other climbing vegetables; or in the efforts to turn the upper
+surface of their leaves, or their flowers to the light.
+
+IV. The associations of fibrous motions are observable in the vegetable
+world, as well as in the animal. The divisions of the leaves of the
+sensitive plant have been accustomed to contract at the same time from the
+absence of light; hence if by any other circumstance, as a slight stroke or
+injury, one division is irritated into contraction, the neighbouring ones
+contract also, from their motions being associated with those of the
+irritated part. So the various stamina of the class of syngenesia have been
+accustomed to contract together in the evening, and thence if you stimulate
+one of them with a pin, according to the experiment of M. Colvolo, they all
+contract from their acquired associations.
+
+To evince that the collapsing of the sensitive plant is not owing to any
+mechanical vibrations propagated along the whole branch, when a single leaf
+is struck with the finger, a leaf of it was slit with sharp scissors, and
+some seconds of time passed before the plant seemed sensible of the injury;
+and then the whole branch collapsed as far as the principal stem: this
+experiment was repeated several times with the least possible impulse to
+the plant.
+
+V. 1. For the numerous circumstances in which vegetable buds are analogous
+to animals, the reader is referred to the additional notes at the end of
+the Botanic Garden, Part I. It is there shewn, that the roots of vegetables
+resemble the lacteal system of animals; the sap-vessels in the early
+spring, before their leaves expand, are analogous to the placental vessels
+of the foetus; that the leaves of land-plants resemble lungs, and those of
+aquatic plants the gills of fish; that there are other systems of vessels
+resembling the vena portarum of quadrupeds, or the aorta of fish; that the
+digestive power of vegetables is similar to that of animals converting the
+fluids, which they absorb, into sugar; that their seeds resemble the eggs
+of animals, and their buds and bulbs their viviparous offspring. And,
+lastly, that the anthers and stigmas are real animals, attached indeed to
+their parent tree like polypi or coral insects, but capable of spontaneous
+motion; that they are affected with the passion of love, and furnished with
+powers of reproducing their species, and are fed with honey like the moths
+and butterflies, which plunder their nectaries. See Botanic Garden, Part I.
+add. note XXXIX.
+
+The male flowers of vallisneria approach still nearer to apparent
+animality, as they detach themselves from the parent plant, and float on
+the surface of the water to the female ones. Botanic Garden, Part II. Art.
+Vallisneria. Other flowers of the classes of monecia and diecia, and
+polygamia, discharge the fecundating farina, which floating in the air is
+carried to the stigma of the female flowers, and that at considerable
+distances. Can this be effected by any specific attraction? or, like the
+diffusion of the odorous particles of flowers, is it left to the currents
+of winds, and the accidental miscarriages of it counteracted by the
+quantity of its production?
+
+2. This leads us to a curious enquiry, whether vegetables have ideas of
+external things? As all our ideas are originally received by our senses,
+the question may be changed to, whether vegetables possess any organs of
+sense? Certain it is, that they possess a sense of heat and cold, another
+of moisture and dryness, and another of light and darkness; for they close
+their petals occasionally from the presence of cold, moisture, or darkness.
+And it has been already shewn, that these actions cannot be performed
+simply from irritation, because cold and darkness are negative quantities,
+and on that account sensation or volition are implied, and in consequence a
+sensorium or union of their nerves. So when we go into the light, we
+contract the iris; not from any stimulus of the light on the fine muscles
+of the iris, but from its motions being associated with the sensation of
+too much light on the retina: which could not take place without a
+sensorium or center of union of the nerves of the iris with those of
+vision. See Botanic Garden, Part I. Canto 3. l. 440. note.
+
+Besides these organs of sense, which distinguish cold, moisture, and
+darkness, the leaves of mimosa, and of dionæa, and of drosera, and the
+stamens of many flowers, as of the berbery, and the numerous class of
+syngenesia, are sensible to mechanic impact, that is, they possess a sense
+of touch, as well as a common sensorium; by the medium of which their
+muscles are excited into action. Lastly, in many flowers the anthers, when
+mature, approach the stigma, in others the female organ approaches to the
+male. In a plant of collinsonia, a branch of which is now before me, the
+two yellow stamens are about three eights of an inch high, and diverge from
+each other, at an angle of about fifteen degrees, the purple style is half
+an inch high, and in some flowers is now applied to the stamen on the right
+hand, and in others to that of the left; and will, I suppose, change place
+to-morrow in those, where the anthers have not yet effused their powder.
+
+I ask, by what means are the anthers in many flowers, and stigmas in other
+flowers, directed to find their paramours? How do either of them know, that
+the other exists in their vicinity? Is this curious kind of storge produced
+by mechanic attraction, or by the sensation of love? The latter opinion is
+supported by the strongest analogy, because a reproduction of the species
+is the consequence; and then another organ of sense must be wanted to
+direct these vegetable amourettes to find each other, one probably
+analogous to our sense of smell, which in the animal world directs the
+new-born infant to its source of nourishment, and they may thus possess a
+faculty of perceiving as well as of producing odours.
+
+Thus, besides a kind of taste at the extremities of their roots, similar to
+that of the extremities of our lacteal vessels, for the purpose of
+selecting their proper food: and besides different kinds of irritability
+residing in the various glands, which separate honey, wax, resin, and other
+juices from their blood; vegetable life seems to possess an organ of sense
+to distinguish the variations of heat, another to distinguish the varying
+degrees of moisture, another of light, another of touch, and probably
+another analogous to our sense of smell. To these must be added the
+indubitable evidence of their passion of love, and I think we may truly
+conclude, that they are furnished with a common sensorium belonging to each
+bud and that they must occasionally repeat those perceptions either in
+their dreams or waking hours, and consequently possess ideas of so many of
+the properties of the external world, and of their own existence.
+
+       *       *       *       *       *
+
+SECT. XIV.
+
+OF THE PRODUCTION OF IDEAS.
+
+    I. _Of material and immaterial beings. Doctrine of St. Paul._ II. 1.
+    _Of the sense of touch. Of solidity._ 2. _Of figure. Motion. Time.
+    Place. Space. Number._ 3. _Of the penetrability of matter._ 4. _Spirit
+    of animation possesses solidity, figure, visibility, &c. Of Spirits and
+    angels._ 5. _The existence of external things._ III. _Of vision._ IV.
+    _Of hearing._ V. _Of smell and taste._ VI. _Of the organ of sense by
+    which we perceive heat and cold, not by the sense of touch._ VII. _Of
+    the sense of extension, the whole of the locomotive muscles may be
+    considered as one organ of sense._ VIII. _Of the senses of hunger,
+    thirst, want of fresh air, suckling children, and lust._ IX. _Of many
+    other organs of sense belonging to the glands. Of painful sensations
+    from the excess of light, pressure, heat, itching, caustics, and
+    electricity._
+
+I. Philosophers have been much perplexed to understand, in what manner we
+become acquainted with the external world; insomuch that Dr. Berkly even
+doubted its existence, from having observed (as he thought) that none of
+our ideas resemble their correspondent objects. Mr. Hume asserts, that our
+belief depends on the greater distinctness or energy of our ideas from
+perception; and Mr. Reid has lately contended, that our belief of external
+objects is an innate principle necessarily joined with our perceptions.
+
+So true is the observation of the famous Malbranch, "that our senses are
+not given us to discover the essences of things, but to acquaint us with
+the means of preserving our existence," (L. I. ch. v.) a melancholy
+reflection to philosophers!
+
+Some philosophers have divided all created beings into material and
+immaterial: the former including all that part of being, which obeys the
+mechanic laws of action and reaction, but which can begin no motion of
+itself; the other is the cause of all motion, and is either termed the
+power of gravity, or of specific attraction, or the spirit of animation.
+This immaterial agent is supposed to exist in or with matter, but to be
+quite distinct from it, and to be equally capable of existence, after the
+matter, which now possesses it, is decomposed.
+
+Nor is this theory ill supported by analogy, since heat, electricity, and
+magnetism, can be given to or taken from a piece of iron; and must
+therefore exist, whether separated from the metal, or combined with it.
+From a parity of reasoning, the spirit of animation, would appear to be
+capable of existing as well separately from the body as with it.
+
+I beg to be understood, that I do not wish to dispute about words, and am
+ready to allow, that the powers of gravity, specific attraction,
+electricity, magnetism, and even the spirit of animation, may consist of
+matter of a finer kind; and to believe, with St. Paul and Malbranch, that
+the ultimate cause only of all motion is immaterial, that is God. St. Paul
+says, "in him we live and move, and have our being;" and, in the 15th
+chapter to the Corinthians, distinguishes between the psyche or living
+spirit, and the pneuma or reviving spirit. By the words spirit of animation
+or sensorial power, I mean only that animal life, which mankind possesses
+in common with brutes, and in some degree even with vegetables, and leave
+the consideration of the immortal part of us, which is the object of
+religion, to those who treat of revelation.
+
+II. 1. _Of the Sense of Touch._
+
+The first idea we become acquainted with, are those of the sense of touch;
+for the foetus must experience some varieties of agitation, and exert some
+muscular action, in the womb; and may with great probability be supposed
+thus to gain some ideas of its own figure, of that of the uterus, and of
+the tenacity of the fluid, that surrounds it, (as appears from the facts
+mentioned in the succeeding Section upon Instinct.)
+
+Many of the organs of sense are confined to a small part of the body, as
+the nostrils, ear, or eye, whilst the sense of touch is diffused over the
+whole skin, but exists with a more exquisite degree of delicacy at the
+extremities of the fingers and thumbs, and in the lips. The sense of touch
+is thus very commodiously disposed for the purpose of encompassing smaller
+bodies, and for adapting itself to the inequalities of larger ones. The
+figure of small bodies seems to be learnt by children by their lips as much
+as by their fingers; on which account they put every new object to their
+mouths, when they are satiated with food, as well as when they are hungry.
+And puppies seem to learn their ideas of figure principally by the lips in
+their mode of play.
+
+We acquire our tangible ideas of objects either by the simple pressure of
+this organ of touch against a solid body, or by moving our organ of touch
+along the surface of it. In the former case we learn the length and breadth
+of the object by the quantity of our organ of touch, that is impressed by
+it: in the latter case we learn the length and breadth of objects by the
+continuance of their pressure on our moving organ of touch.
+
+It is hence, that we are very slow in acquiring our tangible ideas, and
+very slow in recollecting them; for if I now think of the tangible idea of
+a cube, that is, if I think of its figure, and of the solidity of every
+part of that figure, I must conceive myself as passing my fingers over it,
+and seem in some measure to feel the idea, as I formerly did the
+impression, at the ends of them, and am thus very slow in distinctly
+recollecting it.
+
+When a body compresses any part of our sense of touch, what happens? First,
+this part of our sensorium undergoes a mechanical compression, which is
+termed a stimulus; secondly, an idea, or contraction of a part of the organ
+of sense is excited; thirdly, a motion of the central parts, or of the
+whole sensorium, which is termed sensation, is produced; and these three
+constitute the perception of solidity.
+
+2. _Of Figure, Motion, Time, Place, Space, Number._
+
+No one will deny, that the medulla of the brain and nerves has a certain
+figure; which, as it is diffused through nearly the whole of the body, must
+have nearly the figure of that body. Now it follows, that the spirit of
+animation, or living principle, as it occupies this medulla, and no other
+part, (which is evinced by a great variety of cruel experiments on living
+animals,) it follows, that this spirit of animation has also the same
+figure as the medulla above described. I appeal to common sense! the spirit
+of animation acts, Where does it act? It acts wherever there is the medulla
+above mentioned; and that whether the limb is yet joined to a living
+animal, or whether it be recently detached from it; as the heart of a viper
+or frog will renew its contractions, when pricked with a pin, for many
+minutes of time after its exsection from the body.--Does it act any where
+else?--No; then it certainly exists in this part of space, and no where
+else; that is, it hath figure; namely, the figure of the nervous system,
+which is nearly the figure of the body. When the idea of solidity is
+excited, as above explained, a part of the extensive organ of touch is
+compressed by some external body, and this part of the sensorium so
+compressed exactly resembles _in figure_ the figure of the body that
+compressed it. Hence, when we acquire the idea of solidity, we acquire at
+the same time the idea of FIGURE; and this idea of figure, or motion of _a
+part_ of the organ of touch, exactly resembles _in its figure_ the figure
+of the body that occasions it; and thus exactly acquaints us with this
+property of the external world.
+
+Now, as the whole universe with all its parts possesses a certain form or
+figure, if any part of it moves, that form or figure of the whole is
+varied: hence, as MOTION is no other than a perpetual variation of figure,
+our idea of motion is also a real resemblance of the motion that produced
+it.
+
+It may be said in objection to this definition of motion, that an ivory
+globe may revolve on its axis, and that here will be a motion without
+change of figure. But the figure of the particle _x_ on one side of this
+globe is not the _same_ figure as the figure of _y_ on the other side, any
+more than the particles themselves are the same, though they are _similar_
+figures; and hence they cannot change place with each other without
+disturbing or changing the figure of the whole.
+
+Our idea of TIME is from the same source, but is more abstracted, as it
+includes only the comparative velocities of these variations of figure;
+hence if it be asked, How long was this book in printing? it may be
+answered, Whilst the sun was passing through Aries.
+
+Our idea of PLACE includes only the figure of a group of bodies, not the
+figures of the bodies themselves. If it be asked where is Nottinghamshire,
+the answer is, it is surrounded by Derbyshire, Lincolnshire and
+Leicestershire; hence place is our idea of the figure of one body
+surrounded by the figures of other bodies.
+
+The idea of SPACE is a more abstracted idea of place excluding the group of
+bodies.
+
+The idea of NUMBER includes only the particular arrangements, or
+distributions of a group of bodies, and is therefore only a more abstracted
+idea of the parts of the figure of the group of bodies; thus when I say
+England is divided into forty counties, I only speak of certain divisions
+of its figure.
+
+Hence arises the certainty of the mathematical sciences, as they explain
+these properties of bodies, which are exactly resembled by our ideas of
+them, whilst we are obliged to collect almost all our other knowledge from
+experiment; that is, by observing the effects exerted by one body upon
+another.
+
+3. _Of the Penetrability of Matter._
+
+The impossibility of two bodies existing together in the same space cannot
+be deduced from our idea of solidity, or of figure. As soon as we perceive
+the motions of objects that surround us, and learn that we possess a power
+to move our own bodies, we experience, that those objects, which excite in
+us the idea of solidity and of figure, oppose this voluntary movement of
+our own organs; as whilst I endeavour to compress between my hands an ivory
+ball into a spheroid. And we are hence taught by experience, that our own
+body and those, which we touch, cannot exist in the same part of space.
+
+But this by no means demonstrates, that no two bodies can exist together in
+the same part of space. Galilæo in the preface to his works seems to be of
+opinion, that matter is not impenetrable; Mr. Michel, and Mr. Boscowich in
+his Theoria. Philos. Natur. have espoused this hypothesis: which has been
+lately published by Dr. Priestley, to whom the world is much indebted for
+so many important discoveries in science. (Hist. of Light and Colours, p.
+391.) The uninterrupted passage of light through transparent bodies, of the
+electric æther through metallic and aqueous bodies, and of the magnetic
+effluvia through all bodies, would seem to give some probability to this
+opinion. Hence it appears, that beings may exist without possessing the
+property of solidity, as well as they can exist without possessing the
+properties, which excite our smell or taste, and can thence occupy space
+without detruding other bodies from it; but we cannot become acquainted
+with such beings by our sense of touch, any more than we can with odours or
+flavours without our senses of smell and taste.
+
+But that any being can exist without existing in space, is to my ideas
+utterly incomprehensible. My appeal is to common sense. _To be_ implies a
+when and a where; the one is comparing it with the motions of other beings,
+and the other with their situations.
+
+If there was but one object, as the whole creation may be considered as one
+object, then I cannot ask where it exists? for there are no other objects
+to compare its situation with. Hence if any one denies, that a being exists
+in space, he denies, that there are any other beings but that one; for to
+answer the question, "Where does it exist?" is only to mention the
+situation of the objects that surround it.
+
+In the same manner if it be asked--"When does a being exist?" The answer
+only specifies the successive motions either of itself, or of other bodies;
+hence to say, a body exists not in time, is to say, that there is, or was,
+no motion in the world.
+
+4. _Of the Spirit of Animation._
+
+But though there may exist beings in the universe, that have not the
+property of solidity; that is, which can possess any part of space, at the
+same time that it is occupied by other bodies; yet there may be other
+beings, that can assume this property of solidity, or disrobe themselves of
+it occasionally, as we are taught of spirits, and of angels; and it would
+seem, that THE SPIRIT OF ANIMATION must be endued with this property,
+otherwise how could it occasionally give motion to the limbs of
+animals?--or be itself stimulated into motion by the obtrusions of
+surrounding bodies, as of light, or odour?
+
+If the spirit of animation was always necessarily penetrable, it could not
+influence or be influenced by the solidity of common matter; they would
+exist together, but could not detrude each other from the part of space,
+where they exist; that is, they could not communicate motion to each other.
+_No two things can influence or affect each other, which have not some
+property common to both of them_; for to influence or affect another body
+is to give or communicate some property to it, that it had not before; but
+how can one body give that to another, which it does not possess
+itself?--The words imply, that they must agree in having the power or
+faculty of possessing some common property. Thus if one body removes
+another from the part of space, that it possesses, it must have the power
+of occupying that space itself: and if one body communicates heat or motion
+to another, it follows, that they have alike the property of possessing
+heat or motion.
+
+Hence the spirit of animation at the time it communicates or receives
+motion from solid bodies, must itself possess some property of solidity.
+And in consequence at the time it receives other kinds of motion from
+light, it must possess that property, which light possesses, to communicate
+that kind of motion; and for which no language has a name, unless it may be
+termed Visibility. And at the time it is stimulated into other kinds of
+animal motion by the particles of sapid and odorous bodies affecting the
+senses of taste and smell, it must resemble these particles of flavour, and
+of odour, in possessing some similar or correspondent property; and for
+which language has no name, unless we may use the words Saporosity and
+Odorosity for those common properties, which are possessed by our organs of
+taste and smell, and by the particles of sapid and odorous bodies; as the
+words Tangibility and Audibility may express the common property possessed
+by our organs of touch, and of hearing, and by the solid bodies, or their
+vibrations, which affect those organs.
+
+5. Finally, though the figures of bodies are in truth resembled by the
+figure of the part of the organ of touch, which is stimulated into motion;
+and that organ resembles the solid body, which stimulates it, in its
+property of solidity; and though the sense of hearing resembles the
+vibrations of external bodies in its capability of being stimulated into
+motion by those vibrations; and though our other organs of sense resemble
+the bodies, that stimulate them, in their capability of being stimulated by
+them; and we hence become acquainted with these properties of the external
+world; yet as we can repeat all these motions of our organs of sense by the
+efforts of volition, or in consequence of the sensation of pleasure or
+pain, or by their association with other fibrous motions, as happens in our
+reveries or in sleep, there would still appear to be some difficulty in
+demonstrating the existence of any thing external to us.
+
+In our dreams we cannot determine this circumstance, because our power of
+volition is suspended, and the stimuli of external objects are excluded;
+but in our waking hours we can compare our ideas belonging to one sense
+with those belonging to another, and can thus distinguish the ideas
+occasioned by irritation from those excited by sensation, volition, or
+association. Thus if the idea of the sweetness of sugar should be excited
+in our dreams, the whiteness and hardness of it occur at the same time by
+association; and we believe a material lump of sugar present before us. But
+if, in our waking hours, the idea of the sweetness of sugar occurs to us,
+the stimuli of surrounding objects, as the edge of the table, on which we
+press, or green colour of the grass, on which we tread, prevent the other
+ideas of the hardness and whiteness of the sugar from being exerted by
+association. Or if they should occur, we voluntarily compare them with the
+irritative ideas of the table or grass above mentioned, and detect their
+fallacy. We can thus distinguish the ideas caused by the stimuli of
+external objects from those, which are introduced by association,
+sensation, or volition; and during our waking hours can thus acquire a
+knowledge of the external world. Which nevertheless we cannot do in our
+dreams, because we have neither perceptions of external bodies, nor the
+power of volition to enable us to compare them with the ideas of
+imagination.
+
+III. _Of Vision._
+
+Our eyes observe a difference of colour, or of shade, in the prominences
+and depressions of objects, and that those shades uniformly vary, when the
+sense of touch observes any variation. Hence when the retina becomes
+stimulated by colours or shades of light in a certain form, as in a
+circular spot; we know by experience, that this is a sign, that a tangible
+body is before us; and that its figure is resembled by the miniature figure
+of the part of the organ of vision, that is thus stimulated.
+
+Here whilst the stimulated part of the retina resembles exactly the visible
+figure of the whole in miniature, the various kinds of stimuli from
+different colours mark the visible figures of the minuter parts; and by
+habit we instantly recall the tangible figures.
+
+Thus when a tree is the object of sight, a part of the retina resembling a
+flat branching figure is stimulated by various shades of colours; but it is
+by suggestion, that the gibbosity of the tree, and the moss, that fringes
+its trunk, appear before us. These are ideas of suggestion, which we feel
+or attend to, associated with the motions of the retina, or irritative
+ideas, which we do not attend to.
+
+So that though our visible ideas resemble in miniature the outline of the
+figure of coloured bodies, in other respects they serve only as a language,
+which by acquired associations introduce the tangible ideas of bodies.
+Hence it is, that this sense is so readily deceived by the art of the
+painter to our amusement and instruction. The reader will find much very
+curious knowledge on this subject in Bishop Berkley's Essay on Vision, a
+work of great ingenuity.
+
+The immediate object however of the sense of vision is light; this fluid,
+though its velocity is so great, appears to have no perceptible mechanical
+impulse, as was mentioned in the third Section, but seems to stimulate the
+retina into animal motion by its transmission through this part of the
+sensorium: for though the eyes of cats or other animals appear luminous in
+obscure places; yet it is probable, that none of the light, which falls on
+the retina, is reflected from it, but adheres to or enters into combination
+with the choroide coat behind it.
+
+The combination of the particles of light with opake bodies, and therefore
+with the choroide coat of the eye, is evinced from the heat, which is given
+out, as in other chemical combinations. For the sunbeams communicate no
+heat in their passage through transparent bodies, with which they do not
+combine, as the air continues cool even in the focus of the largest
+burning-glasses, which in a moment vitrifies a particle of opaque matter.
+
+IV. _Of the Organ of Hearing._
+
+It is generally believed, that the tympanum of the ear vibrates
+mechanically, when exposed to audible sounds, like the strings of one
+musical instrument, when the same notes are struck upon another. Nor is
+this opinion improbable, as the muscles and cartilages of the larynx are
+employed in producing variety of tones by mechanical vibration: so the
+muscles and bones of the ear seem adapted to increase or diminish the
+tension of the tympanum for the purposes of similar mechanical vibrations.
+
+But it appears from dissection, that the tympanum is not the immediate
+organ of hearing, but that like the humours and cornea of the eye, it is
+only of use to prepare the object for the immediate organ. For the portio
+mollis of the auditory nerve is not spread upon the tympanum, but upon the
+vestibulum, and cochlea, and semicircular canals of the ear; while between
+the tympanum and the expansion of the auditory nerve the cavity is said by
+Dr. Cotunnus and Dr. Meckel to be filled with water; as they had frequently
+observed by freezing the heads of dead animals before they dissected them;
+and water being a more dense fluid than air is much better adapted to the
+propagation of vibrations. We may add, that even the external opening of
+the ear is not absolutely necessary for the perception of sound: for some
+people, who from these defects would have been completely deaf, have
+distinguished acute or grave sounds by the tremours of a stick held between
+their teeth propagated along the bones of the head, (Haller. Phys. T. V. p.
+295).
+
+Hence it appears, that the immediate organ of hearing is not affected by
+the particles of the air themselves, but is stimulated into animal motion
+by the vibrations of them. And it is probable from the loose bones, which
+are found in the heads of some fishes, that the vibrations of water are
+sensible to the inhabitants of that element by a similar organ.
+
+The motions of the atmosphere, which we become acquainted with by the sense
+of touch, are combined with its solidity, weight, or vis intertiæ; whereas
+those, that are perceived by this organ, depend alone on its elasticity.
+But though the vibration of the air is the immediate object of the sense of
+hearing, yet the ideas, we receive by this sense, like those received from
+light, are only as a language, which by acquired associations acquaints us
+with those motions of tangible bodies, which depend on their elasticity;
+and which we had before learned by our sense of touch.
+
+V. _Of Smell and of Taste._
+
+The objects of smell are dissolved in the fluid atmosphere, and those of
+taste in the saliva, or other aqueous fluid, for the better diffusing them
+on their respective organs, which seem to be stimulated into animal motion
+perhaps by the chemical affinities of these particles, which constitute the
+sapidity and odorosity of bodies with the nerves of sense, which perceive
+them.
+
+Mr. Volta has lately observed a curious circumstance relative to our sense
+of taste. If a bit of clean lead and a bit of clean silver be separately
+applied to the tongue and palate no taste is perceived; but by applying
+them in contact in respect to the parts out of the mouth, and nearly so in
+respect to the parts, which are immediately applied to the tongue and
+palate, a saline or acidulous taste is perceived, as of a fluid like a
+stream of electricity passing from one of them to the other. This new
+application of the sense of taste deserves further investigation, as it may
+acquaint us with new properties of matter.
+
+From the experiments above mentioned of Galvani, Volta, Fowler, and others,
+it appears, that a plate of zinc and a plate of silver have greater effect
+than lead and silver. If one edge of a plate of silver about the size of
+half a crown-piece be placed upon the tongue, and one edge of a plate of
+zinc about the same size beneath the tongue, and if their opposite edges
+are then brought into contact before the point of the tongue, a taste is
+perceived at the moment of their coming into contact; secondly, if one of
+the above plates be put between the upper lip and the gum of the
+fore-teeth, and the other be placed under the tongue, and their exterior
+edges be then brought into contact in a darkish room, a flash of light is
+perceived in the eyes.
+
+These effects I imagine only shew the sensibility of our nerves of sense to
+very small quantities of the electric fluid, as it passes through them; for
+I suppose these sensations are occasioned by slight electric shocks
+produced in the following manner. By the experiments published by Mr.
+Bennet, with his ingenious doubler of electricity, which is the greatest
+discovery made in that science since the coated jar, and the eduction of
+lightning from the skies, it appears that zinc was always found minus, and
+silver was always found plus, when both of them were in their separate
+state. Hence, when they are placed in the manner above described, as soon
+as their exterior edges come nearly into contact, so near as to have an
+extremely thin plate of air between them, that plate of air becomes charged
+in the same manner as a plate of coated glass; and is at the same instant
+discharged through the nerves of taste or of sight, and gives the
+sensations, as above described, of light or of saporocity; and only shews
+the great sensibility of these organs of sense to the stimulus of the
+electric fluid in suddenly passing through them.
+
+VI. _Of the Sense of Heat._
+
+There are many experiments in chemical writers, that evince the existence
+of heat as a fluid element, which covers and pervades all bodies, and is
+attracted by the solutions of some of them, and is detruded from the
+combination of others. Thus from the combinations of metals with acids, and
+from those combinations of animal fluids, which are termed secretions, this
+fluid matter of heat is given out amongst the neighbouring bodies; and in
+the solutions of salts in water, or of water in air, it is absorbed from
+the bodies, that surround them; whilst in its facility in passing through
+metallic bodies, and its difficulty in pervading resins and glass, it
+resembles the properties of the electric aura; and is like that excited by
+friction, and seems like that to gravitate amongst other bodies in its
+uncombined state, and to find its equilibrium.
+
+There is no circumstance of more consequence in the animal economy than a
+due proportion of this fluid of heat; for the digestion of our nutriment in
+the stomach and bowels, and the proper qualities of all our secreted
+fluids, as they are produced or prepared partly by animal and partly by
+chemical processes, depend much on the quantity of heat; the excess of
+which, or its deficiency, alike gives us pain, and induces us to avoid the
+circumstances that occasion them. And in this the perception of heat
+essentially differs from the perceptions of the sense of touch, as we
+receive pain from too great pressure of solid bodies, but none from the
+absence of it. It is hence probable, that nature has provided us with a set
+of nerves for the perception of this fluid, which anatomists have not yet
+attended to.
+
+There may be some difficulty in the proof of this assertion; if we look at
+a hot fire, we experience no pain of the optic nerve, though the heat along
+with the light must be concentrated upon it. Nor does warm water or warm
+oil poured into the ear give pain to the organ of hearing; and hence as
+these organs of sense do not perceive small excesses or deficiences of
+heat; and as heat has no greater analogy to the solidity or to the figures
+of bodies, than it has to their colours or vibrations; there seems no
+sufficient reason for our ascribing the perception of heat and cold to the
+sense of touch; to which it has generally been attributed, either because
+it is diffused beneath the whole skin like the sense of touch, or owing to
+the inaccuracy of our observations, or the defect of our languages.
+
+There is another circumstance would induce us to believe, that the
+perceptions of heat and cold do not belong to the organ of touch; since the
+teeth, which are the least adapted for the perceptions of solidity or
+figure, are the most sensible to heat or cold; whence we are forewarned
+from swallowing those materials, whose degree of coldness or of heat would
+injure our stomachs.
+
+The following is an extract from a letter of Dr. R.W. Darwin, of
+Shrewsbury, when he was a student at Edinburgh. "I made an experiment
+yesterday in our hospital, which much favours your opinion, that the
+sensation of heat and of touch depend on different sets of nerves. A man
+who had lately recovered from a fever, and was still weak, was seized with
+violent cramps in his legs and feet; which were removed by opiates, except
+that one of his feet remained insensible. Mr. Ewart pricked him with a pin
+in five or six places, and the patient declared he did not feel it in the
+least, nor was he sensible of a very smart pinch. I then held a red-hot
+poker at some distance, and brought it gradually nearer till it came within
+three inches, when he asserted that he felt it quite distinctly. I suppose
+some violent irritation on the nerves of touch had caused the cramps, and
+had left them paralytic; while the nerves of heat, having suffered no
+increased stimulus, retained their irritability."
+
+Add to this, that the lungs, though easily stimulated into inflammation,
+are not sensible to heat. See Class. III. 1. 1. 10.
+
+VII. _Of the Sense of Extension._
+
+The organ of touch is properly the sense of pressure, but the muscular
+fibres themselves constitute the organ of sense, that feels extension. The
+sense of pressure is always attended with the ideas of the figure and
+solidity of the object, neither of which accompany our perception of
+extension. The whole set of muscles, whether they are hollow ones, as the
+heart, arteries, and intestines, or longitudinal ones attached to bones,
+contract themselves, whenever they are stimulated by forcible elongation;
+and it is observable, that the white muscles, which constitute the arterial
+system, seem to be excited into contraction from no other kinds of
+stimulus, according to the experiments of Haller. And hence the violent
+pain in some inflammations, as in the paronychia, obtains immediate relief
+by cutting the membrane, that was stretched by the tumour of the subjacent
+parts.
+
+Hence the whole muscular system may be considered as one organ of sense,
+and the various attitudes of the body, as ideas belonging to this organ, of
+many of which we are hourly conscious, while many others, like the
+irritative ideas of the other senses, are performed without our attention.
+
+When the muscles of the heart cease to act, the refluent blood again
+distends or elongates them; and thus irritated they contract as before. The
+same happens to the arterial system, and I suppose to the capillaries,
+intestines, and various glands of the body.
+
+When the quantity of urine, or of excrement, distends the bladder, or
+rectum, those parts contract, and exclude their contents, and many other
+muscles by association act along with them; but if these evacuations are
+not soon complied with, pain is produced by a little further extension of
+the muscular fibres: a similar pain is caused in the muscles, when a limb
+is much extended for the reduction of dislocated bones; and in the
+punishment of the rack: and in the painful cramps of the calf of the leg,
+or of other muscles, for a greater degree of contraction of a muscle, than
+the movement of the two bones, to which its ends are affixed, will admit
+of, must give similar pain to that, which is produced by extending it
+beyond its due length. And the pain from punctures or incisions arises from
+the distention of the fibres, as the knife passes through them; for it
+nearly ceases as soon as the division is completed.
+
+All these motions of the muscles, that are thus naturally excited by the
+stimulus of distending bodies, are also liable to be called into strong
+action by their catenation, with the irritations or sensations produced by
+the momentum of the progressive particles of blood in the arteries, as in
+inflammatory fevers, or by acrid substances on other sensible organs, as in
+the strangury, or tenesmus, or cholera.
+
+We shall conclude this account of the sense of extension by observing, that
+the want of its object is attended with a disagreeable sensation, as well
+as the excess of it. In those hollow muscles, which have been accustomed to
+it, this disagreeable sensation is called faintness, emptiness, and
+sinking; and, when it arises to a certain degree, is attended with syncope,
+or a total quiescence of all motions, but the internal irritative ones, as
+happens from sudden loss of blood, or in the operation of tapping in the
+dropsy.
+
+VIII. _Of the Appetites of Hunger, Thirst, Heat, Extension, the want of
+fresh Air, animal Love, and the Suckling of Children._
+
+Hunger is most probably perceived by those numerous ramifications of nerves
+that are seen about the upper opening of the stomach; and thirst by the
+nerves about the fauces, and the top of the gula. The ideas of these senses
+are few in the generality of mankind, but are more numerous in those, who
+by disease, or indulgence, desire particular kinds of foods or liquids.
+
+A sense of heat has already been spoken of, which may with propriety be
+called an appetite, as we painfully desire it, when it is deficient in
+quantity.
+
+The sense of extension may be ranked amongst these appetites, since the
+deficiency of its object gives disagreeable sensation; when this happens in
+the arterial system, it is called faintness, and seems to bear some analogy
+to hunger and to cold; which like it are attended with emptiness of a part
+of the vascular system.
+
+The sense of want of fresh air has not been attended to, but is as distinct
+as the others, and the first perhaps that we experience after our nativity;
+from the want of the object of this sense many diseases are produced, as
+the jail-fever, plague, and other epidemic maladies. Animal love is another
+appetite, which occurs later in life, and the females of lactiferous
+animals have another natural inlet of pleasure or pain from the suckling
+their offspring. The want of which either owing to the death of their
+progeny, or to the fashion of their country, has been fatal to many of the
+sex. The males have also pectoral glands, which are frequently turgid with
+a thin milk at their nativity, and are furnished with nipples, which erect
+on titillation like those of the female; but which seem now to be of no
+further use, owing perhaps to some change which these animals have
+undergone in the gradual progression of the formation of the earth, and of
+all that it inhabit.
+
+These seven last mentioned senses may properly be termed appetites, as they
+differ from those of touch, sight, hearing, taste, and smell, in this
+respect; that they are affected with pain as well by the defect of their
+objects as by the excess of them, which is not so in the latter. Thus cold
+and hunger give us pain, as well as an excess of heat or satiety; but it is
+not so with darkness and silence.
+
+IX. Before we conclude this Section on the organs of sense, we must
+observe, that, as far as we know, there are many more senses, than have
+been here mentioned, as every gland seems to be influenced to separate from
+the blood, or to absorb from the cavities of the body, or from the
+atmosphere, its appropriated fluid, by the stimulus of that fluid on the
+living gland; and not by mechanical capillary absorption, nor by chemical
+affinity. Hence it appears, that each of these glands must have a peculiar
+organ to perceive these irritations, but as these irritations are not
+succeeded by sensation, they have not acquired the names of senses.
+
+However when these glands are excited into motions stronger than usual,
+either by the acrimony of their fluids, or by their own irritability being
+much increased, then the sensation of pain is produced in them as in all
+the other senses of the body; and these pains are all of different kinds,
+and hence the glands at this time really become each a different organ of
+sense, though these different kinds of pain have acquired no names.
+
+Thus a great excess of light does not give the idea of light but of pain;
+as in forcibly opening the eye when it is much inflamed. The great excess
+of pressure or distention, as when the point of a pin is pressed upon our
+skin, produces pain, (and when this pain of the sense of distention is
+slighter, it is termed itching, or tickling), without any idea of solidity
+or of figure: an excess of heat produces smarting, of cold another kind of
+pain; it is probable by this sense of heat the pain produced by caustic
+bodies is perceived, and of electricity, as all these are fluids, that
+permeate, distend, or decompose the parts that feel them.
+
+       *       *       *       *       *
+
+SECT. XV.
+
+OF THE CLASSES OF IDEAS.
+
+    I. 1. _Ideas received in tribes._ 2. _We combine them further, or
+    abstract from these tribes._ 3. _Complex ideas._ 4. _Compounded ideas._
+    5. _Simple ideas, modes, substances, relations, general ideas._ 6.
+    _Ideas of reflexion._ 7. _Memory and imagination imperfectly defined.
+    Ideal presence. Memorandum-rings._ II. 1. _Irritative ideas.
+    Perception._ 2. _Sensitive ideas, imagination._ 3. _Voluntary ideas,
+    recollection._ 4. _Associated ideas, suggestion._ III. 1. _Definitions
+    of perception, memory._ 2. _Reasoning, judgment, doubting,
+    distinguishing, comparing._ 3. _Invention._ 4. _Consciousness._ 5.
+    _Identity._ 6. _Lapse of time._ 7. _Free-will._
+
+I. 1. As the constituent elements of the material world are only
+perceptible to our organs of sense in a state of combination; it follows,
+that the ideas or sensual motions excited by them, are never received
+singly, but ever with a greater or less degree of combination. So the
+colours of bodies or their hardnesses occur with their figures: every smell
+and taste has its degree of pungency as well as its peculiar flavour: and
+each note in music is combined with the tone of some instrument. It appears
+from hence, that we can be sensible of a number of ideas at the same time,
+such as the whiteness, hardness, and coldness, of a snow-ball, and can
+experience at the same time many irritative ideas of surrounding bodies,
+which we do not attend to, as mentioned in Section VII. 3. 2. But those
+ideas which belong to the same sense, seem to be more easily combined into
+synchronous tribes, than those which were not received by the same sense,
+as we can more easily think of the whiteness and figure of a lump of sugar
+at the same time, than the whiteness and sweetness of it.
+
+2. As these ideas, or sensual motions, are thus excited with greater or
+less degrees of combination; so we have a power, when we repeat them either
+by our volition or sensation, to increase or diminish this degree of
+combination, that is, to form compounded ideas from those, which were more
+simple; and abstract ones from those, which were more complex, when they
+were first excited; that is, we can repeat a part or the whole of those
+sensual motions, which did constitute our ideas of perception; and the
+repetition of which now constitutes our ideas of recollection, or of
+imagination.
+
+3. Those ideas, which we repeat without change of the quantity of that
+combination, with which we first received them, are called complex ideas,
+as when you recollect Westminster Abbey, or the planet Saturn: but it must
+be observed, that these complex ideas, thus re-excited by volition,
+sensation, or association, are seldom perfect copies of their correspondent
+perceptions, except in our dreams, where other external objects do not
+detract our attention.
+
+4. Those ideas, which are more complex than the natural objects that first
+excited them, have been called compounded ideas, as when we think of a
+sphinx, or griffin.
+
+5. And those that are less complex than the correspondent natural objects,
+have been termed abstracted ideas: thus sweetness, and whiteness, and
+solidity, are received at the same time from a lump of sugar, yet I can
+recollect any of these qualities without thinking of the others, that were
+excited along with them.
+
+When ideas are so far abstracted as in the above example, they have been
+termed simple by the writers of metaphysics, and seem indeed to be more
+complete repetitions of the ideas or sensual motions, originally excited by
+external objects.
+
+Other classes of these ideas, where the abstraction has not been so great,
+have been termed, by Mr. Locke, modes, substances, and relations, but they
+seem only to differ in their degree of abstraction from the complex ideas
+that were at first excited; for as these complex or natural ideas are
+themselves imperfect copies of their correspondent perceptions, so these
+abstract or general ideas are only still more imperfect copies of the same
+perceptions. Thus when I have seen an object but once, as a rhinoceros, my
+abstract idea of this animal is the same as my complex one. I may think
+more or less distinctly of a rhinoceros, but it is the very rhinoceros that
+I saw, or some part or property of him, which recurs to my mind.
+
+But when any class of complex objects becomes the subject of conversation,
+of which I have seen many individuals, as a castle or an army, some
+property or circumstance belonging to it is peculiarly alluded to; and then
+I feel in my own mind, that my abstract idea of this complex object is only
+an idea of that part, property, or attitude of it, that employs the present
+conversation, and varies with every sentence that is spoken concerning it.
+So if any one should say, "one may sit upon a horse safer than on a camel,"
+my abstract idea of the two animals includes only an outline of the level
+back of the one, and the gibbosity on the back of the other. What noise is
+that in the street?--Some horses trotting over the pavement. Here my idea
+of the horses includes principally the shape and motion of their legs. So
+also the abstract ideas of goodness and courage are still more imperfect
+representations of the objects they were received from; for here we
+abstract the material parts, and recollect only the qualities.
+
+Thus we abstract so much from some of our complex ideas, that at length it
+becomes difficult to determine of what perception they partake; and in many
+instances our idea seems to be no other than of the sound or letters of the
+word, that stands for the collective tribe, of which we are said to have an
+abstracted idea, as noun, verb, chimæra, apparition.
+
+6. Ideas have been divided into those of perception and those of
+reflection, but as whatever is perceived must be external to the organ that
+perceives it, all our ideas must originally be ideas of perception.
+
+7. Others have divided our ideas into those of memory, and those of
+imagination; they have said that a recollection of ideas in the order they
+were received constitutes memory, and without that order imagination; but
+all the ideas of imagination, excepting the few that are termed simple
+ideas, are parts of trains or tribes in the order they were received; as if
+I think of a sphinx, or a griffin, the fair face, bosom, wings, claws,
+tail, are all complex ideas in the order they were received: and it behoves
+the writers, who adhere to this definition, to determine, how small the
+trains must be, that shall be called imagination; and how great those, that
+shall be called memory.
+
+Others have thought that the ideas of memory have a greater vivacity than
+those of imagination: but the ideas of a person in sleep, or in a waking
+reverie, where the trains connected with sensation are uninterrupted, are
+more vivid and distinct than those of memory, so that they cannot be
+distinguished by this criterion.
+
+The very ingenious author of the Elements of Criticism has described what
+he conceives to be a species of memory, and calls it ideal presence; but
+the instances he produces are the reveries of sensation, and are therefore
+in truth connections of the imagination, though they are recalled in the
+order they were received.
+
+The ideas connected by association are in common discourse attributed to
+memory, as we talk of memorandum-rings, and tie a knot on our handkerchiefs
+to bring something into our minds at a distance of time. And a school-boy,
+who can repeat a thousand unmeaning lines in Lilly's Grammar, is said to
+have a good memory. But these have been already shewn to belong to the
+class of association; and are termed ideas of suggestion.
+
+II. Lastly, the method already explained of classing ideas into those
+excited by irritation, sensation, volition, or association, we hope will be
+found more convenient both for explaining the operations of the mind, and
+for comparing them with those of the body; and for the illustration and the
+cure of the diseases of both, and which we shall here recapitulate.
+
+1. Irritative ideas are those, which are preceded by irritation, which is
+excited by objects external to the organs of sense: as the idea of that
+tree, which either I attend to, or which I shun in walking near it without
+attention. In the former case it is termed perception, in the latter it is
+termed simply an irritative idea.
+
+2. Sensitive ideas are those, which are preceded by the sensation of
+pleasure or pain; as the ideas, which constitute our dreams or reveries,
+this is called imagination.
+
+3. Voluntary ideas are those, which are preceded by voluntary exertion, as
+when I repeat the alphabet backwards: this is called recollection.
+
+4. Associate ideas are those, which are preceded by other ideas or muscular
+motions, as when we think over or repeat the alphabet by rote in its usual
+order; or sing a tune we are accustomed to; this is called suggestion.
+
+III. 1. Perceptions signify those ideas, which are preceded by irritation
+and succeeded by the sensation of pleasure or pain, for whatever excites
+our attention interests us; that is, it is accompanied with, pleasure or
+pain; however slight may be the degree or quantity of either of them.
+
+The word memory includes two classes of ideas, either those which, are
+preceded by voluntary exertion, or those which are suggested by their
+associations with other ideas.
+
+2. Reasoning is that operation of the sensorium, by which we excite two or
+many tribes of ideas; and then re-excite the ideas, in which they differ,
+or correspond. If we determine this difference, it is called judgment; if
+we in vain endeavour to determine it, it is called doubting.
+
+If we re-excited the ideas, in which they differ, it is called
+distinguishing. If we re-excite those in which they correspond, it is
+called comparing.
+
+3. Invention is an operation of the sensorium, by which we voluntarily
+continue to excite one train of ideas, suppose the design of raising water
+by a machine; and at the same time attend to all other ideas, which are
+connected with this by every kind of catenation; and combine or separate
+them voluntarily for the purpose of obtaining some end.
+
+For we can create nothing new, we can only combine or separate the ideas,
+which we have already received by our perceptions: thus if I wish to
+represent a monster, I call to my mind the ideas of every thing
+disagreeable and horrible, and combine the nastiness and gluttony of a hog,
+the stupidity and obstinacy of an ass, with the fur and awkwardness of a
+bear, and call the new combination Caliban. Yet such a monster may exist in
+nature, as all his attributes are parts of nature. So when I wish to
+represent every thing, that is excellent, and amiable; when I combine
+benevolence with cheerfulness, wisdom, knowledge, taste, wit, beauty of
+person, and elegance of manners, and associate them in one lady as a
+pattern to the world, it is called invention; yet such a person may
+exist,--such a person does exist!--It is ---- ----, who is as much a
+monster as Caliban.
+
+4. In respect to consciousness, we are only conscious of our existence,
+when we think about it; as we only perceive the lapse of time, when we
+attend to it; when we are busied about other objects, neither the lapse of
+time nor the consciousness of our own existence can occupy our attention.
+Hence, when we think of our own existence, we only excite abstracted or
+reflex ideas (as they are termed), of our principal pleasures or pains, of
+our desires or aversions, or of the figure, solidity, colour, or other
+properties of our bodies, and call that act of the sensorium a
+consciousness of our existence. Some philosopher, I believe it is Des
+Cartes, has said, "I think, therefore I exist." But this is not right
+reasoning, because thinking is a mode of existence; and it is thence only
+saying, "I exist, therefore I exist." For there are three modes of
+existence, or in the language of grammarians three kinds of verbs. First,
+simply I am, or exist. Secondly, I am acting, or exist in a state of
+activity, as I move. Thirdly, I am suffering, or exist in a state of being
+acted upon, as I am moved. The when, and the where, as applicable to this
+existence, depends on the successive motions of our own or of other bodies;
+and on their respective situations, as spoken of Sect. XIV. 2. 5.
+
+5. Our identity is known by our acquired habits or catenated trains of
+ideas and muscular motions; and perhaps, when we compare infancy with old
+age, in those alone can our identity be supposed to exist. For what else is
+there of similitude between the first speck of living entity and the mature
+man?--every deduction of reasoning, every sentiment or passion, with every
+fibre of the corporeal part of our system, has been subject almost to
+annual mutation; while some catenations alone of our ideas and muscular
+actions have continued in part unchanged.
+
+By the facility, with which we can in our waking hours voluntarily produce
+certain successive trains of ideas, we know by experience, that we have
+before reproduced them; that is, we are conscious of a time of our
+existence previous to the present time; that is, of our identity now and
+heretofore. It is these habits of action, these catenations of ideas and
+muscular motions, which begin with life, and only terminate with it; and
+which we can in some measure deliver to our posterity; as explained in
+Sect. XXXIX.
+
+6. When the progressive motions of external bodies make a part of our
+present catenation of ideas, we attend to the lapse of time; which appears
+the longer, the more frequently we thus attend to it; as when we expect
+something at a certain hour, which much interests us, whether it be an
+agreeable or disagreeable event; or when we count the passing seconds on a
+stop-watch.
+
+When an idea of our own person, or a reflex idea of our pleasures and
+pains, desires and aversions, makes a part of this catenation, it is termed
+consciousness; and if this idea of consciousness makes a part of a
+catenation, which we excite by recollection, and know by the facility with
+which we excite it, that we have before experienced it, it is called
+identity, as explained above.
+
+7. In respect to freewill, it is certain, that we cannot will to think of a
+new train of ideas, without previously thinking of the first link of it; as
+I cannot will to think of a black swan, without previously thinking of a
+black swan. But if I now think of a tail, I can voluntarily recollect all
+animals, which have tails; my will is so far free, that I can pursue the
+ideas linked to this idea of tail, as far as my knowledge of the subject
+extends; but to will without motive is to will without desire or aversion;
+which is as absurd as to feel without pleasure or pain; they are both
+solecisms in the terms. So far are we governed by the catenations of
+motions, which affect both the body and the mind of man, and which begin
+with our irritability, and end with it.
+
+       *       *       *       *       *
+
+SECT. XVI.
+
+OF INSTINCT.
+
+  Haud equidem credo, quia sit divinitus illis
+  Ingenium, aut rerum fato prudentia major.--Virg. Georg. L. I. 415.
+
+    I. _Instinctive actions defined. Of connate passions._ II. _Of the
+    sensations and motions of the foetus in the womb._ III. _Some animals
+    are more perfectly formed than others before nativity. Of learning to
+    walk._ IV. _Of the swallowing, breathing, sucking, pecking, and lapping
+    of young animals._ V. _Of the sense of smell, and its uses to animals.
+    Why cats do not eat their kittens._ VI. _Of the accuracy of sight in
+    mankind, and their sense of beauty. Of the sense of touch in elephants,
+    monkies, beavers, men._ VII. _Of natural language._ VIII. _The origin
+    of natural language;_ 1. _the language of fear;_ 2. _of grief;_ 3. _of
+    tender pleasure;_ 4. _of serene pleasure;_ 5. _of anger;_ 6. _of
+    attention._ IX. _Artificial language of turkies, hens, ducklings,
+    wagtails, cuckoos, rabbits, dogs, and nightingales._ X. _Of music; of
+    tooth-edge; of a good ear; of architecture._ XI. _Of acquired
+    knowledge; of foxes, rooks, fieldfares, lapwings, dogs, cats, horses,
+    crows, and pelicans._ XII. _Of birds of passage, dormice, snakes, bats,
+    swallows, quails, ringdoves, stare, chaffinch, hoopoe, chatterer,
+    hawfinch, crossbill, rails and cranes._ XIII. _Of birds nests; of the
+    cuckoo; of swallows nests; of the taylor bird._ XIV. _Of the old
+    soldier; of haddocks, cods, and dog fish; of the remora; of crabs,
+    herrings, and salmon._ XV. _Of spiders, caterpillars, ants, and the
+    ichneumon._ XVI. 1. _Of locusts, gnats;_ 2. _bees;_ 3. _dormice, flies,
+    worms, ants, and wasps._ XVII. _Of the faculty that distinguishes man
+    from the brutes._
+
+I. All those internal motions of animal bodies, which contribute to digest
+their aliment, produce their secretions, repair their injuries, or increase
+their growth, are performed without our attention or consciousness. They
+exist as well in our sleep, as in our waking hours, as well in the foetus
+during the time of gestation, as in the infant after nativity, and proceed
+with equal regularity in the vegetable as in the animal system. These
+motions have been shewn in a former part of this work to depend on the
+irritations of peculiar fluids, and as they have never been classed amongst
+the instinctive actions of animals, are precluded from our present
+disquisition.
+
+But all those actions of men or animals, that are attended with
+consciousness, and seem neither to have been directed by their appetites,
+taught by their experience, nor deduced from observation or tradition, have
+been referred to the power of instinct. And this power has been explained
+to be a _divine something_, a kind of inspiration; whilst the poor animal,
+that possesses it, has been thought little better than _a machine_!
+
+The _irksomeness_, that attends a continued attitude of the body, or the
+_pains_, that we receive from heat, cold, hunger, or other injurious
+circumstances, excite us to _general locomotion_: and our senses are so
+formed and constituted by the hand of nature, that certain objects present
+us with pleasure, others with pain, and we are induced to approach and
+embrace these, to avoid and abhor those, as such sensations direct us.
+
+Thus the palates of some animals are gratefully affected by the mastication
+of fruits, others of grains, and others of flesh; and they are thence
+instigated to attain, and to consume those materials; and are furnished
+with powers of muscular motion, and of digestion proper for such purposes.
+
+These _sensations_ and _desires_ constitute a part of our system, as our
+_muscles_ and _bones_ constitute another part: and hence they may alike be
+termed _natural_ or _connate_; but neither of them can properly be termed
+_instinctive_: as the word instinct in its usual acceptation refers only to
+the _actions_ of animals, as above explained: the origin of these _actions_
+is the subject of our present enquiry.
+
+The reader is intreated carefully to attend to this definition of
+_instinctive actions_, lest by using the word instinct without adjoining
+any accurate idea to it, he may not only include the natural desires of
+love and hunger, and the natural sensations of pain or pleasure, but the
+figure and contexture of the body, and the faculty of reason itself under
+this general term.
+
+II. We experience some sensations, and perform some actions before our
+nativity; the sensations of cold and warmth, agitation and rest, fulness
+and inanition, are instances of the former; and the repeated struggles of
+the limbs of the foetus, which begin about the middle of gestation, and
+those motions by which it frequently wraps the umbilical chord around its
+neck or body, and even sometimes ties it on a knot; are instances of the
+latter. Smellie's Midwifery, (Vol. I. p. 182.)
+
+By a due attention to these circumstances many of the actions of young
+animals, which at first sight seemed only referable to an inexplicable
+instinct, will appear to have been acquired like all other animal actions,
+that are attended with consciousness, _by the repeated efforts of our
+muscles under the conduct of our sensations or desires_.
+
+The chick in the shell begins to move its feet and legs on the sixth day of
+incubation (Mattreican, p. 138); or on the seventh day, (Langley);
+afterwards they are seen to move themselves gently in the liquid that
+surrounds them, and to open and shut their mouths, (Harvei, de Generat. p.
+62, and 197. Form de Poulet. ii. p. 129). Puppies before the membranes are
+broken, that involve them, are seen to move themselves, to put out their
+tongues, and to open and shut their mouths, (Harvey, Gipson, Riolan,
+Haller). And calves lick themselves and swallow many of their hairs before
+their nativity: which however puppies do not, (Swammerden, p. 319. Flemyng
+Phil. Trans. Ann. 1755. 42). And towards the end of gestation, the foetus
+of all animals are proved to drink part of the liquid in which they swim,
+(Haller. Physiol. T. 8. 204). The white of egg is found in the mouth and
+gizzard of the chick, and is nearly or quite consumed before it is hatched,
+(Harvie de Generat. 58). And the liquor amnii is found in the mouth and
+stomach of the human foetus, and of calves; and how else should that
+excrement be produced in the intestines of all animals, which is voided in
+great quantity soon after their birth; (Gipson, Med. Essays, Edinb. V. i.
+13. Halleri Physiolog. T. 3. p. 318. and T. 8). In the stomach of a calf
+the quantity of this liquid amounted to about three pints, and the hairs
+amongst it were of the same colour with those on its skin, (Blasii Anat.
+Animal, p.m. 122). These facts are attested by many other writers of
+credit, besides those above mentioned.
+
+III. It has been deemed a surprising instance of instinct, that calves and
+chickens should be able to walk by a few efforts almost immediately after
+their nativity: whilst the human infant in those countries where he is not
+incumbered with clothes, as in India, is five or six months, and in our
+climate almost a twelvemonth, before he can safely stand upon his feet.
+
+The struggles of all animals in the womb must resemble their mode of
+swimming, as by this kind of motion they can best change their attitude in
+water. But the swimming of the calf and chicken resembles their manner of
+walking, which they have thus in part acquired before their nativity, and
+hence accomplish it afterwards with very few efforts, whilst the swimming
+of the human creature resembles that of the frog, and totally differs from
+his mode of walking.
+
+There is another circumstance to be attended to in this affair, that not
+only the growth of those peculiar parts of animals, which are first wanted
+to secure their subsistence, are in general furthest advanced before their
+nativity: but some animals come into the world more completely formed
+throughout their whole system than others: and are thence much forwarder in
+all their habits of motion. Thus the colt, and the lamb, are much more
+perfect animals than the blind puppy, and the naked rabbit; and the chick
+of the pheasant, and the partridge, has more perfect plumage, and more
+perfect eyes, as well as greater aptitude to locomotion, than the callow
+nestlings of the dove, and of the wren. The parents of the former only find
+it necessary to shew them their food, and to teach them to take it up;
+whilst those of the latter are obliged for many days to obtrude it into
+their gaping mouths.
+
+IV. From the facts mentioned in No. 2. of this Section, it is evinced that
+the foetus learns to swallow before its nativity; for it is seen to open
+its mouth, and its stomach is found filled with the liquid that surrounds
+it. It opens its mouth, either instigated by hunger, or by the irksomeness
+of a continued attitude of the muscles of its face; the liquor amnii, in
+which it swims, is agreeable to its palate, as it consists of a nourishing
+material, (Haller Phys. T. 8. p. 204). It is tempted to experience its
+taste further in the mouth, and by a few efforts learns to swallow, in the
+same manner as we learn all other animal actions, which are attended with
+consciousness, _by the repeated efforts of our muscles under the conduct of
+our sensations or volitions_.
+
+The inspiration of air into the lungs is so totally different from that of
+swallowing a fluid in which we are immersed, that it cannot be acquired
+before our nativity. But at this time, when the circulation of the blood is
+no longer continued through the placenta, that suffocating sensation, which
+we feel about the precordia, when we are in want of fresh air, disagreeably
+affects the infant: and all the muscles of the body are excited into action
+to relieve this oppression; those of the breast, ribs, and diaphragm are
+found to answer this purpose, and thus respiration is discovered, and is
+continued throughout our lives, as often as the oppression begins to recur.
+Many infants, both of the human creature, and of quadrupeds, struggle for a
+minute after they are born before they begin to breathe, (Haller Phys. T.
+8. p. 400. ib pt. 2. p. 1). Mr. Buffon thinks the action of the dry air
+upon the nerves of smell of new-born animals, by producing an endeavour to
+sneeze, may contribute to induce this first inspiration, and that the
+rarefaction of the air by the warmth of the lungs contributes to induce
+expiration, (Hist. Nat. Tom. 4. p. 174). Which latter it may effect by
+producing a disagreeable sensation by its delay, and a consequent effort to
+relieve it. Many children sneeze before they respire, but not all, as far
+as I have observed, or can learn from others.
+
+At length, by the direction of its sense of smell, or by the officious care
+of its mother, the young animal approaches the odoriferous rill of its
+future nourishment, already experienced to swallow. But in the act of
+swallowing, it is necessary nearly to close the mouth, whether the creature
+be immersed in the fluid it is about to drink, or not: hence, when the
+child first attempts to suck, it does not slightly compress the nipple
+between its lips, and suck as an adult person would do, by absorbing the
+milk; but it takes the whole nipple into its mouth for this purpose,
+compresses it between its gums, and thus repeatedly chewing (as it were)
+the nipple, presses out the milk, exactly in the same manner as it is drawn
+from the teats of cows by the hands of the milkmaid. The celebrated Harvey
+observes, that the foetus in the womb must have sucked in a part of its
+nourishment, because it knows how to suck the minute it is born, as any one
+may experience by putting a finger between its lips, and because in a few
+days it forgets this art of sucking, and cannot without some difficulty
+again acquire it, (Exercit. de Gener. Anim. 48). The same observation is
+made by Hippocrates.
+
+A little further experience teaches the young animal to suck by absorption,
+as well as by compression; that is, to open the chest as in the beginning
+of respiration, and thus to rarefy the air in the mouth, that the pressure
+of the denser external atmosphere may contribute to force out the milk.
+
+The chick yet in the shell has learnt to drink by swallowing a part of the
+white of the egg for its food; but not having experienced how to take up
+and swallow solid seeds, or grains, is either taught by the felicitous
+industry of its mother; or by many repeated attempts is enabled at length
+to distinguish and to swallow this kind of nutriment.
+
+And puppies, though they know how to suck like other animals from their
+previous experience in swallowing, and in respiration; yet are they long in
+acquiring the art of lapping with their tongues, which from the flaccidity
+of their cheeks, and length of their mouths, is afterwards a more
+convenient way for them to take in water.
+
+V. The senses of smell and taste in many other animals greatly excel those
+of mankind, for in civilized society, as our victuals are generally
+prepared by others, and are adulterated with salt, spice, oil, and
+empyreuma, we do not hesitate about eating whatever is set before us, and
+neglect to cultivate these senses: whereas other animals try every morsel
+by the smell, before they take it into their mouths, and by the taste
+before they swallow it: and are led not only each to his proper nourishment
+by this organ of sense, but it also at a maturer age directs them in the
+gratification of their appetite of love. Which may be further understood by
+considering the sympathies of these parts described in Class IV. 2. 1. 7.
+While the human animal is directed to the object of his love by his sense
+of beauty, as mentioned in No. VI. of this Section. Thus Virgil. Georg.
+III. 250.
+
+  Nonne vides, ut tota tremor pertentat equorum
+  Corpora, si tantum notas odor attulit auras?
+  Nonne canis nidum veneris nasutus odore
+  Quærit, et erranti trahitur sublambere linguâ?
+  Respuit at gustum cupidus, labiisque retractis
+  Elevat os, trepidansque novis impellitur æstris
+  Inserit et vivum felici vomere semen.--
+  Quam tenui filo cæcos adnectit amores
+  Docta Venus, vitæque monet renovare favillam!--ANON.
+
+The following curious experiment is related by Galen. "On dissecting a goat
+great with young I found a brisk embryon, and having detached it from the
+matrix, and snatching it away before it saw its dam, I brought it into a
+certain room, where there were many vessels, some filled with wine, others
+with oil, some with honey, others with milk, or some other liquor; and in
+others were grains and fruits; we first observed the young animal get upon
+its feet, and walk; then it shook itself, and afterwards scratched its side
+with one of its feet: then we saw it smelling to every one of these things,
+that were set in the room; and when it had smelt to them all, it drank up
+the milk." L. 6. de locis. cap. 6.
+
+Parturient quadrupeds, as cats, and bitches, and sows, are led by their
+sense of smell to eat the placenta as other common food; why then do they
+not devour their whole progeny, as is represented in an antient emblem of
+TIME? This is said sometimes to happen in the unnatural state in which we
+confine sows; and indeed nature would seem to have endangered her offspring
+in this nice circumstance! But at this time the stimulus of the milk in the
+tumid teats of the mother excites her to look out for, and to desire some
+unknown circumstance to relieve her. At the same time the smell of the milk
+attracts the exertions of the young animals towards its source, and thus
+the delighted mother discovers a new appetite, as mentioned in Sect. XIV.
+8. and her little progeny are led to receive and to communicate pleasure by
+this most beautiful contrivance.
+
+VI. But though the human species in some of their sensations are much
+inferior to other animals, yet the accuracy of the sense of touch, which
+they possess in so eminent a degree, gives them a great superiority of
+understanding; as is well observed by the ingenious Mr. Buffon. The
+extremities of other animals terminate in horns, and hoofs, and claws, very
+unfit for the sensation of touch; whilst the human hand is finely adapted
+to encompass its object with this organ of sense.
+
+The elephant is indeed endued with a fine sense of feeling at the extremity
+of his proboscis, and hence has acquired much more accurate ideas of touch
+and of sight than most other creatures. The two following instances of the
+sagacity of these animals may entertain the reader, as they were told me by
+some gentlemen of distinct observation, and undoubted veracity, who had
+been much conversant with our eastern settlements. First, the elephants
+that are used to carry the baggage of our armies, are put each under the
+care of one of the natives of Indostan, and whilst himself and his wife go
+into the woods to collect leaves and branches of trees for his food, they
+fix him to the ground by a length of chain, and frequently leave a child
+yet unable to walk, under his protection: and the intelligent animal not
+only defends it, but as it creeps about, when it arrives near the extremity
+of his chain, he wraps his trunk gently round its body, and brings it again
+into the centre of his circle. Secondly, the traitor elephants are taught
+to walk on a narrow path between two pit-falls, which are covered with
+turf, and then to go into the woods, and to seduce the wild elephants to
+come that way, who fall into these wells, whilst he passes safe between
+them: and it is universally observed, that those wild elephants that escape
+the snare, pursue the traitor with the utmost vehemence, and if they can
+overtake him, which sometimes happens, they always beat him to death.
+
+The monkey has a hand well enough adapted for the sense of touch, which
+contributes to his great facility of imitation; but in taking objects with
+his hands, as a stick or an apple, he puts his thumb on the same side of
+them with his fingers, instead of counteracting the pressure of his fingers
+with it: from this neglect he is much slower in acquiring the figures of
+objects, as he is less able to determine the distances or diameters of
+their parts, or to distinguish their vis inertiæ from their hardness.
+Helvetius adds, that the shortness of his life, his being fugitive before
+mankind, and his not inhabiting all climates, combine to prevent his
+improvement. (De l'Esprit. T. 1. p.) There is however at this time an old
+monkey shewn in Exeter Change, London, who having lost his teeth, when nuts
+are given him, takes a stone into his hand, and cracks them with it one by
+one; thus using tools to effect his purpose like mankind.
+
+The beaver is another animal that makes much use of his hands, and if we
+may credit the reports of travellers, is possessed of amazing ingenuity.
+This however, M. Buffon affirms, is only where they exist in large numbers,
+and in countries thinly peopled with men; while in France in their solitary
+state they shew no uncommon ingenuity.
+
+Indeed all the quadrupeds, that have collar-bones, (claviculæ) use their
+fore-limbs in some measure as we use our hands, as the cat, squirrel,
+tyger, bear and lion; and as they exercise the sense of touch more
+universally than other animals, so are they more sagacious in watching and
+surprising their prey. All those birds, that use their claws for hands, as
+the hawk, parrot, and cuckoo, appear to be more docile and intelligent;
+though the gregarious tribes of birds have more acquired knowledge.
+
+Now as the images, that are painted on the retina of the eye, are no other
+than signs, which recall to our imaginations the objects we had before
+examined by the organ of touch, as is fully demonstrated by Dr. Berkley in
+his treatise on vision; it follows that the human creature has greatly more
+accurate and distinct sense of vision than that of any other animal. Whence
+as he advances to maturity he gradually acquires a sense of female beauty,
+which at this time directs him to the object of his new passion.
+
+Sentimental love, as distinguished from the animal passion of that name,
+with which it is frequently accompanied, consists in the desire or
+sensation of beholding, embracing, and saluting a beautiful object.
+
+The characteristic of beauty therefore is that it is the object of love;
+and though many other objects are in common language called beautiful, yet
+they are only called so metaphorically, and ought to be termed agreeable. A
+Grecian temple may give us the pleasurable idea of sublimity, a Gothic
+temple may give us the pleasurable idea of variety, and a modern house the
+pleasurable idea of utility; music and poetry may inspire our love by
+association of ideas; but none of these, except metaphorically, can be
+termed beautiful; as we have no wish to embrace or salute them.
+
+Our perception of beauty consists in our recognition by the sense of vision
+of those objects, first, which have before inspired our love by the
+pleasure, which they have afforded to many of our senses: as to our sense
+of warmth, of touch, of smell, of taste, hunger and thirst; and, secondly,
+which bear any analogy of form to such objects.
+
+When the babe, soon after it is born into this cold world, is applied to
+its mother's bosom; its sense of perceiving warmth is first agreeably
+affected; next its sense of smell is delighted with the odour of her milk;
+then its taste is gratified by the flavour of it: afterwards the appetites
+of hunger and of thirst afford pleasure by the possession of their objects,
+and by the subsequent digestion of the aliment; and, lastly, the sense of
+touch is delighted by the softness and smoothness of the milky fountain,
+the source of such variety of happiness.
+
+All these various kinds of pleasure at length become associated with the
+form of the mother's breast; which the infant embraces with its hands,
+presses with its lips, and watches with its eyes; and thus acquires more
+accurate ideas of the form of its mother's bosom, than of the odour and
+flavour or warmth, which it perceives by its other senses. And hence at our
+maturer years, when any object of vision is presented to us, which by its
+waving or spiral lines bears any similitude to the form of the female
+bosom, whether it be found in a landscape with soft gradations of rising
+and descending surface, or in the forms of some antique vases, or in other
+works of the pencil or the chissel, we feel a general glow of delight,
+which seems to influence all our senses; and, if the object be not too
+large, we experience an attraction to embrace it with our arms, and to
+salute it with our lips, as we did in our early infancy the bosom of our
+mother. And thus we find, according to the ingenious idea of Hogarth, that
+the waving lines of beauty were originally taken from the temple of Venus.
+
+This animal attraction is love; which is a sensation, when the object is
+present; and a desire, when it is absent. Which constitutes the purest
+source of human felicity, the cordial drop in the otherwise vapid cup of
+life, and which overpays mankind for the care and labour, which are
+attached to the pre-eminence of his situation above other animals.
+
+It should have been observed, that colour as well as form sometimes enters
+into our idea of a beautiful object, as a good complexion for instance,
+because a fine or fair colour is in general a sign of health, and conveys
+to us an idea of the warmth of the object; and a pale countenance on the
+contrary gives an idea of its being cold to the touch.
+
+It was before remarked, that young animals use their lips to distinguish
+the forms of things, as well as their fingers, and hence we learn the
+origin of our inclination to salute beautiful objects with our lips. For a
+definition of Grace, see Class III. 1. 2. 4.
+
+VII. There are two ways by which we become acquainted with the passions of
+others: first, by having observed the effects of them, as of fear or anger,
+on our own bodies, we know at sight when others are under the influence of
+these affections. So when two cocks are preparing to fight, each feels the
+feathers rise round his own neck, and knows from the same sign the
+disposition of his adversary: and children long before they can speak, or
+understand the language of their parents, may be frightened by an angry
+countenance, or soothed by smiles and blandishments.
+
+Secondly, when we put ourselves into the attitude that any passion
+naturally occasions, we soon in some degree acquire that passion; hence
+when those that scold indulge themselves in loud oaths, and violent actions
+of the arms, they increase their anger by the mode of expressing
+themselves: and on the contrary the counterfeited smile of pleasure in
+disagreeable company soon brings along with it a portion of the reality, as
+is well illustrated by Mr. Burke. (Essay on the Sublime and Beautiful.)
+
+This latter method of entering into the passions of others is rendered of
+very extensive use by the pleasure we take in imitation, which is every day
+presented before our eyes, in the actions of children, and indeed in all
+the customs and fashions of the world. From this our aptitude to imitation,
+arises what is generally understood by the word sympathy so well explained
+by Dr. Smith of Glasgow. Thus the appearance of a cheerful countenance
+gives us pleasure, and of a melancholy one makes us sorrowful. Yawning and
+sometimes vomiting are thus propagated by sympathy, and some people of
+delicate fibres, at the presence of a spectacle of misery, have felt pain
+in the same parts of their own bodies, that were diseased or mangled in the
+other. Amongst the writers of antiquity Aristotle thought this aptitude to
+imitation an essential property of the human species, and calls man an
+imitative animal. [Greek: To zôon mimômenon].
+
+These then are the natural signs by which we understand each other, and on
+this slender basis is built all human language. For without some natural
+signs, no artificial ones could have been invented or understood, as is
+very ingeniously observed by Dr. Reid. (Inquiry into the Human Mind.)
+
+VIII. The origin of this universal language is a subject of the highest
+curiosity, the knowledge of which has always been thought utterly
+inaccessible. A part of which we shall however here attempt.
+
+Light, sound, and odours, are unknown to the foetus in the womb, which,
+except the few sensations and motions already mentioned, sleeps away its
+time insensible of the busy world. But the moment he arrives into day, he
+begins to experience many vivid pains and pleasures; these are at the same
+time attended with certain muscular motions, and from this their early, and
+individual association, they acquire habits of occurring together, that are
+afterwards indissoluble.
+
+1. _Of Fear._
+
+As soon as the young animal is born, the first important sensations, that
+occur to him, are occasioned by the oppression about his precordia for want
+of respiration, and by his sudden transition from ninety-eight degrees of
+heat into so cold a climate.--He trembles, that is, he exerts alternately
+all the muscles of his body, to enfranchise himself from the oppression
+about his bosom, and begins to breathe with frequent and short
+respirations; at the same time the cold contracts his red skin, gradually
+turning it pale; the contents of the bladder and of the bowels are
+evacuated: and from the experience of these first disagreeable sensations
+the passion of fear is excited, which is no other than the expectation of
+disagreeable sensations. This early association of motions and sensations
+persists throughout life; the passion of fear produces a cold and pale
+skin, with tremblings, quick respiration, and an evacuation of the bladder
+and bowels, and thus constitutes the natural or universal language of this
+passion.
+
+On observing a Canary bird this morning, January 28, 1772, at the house of
+Mr. Harvey, near Tutbury, in Derbyshire, I was told it always fainted away,
+when its cage was cleaned, and desired to see the experiment. The cage
+being taken from the ceiling, and its bottom drawn out, the bird began to
+tremble, and turned quite white about the root of his bill: he then opened
+his mouth as if for breath, and respired quick, stood straighter up on his
+perch, hung his wings, spread his tail, closed his eyes, and appeared quite
+stiff and cataleptic for near half an hour, and at length with much
+trembling and deep respirations came gradually to himself.
+
+2. _Of Grief._
+
+That the internal membrane of the nostrils may be kept always moist, for
+the better perception of odours, there are two canals, that conduct the
+tears after they have done their office in moistening and cleaning the ball
+of the eye into a sack, which is called the lacrymal sack; and from which
+there is a duct, that opens into the nostrils: the aperture of this duct is
+formed of exquisite sensibility, and when it is stimulated by odorous
+particles, or by the dryness or coldness of the air, the sack contracts
+itself, and pours more of its contained moisture on the organ of smell. By
+this contrivance the organ is rendered more fit for perceiving such odours,
+and is preserved from being injured by those that are more strong or
+corrosive. Many other receptacles of peculiar fluids disgorge their
+contents, when the ends of their ducts are stimulated; as the gall bladder,
+when the contents of the duodenum stimulate the extremity of the common
+bile duct: and the salivary glands, when the termination of their ducts in
+the mouth are excited by the stimulus of the food we masticate. Atque
+vesiculæ seminales suum exprimunt fluidum glande penis fricatâ.
+
+The coldness and dryness of the atmosphere, compared with the warmth and
+moisture, which the new-born infant had just before experienced,
+disagreeably affects the aperture of this lacrymal sack: the tears, that
+are contained in this sack, are poured into the nostrils, and a further
+supply is secreted by the lacrymal glands, and diffused upon the eye-balls;
+as is very visible in the eyes and nostrils of children soon after their
+nativity. The same happens to us at our maturer age, for in severe frosty
+weather, snivelling and tears are produced by the coldness and dryness of
+the air.
+
+But the lacrymal glands, which separate the tears from the blood, are
+situated on the upper external part of the globes of each eye; and, when a
+greater quantity of tears are wanted, we contract the forehead, and bring
+down the eye-brows, and use many other distortions of the face, to compress
+these glands.
+
+Now as the suffocating sensation, that produces respiration, is removed
+almost as soon as perceived, and does not recur again: this disagreeable
+irritation of the lacrymal ducts, as it must frequently recur, till the
+tender organ becomes used to variety of odours, is one of the first pains
+that is repeatedly attended to: and hence throughout our infancy, and in
+many people throughout their lives, all disagreeable sensations are
+attended with snivelling at the nose, a profusion of tears, and some
+peculiar distortions of countenance: according to the laws of early
+association before mentioned, which constitutes the natural or universal
+language of grief.
+
+You may assure yourself of the truth of this observation, if you will
+attend to what passes, when you read a distressful tale alone; before the
+tears overflow your eyes, you will invariably feel a titillation at that
+extremity of the lacrymal duct, which terminates in the nostril, then the
+compression of the eyes succeeds, and the profusion of tears.
+
+Linnæus asserts, that the female bear sheds tears in grief; the same has
+been said of the hind, and some other animals.
+
+3. _Of Tender Pleasure._
+
+The first most lively impression of pleasure, that the infant enjoys after
+its nativity, is excited by the odour of its mother's milk. The organ of
+smell is irritated by this perfume, and the lacrymal sack empties itself
+into the nostrils, as before explained, and an increase of tears is poured
+into the eyes. Any one may observe this, when very young infants are about
+to suck; for at those early periods of life, the sensation affects the
+organ of smell, much more powerfully, than after the repeated habits of
+smelling has inured it to odours of common strength: and in our adult
+years, the stronger smells, though they are at the same time agreeable to
+us, as of volatile spirits, continue to produce an increased secretion of
+tears.
+
+This pleasing sensation of smell is followed by the early affection of the
+infant to the mother that suckles it, and hence the tender feelings of
+gratitude and love, as well as of hopeless grief, are ever after joined
+with the titillation of the extremity of the lacrymal ducts, and a
+profusion of tears.
+
+Nor is it singular, that the lacrymal sack should be influenced by pleasing
+ideas, as the sight of agreeable food produces the same effect on the
+salivary glands. Ac dum vidimus insomniis lascivæ puellæ simulacrum
+tenditur penis.
+
+Lambs shake or wriggle their tails, at the time when they first suck, to
+get free of the hard excrement, which had been long lodged in their bowels.
+Hence this becomes afterwards a mark of pleasure in them, and in dogs, and
+other tailed animals. But cats gently extend and contract their paws when
+they are pleased, and purr by drawing in their breath, both which resemble
+their manner of sucking, and thus become their language of pleasure, for
+these animals having collar-bones use their paws like hands when they suck,
+which dogs and sheep do not.
+
+4. _Of Serene Pleasure._
+
+In the action of sucking, the lips of the infant are closed around the
+nipple of its mother, till he has filled his stomach, and the pleasure
+occasioned by the stimulus of this grateful food succeeds. Then the
+sphincter of the mouth, fatigued by the continued action of sucking, is
+relaxed; and the antagonist muscles of the face gently acting, produce the
+smile of pleasure: as cannot but be seen by all who are conversant with
+children.
+
+Hence this smile during our lives is associated with gentle pleasure; it is
+visible in kittens, and puppies, when they are played with, and tickled;
+but more particularly marks the human features. For in children this
+expression of pleasure is much encouraged, by their imitation of their
+parents, or friends; who generally address them with a smiling countenance:
+and hence some nations are more remarkable for the gaiety, and others for
+the gravity of their looks.
+
+5. _Of Anger._
+
+The actions that constitute the mode of fighting, are the immediate
+language of anger in all animals; and a preparation for these actions is
+the natural language of threatening. Hence the human creature clenches his
+fist, and sternly surveys his adversary, as if meditating where to make the
+attack; the ram, and the bull, draws himself some steps backwards, and
+levels his horns; and the horse, as he most frequently fights by striking
+with his hinder feet, turns his heels to his foe, and bends back his ears,
+to listen out the place of his adversary, that the threatened blow may not
+be ineffectual.
+
+6. _Of Attention._
+
+The eye takes in at once but half our horizon, and that only in the day,
+and our smell informs us of no very distant objects, hence we confide
+principally in the organ of hearing to apprize us of danger: when we hear
+any the smallest sound, that we cannot immediately account for, our fears
+are alarmed, we suspend our steps, hold every muscle still, open our mouths
+a little, erect our ears, and listen to gain further information: and this
+by habit becomes the general language of attention to objects of sight, as
+well as of hearing; and even to the successive trains of our ideas.
+
+The natural language of violent pain, which is expressed by writhing the
+body, grinning, and screaming; and that of tumultuous pleasure, expressed
+in loud laughter; belong to Section XXXIV. on Diseases from Volition.
+
+IX. It must have already appeared to the reader, that all other animals, as
+well as man, are possessed of this natural language of the passions,
+expressed in signs or tones; and we shall endeavour to evince, that those
+animals, which have preserved themselves from being enslaved by mankind,
+and are associated in flocks, are also possessed of some artificial
+language, and of some traditional knowledge.
+
+The mother-turkey, when she eyes a kite hovering high in air, has either
+seen her own parents thrown into fear at his presence, or has by
+observation been acquainted with his dangerous designs upon her young. She
+becomes agitated with fear, and uses the natural language of that passion,
+her young ones catch the fear by imitation, and in an instant conceal
+themselves in the grass.
+
+At the same time that she shews her fears by her gesture and deportment,
+she uses a certain exclamation, Koe-ut, Koe-ut, and the young ones
+afterwards know, when they hear this note, though they do not see their
+dam, that the presence of their adversary is denounced, and hide themselves
+as before.
+
+The wild tribes of birds have very frequent opportunities of knowing their
+enemies, by observing the destruction they make among their progeny, of
+which every year but a small part escapes to maturity: but to our domestic
+birds these opportunities so rarely occur, that their knowledge of their
+distant enemies must frequently be delivered by tradition in the manner
+above explained, through many generations.
+
+This note of danger, as well as the other notes of the mother-turkey, when
+she calls her flock to their food, or to sleep under her wings, appears to
+be an artificial language, both as expressed by the mother, and as
+understood by the progeny. For a hen teaches this language with equal ease
+to the ducklings, she has hatched from suppositious eggs, and educates as
+her own offspring: and the wagtails, or hedge-sparrows, learn it from the
+young cuckoo their softer nursling, and supply him with food long after he
+can fly about, whenever they hear his cuckooing, which Linnæus tells us, is
+his call of hunger, (Syst. Nat.) And all our domestic animals are readily
+taught to come to us for food, when we use one tone of voice, and to fly
+from our anger, when we use another.
+
+Rabbits, as they cannot easily articulate sounds, and are formed into
+societies, that live under ground, have a very different method of giving
+alarm. When danger is threatened, they thump on the ground with one of
+their hinder feet, and produce a sound, that can be heard a great way by
+animals near the surface of the earth, which would seem to be an artificial
+sign both from its singularity and its aptness to the situation of the
+animal.
+
+The rabbits on the island of Sor, near Senegal, have white flesh, and are
+well tasted, but do not burrow in the earth, so that we may suspect their
+digging themselves houses in this cold climate is an acquired art, as well
+as their note of alarm, (Adanson's Voyage to Senegal).
+
+The barking of dogs is another curious note of alarm, and would seem to be
+an acquired language, rather than a natural sign: for "in the island of
+Juan Fernandes, the dogs did not attempt to bark, till some European dogs
+were put among them, and then they gradually begun to imitate them, but in
+a strange manner at first, as if they were learning a thing that was not
+natural to them," (Voyage to South America by Don G. Juan, and Don Ant. de
+Ulloa. B. 2. c. 4).
+
+Linnæus also observes, that the dogs of South America do not bark at
+strangers, (Syst. Nat.) And the European dogs, that have been carried to
+Guinea, are said in three or four generations to cease to bark, and only
+howl, like the dogs that are natives of that coast, (World Displayed, Vol.
+XVII. p. 26.)
+
+A circumstance not dissimilar to this, and equally curious, is mentioned by
+Kircherus, de Musurgia, in his Chapter de Lusciniis, "That the young
+nightingales, that are hatched under other birds, never sing till they are
+instructed by the company of other nightingales." And Jonston affirms, that
+the nightingales that visit Scotland, have not the same harmony as those of
+Italy, (Pennant's Zoology, octavo, p. 255); which would lead us to suspect
+that the singing of birds, like human music, is an artificial language
+rather than a natural expression of passion.
+
+X. Our music like our language, is perhaps entirely constituted of
+artificial tones, which by habit suggest certain agreeable passions. For
+the same combination of notes and tones do not excite devotion, love, or
+poetic melancholy in a native of Indostan and of Europe. And "the
+Highlander has the same warlike ideas annexed to the sound of a bagpipe (an
+instrument which an Englishman derides), as the Englishman has to that of a
+trumpet or fife," (Dr. Brown's Union of Poetry and Music, p. 58.) So "the
+music of the Turks is very different from the Italian, and the people of
+Fez and Morocco have again a different kind, which to us appears very rough
+and horrid, but is highly pleasing to them," (L'Arte Armoniaca a Giorgio
+Antoniotto). Hence we see why the Italian opera does not delight an
+untutored Englishman; and why those, who are unaccustomed to music, are
+more pleased with a tune, the second or third time they hear it, than the
+first. For then the same melodious train of sounds excites the melancholy,
+they had learned from the song; or the same vivid combination of them
+recalls all the mirthful ideas of the dance and company.
+
+Even the sounds, that were once disagreeable to us, may by habit be
+associated with other ideas, so as to become agreeable. Father Lasitau, in
+his account of the Iroquois, says "the music and dance of those Americans,
+have something in them extremely barbarous, which at first disgusts. We
+grow reconciled to them by degrees, and in the end partake of them with
+pleasure, the savages themselves are fond of them to distraction," (Moeurs
+des Savages, Tom. ii.)
+
+There are indeed a few sounds, that we very generally associate with
+agreeable ideas, as the whistling of birds, or purring of animals, that are
+delighted; and some others, that we as generally associate with
+disagreeable ideas, as the cries of animals in pain, the hiss of some of
+them in anger, and the midnight howl of beasts of prey. Yet we receive no
+terrible or sublime ideas from the lowing of a cow, or the braying of an
+ass. Which evinces, that these emotions are owing to previous associations.
+So if the rumbling of a carriage in the street be for a moment mistaken for
+thunder, we receive a sublime sensation, which ceases as soon as we know it
+is the noise of a coach and six.
+
+There are other disagreeable sounds, that are said to set the teeth on
+edge; which, as they have always been thought a necessary effect of certain
+discordant notes, become a proper subject of our enquiry. Every one in his
+childhood has repeatedly bit a part of the glass or earthen vessel, in
+which his food has been given him, and has thence had a very disagreeable
+sensation in the teeth, which sensation was designed by nature to prevent
+us from exerting them on objects harder than themselves. The jarring sound
+produced between the cup and the teeth is always attendant on this
+disagreeable sensation: and ever after when such a sound is accidentally
+produced by the conflict of two hard bodies, we feel by association of
+ideas the concomitant disagreeable sensation in our teeth.
+
+Others have in their infancy frequently held the corner of a silk
+handkerchief in their mouth, or the end of the velvet cape of their coat,
+whilst their companions in play have plucked it from them, and have given
+another disagreeable sensation to their teeth, which has afterwards
+recurred on touching those materials. And the sight of a knife drawn along
+a china plate, though no sound is excited by it, and even the imagination
+of such a knife and plate so scraped together, I know by repeated
+experience will produce the same disagreeable sensation of the teeth.
+
+These circumstances indisputably prove, that this sensation of the
+tooth-edge is owing to associated ideas; as it is equally excitable by
+sight, touch, hearing, or imagination.
+
+In respect to the artificial proportions of sound excited by musical
+instruments, those, who have early in life associated them with agreeable
+ideas, and have nicely attended to distinguish them from each other, are
+said to have a good ear, in that country where such proportions are in
+fashion: and not from any superior perfection in the organ of hearing, or
+any intuitive sympathy between certain sounds and passions.
+
+I have observed a child to be exquisitely delighted with music, and who
+could with great facility learn to sing any tune that he heard distinctly,
+and yet whole organ of hearing was so imperfect, that it was necessary to
+speak louder to him in common conversation than to others.
+
+Our music, like our architecture, seems to have no foundation in nature,
+they are both arts purely of human creation, as they imitate nothing. And
+the professors of them have only classed those circumstances, that are most
+agreeable to the accidental taste of their age, or country; and have called
+it Proportion. But this proportion must always fluctuate, as it rests on
+the caprices, that are introduced into our minds by our various modes of
+education. And these fluctuations of taste must become more frequent in the
+present age, where mankind have enfranchised themselves from the blind
+obedience to the rules of antiquity in perhaps every science, but that of
+architecture. See Sect. XII. 7. 3.
+
+XI. There are many articles of knowledge, which the animals in cultivated
+countries seem to learn very early in their lives, either from each other,
+or from experience, or observation: one of the most general of these is to
+avoid mankind. There is so great a resemblance in the natural language of
+the passions of all animals, that we generally know, when they are in a
+pacific, or in a malevolent humour, they have the same knowledge of us; and
+hence we can scold them from us by some tones and gestures, and could
+possibly attract them to us by others, if they were not already apprized of
+our general malevolence towards them. Mr. Gmelin, Professor at Petersburg,
+assures us, that in his journey into Siberia, undertaken by order of the
+Empress of Russia, he saw foxes, that expressed no fear of himself or
+companions, but permitted him to come quite near them, having never seen
+the human creature before. And Mr. Bongainville relates, that at his
+arrival at the Malouine, or Falkland's Islands, which were not inhabited by
+men, all the animals came about himself and his people; the fowls settling
+upon their heads and shoulders, and the quadrupeds running about their
+feet. From the difficulty of acquiring the confidence of old animals, and
+the ease of taming young ones, it appears that the fear, they all conceive
+at the sight of mankind, is an acquired article of knowledge.
+
+This knowledge is more nicely understood by rooks, who are formed into
+societies, and build, as it were, cities over our heads; they evidently
+distinguish, that the danger is greater when a man is armed with a gun.
+Every one has seen this, who in the spring of the year has walked under a
+rookery with a gun in his hand: the inhabitants of the trees rise on their
+wings, and scream to the unfledged young to shrink into their nests from
+the sight of the enemy. The vulgar observing this circumstance so uniformly
+to occur, assert that rooks can smell gun-powder.
+
+The fieldfares, (turdus pilarus) which breed in Norway, and come hither in
+the cold season for our winter berries; as they are associated in flocks,
+and are in a foreign country, have evident marks of keeping a kind of
+watch, to remark and announce the appearance of danger. On approaching a
+tree, that is covered with them, they continue fearless till one at the
+extremity of the bush rising on his wings gives a loud and peculiar note of
+alarm, when they all immediately fly, except one other, who continues till
+you approach still nearer, to certify as it were the reality of the danger,
+and then he also flies off repeating the note of alarm.
+
+And in the woods about Senegal there is a bird called uett-uett by the
+negroes, and squallers by the French, which, as soon as they see a man, set
+up a loud scream, and keep flying round him, as if their intent was to warn
+other birds, which upon hearing the cry immediately take wing. These birds
+are the bane of sportsmen, and frequently put me into a passion, and
+obliged me to shoot them, (Adanson's Voyage to Senegal, 78). For the same
+intent the lesser birds of our climate seem to fly after a hawk, cuckoo, or
+owl, and scream to prevent their companions from being surprised by the
+general enemies of themselves, or of their eggs and progeny.
+
+But the lapwing, (charadrius pluvialis Lin.) when her unfledged offspring
+run about the marshes, where they were hatched, not only gives the note of
+alarm at the approach of men or dogs, that her young may conceal
+themselves; but flying and screaming near the adversary, she appears more
+felicitous and impatient, as he recedes from her family, and thus
+endeavours to mislead him, and frequently succeeds in her design. These
+last instances are so apposite to the situation, rather than to the natures
+of the creatures, that use them; and are so similar to the actions of men
+in the same circumstances, that we cannot but believe, that they proceed
+from a similar principle.
+
+Miss M.E. Jacson acquainted me, that she witnessed this autumn an agreeable
+instance of sagacity in a little bird, which seemed to use the means to
+obtain an end; the bird repeatedly hopped upon a poppy-stem, and shook the
+head with its bill, till many seeds were scattered, then it settled on the
+ground, and eat the seeds, and again repeated the same management. Sept. 1,
+1794.
+
+On the northern coast of Ireland a friend of mine saw above a hundred crows
+at once preying upon muscles; each crow took a muscle up into the air
+twenty or forty yards high, and let it fall on the stones, and thus by
+breaking the shell, got possession of the animal.--A certain philosopher (I
+think it was Anaxagoras) walking along the sea-shore to gather shells, one
+of these unlucky birds mistaking his bald head for a stone, dropped a
+shell-fish upon it, and killed at once a philosopher and an oyster.
+
+Our domestic animals, that have some liberty, are also possessed of some
+peculiar traditional knowledge: dogs and cats have been forced into each
+other's society, though naturally animals of a very different kind, and
+have hence learned from each other to eat dog's grass (agrostis canina)
+when they are sick, to promote vomiting. I have seen a cat mistake the
+blade of barley for this grass, which evinces it is an acquired knowledge.
+They have also learnt of each other to cover their excrement and
+urine;--about a spoonful of water was spilt upon my hearth from the
+tea-kettle, and I observed a kitten cover it with ashes. Hence this must
+also be an acquired art, as the creature mistook the application of it.
+
+To preserve their fur clean, and especially their whiskers, cats wash their
+faces, and generally quite behind their ears, every time they eat. As they
+cannot lick those places with their tongues, they first wet the inside of
+the leg with saliva, and then repeatedly wash their faces with it, which
+must originally be an effect of reasoning, because a means is used to
+produce an effect; and seems afterwards to be taught or acquired by
+imitation, like the greatest part of human arts.
+
+These animals seem to possess something like an additional sense by means
+of their whiskers; which have perhaps some analogy to the antennæ of moths
+and butterflies. The whiskers of cats consist not only of the long hairs on
+their upper lips, but they have also four or five long hairs standing up
+from each eyebrow, and also two or three on each cheek; all which, when the
+animal erects them, make with their points so many parts of the periphery
+of a circle, of an extent at least equal to the circumference of any part
+of their own bodies. With this instrument, I conceive, by a little
+experience, they can at once determine, whether any aperture amongst hedges
+or shrubs, in which animals of this genus live in their wild state, is
+large enough to admit their bodies; which to them is a matter of the
+greatest consequence, whether pursuing or pursued. They have likewise a
+power of erecting and bringing forward the whiskers on their lips; which
+probably is for the purpose of feeling, whether a dark hole be further
+permeable.
+
+The antennæ, or horns, of butterflies and moths, who have awkward wings,
+the minute feathers of which are very liable to injury, serve, I suppose, a
+similar purpose of measuring, as they fly or creep amongst the leaves of
+plants and trees, whither their wings can pass without touching them.
+
+Mr. Leonard, a very intelligent friend of mine, saw a cat catch a trout by
+darting upon it in a deep clear water at the mill at Weaford, near
+Lichfield. The cat belonged to Mr. Stanley, who had often seen her catch
+fish in the same manner in summer, when the mill-pool was drawn so low,
+that the fish could be seen. I have heard of other cats taking fish in
+shallow water, as they stood on the bank. This seems a natural art of
+taking their prey in cats, which their acquired delicacy by domestication
+has in general prevented them from using, though their desire of eating
+fish continues in its original strength.
+
+Mr. White, in his ingenious History of Selbourn, was witness to a cat's
+suckling a young hare, which followed her about the garden, and came
+jumping to her call of affection. At Elford, near Lichfield, the Rev. Mr.
+Sawley had taken the young ones out of a hare, which was shot; they were
+alive, and the cat, who had just lost her own kittens, carried them away,
+as it was supposed, to eat them; but it presently appeared, that it was
+affection not hunger which incited her, as she suckled them, and brought
+them up as their mother.
+
+Other instances of the mistaken application of what has been termed
+instinct may be observed in flies in the night, who mistaking a candle for
+day-light, approach and perish in the flame. So the putrid smell of the
+stapelia, or carrion-flower, allures the large flesh-fly to deposit its
+young worms on its beautiful petals, which perish there for want of
+nourishment. This therefore cannot be a necessary instinct, because the
+creature mistakes the application of it.
+
+Though in this country horses shew little vestiges of policy, yet in the
+deserts of Tartary, and Siberia, when hunted by the Tartars they are seen
+to form a kind of community, set watches to prevent their being surprised,
+and have commanders, who direct, and hasten their flight, Origin of
+Language, Vol. I. p. 212. In this country, where four or five horses travel
+in a line, the first always points his ears forward, and the last points
+his backward, while the intermediate ones seem quite careless in this
+respect; which seems a part of policy to prevent surprise. As all animals
+depend most on the ear to apprize them of the approach of danger, the eye
+taking in only half the horizon at once, and horses possess a great nicety
+of this sense; as appears from their mode of fighting mentioned No. 8. 5.
+of this Section, as well as by common observation.
+
+There are some parts of a horse, which he cannot conveniently rub, when
+they itch, as about the shoulder, which he can neither bite with his teeth,
+nor scratch with his hind foot; when this part itches, he goes to another
+horse, and gently bites him in the part which he wishes to be bitten, which
+is immediately done by his intelligent friend. I once observed a young foal
+thus bite its large mother, who did not choose to drop the grass she had in
+her mouth, and rubbed her nose against the foal's neck instead of biting
+it; which evinces that she knew the design of her progeny, and was not
+governed by a necessary instinct to bite where she was bitten.
+
+Many of our shrubs, which would otherwise afford an agreeable food to
+horses, are armed with thorns or prickles, which secure them from those
+animals; as the holly, hawthorn, gooseberry, gorse. In the extensive
+moorlands of Staffordshire, the horses have learnt to stamp upon a
+gorse-bush with one of their fore-feet for a minute together, and when the
+points are broken, they eat it without injury. The horses in the new forest
+in Hampshire are affirmed to do the same by Mr. Gilpin. Forest Scenery, II.
+251, and 112. Which is an art other horses in the fertile parts of the
+country do not possess, and prick their mouths till they bleed, if they are
+induced by hunger or caprice to attempt eating gorse.
+
+Swine have a sense of touch as well as of smell at the end of their nose,
+which they use as a hand, both to root up the soil, and to turn over and
+examine objects of food, somewhat like the proboscis of an elephant. As
+they require shelter from the cold in this climate, they have learnt to
+collect straw in their mouths to make their nest, when the wind blows cold;
+and to call their companions by repeated cries to assist in the work, and
+add to their warmth by their numerous bedfellows. Hence these animals,
+which are esteemed so unclean, have also learned never to befoul their
+dens, where they have liberty, with their own excrement; an art, which cows
+and horses, which have open hovels to run into, have never acquired. I have
+observed great sagacity in swine; but the short lives we allow them, and
+their general confinement, prevents their improvement, which might probably
+be otherwise greater than that of dogs.
+
+Instances of the sagacity and knowledge of animals are very numerous to
+every observer, and their docility in learning various arts from mankind,
+evinces that they may learn similar arts from their own species, and thus
+be possessed of much acquired and traditional knowledge.
+
+A dog whose natural prey is sheep, is taught by mankind, not only to leave
+them unmolested, but to guard them; and to hunt, to set, or to destroy
+other kinds of animals, as birds, or vermin; and in some countries to catch
+fish, in others to find truffles, and to practise a great variety of
+tricks; is it more surprising that the crows should teach each other, that
+the hawk can catch less birds, by the superior swiftness of his wing, and
+if two of them follow him, till he succeeds in his design, that they can by
+force share a part of the capture? This I have formerly observed with
+attention and astonishment.
+
+There is one kind of pelican mentioned by Mr. Osbeck, one of Linnæus's
+travelling pupils (the pelicanus aquilus), whose food is fish; and which it
+takes from other birds, because it is not formed to catch them itself;
+hence it is called by the English a Man-of-war-bird, Voyage to China, p.
+88. There are many other interesting anecdotes of the pelican and
+cormorant, collected from authors of the best authority, in a well-managed
+Natural History for Children, published by Mr. Galton. Johnson. London.
+
+And the following narration from the very accurate Mons. Adanson, in his
+Voyage to Senegal, may gain credit with the reader: as his employment in
+this country was solely to make observations in natural history. On the
+river Niger, in his road to the island Griel, he saw a great number of
+pelicans, or wide throats. "They moved with great state like swans upon the
+water, and are the largest bird next to the ostrich; the bill of the one I
+killed was upwards of a foot and half long, and the bag fastened underneath
+it held two and twenty pints of water. They swim in flocks, and form a
+large circle, which they contract afterwards, driving the fish before them
+with their legs: when they see the fish in sufficient number confined in
+this space, they plunge their bill wide open into the water, and shut it
+again with great quickness. They thus get fish into their throat-bag, which
+they eat afterwards on shore at their leisure." P. 247.
+
+XII. The knowledge and language of those birds, that frequently change
+their climate with the seasons, is still more extensive: as they perform
+these migrations in large societies, and are less subject to the power of
+man, than the resident tribes of birds. They are said to follow a leader
+during the day, who is occasionally changed, and to keep a continual cry
+during the night to keep themselves together. It is probable that these
+emigrations were at first undertaken as accident directed, by the more
+adventurous of their species, and learned from one another like the
+discoveries of mankind in navigation. The following circumstances strongly
+support this opinion.
+
+1. Nature has provided these animals, in the climates where they are
+produced, with another resource: when the season becomes too cold for their
+constitutions, or the food they were supported with ceases to be supplied,
+I mean that of sleeping. Dormice, snakes, and bats, have not the means of
+changing their country; the two former from the want of wings, and the
+latter from his being not able to bear the light of the day. Hence these
+animals are obliged to make use of this resource, and sleep during the
+winter. And those swallows that have been hatched too late in the year to
+acquire their full strength of pinion, or that have been maimed by accident
+or disease, have been frequently found in the hollows of rocks on the sea
+coasts, and even under water in this torpid state, from which they have
+been revived by the warmth of a fire. This torpid state of swallows is
+testified by innumerable evidences both of antient and modern names.
+Aristotle speaking of the swallows says, "They pass into warmer climates in
+winter, if such places are at no great distance; if they are, they bury
+themselves in the climates where they dwell," (8. Hist. c. 16. See also
+Derham's Phys. Theol. v. ii. p. 177.)
+
+Hence their emigrations cannot depend on a _necessary_ instinct, as the
+emigrations themselves are not _necessary_.
+
+2. When the weather becomes cold, the swallows in the neighbourhood
+assemble in large flocks; that is, the unexperienced attend those that have
+before experienced the journey they are about to undertake: they are then
+seen some time to hover on the coast, till there is calm whether, or a
+wind, that suits the direction of their flight. Other birds of passage have
+been drowned by thousands in the sea, or have settled on ships quite
+exhausted with fatigue. And others, either by mistaking their course, or by
+distress of weather, have arrived in countries where they were never seen
+before: and thus are evidently subject to the same hazards that the human
+species undergo, in the execution of their artificial purposes.
+
+3. The same birds are emigrant from some countries and not so from others:
+the swallows were seen at Goree in January by an ingenious philosopher of
+my acquaintance, and he was told that they continued there all the year; as
+the warmth of the climate was at all seasons sufficient for their own
+constitutions, and for the production of the flies that supply them with
+nourishment. Herodotus says, that in Libya, about the springs of the Nile,
+the swallows continue all the year. (L. 2.)
+
+Quails (tetrao corturnix, Lin.) are birds of passage from the coast of
+Barbary to Italy, and have frequently settled in large shoals on ships
+fatigued with their flight. (Ray, Wisdom of God, p. 129. Derham. Physic.
+Theol. v. ii. p. 178,) Dr. Ruffel, in his History of Aleppo, observes that
+the swallows visit that country about the end of February, and having
+hatched their young disappear about the end of July; and returning again
+about the beginning of October, continue about a fortnight, and then again
+disappear. (P. 70.)
+
+When my late friend Dr. Chambres, of Derby, was on the island of Caprea in
+the bay of Naples, he was informed that great flights of quails annually
+settle on that island about the beginning of May, in their passage from
+Africa to Europe. And that they always come when the south-east wind blows,
+are fatigued when they rest on this island, and are taken in such amazing
+quantities and sold to the Continent, that the inhabitants pay the bishop
+his stipend out of the profits arising from the sale of them.
+
+The flights of these birds across the Mediterranean are recorded near three
+thousand years ago. "There went forth a wind from the Lord and brought
+quails from the sea, and let them fall upon the camp, a day's journey round
+about it, and they were two cubits above the earth," (Numbers, chap. ii.
+ver. 31.)
+
+In our country, Mr. Pennant informs us, that some quails migrate, and
+others only remove from the internal parts of the island to the coasts,
+(Zoology, octavo, 210.) Some of the ringdoves and stares breed here, others
+migrate, (ibid. 510, ii.) And the slender billed small birds do not all
+quit these kingdoms in the winter, though the difficulty of procuring the
+worms and insects, that they feed on, supplies the same reason for
+migration to them all, (ibid. 511.)
+
+Linnæus has observed, that in Sweden the female chaffinches quit that
+country in September, migrating into Holland, and leave their mates behind
+till their return in spring. Hence he has called them Fringilla cælebs,
+(Amæn. Acad. ii. 42. iv. 595.) Now in our climate both sexes of them are
+perennial birds. And Mr. Pennant observes that the hoopoe, chatterer,
+hawfinch, and crossbill, migrate into England so rarely, and at such
+uncertain times, as not to deserve to be ranked among our birds of passage,
+(ibid. 511.)
+
+The water fowl, as geese and ducks, are better adapted for long migrations,
+than the other tribes of birds, as, when the weather is calm, they can not
+only rest themselves, or sleep upon the ocean, but possibly procure some
+kind of food from it.
+
+Hence in Siberia, as soon as the lakes are frozen, the water fowl, which
+are very numerous, all disappear, and are supposed to fly to warmer
+climates, except the rail, which, from its inability for long flights,
+probably sleeps, like our bat, in their winter. The following account from
+the Journey of Professor Gmelin, may entertain the reader. "In the
+neighbourhood of Krasnoiark, amongst many other emigrant water fowls, we
+observed a great number of rails, which when pursued never took flight, but
+endeavoured to escape by running. We enquired how these birds, that could
+not fly, could retire into other countries in the winter, and were told,
+both by the Tartars and Assanians, that they well knew those birds could
+not alone pass into other countries: but when the cranes (les grues) retire
+in autumn, each one takes a rail (un rale) upon his back, and carries him
+to a warmer climate."
+
+_Recapitulation._
+
+1. All birds of passage can exist in the climates, where they are produced.
+
+2. They are subject in their migrations to the same accidents and
+difficulties, that mankind are subject to in navigation.
+
+3. The same species of birds migrate from some countries, and are resident
+in others.
+
+From all these circumstances it appears that the migrations of birds are
+not produced by a necessary instinct, but are accidental improvements, like
+the arts among mankind, taught by their cotemporaries, or delivered by
+tradition from one generation of them to another.
+
+XIII. In that season of the year which supplies the nourishment proper for
+the expected brood, the birds enter into a contract of marriage, and with
+joint labour construct a bed for the reception of their offspring. Their
+choice of the proper season, their contracts of marriage, and the
+regularity with which they construct their nests, have in all ages excited
+the admiration of naturalists; and have always been attributed to the power
+of instinct, which, like the occult qualities of the antient philosophers,
+prevented all further enquiry. We shall consider them in their order.
+
+_Their Choice of the Season._
+
+Our domestic birds, that are plentifully supplied throughout the year with
+their adapted food, and are covered with houses from the inclemency of the
+weather, lay their eggs at any season: which evinces that the spring of the
+year is not pointed out to them by a necessary instinct.
+
+Whilst the wild tribes of birds choose this time of the year from their
+acquired knowledge, that the mild temperature of the air is more convenient
+for hatching their eggs, and is soon likely to supply that kind of
+nourishment, that is wanted for their young.
+
+If the genial warmth of the spring produced the passion of love, as it
+expands the foliage of trees, all other animals should feel its influence
+as well as birds: but, the viviparous creatures, as they suckle their
+young, that is, as they previously digest the natural food, that it may
+better suit the tender stomachs of their offspring, experience the
+influence of this passion at all seasons of the year, as cats and bitches.
+The graminivorous animals indeed generally produce their young about the
+time when grass is supplied in the greatest plenty, but this is without any
+degree of exactness, as appears from our cows, sheep, and hares, and may be
+a part of the traditional knowledge, which they learn from the example of
+their parents.
+
+_Their Contracts of Marriage._
+
+Their mutual passion, and the acquired knowledge, that their joint labour
+is necessary to procure sustenance for their numerous family, induces the
+wild birds to enter into a contract of marriage, which does not however
+take place among the ducks, geese, and fowls, that are provided with their
+daily food from our barns.
+
+An ingenious philosopher has lately denied, that animals can enter into
+contracts, and thinks this an essential difference between them and the
+human creature:--but does not daily observation convince us, that they form
+contracts of friendship with each other, and with mankind? When puppies and
+kittens play together, is there not a tacit contract, that they will not
+hurt each other? And does not your favorite dog expect you should give him
+his daily food, for his services and attention to you? And thus barters his
+love for your protection? In the same manner that all contracts are made
+amongst men, that do not understand each others arbitrary language.
+
+_Construction of their Nests._
+
+1. They seem to be instructed how to build their nests from their
+observation of that, in which they were educated, and from their knowledge
+of those things, that are most agreeable to their touch in respect: to
+warmth, cleanliness, and stability. They choose their situations from their
+ideas of safety from their enemies, and of shelter from the weather. Nor is
+the colour of their nests a circumstance unthought of; the finches, that
+build in green hedges, cover their habitations with green moss; the swallow
+or martin, that builds against rocks and houses, covers her's with clay,
+whilst the lark chooses vegetable straw nearly of the colour of the ground
+she inhabits: by this contrivance, they are all less liable to be
+discovered by their adversaries.
+
+2. Nor are the nests of the same species of birds constructed always of the
+same materials, nor in the same form; which is another circumstance that
+ascertains, that they are led by observation.
+
+In the trees before Mr. Levet's house in Lichfield, there are annually
+nests built by sparrows, a bird which usually builds under the tiles of
+houses, or the thatch of barns. Not finding such convenient situations for
+their nests, they build a covered nest bigger than a man's head, with an
+opening like a mouth at the side, resembling that of a magpie, except that
+it is built with straw and hay, and lined with feathers, and so nicely
+managed as to be a defence against both wind and rain.
+
+The following extract from a Letter of the Rev. Mr. J. Darwin, of Carleton
+Scroop in Lincolnshire, authenticates a curious fact of this kind. "When I
+mentioned to you the circumstance of crows or rooks building in the spire
+of Welbourn church, you expressed a desire of being well informed of the
+certainty of the fact. Welbourn is situated in the road from Grantham to
+Lincoln on the Cliff row; I yesterday took a ride thither, and enquired of
+the rector, Mr. Ridgehill, whether the report was true, that rooks built in
+the spire of his church. He assured me it was true, and that they had done
+so time immemorial, as his parishioners affirmed. There was a common
+tradition, he said, that formerly a rookery in some high trees adjoined the
+church yard, which being cut down (probably in the spring, the building
+season), the rooks removed to the church, and built their nests on the
+outside of the spire on the tops of windows, which by their projection a
+little from the spire made them convenient room, but that they built also
+on the inside. I saw two nests made with sticks on the outside, and in the
+spires, and Mr. Ridgehill said there were always a great many.
+
+"I spent the day with Mr. Wright, a clergyman, at Fulbeck, near Welbourn,
+and in the afternoon Dr. Ellis of Headenham, about two miles from Welbourn,
+drank tea at Mr. Wright's, who said he remembered, when Mr. Welby lived at
+Welbourn, that he received a letter from an acquaintance in the west of
+England, desiring an answer, whether the report of rooks building in
+Welbourn church was true, as a wager was depending on that subject; to
+which he returned an answer ascertaining the fact, and decided the wager."
+Aug. 30, 1794.
+
+So the jackdaw (corvus monedula) generally builds in church-steeples, or
+under the roofs of high houses; but at Selbourn, in Southamptonshire, where
+towers and steeples are not sufficiently numerous, these birds build in
+forsaken rabbit burrows. See a curious account of these subterranean nests
+in White's History of Selbourn, p. 59. Can the skilful change of
+architecture in these birds and the sparrows above mentioned be governed by
+instinct? Then they must have two instincts, one for common, and the other
+for extraordinary occasions.
+
+I have seen green worsted in a nest, which no where exists in nature: and
+the down of thistles in those nests, that were by some accident constructed
+later in the summer, which material could not be procured for the earlier
+nests: in many different climates they cannot procure the same materials,
+that they use in ours. And it is well known, that the canary birds, that
+are propagated in this country, and the finches, that are kept tame, will
+build their nests of any flexile materials, that are given them. Plutarch,
+in his Book on Rivers, speaking of the Nile, says, "that the swallows
+collect a material, when the waters recede, with which they form nests,
+that are impervious to water." And in India there is a swallow that
+collects a glutinous substance for this purpose, whose nest is esculent,
+and esteemed a principal rarity amongst epicures, (Lin. Syst. Nat.) Both
+these must be constructed of very different materials from those used by
+the swallows of our country.
+
+In India the birds exert more artifice in building their nests on account
+of the monkeys and snakes: some form their pensile nests in the shape of a
+purse, deep and open at top; others with a hole in the side; and others,
+still more cautious, with an entrance at the very bottom, forming their
+lodge near the summit. But the taylor-bird will not ever trust its nest to
+the extremity of a tender twig, but makes one more advance to safety by
+fixing it to the leaf itself. It picks up a dead leaf, and sews it to the
+side of a living one, its slender bill being its needle, and its thread
+some fine fibres; the lining consists of feathers, gossamer, and down; its
+eggs are white, the colour of the bird light yellow, its length three
+inches, its weight three sixteenths of an ounce; so that the materials of
+the nest, and the weight of the bird, are not likely to draw down an
+habitation so slightly suspended. A nest of this bird is preserved in the
+British Museum, (Pennant's Indian Zoology). This calls to one's mind the
+Mosaic account of the origin of mankind, the first dawning of art there
+ascribed to them, is that of sewing leaves together. For many other curious
+kinds of nests see Natural History for Children, by Mr. Galton. Johnson.
+London. Part I. p. 47. Gen. Oriolus.
+
+3. Those birds that are brought up by our care, and have had little
+communication with others of their own species, are very defective in this
+acquired knowledge; they are not only very awkward in the construction of
+their nests, but generally scatter their eggs in various parts of the room
+or cage, where they are confined, and seldom produce young ones, till, by
+failing in their first attempt, they have learnt something from their own
+observation.
+
+4. During the time of incubation birds are said in general to turn their
+eggs every day; some cover them, when they leave the nest, as ducks and
+geese; in some the male is said to bring food to the female, that she may
+have less occasion of absence, in others he is said to take her place, when
+she goes in quest of food; and all of them are said to leave their eggs a
+shorter time in cold weather than in warm. In Senegal the ostrich sits on
+her eggs only during the night, leaving them in the day to the heat of the
+sun; but at the Cape of Good Hope, where the heat is less, she sits on them
+day and night.
+
+If it should be asked, what induces a bird to sit weeks on its first eggs
+unconscious that a brood of young ones will be the product? The answer must
+be, that it is the same passion that induces the human mother to hold her
+offspring whole nights and days in her fond arms, and press it to her
+bosom, unconscious of its future growth to sense and manhood, till
+observation or tradition have informed her.
+
+5. And as many ladies are too refined to nurse their own children, and
+deliver them to the care and provision of others; so is there one instance
+of this vice in the feathered world. The cuckoo in some parts of England,
+as I am well informed by a very distinct and ingenious gentleman, hatches
+and educates her own young; whilst in other parts she builds no nest, but
+uses that of some lesser bird, generally either of the wagtail, or hedge
+sparrow, and depositing one egg in it, takes no further care of her
+progeny.
+
+As the Rev. Mr. Stafford was walking in Glosop Dale, in the Peak of
+Derbyshire, he saw a cuckoo rise from its nest. The nest was on the stump
+of a tree, that had been some time felled, among some chips that were in
+part turned grey, so as much to resemble the colour of the bird, in this
+nest were two young cuckoos: tying a string about the leg of one of them,
+he pegged the other end of it to the ground, and very frequently for many
+days beheld the old cuckoo feed these her young, as he stood very near
+them.
+
+The following extract of a Letter from the Rev. Mr. Wilmot, of Morley, near
+Derby, strengthens the truth of the fact above mentioned, of the cuckoo
+sometimes making a nest, and hatching her own young.
+
+"In the beginning of July 1792, I was attending some labourers on my farm,
+when one of them said to me, "There is a bird's nest upon one of the
+Coal-slack Hills; the bird is now sitting, and is exactly like a cuckoo.
+They say that cuckoo's never hatch their own eggs, otherwise I should have
+sworn it was one." He took me to the spot, it was in an open fallow ground;
+the bird was upon the nest, I stood and observed her some time, and was
+perfectly satisfied it was a cuckoo; I then put my hand towards her, and
+she almost let me touch her before she rose from the nest, which she
+appeared to quit with great uneasiness, skimming over the ground in the
+manner that a hen partridge does when disturbed from a new hatched brood,
+and went only to a thicket about forty or fifty yards from the nest; and
+continued there as long as I staid to observe her, which was not many
+minutes. In the nest, which was barely a hole scratched out of the
+coal-slack in the manner of a plover's nest, I observed three eggs, but did
+not touch them. As I had labourers constantly at work in that field, I went
+thither every day, and always looked to see if the bird was there, but did
+not disturb her for seven or eight days, when I was tempted to drive her
+from the nest, and found _two_ young ones, that appeared to have been
+hatched some days, but there was no appearance of the third egg. I then
+mentioned this extraordinary circumstance (for such I thought it) to Mr.
+and Mrs. Holyoak of Bidford Grange, Warwickshire, and to Miss M. Willes,
+who were on a visit at my house, and who all went to see it. Very lately I
+reminded Mr. Holyoak of it, who told me he had a perfect recollection of
+the whole, and that, considering it a curiosity, he walked to look at it
+several times, was perfectly satisfied as to its being a cuckoo, and
+thought her more attentive to her young, than any other bird he ever
+observed, having always found her brooding her young. In about a week after
+I first saw the young ones, one of them was missing, and I rather suspected
+my plough-boys having taken it; though it might possibly have been taken by
+a hawk, some time when the old one was seeking food. I never found her off
+her nest but once, and that was the last time I saw the remaining young
+one, when it was almost full feathered. I then went from home for two or
+three days, and, when I returned, the young one was gone, which I take for
+granted had flown. Though during this time I frequently saw cuckoos in the
+thicket I mention, I never observed any one, that I supposed to be the
+cock-bird, paired with this hen."
+
+Nor is this a new observation, though it is entirely overlooked by the
+modern naturalists, for Aristotle speaking of the cuckoo, asserts that she
+sometimes builds her nest among broken rocks, and on high mountains, (L. 6.
+H. c. 1.) but adds in another place that she generally possesses the nest
+of another bird, (L. 6. H. c. 7.) And Niphus says that cuckoos rarely build
+for themselves, most frequently laying their eggs in the nests of other
+birds, (Gesner, L. 3. de Cuculo.)
+
+The Philosopher who is acquainted with these facts concerning the cuckoo,
+would seem to have very little _reason_ himself, if he could imagine this
+neglect of her young to be a necessary _instinct_!
+
+XIV. The deep recesses of the ocean are inaccessible to mankind, which
+prevents us from having much knowledge of the arts and government of its
+inhabitants.
+
+1. One of the baits used by the fisherman is an animal called an Old
+Soldier, his size and form are somewhat like the craw-fish, with this
+difference, that his tail is covered with a tough membrane instead of a
+shell; and to obviate this defect, he seeks out the uninhabited shell of
+some dead fish, that is large enough to receive his tail, and carries it
+about with him as part of his clothing or armour.
+
+2. On the coasts about Scarborough, where the haddocks, cods, and dog-fish,
+are in great abundance, the fishermen universally believe that the dog-fish
+make a line, or semicircle, to encompass a shoal of haddocks and cod,
+confining them within certain limits near the shore, and eating them as
+occasion requires. For the haddocks and cod are always found near the shore
+without any dog-fish among them, and the dog-fish further off without any
+haddocks or cod; and yet the former are known to prey upon the latter, and
+in some years devour such immense quantities as to render this fishery more
+expensive than profitable.
+
+3. The remora, when he wishes to remove his situation, as he is a very slow
+swimmer, is content to take an outside place on whatever conveyance is
+going his way; nor can the cunning animal be tempted to quit his hold of a
+ship when she is sailing, not even for the lucre of a piece of pork, lest
+it should endanger the loss of his passage: at other times he is easily
+caught with the hook.
+
+4. The crab-fish, like many other testaceous animals, annually changes its
+shell; it is then in a soft state, covered only with a mucous membrane, and
+conceals itself in holes in the sand or under weeds; at this place a hard
+shelled crab always stands centinel, to prevent the sea insects from
+injuring the other in its defenceless state; and the fishermen from his
+appearance know where to find the soft ones, which they use for baits in
+catching other fish.
+
+And though the hard shelled crab, when he is on this duty, advances boldly
+to meet the foe, and will with difficulty quit the field; yet at other
+times he shews great timidity, and has a wonderful speed in attempting his
+escape; and, if often interrupted, will pretend death like the spider, and
+watch an opportunity to sink himself into the sand, keeping only his eyes
+above. My ingenious friend Mr. Burdett, who favoured me with these accounts
+at the time he was surveying the coasts, thinks the commerce between the
+sexes takes place at this time, and inspires the courage of the creature.
+
+5. The shoals of herrings, cods, haddocks, and other fish, which approach
+our shores at certain seasons, and quit them at other seasons without
+leaving one behind; and the salmon, that periodically frequent our rivers,
+evince, that there are vagrant tribes of fish, that perform as regular
+migrations as the birds of passage already mentioned.
+
+6. There is a cataract on the river Liffey in Ireland about nineteen feet
+high: here in the salmon season many of the inhabitants amuse themselves in
+observing these fish leap up the torrent. They dart themselves quite out of
+the water as they ascend, and frequently fall back many times before they
+surmount it, and baskets made of twigs are placed near the edge of the
+stream to catch them in their fall.
+
+I have observed, as I have sat by a spout of water, which descends from a
+stone trough about two feet into a stream below, at particular seasons of
+the year, a great number of little fish called minums, or pinks, throw
+themselves about twenty times their own length out of the water, expecting
+to get into the trough above.
+
+This evinces that the storgee, or attention of the dam to provide for the
+offspring, is strongly exerted amongst the nations of fish, where it would
+seem to be the most neglected; as these salmon cannot be supposed to
+attempt so difficult and dangerous a task without being conscious of the
+purpose or end of their endeavours.
+
+It is further remarkable, that most of the old salmon return to the sea
+before it is proper for the young shoals to attend them, yet that a few old
+ones continue in the rivers so late, that they become perfectly emaciated
+by the inconvenience of their situation, and this apparently to guide or to
+protect the unexperienced brood.
+
+Of the smaller water animals we have still less knowledge, who nevertheless
+probably possess many superior arts; some of these are mentioned in Botanic
+Garden, P. I. Add. Note XXVII. and XXVIII. The nympha of the water-moths of
+our rivers, which cover themselves with cases of straw, gravel, and shell,
+contrive to make their habitations, nearly in equilibrium with the water;
+when too heavy, they add a bit of wood or straw; when too light, a bit of
+gravel. Edinb. Trans.
+
+All these circumstances bear a near resemblance to the deliberate actions
+of human reason.
+
+XV. We have a very imperfect acquaintance with the various tribes of
+insects: their occupations, manner of life, and even the number of their
+senses, differ from our own, and from each other; but there is reason to
+imagine, that those which possess the sense of touch in the most exquisite
+degree, and whole occupations require the most constant exertion of their
+powers, are induced with a greater proportion or knowledge and ingenuity.
+
+The spiders of this country manufacture nets of various forms, adapted to
+various situations, to arrest the flies that are their food; and some of
+them have a house or lodging-place in the middle of the net, well contrived
+for warmth, security, or concealment. There is a large spider in South
+America, who constructs nets of so strong a texture as to entangle small
+birds, particularly the humming bird. And in Jamaica there is another
+spider, who digs a hole in the earth obliquely downwards, about three
+inches in length, and one inch in diameter, this cavity she lines with a
+tough thick web, which when taken out resembles a leathern purse: but what
+is most curious, this house has a door with hinges, like the operculum of
+some sea shells; and herself and family, who tenant this nest, open and
+shut the door, whenever they pass or repass. This history was told me, and
+the nest with its operculum shewn me by the late Dr. Butt of Bath, who was
+some years physician in Jamaica.
+
+The production of these nets is indeed a part of the nature or conformation
+of the animal, and their natural use is to supply the place of wings, when
+she wishes to remove to another situation. But when she employs them to
+entangle her prey, there are marks of evident design, for she adapts the
+form of each net to its situation, and strengthens those lines, that
+require it, by joining others to the middle of them, and attaching those
+others to distant objects, with the same individual art, that is used by
+mankind in supporting the masts and extending the sails of ships. This work
+is executed with more mathematical exactness and ingenuity by the field
+spiders, than by those in our houses, as their constructions are more
+subjected to the injuries of dews and tempests.
+
+Besides the ingenuity shewn by these little creatures in taking their prey,
+the circumstance of their counterfeiting death, when they are put into
+terror, is truly wonderful; and as soon as the object of terror is removed,
+they recover and run away. Some beetles are also said to possess this piece
+of hypocrisy.
+
+The curious webs, or chords, constructed by some young caterpillars to
+defend themselves from cold, or from insects of prey; and by silk-worms and
+some other caterpillars, when they transmigrate into aureliæ or larvæ, have
+deservedly excited the admiration of the inquisitive. But our ignorance of
+their manner of life, and even of the number of their senses, totally
+precludes us from understanding the means by which they acquire this
+knowledge.
+
+The care of the salmon in choosing a proper situation for her spawn, the
+structure of the nests of birds, their patient incubation, and the art of
+the cuckoo in depositing her egg in her neighbour's nursery, are instances
+of great sagacity in those creatures: and yet they are much inferior to the
+arts exerted by many of the insect tribes on similar occasions. The hairy
+excrescences on briars, the oak apples, the blasted leaves of trees, and
+the lumps on the backs of cows, are situations that are rather produced
+than chosen by the mother insect for the convenience of her offspring. The
+cells of bees, wasps, spiders, and of the various coralline insects,
+equally astonish us, whether we attend to the materials or to the
+architecture.
+
+But the conduct of the ant, and of some species of the ichneumon fly in the
+incubation of their eggs, is equal to any exertion of human science. The
+ants many times in a day move their eggs nearer the surface of their
+habitation, or deeper below it, as the heat of the weather varies; and in
+colder days lie upon them in heaps for the purpose of incubation: if their
+mansion is too dry, they carry them to places where there is moisture, and
+you may distinctly see the little worms move and suck up the water. When
+too much moisture approaches their nest, they convey their eggs deeper in
+the earth, or to some other place of safety. (Swammerd. Epil. ad Hist.
+Insects, p. 153. Phil. Trans. No. 23. Lowthrop. V. 2. p. 7.)
+
+There is one species of ichneumon-fly, that digs a hole in the earth, and
+carrying into it two or three living caterpillars, deposits her eggs, and
+nicely closing up the nest leaves them there; partly doubtless to assist
+the incubation, and partly to supply food to her future young, (Derham. B.
+4, c. 13. Aristotle Hist. Animal, L. 5. c. 20.)
+
+A friend of mine put about fifty large caterpillars collected from cabbages
+on some bran and a few leaves into a box, and covered it with gauze to
+prevent their escape. After a few days we saw, from more than three fourths
+of them, about eight or ten little caterpillars of the ichneumon-fly come
+out of their backs, and spin each a small cocoon of silk, and in a few days
+the large caterpillars died. This small fly it seems lays its egg in the
+back of the cabbage caterpillar, which when hatched preys upon the
+material, which is produced there for the purpose of making silk for the
+future nest of the cabbage caterpillar; of which being deprived, the
+creature wanders about till it dies, and thus our gardens are preserved by
+the ingenuity of this cruel fly. This curious property of producing a silk
+thread, which is common to some sea animals, see Botanic Garden, Part I.
+Note XXVII. and is designed for the purpose of their transformation as in
+the silk-worm, is used for conveying themselves from higher branches to
+lower ones of trees by some caterpillars, and to make themselves temporary
+nests or tents, and by the spider for entangling his prey. Nor is it
+strange that so much knowledge should be acquired by such small animals;
+since there is reason to imagine, that these insects have the sense of
+touch, either in their proboscis, or their antennæ, to a great degree of
+perfection; and thence may possess, as far as their sphere extends, as
+accurate knowledge, and as subtle invention, as the discoverers of human
+arts.
+
+XVI. 1. If we were better acquainted with the histories of those insects
+that are formed into societies, as the bees, wasps, and ants, I make no
+doubt but we should find, that their arts and improvements are not so
+similar and uniform as they now appear to us, but that they arose in the
+same manner from experience and tradition, as the arts of our own species;
+though their reasoning is from fewer ideas, is busied about fewer objects,
+and is exerted with less energy.
+
+There are some kinds of insects that migrate like the birds before
+mentioned. The locust of warmer climates has sometimes come over to
+England; it is shaped like a grasshopper, with very large wings, and a body
+above an inch in length. It is mentioned as coming into Egypt with an east
+wind, "The lord brought an east wind upon the land all that day and night,
+and in the morning the east wind brought the locusts, and covered the face
+of the earth, so that the land was dark," Exod. x. 13. The migrations of
+these insects are mentioned in another part of the scripture, "The locusts
+have no king, yet go they forth all of them in bands," Prov. xxx. 27.
+
+The accurate Mr. Adanson, near the river Gambia in Africa, was witness to
+the migration of these insects. "About eight in the morning, in the month
+of February, there suddenly arose over our heads a thick cloud, which
+darkened the air, and deprived us of the rays of the sun. We found it was a
+cloud of locusts raised about twenty or thirty fathoms from the ground, and
+covering an extent of several leagues; at length a shower of these insects
+descended, and after devouring every green herb, while they rested, again
+resumed their flight. This cloud was brought by a strong east-wind, and was
+all the morning in passing over the adjacent country." (Voyage to Senegal,
+158.)
+
+In this country the gnats are sometimes seen to migrate in clouds, like the
+musketoes of warmer climates, and our swarms of bees frequently travel many
+miles, and are said in North America always to fly towards the south. The
+prophet Isaiah has a beautiful allusion to these migrations, "The Lord
+shall call the fly from the rivers of Egypt, and shall hiss for the bee
+that is in the land of Assyria," Isa. vii. 18. which has been lately
+explained by Mr. Bruce, in his travels to discover the source of the Nile.
+
+2. I am well informed that the bees that were carried into Barbadoes, and
+other western islands, ceased to lay up any honey after the first year, as
+they found it not useful to them: and are now become very troublesome to
+the inhabitants of those islands by infesting their sugar houses; but those
+in Jamaica continue to make honey, as the cold north winds, or rainy
+seasons of that island, confine them at home for several weeks together.
+And the bees of Senegal, which differ from those of Europe only in size,
+make their honey not only superior to ours in delicacy of flavour, but it
+has this singularity, that it never concretes, but remains liquid as syrup,
+(Adanson). From some observations of Mr. Wildman, and of other people of
+veracity, it appears, that during the severe part of the winter season for
+weeks together the bees are quite benumbed and torpid from the cold, and do
+not consume any of their provision. This state of sleep, like that of
+swallows and bats, seems to be the natural resource of those creatures in
+cold climates, and the making of honey to be an artificial improvement.
+
+As the death of our hives of bees appears to be owning to their being kept
+so warm, as to require food when their stock is exhausted; a very observing
+gentleman at my request put two hives for many weeks into a dry cellar, and
+observed, during all that time, they did not consume any of their
+provision, for their weight did not decrease as it had done when they were
+kept in the open air. The same observation is made in the Annual Register
+for 1768, p. 113. And the Rev. Mr. White, in his Method of preserving Bees,
+adds, that those on the north side of his house consumed less honey in the
+winter than those on the south side.
+
+There is another observation on bees well ascertained, that they at various
+times, when the season begins to be cold, by a general motion of their legs
+as they hang in clusters produce a degree of warmth, which is easily
+perceptible by the hand. Hence by this ingenious exertion, they for a long
+time prevent the torpid state they would naturally fall into.
+
+According to the late observations of Mr. Hunter, it appears that the
+bee's-wax is not made from the dust of the anthers of flowers, which they
+bring home on their thighs, but that this makes what is termed bee-bread,
+and is used for the purpose of feeding the bee-maggots; in the same manner
+butterflies live on honey, but the previous caterpillar lives on vegetable
+leaves, while the maggots of large flies require flesh for their food, and
+those of the ichneumon fly require insects for their food. What induces the
+bee who lives on honey to lay up vegetable powder for its young? What
+induces the butterfly to lay its eggs on leaves, when itself feeds on
+honey? What induces the other flies to seek a food for their progeny
+different from what they consume themselves? If these are not deductions
+from their own previous experience or observation, all the actions of
+mankind must be resolved into instinct.
+
+3. The dormouse consumes but little of its food during the rigour of the
+season, for they roll themselves up, or sleep, or lie torpid the greatest
+part of the time; but on warm sunny days experience a short revival, and
+take a little food, and then relapse into their former state." (Pennant
+Zoolog. p. 67.) Other animals, that sleep in winter without laying up any
+provender, are observed to go into their winter beds fat and strong, but
+return to day-light in the spring season very lean and feeble. The common
+flies sleep during the winter without any provision for their nourishment,
+and are daily revived by the warmth of the sun, or of our fires. These
+whenever they see light endeavour to approach it, having observed, that by
+its greater vicinity they get free from the degree of torpor, that the cold
+produces; and are hence induced perpetually to burn themselves in our
+candles: deceived, like mankind, by the misapplication of their knowledge.
+Whilst many of the subterraneous insects, as the common worms, seem to
+retreat so deep into the earth as not to be enlivened or awakened by the
+difference of our winter days; and stop up their holes with leaves or
+straws, to prevent the frosts from injuring them, or the centipes from
+devouring them. The habits of peace, or the stratagems of war, of these
+subterranean nations are covered from our view; but a friend of mine
+prevailed on a distressed worm to enter the hole of another worm on a
+bowling-green, and he presently returned much wounded about his head. And I
+once saw a worm rise hastily out of the earth into the sunshine, and
+observed a centipes hanging at its tail: the centipes nimbly quitted the
+tail, and seizing the worm about its middle cut it in half with its
+forceps, and preyed upon one part, while the other escaped. Which evinces
+they have design in stopping the mouths of their habitations.
+
+4. The wasp of this country fixes his habitation under ground, that he may
+not be affected with the various changes of our climate; but in Jamaica he
+hangs it on the bough of a tree, where the seasons are less severe. He
+weaves a very curious paper of vegetable fibres to cover his nest, which is
+constructed on the same principle with that of the bee, but with a
+different material; but as his prey consists of flesh, fruits, and insects,
+which are perishable commodities, he can lay up no provender for the
+winter.
+
+M. de la Loubiere, in his relation of Siam, says, "That in a part of that
+kingdom, which lies open to great inundations, all the ants make their
+settlements upon trees; no ants' nests are to be seen any where else."
+Whereas in our country the ground is their only situation. From the
+scriptual account of these insects, one might be led to suspect, that in
+some climates they lay up a provision for the winter. Origen affirms the
+same, (Cont. Cels. L. 4.) But it is generally believed that in this country
+they do not, (Prov. vi. 6. xxx. 25.) The white ants of the coast of Africa
+make themselves pyramids eight or ten feet high, on a base of about the
+same width, with a smooth surface of rich clay, excessively hard and well
+built, which appear at a distance like an assemblage of the huts of the
+negroes, (Adanson). The history of these has been lately well described in
+the Philosoph. Transactions, under the name of termes, or termites. These
+differ very much from the nest of our large ant; but the real history of
+this creature, as well as of the wasp, is yet very imperfectly known.
+
+Wasps are said to catch large spiders, and to cut off their legs, and carry
+their mutilated bodies to their young, Dict. Raison. Tom. I. p. 152.
+
+One circumstance I shall relate which fell under my own eye, and shewed the
+power or reason in a wasp, as it is exercised among men. A wasp, on a
+gravel walk, had caught a fly nearly as large as himself; kneeling on the
+ground I observed him separate the tail and the head from the body part, to
+which the wings were attached. He then took the body part in his paws, and
+rose about two feet from the ground with it; but a gentle breeze wafting
+the wings of the fly turned him round in the air, and he settled again with
+his prey upon the gravel. I then distinctly observed him cut off with his
+mouth, first one of the wings, and then the other, after which he flew away
+with it unmolested by the wind.
+
+Go, thou sluggard, learn arts and industry from the bee, and from the ant!
+
+Go, proud reasoner, and call the worm thy sister!
+
+XVII. _Conclusion._
+
+It was before observed how much the superior accuracy of our sense of touch
+contributes to increase our knowledge; but it is the greater energy and
+activity of the power of volition (as explained in the former Sections of
+this work) that marks mankind, and has given him the empire of the world.
+
+There is a criterion by which we may distinguish our voluntary acts or
+thoughts from those that are excited by our sensations: "The former are
+always employed about the _means_ to acquire pleasureable objects, or to
+avoid painful ones: while the latter are employed about the _possession_ of
+those that are already in our power."
+
+If we turn our eyes upon the fabric of our fellow animals, we find they are
+supported with bones, covered with skins, moved by muscles; that they
+possess the same senses, acknowledge the same appetites, and are nourished
+by the same aliment with ourselves; and we should hence conclude from the
+strongest analogy, that their internal faculties were also in some measure
+similar to our own.
+
+Mr. Locke indeed published an opinion, that other animals possessed no
+abstract or general ideas, and thought this circumstance was the barrier
+between the brute and the human world. But these abstracted ideas have been
+since demonstrated by Bishop Berkley, and allowed by Mr. Hume, to have no
+existence in nature, not even in the mind of their inventor, and we are
+hence necessitated to look for some other mark of distinction.
+
+The ideas and actions of brutes, like those of children, are almost
+perpetually produced by their present pleasures, or their present pains;
+and, except in the few instances that have been mentioned in this Section,
+they seldom busy themselves about the _means_ of procuring future bliss, or
+of avoiding future misery.
+
+Whilst the acquiring of languages, the making of tools, and the labouring
+for money; which are all only the _means_ of procuring pleasure; and the
+praying to the Deity, as another _means_ to procure happiness, are
+characteristic of human nature.
+
+       *       *       *       *       *
+
+SECT. XVII.
+
+THE CATENATION OF MOTIONS.
+
+    I. 1. _Catenations of animal motion._ 2. _Are produced by irritations,
+    by sensations, by volitions._ 3. _They continue some time after they
+    have been excited. Cause of catenation._ 4. _We can then exert our
+    attention on other objects._ 5. _Many catenations of motions go on
+    together._ 6. _Some links of the catenations of motions may be left out
+    without disuniting the chain._ 7. _Interrupted circles of motion
+    continue confusedly till they come to the part of the circle, where
+    they were disturbed._ 8. _Weaker catenations are dissevered by
+    stronger._ 9. _Then new catenations take place._ 10. _Much effort
+    prevents their reuniting. Impediment of speech._ 11. _Trains more
+    easily dissevered than circles._ 12. _Sleep destroys volition and
+    external stimulus._ II. _Instances of various catenations in a young
+    lady playing on the harpsichord._ III. 1. _What catenations are the
+    strongest._ 2. _Irritations joined with associations from strongest
+    connexions. Vital motions._ 3. _New links with increased force, cold
+    fits of fever produced._ 4. _New links with decreased force. Cold
+    bath._ 5. _Irritation joined with sensation. Inflammatory fever. Why
+    children cannot tickle themselves. 6. Volition joined with sensation.
+    Irritative ideas of sound become sensible._ 7. _Ideas of imagination,
+    dissevered by irritations, by volition, production of surprise._
+
+I. 1. To investigate with precision the catenations of animal motions, it
+would be well to attend to the manner of their production; but we cannot
+begin this disquisition early enough for this purpose, as the catenations
+of motion seem to begin with life, and are only extinguishable with it; We
+have spoken of the power of irritation, of sensation, of volition, and of
+association, as preceding the fibrous motions; we now step forwards, and
+consider, that conversely they are in their turn preceded by those motions;
+and that all the successive trains or circles of our actions are composed
+of this twofold concatenation. Those we shall call trains of action, which
+continue to proceed without any stated repetitions; and those circles of
+action, when the parts of them return at certain periods, though the
+trains, of which they consist, are not exactly similar. The reading an epic
+poem is a train of actions; the reading a song with a chorus at equal
+distances in the measure constitutes so many circles of action.
+
+2. Some catenations of animal motion are produced by reiterated successive
+irritations, as when we learn to repeat the alphabet in its order by
+frequently reading the letters of it. Thus the vermicular motions of the
+bowels were originally produced by the successive irritations of the
+passing aliment; and the succession of actions of the auricles and
+ventricles of the heart was originally formed by successive stimulus of the
+blood, these afterwards become part of the diurnal circles of animal
+actions, as appears by the periodical returns of hunger, and the quickened
+pulse of weak people in the evening.
+
+Other catenations of animal motion are gradually acquired by successive
+agreeable sensations, as in learning a favourite song or dance; others by
+disagreeable sensations, as in coughing or nictitation; these become
+associated by frequent repetition, and afterwards compose parts of greater
+circles of action like those above mentioned.
+
+Other catenations of motions are gradually acquired by frequent voluntary
+repetitions; as when we deliberately learn to march, read, fence, or any
+mechanic art, the motions of many of our muscles become gradually linked
+together in trains, tribes, or circles of action. Thus when any one at
+first begins to use the tools in turning wood or metals in a lathe, he
+wills the motions of his hand or fingers, till at length these actions
+become so connected with the effect, that he seems only to will the point
+of the chisel. These are caused by volition, connected by association like
+those above described, and afterwards become parts of our diurnal trains or
+circles of action.
+
+3. All these catenations of animal motions, are liable to proceed some time
+after they are excited, unless they are disturbed or impeded by other
+irritations, sensations, or volitions; and in many instances in spite of
+our endeavours to stop them; and this property of animal motions is
+probably the cause of their catenation. Thus when a child revolves some
+minute on one foot, the spectra of the ambient objects appear to circulate
+round him some time after he falls upon the ground. Thus the palpitation of
+the heart continues some time after the object of fear, which occasioned
+it, is removed. The blush of shame, which is an excess of sensation, and
+the glow of anger, which is an excess of volition, continue some time,
+though the affected person finds, that those emotions were caused by
+mistaken facts, and endeavours to extinguish their appearance. See Sect.
+XII. 1. 5.
+
+4. When a circle of motions becomes connected, by frequent repetitions as
+above, we can exert our attention strongly on other objects, and the
+concatenated circle of motions will nevertheless proceed in due order; as
+whilst you are thinking on this subject, you use variety of muscles in
+walking about your parlour, or in sitting at your writing-table.
+
+5. Innumerable catenations of motions may proceed at the same time, without
+incommoding each other. Of these are the motions of the heart and arteries;
+those of digestion and glandular secretion; of the ideas, or sensual
+motions; those of progression, and of speaking; the great annual circle of
+actions so apparent in birds in their times of breeding and moulting; the
+monthly circles of many female animals; and the diurnal circles of sleeping
+and waking, of fulness and inanition.
+
+6. Some links of successive trains or of synchronous tribes of action may
+be left out without disjoining the whole. Such are our usual trains of
+recollection; after having travelled through an entertaining country, and
+viewed many delightful lawns, rolling rivers, and echoing rocks; in the
+recollection of our journey we leave out the many districts, that we
+crossed, which were marked with no peculiar pleasure. Such also are our
+complex ideas, they are catenated tribes of ideas, which do not perfectly
+resemble their correspondent perceptions, because some of the parts are
+omitted.
+
+7. If an interrupted circle of actions is not entirely dissevered, it will
+continue to proceed confusedly, till it comes to the part of the circle,
+where it was interrupted.
+
+The vital motions in a fever from drunkenness, and in other periodical
+diseases, are instances of this circumstance. The accidental inebriate does
+not recover himself perfectly till about the same hour on the succeeding
+day. The accustomed drunkard is disordered, if he has not his usual
+potation of fermented liquor. So if a considerable part of a connected
+tribe of action be disturbed, that whole tribe goes on with confusion, till
+the part of the tribe affected regains its accustomed catenations. So
+vertigo produces vomiting, and a great secretion of bile, as in
+sea-sickness, all these being parts of the tribe of irritative catenations.
+
+8. Weaker catenated trains may be dissevered by the sudden exertion of the
+stronger. When a child first attempts to walk across a room, call to him,
+and he instantly falls upon the ground. So while I am thinking over the
+virtues of my friends, if the tea-kettle spurt out some hot water on my
+stocking; the sudden pain breaks the weaker chain of ideas, and introduces
+a new group of figures of its own. This circumstance is extended to some
+unnatural trains of action, which have not been confirmed by long habit; as
+the hiccough, or an ague-fit, which are frequently curable by surprise. A
+young lady about eleven years old had for five days had a contraction of
+one muscle in her fore arm, and another in her arm, which occurred four or
+five times every minute; the muscles were seen to leap, but without bending
+the arm. To counteract this new morbid habit, an issue was placed over the
+convulsed muscle of her arm, and an adhesive plaster wrapped tight like a
+bandage over the whole fore arm, by which the new motions were immediately
+destroyed, but the means were continued some weeks to prevent a return.
+
+9. If any circle of actions is dissevered, either by omission of some of
+the links, as in sleep, or by insertion of other links, as in surprise, new
+catenations take place in a greater or less degree. The last link of the
+broken chain of actions becomes connected with the new motion which has
+broken it, or with that which was nearest the link omitted; and these new
+catenations proceed instead of the old ones. Hence the periodic returns of
+ague-fits, and the chimeras of our dreams.
+
+10. If a train of actions is dissevered, much effort of volition or
+sensation will prevent its being restored. Thus in the common impediment of
+speech, when the association of the motions of the muscles of enunciation
+with the idea of the word to be spoken is disordered, the great voluntary
+efforts, which distort the countenance, prevent the rejoining of the broken
+associations. See No. II. 10. of this Section. It is thus likewise
+observable in some inflammations of the bowels, the too strong efforts made
+by the muscles to carry forwards the offending material fixes it more
+firmly in its place, and prevents the cure. So in endeavouring to recal to
+our memory some particular word of a sentence, if we exert ourselves too
+strongly about it, we are less likely to regain it.
+
+11. Catenated trains or tribes of action are easier dissevered than
+catenated circles of action. Hence in epileptic fits the synchronous
+connected tribes of action, which keep the body erect, are dissevered, but
+the circle of vital motions continues undisturbed.
+
+12. Sleep destroys the power of volition, and precludes the stimuli of
+external objects, and thence dissevers the trains, of which these are a
+part; which confirms the other catenations, as those of the vital motions,
+secretions, and absorptions; and produces the new trains of ideas, which
+constitute our dreams.
+
+II. 1. All the preceding circumstances of the catenations of animal motions
+will be more clearly understood by the following example of a person
+learning music; and when we recollect the variety of mechanic arts, which
+are performed by associated trains of muscular actions catenated with the
+effects they produce, as in knitting, netting, weaving; and the greater
+variety of associated trains of ideas caused or catenated by volitions or
+sensations, as in our hourly modes of reasoning, or imagining, or
+recollecting, we shall gain some idea of the innumerable catenated trains
+and circles of action, which form the tenor of our lives, and which began,
+and will only cease entirely with them.
+
+2. When a young lady begins to learn music, she voluntarily applies herself
+to the characters of her music-book, and by many repetitions endeavours to
+catenate them with the proportions of sound, of which they are symbols. The
+ideas excited by the musical characters are slowly connected with the keys
+of the harpsichord, and much effort is necessary to produce every note with
+the proper finger, and in its due place and time; till at length a train of
+voluntary exertions becomes catenated with certain irritations. As the
+various notes by frequent repetitions become connected in the order, in
+which they are produced, a new catenation of sensitive exertions becomes
+mixed with the voluntary ones above described; and not only the musical
+symbols of crotchets and quavers, but the auditory notes and tones at the
+same time, become so many successive or synchronous links in this circle of
+catenated actions.
+
+At length the motions of her fingers become catenated with the musical
+characters; and these no sooner strike the eye, than the finger presses
+down the key without any voluntary attention between them; the activity of
+the hand being connected with the irritation of the figure or place of the
+musical symbol on the retina; till at length by frequent repetitions of the
+same tune the movements of her fingers in playing, and the muscles of the
+larynx in singing, become associated with each other, and form part of
+those intricate trains and circles of catenated motions, according with the
+second article of the preceding propositions in No. 1. of this Section.
+
+3. Besides the facility, which by habit attends the execution of this
+musical performance, a curious circumstance occurs, which is, that when our
+young musician has began a tune, she finds herself inclined to continue it;
+and that even when she is carelessly singing alone without attending to her
+own song; according with the third preceding article.
+
+4. At the same time that our young performer continues to play with great
+exactness this accustomed tune, she can bend her mind, and that intensely,
+on some other object, according with the fourth article of the preceding
+proportions.
+
+The manuscript copy of this work was lent to many of my friends at
+different times for the purpose of gaining their opinions and criticisms on
+many parts of it, and I found the following anecdote written with a pencil
+opposite to this page, but am not certain by whom. "I remember seeing the
+pretty young actress, who succeeded Mrs. Arne in the performance of the
+celebrated Padlock, rehearse the musical parts at her harpsichord under the
+eye of her master with great taste and accuracy; though I observed her
+countenance full of emotion, which I could not account for; at last she
+suddenly burst into tears; for she had all this time been eyeing a beloved
+canary bird, suffering great agonies, which at that instant fell dead from
+its perch."
+
+5. At the same time many other catenated circles of action are going on in
+the person of our fair musician, as well as the motions of her fingers,
+such as the vital motions, respiration, the movements of her eyes and
+eyelids, and of the intricate muscles of vocality, according with the fifth
+preceding article.
+
+6. If by any strong impression on the mind of our fair musician she should
+be interrupted for a very inconsiderable time, she can still continue her
+performance, according to the sixth article.
+
+7. If however this interruption be greater, though the chain of actions be
+not dissevered, it proceeds confusedly, and our young performer continues
+indeed to play, but in a hurry without accuracy and elegance, till she
+begins the tune again, according to the seventh of the preceding articles.
+
+8. But if this interruption be still greater, the circle of actions becomes
+entirely dissevered, and she finds herself immediately under the necessity
+to begin over again to recover the lost catenation, according to the eighth
+preceding article.
+
+9. Or in trying to recover it she will sing some dissonant notes, or strike
+some improper keys, according to the ninth preceding article.
+
+10. A very remarkable thing attends this breach of catenation, if the
+performer has forgotten some word of her song, the more energy of mind she
+uses about it, the more distant is she from regaining it; and artfully
+employs her mind in part on some other object, or endeavours to dull its
+perceptions, continuing to repeat, as it were inconsciously, the former
+part of the song, that she remembers, in hopes to regain the lost
+connexion.
+
+For if the activity of the mind itself be more energetic, or takes its
+attention more, than the connecting word, which is wanted; it will not
+perceive the slighter link of this lost word; as who listens to a feeble
+sound, must be very silent and motionless; so that in this case the very
+vigour of the mind itself seems to prevent it from regaining the lost
+catenation, as well as the too great exertion in endeavouring to regain it,
+according to the tenth preceding article.
+
+We frequently experience, when we are doubtful about the spelling of a
+word, that the greater voluntary exertion we use, that is the more
+intensely we think about it, the further are we from regaining the lost
+association between the letters of it, but which readily recurs when we
+have become careless about it. In the same manner, after having for an hour
+laboured to recollect the name of some absent person, it shall seem,
+particularly after sleep, to come into the mind as it were spontaneously;
+that is the word we are in search of, was joined to the preceding one by
+association; this association being dissevered, we endeavour to recover it
+by volition; this very action of the mind strikes our attention more, than
+the faint link of association, and we find it impossible by this means to
+retrieve the lost word. After sleep, when volition is entirely suspended,
+the mind becomes capable of perceiving the fainter link of association, and
+the word is regained.
+
+On this circumstance depends the impediment of speech before mentioned; the
+first syllable of a word is causable by volition, but the remainder of it
+is in common conversation introduced by its associations with this first
+syllable acquired by long habit. Hence when the mind of the stammerer is
+vehemently employed on some idea of ambition of shining, or fear of not
+succeeding, the associations of the motions of the muscles of articulation
+with each other become dissevered by this greater exertion, and he
+endeavours in vain by voluntary efforts to rejoin the broken association.
+For this purpose he continues to repeat the first syllable, which is
+causable by volition, and strives in vain, by various distortions of
+countenance, to produce the next links, which are subject to association.
+See Class IV. 3. 1. 1.
+
+11. After our accomplished musician has acquired great variety of tunes and
+songs, so that some of them begin to cease to be easily recollected, she
+finds progressive trains of musical notes more frequently forgotten, than
+those which are composed of reiterated circles, according with the eleventh
+preceding article.
+
+12. To finish our example with the preceding articles we must at length
+suppose, that our fair performer falls asleep over her harpsichord; and
+thus by the suspension of volition, and the exclusion of external stimuli,
+she dissevers the trains and circles of her musical exertions.
+
+III. 1. Many of these circumstances of catenations of motions receive an
+easy explanation from the four following consequences to the seventh law of
+animal causation in Sect. IV. These are, first, that those successions or
+combinations of animal motions, whether they were united by causation,
+association, or catenation, which have been most frequently repeated,
+acquire the strongest connection. Secondly, that of these, those, which
+have been less frequently mixed with other trains or tribes of motion, have
+the strongest connection. Thirdly, that of these, those, which were first
+formed, have the strongest connection. Fourthly, that if an animal motion
+be excited by more than one causation, association, or catenation, at the
+same time, it will be performed with greater energy.
+
+2. Hence also we understand, why the catenations of irritative motions are
+more strongly connected than those of the other classes, where the quantity
+of unmixed repetition has been equal; because they were first formed. Such
+are those of the secerning and absorbent systems of vessels, where the
+action of the gland produces a fluid, which stimulates the mouths of its
+correspondent absorbents. The associated motions seem to be the next most
+strongly united, from their frequent repetition; and where both these
+circumstances unite, as in the vital motions, their catenations are
+indissoluble but by the destruction of the animal.
+
+3. Where a new link has been introduced into a circle of actions by some
+accidental defect of stimulus; if that defect of stimulus be repeated at
+the same part of the circle a second or a third time, the defective motions
+thus produced, both by the repeated defect of stimulus and by their
+catenation with the parts of the circle of actions, will be performed with
+less and less energy. Thus if any person is exposed to cold at a certain
+hour to-day, so long as to render some part of the system for a time
+torpid; and is again exposed to it at the same hour to-morrow, and the next
+day; he will be more and more affected by it, till at length a cold fit of
+fever is completely formed, as happens at the beginning of many of those
+fevers, which are called nervous or low fevers. Where the patient has
+slight periodical shiverings and paleness for many days before the febrile
+paroxysm is completely formed.
+
+4. On the contrary, if the exposure to cold be for so short a time, as not
+to induce any considerable degree of torpor or quiescence, and is repeated
+daily as above mentioned, it loses its effect more and more at every
+repetition, till the constitution can bear it without inconvenience, or
+indeed without being conscious of it. As in walking into the cold air in
+frosty weather. The same rule is applicable to increased stimulus, as of
+heat, or of vinous spirit, within certain limits, as is applied in the two
+last paragraphs to Deficient Stimulus; as is further explained in Sect.
+XXXVI. on the Periods of Diseases.
+
+5. Where irritation coincides with sensation to produce the same
+catenations of motion, as in inflammatory fevers, they are excited with
+still greater energy than by the irritation alone. So when children expect
+to be tickled in play, by a feather lightly passed over the lips, or by
+gently vellicating the soles of their feet, laughter is most vehemently
+excited; though they can stimulate these parts with their own fingers
+unmoved. Here the pleasureable idea of playfulness coincides with the
+vellication; and there is no voluntary exertion used to diminish the
+sensation, as there would be, if a child should endeavour to tickle
+himself. See Sect. XXXIV. 1. 4.
+
+6. And lastly, the motions excited by the junction of voluntary exertion
+with irritation are performed with more energy, than those by irritation
+singly; as when we listen to small noises, as to the ticking of a watch in
+the night, we perceive the most weak sounds, that are at other times
+unheeded. So when we attend to the irritative ideas of sound in our ears,
+which are generally not attended to, we can hear them; and can see the
+spectra of objects, which remain in the eye, whenever we please to exert
+our voluntary power in aid of those weak actions of the retina, or of the
+auditory nerve.
+
+7. The temporary catenations of ideas, which are caused by the sensations
+of pleasure or pain, are easily dissevered either by irritations, as when a
+sudden noise disturbs a day-dream; or by the power of volition, as when we
+awake from sleep. Hence in our waking hours, whenever an idea occurs, which
+is incongruous to our former experience, we instantly dissever the train of
+imagination by the power of volition, and compare the incongruous idea with
+our previous knowledge of nature, and reject it. This operation of the mind
+has not yet acquired a specific name, though it is exerted every minute of
+our waking hours; unless it may be termed INTUITIVE ANALOGY. It is an act
+of reasoning of which we are unconscious except from its effects in
+preserving the congruity of our ideas, and bears the same relation to the
+sensorial power of volition, that irritative ideas, of which we are
+inconscious except by their effects, do to the sensorial power of
+irritation; as the former is produced by volition without our attention to
+it, and the latter by irritation without our attention to them.
+
+If on the other hand a train of imagination or of voluntary ideas are
+excited with great energy, and passing on with great vivacity, and become
+dissevered by some violent stimulus, as the discharge of a pistol near
+one's ear, another circumstance takes place, which is termed SURPRISE;
+which by exciting violent irritation, and violent sensation, employs for a
+time the whole sensorial energy, and thus dissevers the passing trains of
+ideas, before the power of volition has time to compare them with the usual
+phenomena of nature. In this case fear is generally the companion of
+surprise, and adds to our embarrassment, as every one experiences in some
+degree when he hears a noise in the dark, which he cannot instantly account
+for. This catenation of fear with surprise is owing to our perpetual
+experience of injuries from external bodies in motion, unless we are upon
+our guard against them. See Sect. XVIII. 17. XIX. 2.
+
+Many other examples of the catenations of animal motions are explained in
+Sect. XXXVI. on the Periods of Diseases.
+
+       *       *       *       *       *
+
+SECT. XVIII.
+
+OF SLEEP.
+
+    1. _Volition is suspended in sleep._ 2. _Sensation continues. Dreams
+    prevent delirium and inflammation._ 3. _Nightmare._ 4. _Ceaseless flow
+    of ideas in dreams._ 5. _We seem to receive them by the senses. Optic
+    nerve perfectly sensible in sleep. Eyes less dazzled after dreaming of
+    visible objects._ 6. _Reverie, belief._ 7. _How we distinguish ideas
+    from perceptions._ 8. _Variety of scenery in dreams, excellence of the
+    sense of vision._ 9. _Novelty of combination in dreams._ 10.
+    _Distinctness of imagery in dreams._ 11. _Rapidity of transaction in
+    dreams._ 12. _Of measuring time. Of dramatic time and place. Why a dull
+    play induces sleep, and an interesting one reverie._ 13. _Consciousness
+    of our existence and identity in dreams._ 14. _How we awake sometimes
+    suddenly, sometimes frequently._ 15. _Irritative motions continue in
+    sleep, internal irritations are succeeded by sensation. Sensibility
+    increases during sleep, and irritability. Morning dreams. Why
+    epilepsies occur in sleep. Ecstacy of children. Case of convulsions in
+    sleep. Cramp, why painful. Asthma. Morning sweats. Increase of heat.
+    Increase of urine in sleep. Why more liable to take cold in sleep.
+    Catarrh from thin night-caps. Why we feel chilly at the approach of
+    sleep, and at waking in the open air._ 16. _Why the gout commences in
+    sleep. Secretions are more copious in sleep, young animals and plants
+    grow more in sleep._ 17. _Inconsistency of dreams. Absence of surprise
+    in dreams._ 18. _Why we forget some dreams and not others._ 19.
+    _Sleep-talkers awake with surprise._ 20. _Remote causes of sleep.
+    Atmosphere with less oxygene. Compression of the brain in spina bifida.
+    By whirling on an horizontal wheel. By cold._ 21. _Definition of
+    sleep._
+
+1. There are four situations of our system, which in their moderate degrees
+are not usually termed diseases, and yet abound with many very curious and
+instructive phenomena; these are sleep, reverie, vertigo, drunkenness.
+These we shall previously consider, before we step forwards to develop the
+causes and cures of diseases with the modes of the operation of medicines.
+
+As all those trains and tribes of animal motion, which are subjected to
+volition, were the last that were caused, their connection is weaker than
+that of the other classes; and there is a peculiar circumstance attending
+this causation, which is, that it is entirely suspended during sleep;
+whilst the other classes of motion, which are more immediately necessary to
+life, as those caused by internal stimuli, for instance the pulsations of
+the heart and arteries, or those catenated with pleasurable sensation, as
+the powers of digestion, continue to strengthen their habits without
+interruption. Thus though man in his sleeping state is a much less perfect
+animal, than in his waking hours; and though he consumes more than one
+third of his life in this his irrational situation; yet is the wisdom of
+the Author of nature manifest even in this seeming imperfection of his
+work!
+
+The truth of this assertion with respect to the large muscles of the body,
+which are concerned in locomotion, is evident; as no one in perfect sanity
+walks about in his sleep, or performs any domestic offices: and in respect
+to the mind, we never exercise our reason or recollection in dreams; we may
+sometimes seem distracted between contending passions, but we never compare
+their objects, or deliberate about the acquisition of those objects, if our
+sleep is perfect. And though many synchronous tribes or successive trains
+of ideas may represent the houses or walks, which have real existence, yet
+are they here introduced by their connection with our sensations, and are
+in truth ideas of imagination, not of recollection.
+
+2. For our sensations of pleasure and pain are experienced with great
+vivacity in our dreams; and hence all that motley group of ideas, which are
+caused by them, called the ideas of imagination, with their various
+associated trains, are in a very vivid manner acted over in the sensorium;
+and these sometimes call into action the larger muscles, which have been
+much associated with them; as appears from the muttering sentences, which
+some people utter in their dreams, and from the obscure barking of sleeping
+dogs, and the motions of their feet and nostrils.
+
+This perpetual flow of the trains of ideas, which constitute our dreams,
+and which are caused by painful or pleasurable sensation, might at first
+view be conceived to be an useless expenditure of sensorial power. But it
+has been shewn, that those motions, which are perpetually excited, as those
+of the arterial system by the stimulus of the blood, are attended by a
+great accumulation of sensorial power, after they have been for a time
+suspended; as the hot-fit of fever is the consequence of the cold one. Now
+as these trains of ideas caused by sensation are perpetually excited during
+our waking hours, if they were to be suspended in sleep like the voluntary
+motions, (which are exerted only by intervals during our waking hours,) an
+accumulation of sensorial power would follow; and on our awaking a delirium
+would supervene, since these ideas caused by sensation would be produced
+with such energy, that we should mistake the trains of imagination for
+ideas excited by irritation; as perpetually happens to people debilitated
+by fevers on their first awaking; for in these fevers with debility the
+general quantity of irritation being diminished, that of sensation is
+increased. In like manner if the actions of the stomach, intestines, and
+various glands, which are perhaps in part at least caused by or catenated
+with agreeable sensation, and which perpetually exist during our waking
+hours, were like the voluntary motions suspended in our sleep; the great
+accumulation of sensorial power, which would necessarily follow, would be
+liable to excite inflammation in them.
+
+3. When by our continued posture in sleep, some uneasy sensations are
+produced, we either gradually awake by the exertion of volition, or the
+muscles connected by habit with such sensations alter the position of the
+body; but where the sleep is uncommonly profound, and those uneasy
+sensations great, the disease called the incubus, or nightmare, is
+produced. Here the desire of moving the body is painfully exerted, by the
+power of moving it, or volition, is incapable of action, till we awake.
+Many less disagreeable struggles in our dreams, as when we wish in vain to
+fly from terrifying objects, constitute a slighter degree of this disease.
+In awaking from the nightmare I have more than once observed, that there
+was no disorder in my pulse; nor do I believe the respiration is laborious,
+as some have affirmed. It occurs to people whose sleep is too profound, and
+some disagreeable sensation exists, which at other times would have
+awakened them, and have thence prevented the disease of nightmare; as after
+great fatigue or hunger with too large a supper and wine, which occasion
+our sleep to be uncommonly profound. See No. 14, of this Section.
+
+4. As the larger muscles of the body are much more frequently excited by
+volition than by sensation, they are but seldom brought into action in our
+sleep: but the ideas of the mind are by habit much more frequently
+connected with sensation than with volition; and hence the ceaseless flow
+of our ideas in dreams. Every one's experience will teach him this truth,
+for we all daily exert much voluntary muscular motion: but few of mankind
+can bear the fatigue of much voluntary thinking.
+
+5. A very curious circumstance attending these our sleeping imaginations
+is, that we seem to receive them by the senses. The muscles, which are
+subservient to the external organs of sense, are connected with volition,
+and cease to act in sleep; hence the eyelids are closed, and the tympanum
+of the ear relaxed; and it is probable a similarity of voluntary exertion
+may be necessary for the perceptions of the other nerves of sense; for it
+is observed that the papillæ of the tongue can be seen to become erected,
+when we attempt to taste any thing extremely grateful. Hewson Exper.
+Enquir. V. 2. 186. Albini Annot. Acad. L. i. c. 15. Add to this, that the
+immediate organs of sense have no objects to excite them in the darkness
+and silence of the night, but their nerves of sense nevertheless continue
+to possess their perfect activity subservient to all their numerous
+sensitive connections. This vivacity of our nerves of sense during the time
+of sleep is evinced by a circumstance, which almost every one must at some
+time or other have experienced; that is, if we sleep in the daylight, and
+endeavour to see some object in our dream, the light is exceedingly painful
+to our eyes; and after repeated struggles we lament in our sleep, that we
+cannot see it. In this case I apprehend the eyelid is in some degree opened
+by the vehemence of our sensations; and, the iris being dilated, the optic
+nerve shews as great or greater sensibility than in our waking hours. See
+No. 15. of this Section.
+
+When we are forcibly waked at midnight from profound sleep, our eyes are
+much dazzled with the light of the candle for a minute or two, after there
+has been sufficient time allowed for the contraction of the iris; which is
+owing to the accumulation of sensorial power in the organ of vision during
+its state of less activity. But when we have dreamt much of visible
+objects, this accumulation of sensorial power in the organ of vision is
+lessened or prevented, and we awake in the morning without being dazzled
+with the light, after the iris has had time to contract itself. This is a
+matter of great curiosity, and may be thus tried by any one in the
+day-light. Close your eyes, and cover them with your hat; think for a
+minute on a tune, which you are accustomed to, and endeavour to sing it
+with as little activity of mind as possible. Suddenly uncover and open your
+eyes, and in one second of time the iris will contract itself, but you will
+perceive the day more luminous for several seconds, owing to the
+accumulation of sensorial power in the optic nerve.
+
+Then again close and cover your eyes, and think intensely on a cube of
+ivory two inches diameter, attending first to the north and south sides of
+it, and then to the other four sides of it; then get a clear image in your
+mind's eye of all the sides of the same cube coloured red; and then of it
+coloured green; and then of it coloured blue; lastly, open your eyes as in
+the former experiment, and after the first second of time allowed for the
+contraction of the iris, you will not perceive any increase of the light of
+the day, or dazzling; because now there is no accumulation of sensorial
+power in the optic nerve; that having been expended by its action in
+thinking over visible objects.
+
+This experiment is not easy to be made at first, but by a few patient
+trials the fact appears very certain; and shews clearly, that our ideas of
+imagination are repetitions of the motions of the nerve, which were
+originally occasioned by the stimulus of external bodies; because they
+equally expend the sensorial power in the organ of sense. See Sect. III. 4.
+which is analogous to our being as much fatigued by thinking as by labour.
+
+6. Nor is it in our dreams alone, but even in our waking reveries, and in
+great efforts of invention, so great is the vivacity of our ideas, that we
+do not for a time distinguish them from the real presence of substantial
+objects; though the external organs of sense are open, and surrounded with
+their usual stimuli. Thus whilst I am thinking over the beautiful valley,
+through which I yesterday travelled, I do not perceive the furniture of my
+room: and there are some, whose waking imaginations are so apt to run into
+perfect reverie, that in their common attention to a favourite idea they do
+not hear the voice of the companion, who accosts them, unless it is
+repeated with unusual energy.
+
+This perpetual mistake in dreams and reveries, where our ideas of
+imagination are attended with a belief of the presence of external objects,
+evinces beyond a doubt, that all our ideas are repetitions of the motions
+of the nerves of sense, by which they were acquired; and that this belief
+is not, as some late philosophers contend, an instinct necessarily
+connected only with our perceptions.
+
+7. A curious question demands our attention in this place; as we do not
+distinguish in our dreams and reveries between our perceptions of external
+objects, and our ideas of them in their absence, how do we distinguish them
+at any time? In a dream, if the sweetness of sugar occurs to my
+imagination, the whiteness and hardness of it, which were ideas usually
+connected with the sweetness, immediately follow in the train; and I
+believe a material lump of sugar present before my senses: but in my waking
+hours, if the sweetness occurs to my imagination, the stimulus of the table
+to my hand, or of the window to my eye, prevents the other ideas of the
+hardness and whiteness of the sugar from succeeding; and hence I perceive
+the fallacy, and disbelieve the existence of objects correspondent to those
+ideas, whose tribes or trains are broken by the stimulus of other objects.
+And further in our waking hours, we frequently exert our volition in
+comparing present appearances with such, as we have usually observed; and
+thus correct the errors of one sense by our general knowledge of nature by
+intuitive analogy. See Sect. XVII. 3. 7. Whereas in dreams the power of
+volition is suspended, we can recollect and compare our present ideas with
+none of our acquired knowledge, and are hence incapable of observing any
+absurdities in them.
+
+By this criterion we distinguish our waking from our sleeping hours, we can
+voluntarily recollect our sleeping ideas, when we are awake, and compare
+them with our waking ones; but we cannot in our sleep _voluntarily_
+recollect our waking ideas at all.
+
+8. The vast variety of scenery, novelty of combination, and distinctness of
+imagery, are other curious circumstances of our sleeping imaginations. The
+variety of scenery seems to arise from the superior activity and excellence
+of our sense of vision; which in an instant unfolds to the mind extensive
+fields of pleasurable ideas; while the other senses collect their objects
+slowly, and with little combination; add to this, that the ideas, which
+this organ presents us with, are more frequently connected with our
+sensation than those of any other.
+
+9. The great novelty of combination is owing to another circumstance; the
+trains of ideas, which are carried on in our waking thoughts, are in our
+dreams dissevered in a thousand places by the suspension of volition, and
+the absence of irritative ideas, and are hence perpetually falling into new
+catenations. As explained in Sect. XVII. 1. 9. For the power of volition is
+perpetually exerted during our waking hours in comparing our passing trains
+of ideas with our acquired knowledge of nature, and thus forms many
+intermediate links in their catenation. And the irritative ideas excited by
+the stimulus of the objects, with which we are surrounded, are every moment
+intruded upon us, and form other links of our unceasing catenations of
+ideas.
+
+10. The absence of the stimuli of external bodies, and of volition, in our
+dreams renders the organs of sense liable to be more strongly affected by
+the powers of sensation, and of association. For our desires or aversions,
+or the obtrusions of surrounding bodies, dissever the sensitive and
+associate tribes of ideas in our waking hours by introducing those of
+irritation and volition amongst them. Hence proceeds the superior
+distinctness of pleasurable or painful imagery in our sleep; for we recal
+the figure and the features of a long lost friend, whom we loved, in our
+dreams with much more accuracy and vivacity than in our waking thoughts.
+This circumstance contributes to prove, that our ideas of imagination are
+reiterations of those motions of our organs of sense, which were excited by
+external objects; because while we are exposed to the stimuli of present
+objects, our ideas of absent objects cannot be so distinctly formed.
+
+11. The rapidity of the succession of transactions in our dreams is almost
+inconceivable; insomuch that, when we are accidentally awakened by the
+jarring of a door, which is opened into our bed-chamber, we sometimes dream
+a whole history of thieves or fire in the very instant of awaking.
+
+During the suspension of volition we cannot compare our other ideas with
+those of the parts of time in which they exist; that is, we cannot compare
+the imaginary scene, which is before us, with those changes of it, which
+precede or follow it: because this act of comparing requires recollection
+or voluntary exertion. Whereas in our waking hours, we are perpetually
+making this comparison, and by that means our waking ideas are kept
+confident with each other by intuitive analogy; but this companion retards
+the succession of them, by occasioning their repetition. Add to this, that
+the transactions of our dreams consist chiefly of visible ideas, and that a
+whole history of thieves and fire may be _beheld_ in an instant of time
+like the figures in a picture.
+
+12. From this incapacity of attending to the parts of time in our dreams,
+arises our ignorance of the length of the night; which, but from our
+constant experience to the contrary, we should conclude was but a few
+minutes, when our sleep is perfect. The same happens in our reveries; thus
+when we are possessed with vehement joy, grief, or anger, time appears
+short, for we exert no volition to compare the present scenery with the
+past or future; but when we are compelled to perform those exercises of
+mind or body, which, are unmixed with passion, as in travelling over a
+dreary country, time appears long; for our desire to finish our journey
+occasions us more frequently to compare our present situation with the
+parts of time or place, which are before and behind us.
+
+So when we are enveloped in deep contemplation of any kind, or in reverie,
+as in reading a very interesting play or romance, we measure time very
+inaccurately; and hence, if a play greatly affects our passions, the
+absurdities of passing over many days or years, and or perpetual changes of
+place, are not perceived by the audience; as is experienced by every one,
+who reads or sees some plays of the immortal Shakespear; but it is
+necessary for inferior authors to observe those rules of the [Greek:
+pithanon] and [Greek: prepon] inculcated by Aristotle, because their works
+do not interest the passions sufficiently to produce complete reverie.
+
+Those works, however, whether a romance or a sermon, which do not interest
+us so much as to induce reverie, may nevertheless incline us to sleep. For
+those pleasurable ideas, which are presented to us, and are too gentle to
+excite laughter, (which is attended with interrupted voluntary exertions,
+as explained Sect. XXXIV. 1. 4.) and which are not accompanied with any
+other emotion, which usually excites some voluntary exertion, as anger, or
+fear, are liable to produce sleep; which consists in a suspension of all
+voluntary power. But if the ideas thus presented to us, and interest our
+attention, are accompanied with so much pleasurable or painful sensation as
+to excite our voluntary exertion at the same time, reverie is the
+consequence. Hence an interesting play produces reverie, a tedious one
+produces sleep: in the latter we become exhausted by attention, and are not
+excited to any voluntary exertion, and therefore sleep; in the former we
+are excited by some emotion, which prevents by its pain the suspension of
+volition, and in as much as it interests us, induces reverie, as explained
+in the next Section.
+
+But when our sleep is imperfect, as when we have determined to rise in half
+an hour, time appears longer to us than in most other situations. Here our
+solicitude not to oversleep the determined time induces us in this
+imperfect sleep to compare the quick changes of imagined scenery with the
+parts of time or place, they would have taken up, had they real exigence;
+and that more frequently than in our waking hours; and hence the time
+appears longer to us: and I make no doubt, but the permitted time appears
+long to a man going to the gallows, as the fear of its quick lapse will
+make him think frequently about it.
+
+13. As we gain our knowledge of time by comparing the present scenery with
+the past and future, and of place by comparing the situations of objects
+with each other; so we gain our idea of consciousness by comparing
+ourselves with the scenery around us; and of identity by comparing our
+present consciousness with our past consciousness: as we never think of
+time or place, but when we make the companions above mentioned, so we never
+think of consciousness, but when we compare our own existence with that of
+other objects; nor of identity, but when we compare our present and our
+past consciousness. Hence the consciousness of our own existence, and of
+our identity, is owing to a voluntary exertion of our minds: and on that
+account in our complete dreams we neither measure time, are surprised at
+the sudden changes of place, nor attend to our own existence, or identity;
+because our power of volition is suspended. But all these circumstances are
+more or less observable in our incomplete ones; for then we attend a little
+to the lapse of time, and the changes of place, and to our own existence;
+and even to our identity of person; for a lady seldom dreams, that she is a
+soldier; nor a man, that he is brought to bed.
+
+14. As long as our sensations only excite their sensual motions, or ideas,
+our sleep continues sound; but as soon as they excite desires or aversions,
+our sleep becomes imperfect; and when that desire or aversion is so strong,
+as to produce voluntary motions, we begin to awake; the larger muscles of
+the body are brought into action to remove that irritation or sensation,
+which a continued posture has caused; we stretch our limbs, and yawn, and
+our sleep is thus broken by the accumulation of voluntary power.
+
+Sometimes it happens, that the act of waking is suddenly produced, and this
+soon after the commencement of sleep; which is occasioned by some sensation
+so disagreeable, as instantaneously to excite the power of volition; and a
+temporary action of all the voluntary motions suddenly succeeds, and we
+start awake. This is sometimes accompanied with loud noise in the ears, and
+with some degree of fear; and when it is in great excess, so as to produce
+continued convulsive motions of those muscles, which are generally
+subservient to volition, it becomes epilepsy: the fits of which in some
+patients generally commence during sleep. This differs from the night-mare
+described in No. 3. of this Section, because in that the disagreeable
+sensation is not so great as to excite the power of volition into action;
+for as soon as that happens, the disease ceases.
+
+Another circumstance, which sometimes awakes people soon after the
+commencement of their sleep, is where the voluntary power is already so
+great in quantity as almost to prevent them from falling asleep, and then a
+little accumulation of it soon again awakens them; this happens in cases of
+insanity, or where the mind has been lately much agitated by fear or anger.
+There is another circumstance in which sleep is likewise of short duration,
+which arises from great debility, as after great over-fatigue, and in some
+fevers, where the strength of the patient is greatly diminished, as in
+these cases the pulse intermits or flutters, and the respiration is
+previously affected, it seems to originate from the want of some voluntary
+efforts to facilitate respiration, as when we are awake. And is further
+treated of in Vol. II. Class I. 2. 1. 2. on the Diseases of the Voluntary
+Power. Art. Somnus interruptus.
+
+15. We come now to those motions which depend on irritation. The motions of
+the arterial and glandular systems continue in our sleep, proceeding slower
+indeed, but stronger and more uniformly, than in our waking hours, when
+they are incommoded by external stimuli, or by the movements of volition;
+the motions of the muscles subservient to respiration continue to be
+stimulated into action, and the other internal senses of hunger, thirst,
+and lust, are not only occasionally excited in our sleep, but their
+irritative motions are succeeded by their usual sensations, and make a part
+of the farrago of our dreams. These sensations of the want of air, of
+hunger, thirst, and lust, in our dreams, contribute to prove, that the
+nerves of the external senses are also alive and excitable in our sleep;
+but as the stimuli of external objects are either excluded from them by the
+darkness and silence of the night, or their access to them is prevented by
+the suspension of volition, these nerves of sense fall more readily into
+their connexions with sensation and with association; because much
+sensorial power, which during the day was expended in moving the external
+organs of sense in consequence of irritation from external stimuli, or in
+consequence of volition, becomes now in some degree accumulated, and
+renders the internal or immediate organs of sense more easily excitable by
+the other sensorial powers. Thus in respect to the eye, the irritation from
+external stimuli, and the power of volition during our waking hours,
+elevate the eye-lids, adapt the aperture of the iris to the quantity of
+light, the focus of the crystalline humour, and the angle of the optic
+axises to the distance of the object, all which perpetual activity during
+the day expends much sensorial power, which is saved during our sleep.
+
+Hence it appears, that not only those parts of the system, which are always
+excited by internal stimuli, as the stomach, intestinal canal, bile-ducts,
+and the various glands, but the organs of sense also may be more violently
+excited into action by the irritation from internal stimuli, or by
+sensation, during our sleep than in our waking hours; because during the
+suspension of volition, there is a greater quantity of the spirit of
+animation to be expended by the other sensorial powers. On this account our
+irritability to internal stimuli, and our sensibility to pain or pleasure,
+is not only greater in sleep, but increases as our sleep is prolonged.
+Whence digestion and secretion are performed better in sleep, than in our
+waking hours, and our dreams in the morning have greater variety and
+vivacity, as our sensibility increases, than at night when we first lie
+down. And hence epileptic fits, which are always occasioned by some
+disagreeable sensation, so frequently attack those, who are subject to
+them, in their sleep; because at this time the system is more excitable by
+painful sensation in consequence of internal stimuli; and the power of
+volition is then suddenly exerted to relieve this pain, as explained Sect.
+XXXIV. 1. 4.
+
+There is a disease, which frequently affects children in the cradle, which
+is termed ecstasy, and seems to consist in certain exertions to relieve
+painful sensation, in which the voluntary power is not so far excited as
+totally to awaken them, and yet is sufficient to remove the disagreeable
+sensation, which excites it; in this case changing the posture of the child
+frequently relieves it.
+
+I have at this time under my care an elegant young man about twenty-two
+years of age, who seldom sleeps more than an hour without experiencing a
+convulsion fit; which ceases in about half a minute without any subsequent
+stupor. Large doses of opium only prevented the paroxysms, so long as they
+prevented him from sleeping by the intoxication, which they induced. Other
+medicines had no effect on him. He was gently awakened every half hour for
+one night, but without good effect, as he soon slept again, and the fit
+returned at about the same periods of time, for the accumulated sensorial
+power, which occasioned the increased sensibility to pain, was not thus
+exhausted. This case evinces, that the sensibility of the system to
+internal excitation increases, as our sleep is prolonged; till the pain
+thus occasioned produces voluntary exertion; which, when it is in its usual
+degree, only awakens us; but when it is more violent, it occasions
+convulsions.
+
+The cramp in the calf of the leg is another kind of convulsion, which
+generally commences in sleep, occasioned by the continual increase of
+irritability from internal stimuli, or of sensibility, during that state of
+our existence. The cramp is a violent exertion to relieve pain, generally
+either of the skin from cold, or of the bowels, as in some diarrhoeas, or
+from the muscles having been previously overstretched, as in walking up or
+down steep hills. But in these convulsions of the muscles, which form the
+calf of the leg, the contraction is so violent as to occasion another pain
+in consequence of their own too violent contraction; as soon as the
+original pain, which caused the contraction, is removed. And hence the
+cramp, or spasm, of these muscles is continued without intermission by this
+new pain, unlike the alternate convulsions and remissions in epileptic
+fits. The reason, that the contraction of these muscles of the calf of the
+leg is more violent during their convulsion than that of others, depends on
+the weakness of their antagonist muscles; for after these have been
+contracted in their usual action, as at every step in walking, they are
+again extended, not, as most other muscles are, by their antagonists, but
+by the weight of the whole body on the balls of the toes; and that weight
+applied to great mechanical advantage on the heel, that is, on the other
+end of the bone of the foot, which thus acts as a lever.
+
+Another disease, the periods of which generally commence during our sleep,
+is the asthma. Whatever may be the remote cause of paroxysms of asthma, the
+immediate cause of the convulsive respiration, whether in the common
+asthma, or in what is termed the convulsive asthma, which are perhaps only
+different degrees of the same disease, must be owing to violent voluntary
+exertions to relieve pain, as in other convulsions; and the increase of
+irritability to internal stimuli, or of sensibility, during sleep must
+occasion them to commence at this time.
+
+Debilitated people, who have been unfortunately accustomed to great
+ingurgitation of spirituous potation, frequently part with a great quantity
+of water during the night, but with not more than usual in the day-time.
+This is owing to a beginning torpor of the absorbent system, and precedes
+anasarca, which commences in the day, but is cured in the night by the
+increase of the irritability of the absorbent system during sleep, which
+thus imbibes from the cellular membrane the fluids, which had been
+accumulated there during the day; though it is possible the horizontal
+position of the body may contribute something to this purpose, and also the
+greater irritability of some branches of the absorbent vessels, which open
+their mouths in the cells of the cellular membrane, than that of other
+branches.
+
+As soon as a person begins to sleep, the irritability and sensibility of
+the system begins to increase, owing to the suspension of volition and the
+exclusion of external stimuli. Hence the actions of the vessels in
+obedience to internal stimulation become stronger and more energetic,
+though less frequent in respect to number. And as many of the secretions
+are increased, so the heat of the system is gradually increased, and the
+extremities of feeble people, which had been cold during the day, become
+warm. Till towards morning many people become so warm, as to find it
+necessary to throw off some of their bed-clothes, as soon as they awake;
+and in others sweats are so liable to occur towards morning during their
+sleep.
+
+Thus those, who are not accustomed to sleep in the open air, are very
+liable to take cold, if they happen to fall asleep on a garden bench, or in
+a carriage with the window open. For as the system is warmer during sleep,
+as above explained, if a current of cold air affects any part of the body,
+a torpor of that part is more effectually produced, as when a cold blast of
+air through a key-hole or casement falls upon a person in a warm room. In
+those cases the affected part possesses less irritability in respect to
+heat, from its having previously been exposed to a greater stimulus of
+heat, as in the warm room, or during sleep; and hence, when the stimulus of
+heat is diminished, a torpor is liable to ensue; that is, we take cold.
+Hence people who sleep in the open air, generally feel chilly both at the
+approach of sleep, and on their awaking; and hence many people are
+perpetually subject to catarrhs if they sleep in a less warm head-dress,
+than that which they wear in the day.
+
+16. Not only the sensorial powers of irritation and of sensation, but that
+of association also appear to act with greater vigour during the suspension
+of volition in sleep. It will be shewn in another place, that the gout
+generally first attacks the liver, and that afterwards an inflammation of
+the ball of the great toe commences by association, and that of the liver
+ceases. Now as this change or metastasis of the activity of the system
+generally commences in sleep, it follows, that these associations of motion
+exist with greater energy at that time; that is, that the sensorial faculty
+of association, like those of irritation and of sensation, becomes in some
+measure accumulated during the suspension of volition.
+
+Other associate tribes and trains of motions, as well as the irritative and
+sensitive ones, appear to be increased in their activity during the
+suspension of volition in sleep. As those which contribute to circulate the
+blood, and to perform the various secretions; as well as the associate
+tribes and trains of ideas, which contribute to furnish the perpetual
+dreams of our dreaming imaginations.
+
+In sleep the secretions have generally been supposed to be diminished, as
+the expectorated mucus in coughs, the fluids discharged in diarrhoeas, and
+in salivation, except indeed the secretion of sweat, which is often visibly
+increased. This error seems to have arisen from attention to the excretions
+rather than to the secretions. For the secretions, except that of sweat,
+are generally received into reservoirs, as the urine into the bladder, and
+the mucus of the intestines and lungs into their respective cavities; but
+these reservoirs do not exclude these fluids immediately by their stimulus,
+but require at the same time some voluntary efforts, and therefore permit
+them to remain during sleep. And as they thus continue longer in those
+receptacles in our sleeping hours, a greater part is absorbed from them,
+and the remainder becomes thicker, and sometimes in less quantity, though
+at the time it was secreted the fluid was in greater quantity than in our
+waking hours. Thus the urine is higher coloured after long sleep; which
+shews that a greater quantity has been secreted, and that more of the
+aqueous and saline part has been reabsorbed, and the earthy part left in
+the bladder; hence thick urine in fevers shews only a greater action of the
+vessels which secrete it in the kidneys, and of those which absorb it from
+the bladder.
+
+The same happens to the mucus expectorated in coughs, which is thus
+thickened by absorption of its aqueous and saline parts; and the same of
+the feces of the intestines. From hence it appears, and from what has been
+said in No. 15. of this Section concerning the increase of irritability and
+of sensibility during sleep, that the secretions are in general rather
+increased than diminished during these hours of our existence; and it is
+probable that nutrition is almost entirely performed in sleep; and that
+young animals grow more at this time than in their waking hours, as young
+plants have long since been observed to grow more in the night, which is
+their time of sleep.
+
+17. Two other remarkable circumstances of our dreaming ideas are their
+inconsistency, and the total absence of surprise. Thus we seem to be
+present at more extraordinary metamorphoses of animals or trees, than are
+to be met with in the fables of antiquity; and appear to be transported
+from place to place, which seas divide, as quickly as the changes of
+scenery are performed in a play-house; and yet are not sensible of their
+inconsistency, nor in the least degree affected with surprise.
+
+We must consider this circumstance more minutely. In our waking trains of
+ideas, those that are inconsistent with the usual order of nature, so
+rarely have occurred to us, that their connexion is the slightest of all
+others: hence, when a consistent train of ideas is exhausted, we attend to
+the external stimuli, that usually surround us, rather than to any
+inconsistent idea, which might otherwise present itself; and if an
+inconsistent idea should intrude itself, we immediately compare it with the
+preceding one, and voluntarily reject the train it would introduce; this
+appears further in the Section on Reverie, in which state of the mind
+external stimuli are not attended to, and yet the streams of ideas are kept
+consistent by the efforts of volition. But as our faculty of volition is
+suspended, and all external stimuli are excluded in sleep, this slighter
+connexion of ideas takes place; and the train is said to be inconsistent;
+that is, dissimilar to the usual order of nature.
+
+But, when any consistent train of sensitive or voluntary ideas is flowing
+along, if any external stimulus affects us so violently, as to intrude
+irritative ideas forcibly into the mind, it disunites the former train of
+ideas, and we are affected with surprise. These stimuli of unusual energy
+or novelty not only disunite our common trains of ideas, but the trains of
+muscular motions also, which have not been long established by habit, and
+disturb those that have. Some people become motionless by great surprise,
+the fits of hiccup and or ague have been often removed by it, and it even
+affects the movements of the heart, and arteries; but in our sleep, all
+external stimuli are excluded, and in consequence no surprise can exist.
+See Section XVII. 3. 7.
+
+18. We frequently awake with pleasure from a dream, which has delighted us,
+without being able to recollect the transactions of it; unless perhaps at a
+distance of time, some analogous idea may introduce afresh this forgotten
+train: and in our waking reveries we sometimes in a moment lose the train
+of thought, but continue to feel the glow of pleasure, or the depression of
+spirits, it occasioned: whilst at other times we can retrace with ease
+these histories of our reveries and dreams.
+
+The above explanation of surprise throws light upon this subject. When we
+are suddenly awaked by any violent stimulus, the surprise totally disunites
+the trains of our sleeping ideas from these of our waking ones; but if we
+gradually awake, this does not happen; and we readily unravel the preceding
+trains of imagination.
+
+19. There are various degrees of surprise; the more intent we are upon the
+train of ideas, which we are employed about, the more violent must be the
+stimulus that interrupts them, and the greater is the degree of surprise. I
+have observed dogs, who have slept by the fire, and by their obscure
+barking and struggling have appeared very intent on their prey, that shewed
+great surprise for a few seconds after their awaking by looking eagerly
+around them; which they did not do at other times of waking. And an
+intelligent friend of mine has remarked, that his lady, who frequently
+speaks much and articulately in her sleep, could never recollect her dreams
+in the morning, when this happened to her: but that when she did not speak
+in her sleep, she could always recollect them.
+
+Hence, when our sensations act so strongly in sleep as to influence the
+larger muscles, as in those, who talk or struggle in their dreams; or in
+those, who are affected with complete reverie (as described in the next
+Section), great surprise is produced, when they awake; and these as well as
+those, who are completely drunk or delirious, totally forget afterwards
+their imaginations at those times.
+
+20. As the immediate cause of sleep consists in the suspension of volition,
+it follows, that whatever diminishes the general quantity of sensorial
+power, or derives it from the faculty of volition, will constitute a remote
+cause of sleep; such as fatigue from muscular or mental exertion, which
+diminishes the general quantity of sensorial power; or an increase of the
+sensitive motions, as by attending to soft music, which diverts the
+sensorial power from the faculty of volition; or lastly, by increase of the
+irritative motions, as by wine, or food; or warmth; which not only by their
+expenditure of sensorial power diminish the quantity of volition; but also
+by their producing pleasureable sensations (which occasion other muscular
+or sensual motions in consequence), doubly decrease the voluntary power,
+and thus more forcibly produce sleep. See Sect. XXXIV. 1. 4.
+
+Another method of inducing sleep is delivered in a very ingenious work
+lately published by Dr. Beddoes. Who, after lamenting that opium frequently
+occasions restlessness, thinks, "that in most cases it would be better to
+induce sleep by the abstraction of stimuli, than by exhausting the
+excitability;" and adds, "upon this principle we could not have a better
+soporific than an atmosphere with a diminished proportion of oxygene air,
+and that common air might be admitted after the patient was asleep."
+(Observ. on Calculus, &c. by Dr. Beddoes, Murray.) If it should be found to
+be true, that the excitability of the system depends on the quantity of
+oxygene absorbed by the lungs in respiration according to the theory of Dr.
+Beddoes, and of M. Girtanner, this idea of sleeping in an atmosphere with
+less oxygene in its composition might be of great service in epileptic
+cases, and in cramp, and even in fits of the asthma, where their periods
+commence from the increase of irritability during sleep.
+
+Sleep is likewise said to be induced by mechanic pressure on the brain in
+the cases of spina bifida. Where there has been a defect of one of the
+vertebræ of the back, a tumour is protruded in consequence; and, whenever
+this tumour has been compressed by the hand, sleep is said to be induced,
+because the whole of the brain both within the head and spine becomes
+compressed by the retrocession of the fluid within the tumour. But by what
+means a compression of the brain induces sleep has not been explained, but
+probably by diminishing the secretion of sensorial power, and then the
+voluntary motions become suspended previously to the irritative ones, as
+occurs in most dying persons.
+
+Another way of procuring sleep mechanically was related to me by Mr.
+Brindley, the famous canal engineer, who was brought up to the business of
+a mill-wright; he told me, that he had more than once seen the experiment
+of a man extending himself across the large stone of a corn-mill, and that
+by gradually letting the stone whirl, the man fell asleep, before the stone
+had gained its full velocity, and he supposed would have died without pain
+by the continuance or increase of the motion. In this case the centrifugal
+motion of the head and feet must accumulate the blood in both those
+extremities of the body, and thus compress the brain.
+
+Lastly, we should mention the application of cold; which, when in a less
+degree, produces watchfulness by the pain it occasions, and the tremulous
+convulsions of the subcutaneous muscles; but when it is applied in great
+degree, is said to produce sleep. To explain this effect it has been said,
+that as the vessels of the skin and extremities become first torpid by the
+want of the stimulus of heat, and as thence less blood is circulated
+through them, as appears from their paleness, a greater quantity of blood
+poured upon the brain produces sleep by its compression of that organ. But
+I should rather imagine, that the sensorial power becomes exhausted by the
+convulsive actions in consequence of the pain of cold, and of the voluntary
+exercise previously used to prevent it, and that the sleep is only the
+beginning to die, as the suspension of voluntary power in lingering deaths
+precedes for many hours the extinction of the irritative motions.
+
+21. The following are the characteristic circumstances attending perfect
+sleep.
+
+1. The power of volition is totally suspended.
+
+2. The trains of ideas caused by sensation proceed with greater facility
+and vivacity; but become inconsistent with the usual order of nature. The
+muscular motions caused by sensation continue; as those concerned in our
+evacuations during infancy, and afterwards in digestion, and in priapismus.
+
+3. The irritative muscular motions continue, as those concerned in the
+circulation, in secretion, in respiration. But the irritative sensual
+motions, or ideas, are not excited; as the immediate organs of sense are
+not stimulated into action by external objects, which are excluded by the
+external organs of sense; which are not in sleep adapted to their reception
+by the power of volition, as in our waking hours.
+
+4. The associate motions continue; but their first link is not excited into
+action by volition, or by external stimuli. In all respects, except those
+above mentioned, the three last sensorial powers are somewhat increased in
+energy during the suspension of volition, owing to the consequent
+accumulation of the spirit of animation.
+
+       *       *       *       *       *
+
+SECT. XIX.
+
+OF REVERIE.
+
+    1. _Various degrees of reverie._ 2. _Sleep-walkers. Case of a young
+    lady. Great surprise at awaking. And total forgetfulness of what passed
+    in reverie._ 3. _No suspension of volition in reverie._ 4. _Sensitive
+    motions continue, and are consistent._ 5. _Irritative motions continue,
+    but are not succeeded by sensation._ 6. _Volition necessary for the
+    perception of feeble impressions._ 7. _Associated motions continue._ 8.
+    _Nerves of sense are irritable in sleep, but not in reverie._ 9.
+    _Somnambuli are not asleep. Contagion received but once._ 10.
+    _Definition of reverie._
+
+1. When we are employed with great sensation of pleasure, or with great
+efforts of volition, in the pursuit of some interesting train of ideas, we
+cease to be conscious of our existence, are inattentive to time and place,
+and do not distinguish this train of sensitive and voluntary ideas from the
+irritative ones excited by the presence of external objects, though our
+organs of sense are furnished with their accustomed stimuli, till at length
+this interesting train of ideas becomes exhausted, or the appulses of
+external objects are applied with unusual violence, and we return with
+surprise, or with regret, into the common track of life. This is termed
+reverie or studium.
+
+In some constitutions these reveries continue a considerable time, and are
+not to be removed without greater difficulty, but are experienced in a less
+degree by us all; when we attend earnestly to the ideas excited by volition
+or sensation, with their associated connexions, but are at the same time
+conscious at intervals of the stimuli of surrounding bodies. Thus in being
+present at a play, or in reading a romance, some persons are so totally
+absorbed as to forget their usual time of sleep, and to neglect their
+meals; while others are said to have been so involved in voluntary study as
+not to have heard the discharge of artillery; and there is a story of an
+Italian politician, who could think so intensely on other subjects, as to
+be insensible to the torture of the rack.
+
+From hence it appears, that these catenations of ideas and muscular
+motions, which form the trains of reverie, are composed both of voluntary
+and sensitive associations of them; and that these ideas differ from those
+of delirium or of sleep, as they are kept consistent by the power of
+volition; and they differ also from the trains of ideas belonging to
+insanity, as they are as frequently excited by sensation as by volition.
+But lastly, that the whole sensorial power is so employed on these trains
+of complete reverie, that like the violent efforts of volition, as in
+convulsions or insanity; or like the great activity of the irritative
+motions in drunkenness; or of the sensitive motions in delirium; they
+preclude all sensation consequent to external stimulus.
+
+2. Those persons, who are said to walk in their sleep, are affected with
+reverie to so great a degree, that it becomes a formidable disease; the
+essence of which consists in the inaptitude of the mind to attend to
+external stimuli. Many histories of this disease have been published by
+medical writers; of which there is a very curious one in the Lausanne
+Transactions. I shall here subjoin an account of such a case, with its
+cure, for the better illustration of this subject.
+
+A very ingenious and elegant young lady, with light eyes and hair, about
+the age of seventeen, in other respects well, was suddenly seized soon
+after her usual menstruation with this very wonderful malady. The disease
+began with vehement convulsions of almost every muscle of her body, with
+great but vain efforts to vomit, and the most violent hiccoughs, that can
+be conceived: these were succeeded in about an hour with a fixed spasm; in
+which one hand was applied to her head, and the other to support it: in
+about half an hour these ceased, and the reverie began suddenly, and was at
+first manifest by the look of her eyes and countenance, which seemed to
+express attention. Then she conversed aloud with imaginary persons with her
+eyes open, and could not for about an hour be brought to attend to the
+stimulus of external objects by any kind of violence, which it was proper
+to use; these symptoms returned in this order every day for five or six
+weeks.
+
+These conversations were quite consistent, and we could understand, what
+she supposed her imaginary companions to answer, by the continuation of her
+part of the discourse. Sometimes she was angry, at other times shewed much
+wit and vivacity, but was most frequently inclined to melancholy. In these
+reveries she sometimes sung over some music with accuracy, and repeated
+whole pages from the English poets. In repeating some lines from Mr. Pope's
+works she had forgot one word, and began again, endeavouring to recollect
+it; when she came to the forgotten word, it was shouted aloud in her ear,
+and this repeatedly, to no purpose; but by many trials she at length
+regained it herself.
+
+These paroxysms were terminated with the appearance of inexpressible
+surprise, and great fear, from which she was some minutes in recovering
+herself, calling on her sister with great agitation, and very frequently
+underwent a repetition of convulsions, apparently from the pain of fear.
+See Sect. XVII. 3. 7.
+
+After having thus returned for about an hour every day for two or three
+weeks, the reveries seemed to become less complete, and some of their
+circumstances varied; so that she could walk about the room in them without
+running against any of the furniture; though these motions were at first
+very unsteady and tottering. And afterwards she once drank a dish of tea,
+when the whole apparatus of the tea-table was set before her; and expressed
+some suspicion, that a medicine was put into it, and once seemed to smell
+of a tuberose, which was in flower in her chamber, and deliberated aloud
+about breaking it from the stem, saying, "it would make her sister so
+charmingly angry." At another time in her melancholy moments she heard the
+sound of a passing bell, "I wish I was dead," she cried, listening to the
+bell, and then taking off one of her shoes, as she sat upon the bed, "I
+love the colour black," says she, "a little wider, and a little longer,
+even this might make me a coffin!"--Yet it is evident, she was not sensible
+at this time, any more than formerly, of seeing or hearing any person about
+her; indeed when great light was thrown upon her by opening the shutters of
+the window, her trains of ideas seemed less melancholy; and when I have
+forcibly held her hands, or covered her eyes, she appeared to grow
+impatient, and would say, she could not tell what to do, for she could
+neither see nor move. In all these circumstances her pulse continued
+unaffected as in health. And when the paroxysm was over, she could never
+recollect a single idea of what had passed in it.
+
+This astonishing disease, after the use of many other medicines and
+applications in vain, was cured by very large doses of opium given about an
+hour before the expected returns of the paroxysms; and after a few
+relapses, at the intervals of three or four months, entirely disappeared.
+But she continued at times to have other symptoms of epilepsy.
+
+3. We shall only here consider, what happened during the time of her
+reveries, as that is our present subject; the fits of convulsion belong to
+another part of this treatise. Sect. XXXIV. 1. 4.
+
+There seems to have been no suspension of volition during the fits of
+reverie, because she endeavoured to regain the lost idea in repeating the
+lines of poetry, and deliberated about breaking the tuberose, and suspected
+the tea to have been medicated.
+
+4. The ideas and muscular movements depending on sensation were exerted
+with their usual vivacity, and were kept from being inconsistent by the
+power of volition, as appeared from her whole conversation, and was
+explained in Sect. XVII. 3. 7. and XVIII. 16.
+
+5. The ideas and motions dependant on irritation during the first weeks of
+her disease, whilst the reverie was complete, were never succeeded by the
+sensation of pleasure or pain; as she neither saw, heard, nor felt any of
+the surrounding objects. Nor was it certain that any irritative motions
+succeeded the stimulus of external objects, till the reverie became less
+complete, and then she could walk about the room without running against
+the furniture of it. Afterwards, when the reverie became still less
+complete from the use of opium, some few irritations were at times
+succeeded by her attention to them. As when she smelt at a tuberose, and
+drank a dish of tea, but this only when she seemed voluntarily to attend to
+them.
+
+6. In common life when we listen to distant sounds, or wish to distinguish
+objects in the night, we are obliged strongly to exert our volition to
+dispose the organs of sense to perceive them, and to suppress the other
+trains of ideas, which might interrupt these feeble sensations. Hence in
+the present history the strongest stimuli were not perceived, except when
+the faculty of volition was exerted on the organ of sense; and then even
+common stimuli were sometimes perceived: for her mind was so strenuously
+employed in pursuing its own trains of voluntary or sensitive ideas, that
+no common stimuli could so far excite her attention as to disunite them;
+that is, the quantity of volition or of sensation already existing was
+greater than any, which could be produced in consequence of common degrees
+of stimulation. But the few stimuli of the tuberose, and of the tea, which
+she did perceive, were such, as accidentally coincided with the trains of
+thought, which were passing in her mind; and hence did not disunite those
+trains, and create surprise. And their being perceived at all was owing to
+the power of volition preceding or coinciding with that of irritation.
+
+This explication is countenanced by a fact mentioned concerning a
+somnambulist in the Lausanne Transactions, who sometimes opened his eyes
+for a short time to examine, where he was, or where his ink-pot stood, and
+then shut them again, dipping his pen into the pot every now and then, and
+writing on, but never opening his eyes afterwards, although he wrote on
+from line to line regularly, and corrected some errors of the pen, or in
+spelling: so much easier was it to him to refer to his ideas of the
+positions of things, than to his perceptions of them.
+
+7. The associated motions persisted in their usual channel, as appeared by
+the combinations of her ideas, and the use of her muscles, and the equality
+of her pulse; for the natural motions of the arterial system, though
+originally excited like other motions by stimulus, seem in part to continue
+by their association with each other. As the heart of a viper pulsates long
+after it is cut out of the body, and removed from the stimulus of the
+blood.
+
+8. In the section on sleep, it was observed that the nerves of sense are
+equally alive and susceptible to irritation in that state, as when we are
+awake; but that they are secluded from stimulating objects, or rendered
+unfit to receive them: but in complete reverie the reverse happens, the
+immediate organs of sense are exposed to their usual stimuli; but are
+either not excited into action at all, or not into so great action, as to
+produce attention or sensation.
+
+The total forgetfulness of what passes in reveries; and the surprise on
+recovering from them, are explained in Section XVIII. 19. and in Section
+XVII. 3. 7.
+
+9. It appears from hence, that reverie is a disease of the epileptic or
+cataleptic kind, since the paroxysms of this young lady always began and
+frequently terminated with convulsions; and though in its greatest degree
+it has been called somnambulation, or sleep-walking, it is totally
+different from sleep; because the essential character of sleep consists in
+the total suspension of volition, which in reverie is not affected; and the
+essential character of reverie consists not in the absence of those
+irritative motions of our senses, which are occasioned by the stimulus of
+external objects, but in their never being productive of sensation. So that
+during a fit of reverie that strange event happens to the whole system of
+nerves, which occurs only to some particular branches of them in those, who
+are a second time exposed to the action of contagious matter. If the matter
+of the small-pox be inserted into the arm of one, who has previously had
+that disease, it will stimulate the wound, but the general sensation or
+inflammation of the system does not follow, which constitutes the disease.
+See Sect. XII. 3. 6. XXXIII. 2. 8.
+
+10. The following is the definition or character of complete reverie. 1.
+The irritative motions occasioned by internal stimuli continue, those from
+the stimuli of external objects are either not produced at all, or are
+never succeeded by sensation or attention, unless they are at the same time
+excited by volition. 2. The sensitive motions continue, and are kept
+consistent by the power of volition. 3. The voluntary motions continue
+undisturbed. 4. The associate motions continue undisturbed.
+
+Two other cases of reverie are related in Section XXXIV. 3. which further
+evince, that reverie is an effort of the mind to relieve some painful
+sensation, and is hence allied to convulsion, and to insanity. Another case
+is related in Class III. 1. 2. 2.
+
+       *       *       *       *       *
+
+SECT. XX.
+
+OF VERTIGO.
+
+    1. _We determine our perpendicularity by the apparent motions of
+    objects. A person hood-winked cannot walk in a straight line. Dizziness
+    in looking from a tower, in a room stained with uniform lozenges, on
+    riding over snow._ 2. _Dizziness from moving objects. A whirling-wheel.
+    Fluctuations of a river. Experiment with a child._ 3. _Dizziness from
+    our own motions and those of other objects._ 4. _Riding over a broad
+    stream. Sea-sickness._ 5. _Of turning round on one foot. Dervises in
+    Turkey. Attention of the mind prevents slight sea-sickness. After a
+    voyage ideas of vibratory motions are still perceived on shore._ 6.
+    _Ideas continue some time after they are excited. Circumstances of
+    turning on one foot, standing on a tower, and walking in the dark,
+    explained._ 7. _Irritative ideas of apparent motions. Irritative ideas
+    of sounds. Battèment of the sound of bells and organ-pipes. Vertiginous
+    noise in the head. Irritative motions of the stomach, intestines, and
+    glands._ 8. _Symptoms that accompany vertigo. Why vomiting comes on in
+    strokes of the palsy. By the motion of a ship. By injuries on the head.
+    Why motion makes sick people vomit._ 9. _Why drunken people are
+    vertiginous. Why a stone in the ureter, or bile-duct, produces
+    vomiting._ 10. _Why after a voyage ideas of vibratory motions are
+    perceived on shore._ 11. _Kinds of vertigo and their cure._ 12.
+    _Definition of vertigo._
+
+1. In learning to walk we judge of the distances of the objects, which we
+approach, by the eye; and by observing their perpendicularity determine our
+own. This circumstance not having been attended to by the writers on
+vision, the disease called vertigo or dizziness has been little understood.
+
+When any person loses the power of muscular action, whether he is erect or
+in a sitting posture, he sinks down upon the ground; as is seen in fainting
+fits, and other instances of great debility. Hence it follows, that some
+exertion of muscular power is necessary to preserve our perpendicular
+attitude. This is performed by proportionally exerting the antagonist
+muscles of the trunk, neck, and limbs; and if at any time in our
+locomotions we find ourselves inclining to one side, we either restore our
+equilibrium by the efforts of the muscles on the other side, or by moving
+one of our feet extend the base, which we rest upon, to the new center of
+gravity.
+
+But the most easy and habitual manner of determining our want of
+perpendicularity, is by attending to the apparent motion of the objects
+within the sphere of distinct vision; for this apparent motion of objects,
+when we incline from our perpendicularity, or begin to fall, is as much
+greater than the real motion of the eye, as the diameter of the sphere of
+distinct vision is to our perpendicular height.
+
+Hence no one, who is hood-winked, can walk in a straight line for a hundred
+steps together; for he inclines so greatly, before he is warned of his want
+of perpendicularity by the sense of touch, not having the apparent motions
+of ambient objects to measure this inclination by, that he is necessitated
+to move one of his feet outwards, to the right or to the left, to support
+the new centre of gravity, and thus errs from the line he endeavours to
+proceed in.
+
+For the same reason many people become dizzy, when they look from the
+summit of a tower, which is raised much above all other objects, as these
+objects are out of the sphere of distinct vision, and they are obliged to
+balance their bodies by the less accurate feelings of their muscles.
+
+There is another curious phenomenon belonging to this place, if the
+circumjacent visible objects are so small, that we do not distinguish their
+minute parts; or so similar, that we do not know them from each other; we
+cannot determine our perpendicularity by them. Thus in a room hung with a
+paper, which is coloured over with similar small black lozenges or
+rhomboids, many people become dizzy; for when they begin to fall, the next
+and the next lozenge succeeds upon the eye; which they mistake for the
+first, and are not aware, that they have any apparent motion. But if you
+fix a sheet of paper, or draw any other figure, in the midst of these
+lozenges, the charm ceases, and no dizziness is perceptible.--The same
+occurs, when we ride over a plain covered with snow without trees or other
+eminent objects.
+
+2. But after having compared visible objects at rest with the sense of
+touch, and learnt to distinguish their shapes and shades, and to measure
+our want of perpendicularity by their apparent motions, we come to consider
+them in real motion. Here a new difficulty occurs, and we require some
+experience to learn the peculiar mode of motion of any moving objects,
+before we can make use of them for the purposes of determining our
+perpendicularity. Thus some people become dizzy at the sight of a whirling
+wheel, or by gazing on the fluctuations of a river, if no steady objects
+are at the same time within the sphere of their distinct vision; and when a
+child first can stand erect upon his legs, if you gain his attention to a
+white handkerchief steadily extended like a sail, and afterwards make it
+undulate, he instantly loses his perpendicularity, and tumbles on the
+ground.
+
+3. A second difficulty we have to encounter is to distinguish our own real
+movements from the apparent motions of objects. Our daily practice of
+walking and riding on horseback soon instructs us with accuracy to discern
+these modes of motion, and to ascribe the apparent motions of the ambient
+objects to ourselves; but those, which we have not acquired by repeated
+habit, continue to confound us. So as we ride on horseback the trees and
+cottages, which occur to us, appear at rest; we can measure their distances
+with our eye, and regulate our attitude by them; yet if we carelessly
+attend to distant hills or woods through a thin hedge, which is near us, we
+observe the jumping and progressive motions of them; as this is increased
+by the paralax of these objects; which we have not habituated ourselves to
+attend to. When first an European mounts an elephant sixteen feet high, and
+whose mode of motion he is not accustomed to, the objects seem to undulate,
+as he passes, and he frequently becomes sick and vertiginous, as I am well
+informed. Any other unusual movement of our bodies has the same effect, as
+riding backwards in a coach, swinging on a rope, turning round swiftly on
+one leg, scating on the ice, and a thousand others. So after a patient has
+been long confined to his bed, when he first attempts to walk, he finds
+himself vertiginous, and is obliged by practice to learn again the
+particular modes of the apparent motions of objects, as he walks by them.
+
+4. A third difficulty, which occurs to us in learning to balance ourselves
+by the eye, is, when both ourselves and the circumjacent objects are in
+real motion. Here it is necessary, that we should be habituated to both
+these modes of motion in order to preserve our perpendicularity. Thus on
+horseback we accurately observe another person, whom we meet, trotting
+towards us, without confounding his jumping and progressive motion with our
+own, because we have been accustomed to them both; that is, to undergo the
+one, and to see the other at the same time. But in riding over a broad and
+fluctuating stream, though we are well experienced in the motions of our
+horse, we are liable to become dizzy from our inexperience in that of the
+water. And when first we go on ship-board, where the movements of
+ourselves, and the movements of the large waves are both new to us, the
+vertigo is almost unavoidable with the terrible sickness, which attends it.
+And this I have been assured has happened to several from being removed
+from a large ship into a small one; and again from a small one into a man
+of war.
+
+5. From the foregoing examples it is evident, that, when we are surrounded
+with unusual motions, we lose our perpendicularity: but there are some
+peculiar circumstances attending this effect of moving objects, which we
+come now to mention, and shall hope from the recital of them to gain some
+insight into the manner of their production.
+
+When a child moves round quick upon one foot, the circumjacent objects
+become quite indistinct, as their distance increases their apparent
+motions; and this great velocity confounds both their forms, and their
+colours, as is seen in whirling round a many coloured wheel; he then loses
+his usual method of balancing himself by vision, and begins to stagger, and
+attempts to recover himself by his muscular feelings. This staggering adds
+to the instability of the visible objects by giving a vibratory motion
+besides their rotatory one. The child then drops upon the ground, and the
+neighbouring objects seem to continue for some seconds of time to circulate
+around him, and the earth under him appears to librate like a balance. In
+some seconds of time these sensations of a continuation of the motion of
+objects vanish; but if he continues turning round somewhat longer, before
+he falls, sickness and vomiting are very liable to succeed. But none of
+these circumstances affect those who have habituated themselves to this
+kind of motion, as the dervises in Turkey, amongst whom these swift
+gyrations are a ceremony of religion.
+
+In an open boat passing from Leith to Kinghorn in Scotland, a sudden change
+of the wind shook the undistended sail, and stopt our boat; from this
+unusual movement the passengers all vomited except myself. I observed, that
+the undulation of the ship, and the instability of all visible objects,
+inclined me strongly to be sick; and this continued or increased, when I
+closed my eyes, but as often as I bent my attention with energy on the
+management and mechanism of the ropes and sails, the sickness ceased; and
+recurred again, as often as I relaxed this attention; and I am assured by a
+gentleman of observation and veracity, that he has more than once observed,
+when the vessel has been in immediate danger, that the sea-sickness of the
+passengers has instantaneously ceased, and recurred again, when the danger
+was over.
+
+Those, who have been upon the water in a boat or ship so long, that they
+have acquired the necessary habits of motion upon that unstable element, at
+their return on land frequently think in their reveries, or between
+sleeping and waking, that they observe the room, they sit in, or some of
+its furniture, to librate like the motion of the vessel. This I have
+experienced myself, and have been told, that after long voyages, it is some
+time before these ideas entirely vanish. The same is observable in a less
+degree after having travelled some days in a stage coach, and particularly
+when we lie down in bed, and compose ourselves to sleep; in this case it is
+observable, that the rattling noise of the coach, as well as the undulatory
+motion, haunts us. The drunken vertigo, and the vulgar custom of rocking
+children, will be considered in the next Section.
+
+6. The motions, which are produced by the power of volition, may be
+immediately stopped by the exertion of the same power on the antagonist
+muscles; otherwise these with all the other classes of motion continue to
+go on, some time after they are excited, as the palpitation of the heart
+continues after the object of fear, which occasioned it, is removed. But
+this circumstance is in no class of motions more remarkable than in those
+dependent on irritation; thus if any one looks at the sun, and then covers
+his eyes with his hand, he will for many seconds of time, perceive the
+image of the sun marked on his retina: a similar image of all other visible
+objects would remain some time formed on the retina, but is extinguished by
+the perpetual change of the motions of this nerve in our attention to other
+objects. To this must be added, that the longer time any movements have
+continued to be excited without fatigue to the organ, the longer will they
+continue spontaneously, after the excitement is withdrawn: as the taste of
+tobacco in the mouth after a person has been smoaking it.
+
+This taste remains so strong, that if a person continues to draw air
+through a tobacco pipe in the dark, after having been smoking some time, he
+cannot distinguish whether his pipe be lighted or not.
+
+From these two considerations it appears, that the dizziness felt in the
+head, after seeing objects in unusual motion, is no other than a
+continuation of the motions of the optic nerve excited by those objects and
+which engage our attention. Thus on turning round on one foot, the vertigo
+continues for some seconds of time after the person is fallen on the
+ground; and the longer he has continued to revolve, the longer will
+continue these successive motions of the parts of the optic nerve.
+
+    _Additional Observations on _VERTIGO.
+
+    After revolving with your eyes open till you become vertiginous, as
+    soon as you cease to revolve, not only the circum-ambient objects
+    appear to circulate round you in a direction contrary to that, in which
+    you have been turning, but you are liable to roll your eyes forwards
+    and backwards; as is well observed, and ingeniously demonstrated by Dr.
+    Wells in a late publication on vision. The same occurs, if you revolve
+    with your eyes closed, and open them immediately at the time of your
+    ceasing to turn; and even during the whole time of revolving, as may be
+    felt by your hand pressed lightly on your closed eyelids. To these
+    movements of the eyes, of which he supposes the observer to be
+    inconscious, Dr. Wells ascribes the apparent circumgyration of objects
+    on ceasing to revolve.
+
+    The cause of thus turning our eyes forwards, and then back again, after
+    our body is at rest, depends, I imagine, on the same circumstance,
+    which induces us to follow the indistinct spectra, which are formed on
+    one side of the center of the retina, when we observe them apparently
+    on clouds, as described in Sect. XL. 2. 2.; and then not being able to
+    gain a more distinct vision of them, we turn our eyes back, and again
+    and again pursue the flying shade.
+
+    But this rolling of the eyes, after revolving till we become
+    vertiginous, cannot cause the apparent circumgyration of objects, in a
+    direction contrary to that in which we have been revolving, for the
+    following reasons. 1. Because in pursuing a spectrum in the sky, or on
+    the ground, as above mentioned, we perceive no retrograde motions of
+    objects. 2. Because the apparent retrograde motions of objects, when we
+    have revolved till we are vertiginous, continues much longer than the
+    rolling of the eyes above described.
+
+    3. When we have revolved from right to left, the apparent motion of
+    objects, when we stop, is from left to right; and when we have revolved
+    from left to right, the apparent circulation of objects is from right
+    to left; yet in both these cases the eyes of the revolver are seen
+    equally to roll forwards and backwards.
+
+    4. Because this rolling of the eyes backwards and forwards takes place
+    during our revolving, as may be perceived by the hand lightly pressed
+    on the closed eyelids, and therefore exists before the effect ascribed
+    to it.
+
+    And fifthly, I now come to relate an experiment, in which the rolling
+    of the eyes does not take place at all after revolving, and yet the
+    vertigo is more distressing than in the situations above mentioned. If
+    any one looks steadily at a spot in the ceiling over his head, or
+    indeed at his own finger held up high over his head, and in that
+    situation turns round till he becomes giddy; and then stops, and looks
+    horizontally; he now finds, that the apparent rotation of objects is
+    from above downwards, or from below upwards; that is, that the apparent
+    circulation of objects is now vertical instead of horizontal, making
+    part of a circle round the axis of his _eye_; and this without any
+    rolling of his eyeballs. The reason of there being no rolling of the
+    eyeballs, perceived after this experiment, is, because the images of
+    objects are formed in rotation round the axis of the eye, and not from
+    one side to the other of the axis of it; so that, as the eyeball has
+    not power to turn in its socket round its own axis, it cannot follow
+    the apparent motions of these evanescent spectra, either before or
+    after the body is at rest. From all which arguments it is manifest,
+    that these apparent retrograde gyrations of objects are not caused by
+    the rolling of the eyeballs; first, because no apparent retrogression
+    of objects is observed in other rollings of the eyes: secondly, because
+    the apparent retrogression of objects continues many seconds after the
+    rolling of the eyeballs ceases. Thirdly, because the apparent
+    retrogression of objects is sometimes one way, and sometimes another,
+    yet the rolling of the eyeballs is the same. Fourthly, because the
+    rolling of the eyeballs exists before the apparent retrograde motions
+    of objects is observed; that is, before the revolving person stops. And
+    fifthly, because the apparent retrograde gyration of objects is
+    produced, when there is no rolling of the eyeballs at all.
+
+    Doctor Wells imagines, that no spectra can be gained in the eye, if a
+    person revolves with his eyelids closed, and thinks this a sufficient
+    argument against the opinion, that the apparent progression of the
+    spectra of light or colours in the eye can cause the apparent
+    retrogression of objects in the vertigo above described; but it is
+    certain, when any person revolves in a light room with his eyes closed,
+    that he nevertheless perceives differences of light both in quantity
+    and colour through his eyelids, as he turns round; and readily gains
+    spectra of those differences. And these spectra are not very different
+    except in vivacity from those, which he acquires, when he revolves with
+    unclosed eyes, since if he then revolves very rapidly the colours and
+    forms of surrounding objects are as it were mixed together in his eye;.
+    as when, the prismatic colours are painted on a wheel, they appear
+    white as they revolve. The truth of this is evinced by the staggering
+    or vertigo of men perfectly blind, when they turn round; which is not
+    attended with apparent circulation of objects, but is a vertiginous
+    disorder of the sense of touch. Blind men balance themselves by their
+    sense of touch; which, being less adapted for perceiving small
+    deviations from their perpendicular, occasions them to carry themselves
+    more erect in walking. This method of balancing themselves by the
+    direction of their pressure against the floor, becomes disordered by
+    the unusual mode of action in turning round, and they begin to lose
+    their perpendicularity, that is, they become vertiginous; but without
+    any apparent circular motions of visible objects.
+
+    It will appear from the following experiments, that the apparent
+    progression of the ocular spectra of light or colours is the cause of
+    the apparent retrogression of objects, after a person has revolved,
+    till he is vertiginous.
+
+    First, when a person turns round in a light room with his eyes open,
+    but closes them before he stops, he will seem to be carried forwards in
+    the direction he was turning for a short time after he stops. But if he
+    opens his eyes again, the objects before him instantly appear to move
+    in a retrograde direction, and he loses the sensation of being carried
+    forwards. The same occurs if a person revolves in a light room with his
+    eyes closed; when he stops, he seems to be for a time carried forwards,
+    if his eyes are still closed; but the instant he opens them, the
+    surrounding objects appear to move in retrograde gyration. From hence
+    it may be concluded, that it is the sensation or imagination of our
+    continuing to go forwards in the direction in which we were turning,
+    that causes the apparent retrograde circulation of objects.
+
+    Secondly, though there is an audible vertigo, as is known by the
+    battement, or undulations of sound in the ears, which many vertiginous
+    people experience; and though there is also a tangible vertigo, as when
+    a blind person turns round, as mentioned above; yet as this
+    circumgyration of objects is an hallucination or deception of the sense
+    of sight, we are to look for the cause of our appearing to move
+    forward, when we stop with our eyes closed after gyration, to some
+    affection of this sense. Now, thirdly, if the spectra formed in the eye
+    during our rotation, continue to change, when we stand still, like the
+    spectra described in Sect. III. 3. 6. such changes must suggest to us
+    the idea or sensation of our still continuing to turn round; as is the
+    case, when we revolve in a light room, and close our eyes before we
+    stop. And lastly, on opening our eyes in the situation above described,
+    the objects we chance to view amid these changing spectra in the eye,
+    must seem to move in a contrary direction; as the moon sometimes
+    appears to move retrograde, when swift-gliding clouds are passing
+    forwards so much nearer the eye of the beholder.
+
+    To make observations on faint ocular spectra requires some degree of
+    habit, and composure of mind, and even patience; some of those
+    described in Sect. XL. were found difficult to see, by many, who tried
+    them; now it happens, that the mind, during the confusion of vertigo,
+    when all the other irritative tribes of motion, as well as those of
+    vision, are in some degree disturbed, together with the fear of
+    falling, is in a very unfit state for the contemplation of such weak
+    sensations, as are occasioned by faint ocular spectra. Yet after
+    frequently revolving, both with my eyes closed, and with them open, and
+    attending to the spectra remaining in them, by shading the light from
+    my eyelids more or less with my hand, I at length ceased to have the
+    idea of going forward, after I stopped with my eyes closed; and saw
+    changing spectra in my eyes, which seemed to move, as it were, over the
+    field of vision; till at length, by repeated trials on sunny days, I
+    persuaded myself, on opening my eyes, after revolving some time, on a
+    shelf of gilded books in my library, that I could perceive the spectra
+    in my eyes move forwards over one or two of the books, like the vapours
+    in the air of a summer's day; and could so far undeceive myself, as to
+    perceive the books to stand still. After more trials I sometimes
+    brought myself to believe, that I saw changing spectra of lights and
+    shades moving in my eyes, after turning round for some time, but did
+    not imagine either the spectra or the objects to be in a state of
+    gyration. I speak, however, with diffidence of these facts, as I could
+    not always make the experiments succeed, when there was not a strong
+    light in my room, or when my eyes were not in the most proper state for
+    such observations.
+
+    The ingenious and learned M. Sauvage has mentioned other theories to
+    account for the apparent circumgyration of objects in vertiginous
+    people. As the retrograde motions of the particles of blood in the
+    optic arteries, by spasm, or by fear, as is seen in the tails of
+    tadpoles, and membranes between the fingers of frogs. Another cause he
+    thinks may be from the librations to one side, and to the other, of the
+    crystalline lens in the eye, by means of involuntary actions of the
+    muscles, which constitute the ciliary process. Both these theories lie
+    under the same objection as that of Dr. Wells before mentioned; namely,
+    that the apparent motions of objects, after the observer has revolved
+    for some time, should appear to vibrate this way and that; and not to
+    circulate uniformly in a direction contrary to that, in which the
+    observer had revolved.
+
+    M. Sauvage has, lastly, mentioned the theory of colours left in the
+    eye, which he has termed impressions on the retina. He says,
+    "Experience teaches us, that impressions made on the retina by a
+    visible object remain some seconds after the object is removed; as
+    appears from the circle of fire which we see, when a fire-stick is
+    whirled round in the dark; therefore when we are carried round our own
+    axis in a circle, we undergo a temporary vertigo, when we stop; because
+    the impressions of the circumjacent objects remain for a time
+    afterwards on the retina." Nosolog. Method. Clas. VIII. I. 1. We have
+    before observed, that the changes of these colours remaining in the
+    eye, evinces them to be motions of the fine terminations of the retina,
+    and not impressions on it; as impressions on a passive substance must
+    either remain, or cease intirely. See an additional note at the end of
+    the second volume.
+
+Any one, who stands alone on the top of a high tower, if he has not been
+accustomed to balance himself by objects placed at such distances and with
+such inclinations, begins to stagger, and endeavours to recover himself by
+his muscular feelings. During this time the apparent motion of objects at a
+distance below him is very great, and the spectra of these apparent motions
+continue a little time after he has experienced them; and he is persuaded
+to incline the contrary way to counteract their effects; and either
+immediately falls, or applying his hands to the building, uses his muscular
+feelings to preserve his perpendicular attitude, contrary to the erroneous
+persuasions of his eyes. Whilst the person, who walks in the dark,
+staggers, but without dizziness; for he neither has the sensation of moving
+objects to take off his attention from his muscular feelings, nor has he
+the spectra of those motions continued on his retina to add to his
+confusion. It happens indeed sometimes to one landing on a tower, that the
+idea of his not having room to extend his base by moving one of his feet
+outwards, when he begins to incline, superadds fears to his other
+inconveniences; which like surprise, joy, or any great degree of sensation,
+enervates him in a moment, by employing the whole sensorial power, and by
+thus breaking all the associated trains and tribes of motion.
+
+7. The irritative ideas of objects, whilst we are awake, are perpetually
+present to our sense of sight; as we view the furniture of our rooms, or
+the ground, we tread upon, throughout the whole day without attending to
+it. And as our bodies are never at perfect rest during our waking hours,
+these irritative ideas of objects are attended perpetually with irritative
+ideas of their apparent motions. The ideas of apparent motions are always
+irritative ideas, because we never attend to them, whether we attend to the
+objects themselves, or to their real motions, or to neither. Hence the
+ideas of the apparent motions of objects are a complete circle of
+irritative ideas, which continue throughout the day.
+
+Also during all our waking hours, there is a perpetual confused sound of
+various bodies, as of the wind in our rooms, the fire, distant
+conversations, mechanic business; this continued buzz, as we are seldom
+quite motionless, changes its loudness perpetually, like the sound of a
+bell; which rises and falls as long as it continues, and seems to pulsate
+on the ear. This any one may experience by turning himself round near a
+waterfall; or by striking a glass bell, and then moving the direction of
+its mouth towards the ears, or from them, as long as its vibrations
+continue. Hence this undulation of indistinct sound makes another
+concomitant circle of irritative ideas, which continues throughout the day.
+
+We hear this undulating sound, when we are perfectly at rest ourselves,
+from other sonorous bodies besides bells; as from two organ-pipes, which
+are nearly but not quite in unison, when they are sounded together. When a
+bell is struck, the circular form is changed into an eliptic one; the
+longest axis of which, as the vibrations continue, moves round the
+periphery of the bell; and when either axis of this elipse is pointed
+towards our ears, the sound is louder; and less when the intermediate parts
+of the elipse are opposite to us. The vibrations of the two organ-pipes may
+be compared to Nonius's rule; the sound is louder, when they coincide, and
+less at the intermediate times. But, as the sound of bells is the most
+familiar of those sounds, which have a considerable battement, the
+vertiginous patients, who attend to the irritative circles of sounds above
+described, generally compare it to the noise of bells.
+
+The peristaltic motions of our stomach and intestines, and the secretions
+of the various glands, are other circles of irritative motions, some of
+them more or less complete, according to our abstinence or satiety.
+
+So that the irritative ideas of the apparent motions of objects, the
+irritative battements of sounds, and the movements of our bowels and glands
+compose a great circle of irritative tribes of motion: and when one
+considerable part of this circle of motions becomes interrupted, the whole
+proceeds in confusion, as described in Section XVII. 1. 7. on Catenation of
+Motions.
+
+8. Hence a violent vertigo, from whatever cause it happens, is generally
+attended with undulating noise in the head, perversions of the motions of
+the stomach and duodenum, unusual excretion of bile and gastric juice, with
+much pale urine, sometimes with yellowness of the skin, and a disordered
+secretion of almost every gland of the body, till at length the arterial
+system is affected, and fever succeeds.
+
+Thus bilious vomitings accompany the vertigo occasioned by the motion of a
+ship; and when the brain is rendered vertiginous by a paralytic affection
+of any part of the body, a vomiting generally ensues, and a great discharge
+of bile: and hence great injuries of the head from external violence are
+succeeded with bilious vomitings, and sometimes with abscesses of the
+liver. And hence, when a patient is inclined to vomit from other causes, as
+in some fevers, any motions of the attendants in his room, or of himself
+when he is raised or turned in his bed, presently induces the vomiting by
+superadding a degree of vertigo.
+
+9. And conversely it is very usual with those, whose stomachs are affected
+from internal causes, to be afflicted with vertigo, and noise in the head;
+such is the vertigo of drunken people, which continues, when their eyes are
+closed, and themselves in a recumbent posture, as well as when they are in
+an erect posture, and have their eyes open. And thus the irritation of a
+stone in the bile-duct, or in the ureter, or an inflammation of any of the
+intestines, are accompanied with vomitings and vertigo.
+
+In these cases the irritative motions of the stomach, which are in general
+not attended to, become so changed by some unnatural stimulus, as to become
+uneasy, and excite our sensation or attention. And thus the other
+irritative trains of motions, which are associated with it, become
+disordered by their sympathy. The same happens, when a piece of gravel
+sticks in the ureter, or when some part of the intestinal canal becomes
+inflamed. In these cases the irritative muscular motions are first
+disturbed by unusual stimulus, and a disordered action of the sensual
+motions, or dizziness ensues. While in sea-sickness the irritative sensual
+motions, as vertigo, precedes; and the disordered irritative muscular
+motions, as those of the stomach in vomiting, follow.
+
+10. When these irritative motions are disturbed, if the degree be not very
+great, the exertion of voluntary attention to any other object, or any
+sudden sensation, will disjoin these new habits of motion. Thus some
+drunken people have become sober immediately, when any accident has
+strongly excited their attention; and sea-sickness has vanished, when the
+ship has been in danger. Hence when our attention to other objects is most
+relaxed, as just before we fall asleep, or between our reveries when awake,
+these irritative ideas of motion and sound are most liable to be perceived;
+as those, who have been at sea, or have travelled long in a coach, seem to
+perceive the vibrations of the ship, or the rattling of the wheels, at
+these intervals; which cease again, as soon as they exert their attention.
+That is, at those intervals they attend to the apparent motions, and to the
+battement of sounds of the bodies around them, and for a moment mistake
+them for those real motions of the ship, and noise of wheels, which they
+had lately been accustomed to: or at these intervals of reverie, or on the
+approach of sleep, these supposed motions or sounds may be produced
+entirely by imagination.
+
+We may conclude from this account of vertigo, that sea-sickness is not an
+effort of nature to relieve herself, but a necessary consequence of the
+associations or catenations of animal motions. And may thence infer, that
+the vomiting, which attends the gravel in the ureter, inflammations of the
+bowels, and the commencement of some fevers, has a similar origin, and is
+not always an effort of the vis medicatrix naturæ. But where the action of
+the organ is the immediate consequence of the stimulating cause, it is
+frequently exerted to dislodge that stimulus, as in vomiting up an emetic
+drug; at other times, the action of an organ is a general effort to relieve
+pain, as in convulsions of the locomotive muscles; other actions drink up
+and carry on the fluids, as in absorption and secretion; all which may be
+termed efforts of nature to relieve, or to preserve herself.
+
+11. The cure of vertigo will frequently depend on our previously
+investigating the cause of it, which from what has been delivered above may
+originate from the disorder of any part of the great tribes of irritative
+motions, and of the associate motions catenated with them.
+
+Many people, when they arrive at fifty or sixty years of age, are affected
+with slight vertigo; which is generally but wrongly ascribed to
+indigestion, but in reality arises from a beginning defect of their sight;
+as about this time they also find it necessary to begin to use spectacles,
+when they read small prints, especially in winter, or by candle light, but
+are yet able to read without them during the summer days, when the light is
+stronger. These people do not see objects so distinctly as formerly, and by
+exerting their eyes more than usual, they perceive the apparent motions of
+objects, and confound them with the real motions of them; and therefore
+cannot accurately balance themselves so as easily to preserve their
+perpendicularity by them.
+
+That is, the apparent motions of objects, which are at rest, as we move by
+them, should only excite irritative ideas: but as these are now become less
+distinct, owing to the beginning imperfection of our sight, we are induced
+_voluntarily_ to attend to them; and then these apparent motions become
+succeeded by sensation; and thus the other parts of the trains of
+irritative ideas, or irritative muscular motions, become disordered, as
+explained above. In these cases of slight vertigo I have always promised my
+patients, that they would get free from it in two or three months, as they
+should acquire the habit of balancing their bodies by less distinct
+objects, and have seldom been mistaken in my prognostic.
+
+There is an auditory vertigo, which is called a noise in the head,
+explained in No. 7. of this section, which also is very liable to affect
+people in the advance of life, and is owing to their hearing less perfectly
+than before. This is sometimes called a ringing, and sometimes a singing,
+or buzzing, in the ears, and is occasioned by our first experiencing a
+disagreeable sensation from our not being able distinctly to hear the
+sounds, we used formerly to hear distinctly. And this disagreeable
+sensation excites desire and consequent volition; and when we voluntarily
+attend to small indistinct sounds, even the whispering of the air in a
+room, and the pulsations of the arteries of the ear are succeeded by
+sensation; which minute sounds ought only to have produced irritative
+sensual motions, or unperceived ideas. See Section XVII. 3. 6. These
+patients after a while lose this auditory vertigo, by acquiring a new habit
+of not attending voluntarily to these indistinct sounds, but contenting
+themselves with the less accuracy of their sense of hearing.
+
+Another kind of vertigo begins with the disordered action of some
+irritative muscular motions, as those of the stomach from intoxication, or
+from emetics; or those of the ureter, from the stimulus of a stone lodged
+in it; and it is probable, that the disordered motions of some of the great
+congeries of glands, as of those which form the liver, or of the intestinal
+canal, may occasion vertigo in consequence of their motions being
+associated or catenated with the great circles of irritative motions; and
+from hence it appears, that the means of cure must be adapted to the cause.
+
+To prevent sea-sickness it is probable, that the habit of swinging for a
+week or two before going on shipboard might be of service. For the vertigo
+from failure of sight, spectacles may be used. For the auditory vertigo,
+æther may be dropt into the ear to stimulate the part, or to dissolve
+ear-wax, if such be a part of the cause. For the vertigo arising from
+indigestion, the peruvian bark and a blister are recommended. And for that
+owing to a stone in the ureter, venesection, cathartics, opiates, sal soda
+aerated.
+
+12. Definition of vertigo. 1. Some of the irritative sensual, or muscular
+motions, which were usually not succeeded by sensation, are in this disease
+succeeded by sensation; and the trains or circles of motions, which were
+usually catenated with them, are interrupted, or inverted, or proceed in
+confusion. 2. The sensitive and voluntary motions continue undisturbed. 3.
+The associate trains or circles of motions continue; but their catenations
+with some of the irritative motions are disordered, or inverted, or
+dissevered.
+
+       *       *       *       *       *
+
+SECT. XXI.
+
+OF DRUNKENNESS.
+
+    1. _Sleep from satiety of hunger. From rocking children. From uniform
+    sounds._ 2. _Intoxication from common food after fatigue and
+    inanition._ 3. _From wine or of opium. Chilness after meals. Vertigo.
+    Why pleasure is produced by intoxication, and by swinging and rocking
+    children. And why pain is relieved by it._ 4. _Why drunkards stagger
+    and stammer, and are liable to weep._ 5. _And become delirious, sleepy,
+    and stupid._ 6. _Or make pale urine and vomit._ 7. _Objects are seen
+    double._ 8. _Attention of the mind diminishes drunkenness._ 9.
+    _Disordered irritative motions of all the senses._ 10. _Diseases from
+    drunkenness._ 11. _Definition of drunkenness._
+
+1. In the state of nature when the sense of hunger is appeased by the
+stimulus of agreeable food, the business of the day is over, and the human
+savage is at peace with the world, he then exerts little attention to
+external objects, pleasing reveries of imagination succeed, and at length
+sleep is the result: till the nourishment which he has procured, is carried
+over every part of the system to repair the injuries of action, and he
+awakens with fresh vigour, and feels a renewal of his sense of hunger.
+
+The juices of some bitter vegetables, as of the poppy and the laurocerasus,
+and the ardent spirit produced in the fermentation of the sugar found in
+vegetable juices, are so agreeable to the nerves of the stomach, that,
+taken in a small quantity, they instantly pacify the sense of hunger; and
+the inattention to external stimuli with the reveries of imagination, and
+sleep, succeeds, in the same manner as when the stomach is filled with
+other less intoxicating food.
+
+This inattention to the irritative motions occasioned by external stimuli
+is a very important circumstance in the approach of sleep, and is produced
+in young children by rocking their cradles: during which all visible
+objects become indistinct to them. An uniform soft repeated sound, as the
+murmurs of a gentle current, or of bees, are said to produce the same
+effect, by presenting indistinct ideas of inconsequential sounds, and by
+thus stealing our attention from other objects, whilst by their continued
+reiterations they become familiar themselves, and we cease gradually to
+attend to any thing, and sleep ensues.
+
+2. After great fatigue or inanition, when the stomach is suddenly filled
+with flesh and vegetable food, the inattention to external stimuli, and the
+reveries of imagination, become so conspicuous as to amount to a degree of
+intoxication. The same is at any time produced by superadding a little wine
+or opium to our common meals; or by taking these separately in considerable
+quantity; and this more efficaciously after fatigue or inanition; because a
+less quantity of any stimulating material will excite an organ into
+energetic action, after it has lately been torpid from defect of stimulus;
+as objects appear more luminous, after we have been in the dark; and
+because the suspension of volition, which is the immediate cause of sleep,
+is sooner induced, after a continued voluntary exertion has in part
+exhausted the sensorial power of volition; in the same manner as we cannot
+contract a single muscle long together without intervals of inaction.
+
+3. In the beginning of intoxication we are inclined to sleep, as mentioned
+above, but by the excitement of external circumstances, as of noise, light,
+business, or by the exertion of volition, we prevent the approaches of it,
+and continue to take into our stomach greater quantities of the inebriating
+materials. By these means the irritative movements of the stomach are
+excited into greater action than is natural; and in consequence all the
+irritative tribes and trains of motion, which are catenated with them,
+become susceptible of stronger action from their accustomed stimuli;
+because these motions are excited both by their usual irritation, and by
+their association with the increased actions of the stomach and lacteals.
+Hence the skin glows, and the heat of the body is increased, by the more
+energetic action of the whole glandular system; and pleasure is introduced
+in consequence of these increased motions from internal stimulus. According
+to Law 5. Sect. IV. on Animal Causation.
+
+From this great increase of irritative motions from internal stimulus, and
+the increased sensation introduced into the system in consequence; and
+secondly, from the increased sensitive motions in consequence of this
+additional quantity of sensation, so much sensorial power is expended, that
+the voluntary power becomes feebly exerted, and the irritation from the
+stimulus of external objects is less forcible; the external parts of the
+eye are not therefore voluntarily adapted to the distances of objects,
+whence the apparent motions of those objects either are seen double, or
+become too indistinct for the purpose of balancing the body, and vertigo is
+induced.
+
+Hence we become acquainted with that very curious circumstance, why the
+drunken vertigo is attended with an increase of pleasure; for the
+irritative ideas and motions occasioned by internal stimulus, that were not
+attended to in our sober hours, are now just so much increased as to be
+succeeded by pleasurable sensation, in the same manner as the more violent
+motions of our organs are succeeded by painful sensation. And hence a
+greater quantity of pleasurable sensation is introduced into the
+constitution; which is attended in some people with an increase of
+benevolence and good humour.
+
+If the apparent motions of objects is much increased, as when we revolve on
+one foot, or are swung on a rope, the ideas of these apparent motions are
+also attended to, and are succeeded with pleasureable sensation, till they
+become familiar to us by frequent use. Hence children are at first
+delighted with these kinds of exercise, and with riding, and failing, and
+hence rocking young children inclines them to sleep. For though in the
+vertigo from intoxication the irritative ideas of the apparent motions of
+objects are indistinct from their decrease of energy: yet in the vertigo
+occasioned by rocking or swinging the irritative ideas of the apparent
+motions of objects are increased in energy, and hence they induce pleasure
+into the system, but are equally indistinct, and in consequence equally
+unfit to balance ourselves by. This addition of pleasure precludes desire
+or aversion, and in consequence the voluntary power is feebly exerted, and
+on this account rocking young children inclines them to sleep.
+
+In what manner opium and wine act in relieving pain is another article,
+that well deserves our attention. There are many pains that originate from
+defect as well as from excess of stimulus; of these are those of the six
+appetites of hunger, thirst, lust, the want of heat, of distention, and of
+fresh air. Thus if our cutaneous capillaries cease to act from the
+diminished stimulus of heat, when we are exposed to cold weather, or our
+stomach is uneasy for want of food; these are both pains from defect of
+stimulus, and in consequence opium, which stimulates all the moving system
+into increased action, must relieve them. But this is not the case in those
+pains, which arise from excess of stimulus, as in violent inflammations: in
+these the exhibition of opium is frequently injurious by increasing the
+action of the system already too great, as in inflammation of the bowels
+mortification is often produced by the stimulus of opium. Where, however,
+no such bad consequences follow; the stimulus of opium, by increasing all
+the motions of the system, expends so much of the sensorial power, that the
+actions of the whole system soon become feebler, and in consequence those
+which produced the pain and inflammation.
+
+4. When intoxication proceeds a little further, the quantity of pleasurable
+sensation is so far increased, that all desire ceases, for there is no pain
+in the system to excite it. Hence the voluntary exertions are diminished,
+staggering and stammering succeed; and the trains of ideas become more and
+more inconsistent from this defect of voluntary exertion, as explained in
+the sections on sleep and reverie, whilst those passions which are unmixed
+with volition are more vividly felt, and shewn with less reserve; hence
+pining love, or superstitious fear, and the maudling tear dropped on the
+remembrance of the most trifling distress.
+
+5. At length all these circumstances are increased; the quantity of
+pleasure introduced into the system by the increased irritative muscular
+motions of the whole sanguiferous, and glandular, and absorbent systems,
+becomes so great, that the organs of sense are more forcibly excited into
+action by this internal pleasurable sensation, than by the irritation from
+the stimulus of external objects. Hence the drunkard ceases to attend to
+external stimuli, and as volition is now also suspended, the trains of his
+ideas become totally inconsistent as in dreams, or delirium: and at length
+a stupor succeeds from the great exhaustion of sensorial power, which
+probably does not even admit of dreams, and in which, as in apoplexy, no
+motions continue but those from internal stimuli, from sensation, and from
+association.
+
+6. In other people a paroxysm of drunkenness has another termination; the
+inebriate, as soon as he begins to be vertiginous, makes pale urine in
+great quantities and very frequently, and at length becomes sick, vomits
+repeatedly, or purges, or has profuse sweats, and a temporary fever ensues
+with a quick strong pulse. This in some hours is succeeded by sleep; but
+the unfortunate bacchanalian does not perfectly recover himself till about
+the same time of the succeeding day, when his course of inebriation began.
+As shewn in Sect. XVII. 1. 7. on Catenation. The temporary fever with
+strong pulse is owing to the same cause as the glow on the skin mentioned
+in the third paragraph of this Section: the flow of urine and sickness
+arises from the whole system of irritative motions being thrown into
+confusion by their associations with each other; as in sea-sickness,
+mentioned in Sect. XX. 4. on Vertigo; and which is more fully explained in
+Section XXIX. on Diabetes.
+
+7. In this vertigo from internal causes we see objects double, as two
+candles instead of one, which is thus explained. Two lines drawn through
+the axes of our two eyes meet at the object we attend to: this angle of the
+optic axes increases or diminishes with the less or greater distances of
+objects. All objects before or behind the place where this angle is formed,
+appear double; as any one may observe by holding up a pen between his eyes
+and the candle; when he looks attentively at a spot on the pen, and
+carelessly at the candle, it will appear double; and the reverse when he
+looks attentively at the candle and carelessly at the pen; so that in this
+case the muscles of the eye, like those of the limbs, stagger and are
+disobedient to the expiring efforts of volition. Numerous objects are
+indeed sometimes seen by the inebriate, occasioned by the refractions made
+by the tears, which stand upon his eye-lids.
+
+8. This vertigo also continues, when the inebriate lies in his bed, in the
+dark, or with his eyes closed; and this more powerfully than when he is
+erect, and in the light. For the irritative ideas of the apparent motions
+of objects are now excited by irritation from internal stimulus, or by
+association with other irritative motions; and the inebriate, like one in a
+dream, believes the objects of these irritative motions to be present, and
+feels himself vertiginous. I have observed in this situation, so long as my
+eyes and mind were intent upon a book, the sickness and vertigo ceased, and
+were renewed again the moment I discontinued this attention; as was
+explained in the preceding account of sea-sickness. Some drunken people
+have been known to become sober instantly from some accident, that has
+strongly excited their attention, as the pain of a broken bone, or the news
+of their house being on fire.
+
+9. Sometimes the vertigo from internal causes, as from intoxication, or at
+the beginning of some fevers, becomes so universal, that the irritative
+motions which belong to other organs of sense are succeeded by sensation or
+attention, as well as those of the eye. The vertiginous noise in the ears
+has been explained in Section XX. on Vertigo. The taste of the saliva,
+which in general is not attended to, becomes perceptible, and the patients
+complain of a bad taste in their mouth.
+
+The common smells of the surrounding air sometimes excite the attention of
+these patients, and bad smells are complained of, which to other people are
+imperceptible. The irritative motions that belong to the sense of pressure,
+or of touch, are attended to, and the patient conceives the bed to librate,
+and is fearful of falling out of it. The irritative motions belonging to
+the senses of distention, and of heat, like those above mentioned, become
+attended to at this time: hence we feel the pulsation of our arteries all
+over us, and complain of heat, or of cold, in parts of the body where there
+is no accumulation or diminution of actual heat. All which are to be
+explained, as in the last paragraph, by the irritative ideas belonging to
+the various senses being now excited by internal stimuli, or by their
+associations with other irritative motions. And that the inebriate, like
+one in a dream, believes the external objects, which usually caused these
+irritative ideas, to be now present.
+
+10. The diseases in consequence of frequent inebriety, or of daily taking
+much vinous spirit without inebriety, consist in the paralysis, which is
+liable to succeed violent stimulation. Organs, whose actions are associated
+with others, are frequently more affected than the organ, which is
+stimulated into too violent action. See Sect. XXIV. 2. 8. Hence in drunken
+people it generally happens, that the secretory vessels of the liver become
+first paralytic, and a torpor with consequent gall-stones or schirrus of
+this viscus is induced with concomitant jaundice; otherwise it becomes
+inflamed in consequence of previous torpor, and this inflammation is
+frequently transferred to a more sensible part, which is associated with
+it, and produces the gout, or the rosy eruption of the face, or some other
+leprous eruption on the head, or arms, or legs. Sometimes the stomach is
+first affected, and paralysis of the lacteal system is induced: whence a
+total abhorrence from flesh-food, and general emaciation. In others the
+lymphatic system is affected with paralysis, and dropsy is the consequence.
+In some inebriates the torpor of the liver produces pain without apparent
+schirrus, or gall stones, or inflammation, or consequent gout, and in these
+epilepsy or insanity are often the consequence. All which will be more
+fully treated of in the course of the work.
+
+I am well aware, that it is a common opinion, that the gout is as
+frequently owing to gluttony in eating, as to intemperance in drinking
+fermented or spirituous liquors. To this I answer, that I have seen no
+person afflicted with the gout, who has not drank freely of fermented
+liquor, as wine and water, or small beer; though as the disposition to all
+the diseases, which have originated from intoxication, is in some degree
+hereditary, a less quantity of spirituous potation will induce the gout in
+those, who inherit the disposition from their parents. To which I must add,
+that in young people the rheumatism is frequently mistaken for the gout.
+
+Spice is seldom taken in such quantity as to do any material injury to the
+system, flesh-meats as well as vegetables are the natural diet of mankind;
+with these a glutton may be crammed up to the throat, and fed fat like a
+stalled ox; but he will not be diseased, unless he adds spirituous or
+fermented liquor to his food. This is well known in the distilleries, where
+the swine, which are fattened by the spirituous sediments of barrels,
+acquire diseased livers. But mark what happens to a man, who drinks a quart
+of wine or of ale, if he has not been habituated to it. He loses the use
+both of his limbs and of his understanding! He becomes a temporary idiot,
+and has a temporary stroke of the palsy! And though he slowly recovers
+after some hours, is it not reasonable to conclude, that a perpetual
+repetition of so powerful a poison must at length permanently affect
+him?--If a person accidentally becomes intoxicated by eating a few
+mushrooms of a peculiar kind, a general alarm is excited, and he is said to
+be poisoned, and emetics are exhibited; but so familiarised are we to the
+intoxication from vinous spirit, that it occasions laughter rather than
+alarm.
+
+There is however considerable danger in too hastily discontinuing the use
+of so strong a stimulus, lest the torpor of the system, or paralysis,
+should sooner be induced by the omission than by the continuance of this
+habit, when unfortunately acquired. A golden rule for determining the
+quantity, which may with safety be discontinued, is delivered in Sect. XII.
+7. 8.
+
+11. Definition of drunkenness. Many of the irritative motions are much
+increased in energy by internal stimulation.
+
+2. A great additional quantity of pleasurable sensation is occasioned by
+this increased exertion of the irritative motions. And many sensitive
+motions are produced in consequence of this increased sensation.
+
+3. The associated trains and tribes of motions, catenated with the
+increased irritative and sensitive motions, are disturbed, and proceed in
+confusion.
+
+4. The faculty of volition is gradually impaired, whence proceeds the
+instability of locomotion, inaccuracy of perception, and inconsistency of
+ideas; and is at length totally suspended, and a temporary apoplexy
+succeeds.
+
+       *       *       *       *       *
+
+SECT. XXII.
+
+OF PROPENSITY TO MOTION, REPETITION AND IMITATION.
+
+    I. _Accumulation of sensorial power in hemiplagia, in sleep, in cold
+    fit of fever, in the locomotive muscles, in the organs of sense.
+    Produces propensity to action._ II. _Repetition by three sensorial
+    powers. In rhimes and alliterations, in music, dancing, architecture,
+    landscape-painting, beauty._ III. 1. _Perception consists in imitation.
+    Four kinds of imitation._ 2. _Voluntary. Dogs taught to dance._ 3.
+    _Sensitive. Hence sympathy, and all our virtues. Contagious matter of
+    venereal ulcers, of hydrophobia, of jail-fever, of small-pox, produced
+    by imitation, and the sex of the embryon._ 4. _Irritative imitation._
+    5. _Imitations resolvable into associations._
+
+I. 1. In the hemiplagia, when the limbs on one side have lost their power
+of voluntary motion, the patient is for many days perpetually employed in
+moving those of the other. 2. When the voluntary power is suspended during
+sleep, there commences a ceaseless flow of sensitive motions, or ideas of
+imagination, which compose our dreams. 3. When in the cold fit of an
+intermittent fever some parts of the system have for a time continued
+torpid, and have thus expended less than their usual expenditure of
+sensorial power; a hot fit succeeds, with violent action of those vessels,
+which had previously been quiescent. All these are explained from an
+accumulation of sensorial power during the inactivity of some part of the
+system.
+
+Besides the very great quantity of sensorial power perpetually produced and
+expended in moving the arterial, venous, and glandular systems, with the
+various organs or digestion, as described in Section XXXII. 3. 2. there is
+also a constant expenditure of it by the action of our locomotive muscles
+and organs of sense. Thus the thickness of the optic nerves, where they
+enter the eye, and the great expansion of the nerves of touch beneath the
+whole of the cuticle, evince the great consumption of sensorial power by
+these senses. And our perpetual muscular actions in the common offices of
+life, and in constantly preserving the perpendicularity of our bodies
+during the day, evince a considerable expenditure of the spirit of
+animation by our locomotive muscles. It follows, that if the exertion of
+these organs of sense and muscles be for a while intermitted, that some
+quantity of sensorial power must be accumulated, and a propensity to
+activity of some kind ensue from the increased excitability of the system.
+Whence proceeds the irksomeness of a continued attitude, and of an indolent
+life.
+
+However small this hourly accumulation of the spirit of animation may be,
+it produces a propensity to some kind of action; but it nevertheless
+requires either desire or aversion, either pleasure or pain, or some
+external stimulus, or a previous link of association, to excite the system
+into activity; thus it frequently happens, when the mind and body are so
+unemployed as not to possess any of the three first kinds of stimuli, that
+the last takes place, and consumes the small but perpetual accumulation of
+sensorial power. Whence some indolent people repeat the same verse for
+hours together, or hum the same tune. Thus the poet:
+
+  Onward he trudged, not knowing what he sought,
+  And whistled, as he went, for want of thought.
+
+II. The repetitions of motions may be at first produced either by volition,
+or by sensation, or by irritation, but they soon become easier to perform
+than any other kinds of action, because they soon become associated
+together, according to Law the seventh, Section IV. on Animal Causation.
+And because their frequency of repetition, if as much sensorial power be
+produced during every reiteration as is expended, adds to the facility of
+their production.
+
+If a stimulus be repeated at uniform intervals of time, as described in
+Sect. XII. 3. 3. the action, whether of our muscles or organs of sense, is
+produced with still greater facility or energy; because the sensorial power
+of association, mentioned above, is combined with the sensorial power of
+irritation; that is, in common language, the acquired habit assists the
+power of the stimulus.
+
+This not only obtains in the annual, lunar, and diurnal catenations of
+animal motions, as explained in Sect. XXXVI. which are thus performed with
+great facility and energy; but in every less circle of actions or ideas, as
+in the burthen of a song, or the reiterations of a dance. To the facility
+and distinctness, with which we hear sounds at repeated intervals, we owe
+the pleasure, which we receive from musical time, and from poetic time; as
+described in Botanic Garden, P. 2. Interlude 3. And to this the pleasure we
+receive from the rhimes and alliterations of modern verification; the
+source of which without this key would be difficult to discover. And to
+this likewise should be ascribed the beauty of the duplicature in the
+perfect tense of the Greek verbs, and of some Latin ones, as tango tetegi,
+mordeo momordi.
+
+There is no variety of notes referable to the gamut in the beating of the
+drum, yet if it be performed in musical time, it is agreeable to our ears;
+and therefore this pleasurable sensation must be owing to the repetition of
+the divisions of the sounds at certain intervals of time, or musical bars.
+Whether these times or bars are distinguished by a pause, or by an
+emphasis, or accent, certain it is, that this distinction is perpetually
+repeated; otherwise the ear could not determine instantly, whether the
+successions of sound were in common or in triple time. In common time there
+is a division between every two crotchets, or other notes of equivalent
+time; though the bar in written music is put after every fourth crotchet,
+or notes equivalent in time; in triple time the division or bar is after
+every three crotchets, or notes equivalent; so that in common time the
+repetition recurs more frequently than in triple time. The grave or heroic
+verses of the Greek and Latin poets are written in common time; the French
+heroic verses, and Mr. Anstie's humorous verses in his Bath Guide, are
+written in the same time as the Greek and Latin verses, but are one bar
+shorter. The English grave or heroic verses are measured by triple time, as
+Mr. Pope's translation of Homer.
+
+But besides these little circles of musical time, there are the greater
+returning periods, and the still more distant choruses, which, like the
+rhimes at the ends of verses, owe their beauty to repetition; that is, to
+the facility and distinctness with which we perceive sounds, which we
+expect to perceive, or have perceived before; or in the language of this
+work, to the greater ease and energy with which our organ is excited by the
+combined sensorial powers of association and irritation, than by the latter
+singly.
+
+A certain uniformity or repetition of parts enters the very composition of
+harmony. Thus two octaves nearest to each other in the scale commence their
+vibrations together after every second vibration of the higher one. And
+where the first, third, and fifth compose a chord the vibrations concur or
+coincide frequently, though less to than in the two octaves. It is probable
+that these chords bear some analogy to a mixture of three alternate colours
+in the sun's spectrum separated by a prism.
+
+The pleasure we receive from a melodious succession of notes referable to
+the gamut is derived from another source, viz. to the pandiculation or
+counteraction of antagonist fibres. See Botanic Garden, P. 2. Interlude 3.
+If to these be added our early associations of agreeable ideas with certain
+proportions of sound, I suppose, from these three sources springs all the
+delight of music, so celebrated by ancient authors, and so enthusiastically
+cultivated at present. See Sect. XVI. No. 10. on Instinct.
+
+This kind of pleasure arising from repetition, that is from the facility
+and distinctness, with which we perceive and understand repeated
+sensations, enters into all the agreeable arts; and when it is carried to
+excess is termed formality. The art of dancing like that of music depends
+for a great part of the pleasure, it affords, on repetition; architecture,
+especially the Grecian, consists of one part being a repetition of another;
+and hence the beauty of the pyramidal outline in landscape-painting; where
+one side of the picture may be said in some measure to balance the other.
+So universally does repetition contribute to our pleasure in the fine arts,
+that beauty itself has been defined by some writers to consist in a due
+combination of uniformity and variety. See Sect. XVI. 6.
+
+III. 1. Man is termed by Aristotle an imitative animal; this propensity to
+imitation not only appears in the actions of children, but in all the
+customs and fashions of the world: many thousands tread in the beaten paths
+of others, for one who traverses regions of his own discovery. The origin
+of this propensity of imitation has not, that I recollect, been deduced
+from any known principle; when any action presents itself to the view of a
+child, as of whetting a knife, or threading a needle, the parts of this
+action in respect of time, motion, figure, is imitated by a part of the
+retina of his eye; to perform this action therefore with his hands is
+easier to him than to invent any new action, because it consists in
+repeating with another set of fibres, viz. with the moving muscles, what he
+had just performed by some parts of the retina; just as in dancing we
+transfer the times of motion from the actions of the auditory nerves to the
+muscles of the limbs. Imitation therefore consists of repetition, which we
+have shewn above to be the easiest kind of animal action, and which we
+perpetually fall into, when we possess an accumulation of sensorial power,
+which is not otherwise called into exertion.
+
+It has been shewn, that our ideas are configurations of the organs of
+sense, produced originally in consequence of the stimulus of external
+bodies. And that these ideas, or configurations of the organs of sense,
+referable in some property a correspondent property of external matter; as
+the parts of the senses of light and of touch, which are excited into
+action, resemble in figure the figure of the stimulating body; and probably
+also the colour, and the quantity of density, which they perceive. As
+explained in Sect. XIV. 2. 2. Hence it appears, that our perceptions
+themselves are copies, that is, imitations of some properties of external
+matter; and the propensity to imitation is thus interwoven with our
+existence, as it is produced by the stimuli of external bodies, and is
+afterwards repeated by our volitions and sensations, and thus constitutes
+all the operations of our minds.
+
+2. Imitations resolve themselves into four kinds, voluntary, sensitive,
+irritative, and associate. The voluntary imitations are, when we imitate
+deliberately the actions of others, either by mimicry, as in acting a play,
+or in delineating a flower; or in the common actions of our lives, as in
+our dress, cookery, language, manners, and even in our habits of thinking.
+
+Not only the greatest part of mankind learn all the common arts of life by
+imitating others, but brute animals seem capable of acquiring knowledge
+with greater facility by imitating each other, than by any methods by which
+we can teach them; as dogs and cats, when they are sick, learn of each
+other to eat grass; and I suppose, that by making an artificial dog perform
+certain tricks, as in dancing on his hinder legs, a living dog might be
+easily induced to imitate them; and that the readiest way of instructing
+dumb animals is by practising them with others of the same species, which
+have already learned the arts we wish to teach them. The important use of
+imitation in acquiring natural language is mentioned in Section XVI. 7. and
+8. on Instinct.
+
+3. The sensitive imitations are the immediate consequences of pleasure or
+pain, and these are often produced even contrary to the efforts of the
+will. Thus many young men on seeing cruel surgical operations become sick,
+and some even feel pain in the parts of their own bodies, which they see
+tortured or wounded in others; that is, they in some measure imitate by the
+exertions of their own fibres the violent actions, which they witnessed in
+those of others. In this case a double imitation takes place, first the
+observer imitates with the extremities of the optic nerve the mangled
+limbs, which are present before his eyes; then by a second imitation he
+excites to violent action of the fibres of his own limbs as to produce pain
+in those parts of his own body, which he saw wounded in another. In these
+pains produced by imitation the effect has some similarity to the cause,
+which distinguishes them from those produced by association; as the pains
+of the teeth, called tooth-edge, which are produced by association with
+disagreeable sounds, as explained in Sect. XVI. 10.
+
+The effect of this powerful agent, imitation, in the moral world, is
+mentioned in Sect. XVI. 7. as it is the foundation of all our intellectual
+sympathies with the pains and pleasures of others, and is in consequence
+the source of all our virtues. For in what consists our sympathy with the
+miseries, or with the joys, of our fellow creatures, but in an involuntary
+excitation of ideas in some measure similar or imitative of those, which we
+believe to exist in the minds of the persons, whom we commiserate or
+congratulate?
+
+There are certain concurrent or successive actions of some of the glands,
+or other parts of the body, which are possessed of sensation, which become
+intelligible from this propensity to imitation. Of these are the production
+of matter by the membranes of the fauces, or by the skin, in consequence of
+the venereal disease previously affecting the parts of generation. Since as
+no fever is excited, and as neither the blood of such patients, nor even
+the matter from ulcers of the throat, or from cutaneous ulcers, will by
+inoculation produce the venereal disease in others, as observed by Mr.
+Hunter, there is reason to conclude, that no contagious matter is conveyed
+thither by the blood-vessels, but that a milder matter is formed by the
+actions of the fine vessels in those membranes imitating each other. See
+Section XXXIII. 2. 9. In this disease the actions of these vessels
+producing ulcers on the throat and skin are imperfect imitations of those
+producing chanker, or gonorrhoea; since the matter produced by them is not
+infectious, while the imitative actions in the hydrophobia appear to be
+perfect resemblances, as they produce a material equally infectious with
+the original one, which induced them.
+
+The contagion from the bite of a mad dog differs from other contagious
+materials, from its being communicable from other animals to mankind, and
+from many animals to each other; the phenomena attending the hydrophobia
+are in some degree explicable on the foregoing theory. The infectious
+matter does not appear to enter the circulation, as it cannot be traced
+along the course of the lymphatics from the wound, nor is there any
+swelling of the lymphatic glands, nor does any fever attend, as occurs in
+the small-pox, and in many other contagious diseases; yet by some unknown
+process the disease is communicated from the wound to the throat, and that
+many months after the injury, so as to produce pain and hydrophobia, with a
+secretion of infectious saliva of the same kind, as that of the mad dog,
+which inflicted the wound.
+
+This subject is very intricate.--It would appear, that by certain morbid
+actions of the salivary glands of the mad dog, a peculiar kind of saliva is
+produced; which being instilled into a wound of another animal stimulates
+the cutaneous or mucous glands into morbid actions, but which are
+ineffectual in respect to the production of a similar contagious material;
+but the salivary glands by irritative sympathy are thrown into similar
+action, and produce an infectious saliva similar to that instilled into the
+wound.
+
+Though in many contagious fevers a material similar to that which produced
+the disease, is thus generated by imitation; yet there are other infectious
+materials, which do not thus propagate themselves, but which seem to act
+like slow poisons. Of this kind was the contagious matter, which produced
+the jail-fever at the assizes at Oxford about a century ago. Which, though
+fatal to so many, was not communicated to their nurses or attendants. In
+these cases, the imitations of the fine vessels, as above described, appear
+to be imperfect, and do not therefore produce a matter similar to that,
+which stimulates them; in this circumstance resembling the venereal matter
+in ulcers of the throat or skin, according to the curious discovery of Mr.
+Hunter above related, who found, by repeated inoculations, that it would
+not infect. Hunter on Venereal Disease, Part vi. ch. 1.
+
+Another example of morbid imitation is in the production of a great
+quantity of contagious matter, as in the inoculated small-pox, from a small
+quantity of it inserted into the arm, and probably diffused in the blood.
+These particles of contagious matter stimulate the extremities of the fine
+arteries of the skin, and cause them to imitate some properties of those
+particles of contagious matter, so as to produce a thousandfold of a
+similar material. See Sect. XXXIII. 2. 6. Other instances are mentioned in
+the Section on Generation, which shew the probability that the extremities
+of the seminal glands may imitate certain ideas of the mind, or actions of
+the organs of sense, and thus occasion the male or female sex of the
+embryon. See Sect. XXXIX. 6.
+
+4. We come now to those imitations, which are not attended with sensation.
+Of these are all the irritative ideas already explained, as when the retina
+of the eye imitates by its action or configuration the tree or the bench,
+which I shun in walking past without attending to them. Other examples of
+these irritative imitations are daily observable in common life; thus one
+yawning person shall set a whole company a yawning; and some have acquired
+winking of the eyes or impediments of speech by imitating their companions
+without being conscious of it.
+
+5. Besides the three species of imitations above described there may be
+some associate motions, which may imitate each other in the kind as well as
+in the quantity of their action; but it is difficult to distinguish them
+from the associations of motions treated of in Section XXXV. Where the
+actions of other persons are imitated there can be no doubt, or where we
+imitate a preconceived idea by exertion of our locomotive muscles, as in
+painting a dragon; all these imitations may aptly be referred to the
+sources above described of the propensity to activity, and the facility of
+repetition; at the same time I do not affirm, that all those other apparent
+sensitive and irritative imitations may not be resolvable into associations
+of a peculiar kind, in which certain distant parts of similar irritability
+or sensibility, and which have habitually acted together, may affect each
+other exactly with the same kinds of motion; as many parts are known to
+sympathise in the quantity of their motions. And that therefore they may be
+ultimately resolvable into associations of action, as described in Sect.
+XXXV.
+
+       *       *       *       *       *
+
+SECT. XXIII.
+
+OF THE CIRCULATORY SYSTEM.
+
+    I. _The heart and arteries have no antagonist muscles. Veins absorb the
+    blood, propel it forwards, and distend the heart; contraction of the
+    heart distends the arteries. Vena portarum._ II. _Glands which take
+    their fluids from the blood. With long necks, with short necks._ III.
+    _Absorbent system._ IV. _Heat given out from glandular secretions.
+    Blood changes colour in the lungs and in the glands and capillaries._
+    V. _Blood is absorbed by veins, as chyle by lacteal vessels, otherwise
+    they could not join their streams._ VI. _Two kinds of stimulus,
+    agreeable and disagreeable. Glandular appetency. Glands originally
+    possessed sensation._
+
+I. We now step forwards to illustrate some of the phenomena of diseases,
+and to trace out their most efficacious methods of cure; and shall commence
+this subject with a short description of the circulatory system.
+
+As the nerves, whose extremities form our various organs of sense and
+muscles, are all joined, or communicate, by means of the brain, for the
+convenience perhaps of the distribution of a subtile ethereal fluid for the
+purpose of motion; so all those vessels of the body, which carry the
+grosser fluids for the purposes of nutrition, communicate with each other
+by the heart.
+
+The heart and arteries are hollow muscles, and are therefore indued with
+power of contraction in consequence of stimulus, like all other muscular
+fibres; but, as they have no antagonist muscles, the cavities of the
+vessels, which they form, would remain for ever closed, after they have
+contracted themselves, unless some extraneous power be applied to again
+distend them. This extraneous power in respect to the heart is the current
+of blood, which is perpetually absorbed by the veins from the various
+glands and capillaries, and pushed into the heart by a power probably very
+similar to that, which raises the sap in vegetables in the spring, which,
+according to Dr. Hale's experiment on the stump of a vine, exerted a force
+equal to a column of water above twenty feet high. This force of the
+current of blood in the veins is partly produced by their absorbent power,
+exerted at the beginning of every fine ramification; which may be conceived
+to be a mouth absorbing blood, as the mouths of the lacteals and lymphatics
+absorb chyle and lymph. And partly by their intermitted compression by the
+pulsations of their generally concomitant arteries; by which the blood is
+perpetually propelled towards the heart, as the valves in many veins, and
+the absorbent mouths in them all, will not suffer it to return.
+
+The blood, thus forcibly injected into the chambers of the heart, distends
+this combination of hollow muscles; till by the stimulus of distention they
+contract themselves; and, pushing forwards the blood into the arteries,
+exert sufficient force to overcome in less than a second of time the vis
+inertiæ, and perhaps some elasticity, of the very extensive ramifications
+of the two great systems of the aortal and pulmonary arteries. The power
+necessary to do this in so short a time must be considerable, and has been
+variously estimated by different physiologists.
+
+The muscular coats of the arterial system are then brought into action by
+the stimulus of distention, and propel the blood to the mouths, or through
+the convolutions, which precede the secretory apertures of the various
+glands and capillaries.
+
+In the vessels of the liver there is no intervention of the heart; but the
+vena portarum, which does the office of an artery, is distended by the
+blood poured into it from the mesenteric veins, and is by this distention
+stimulated to contract itself, and propel the blood to the mouths of the
+numerous glands, which compose that viscus.
+
+II. The glandular system of vessels may be divided into those, which take
+some fluid from the circulation; and those, which give something to it.
+Those, which take their fluid from the circulation are the various glands,
+by which the tears, bile, urine, perspiration, and many other secretions
+are produced; these glands probably consist of a mouth to select, a belly
+to digest, and an excretory aperture to emit their appropriated fluids; the
+blood is conveyed by the power of the heart and arteries to the mouths of
+these glands, it is there taken up by the living power of the gland, and
+carried forwards to its belly, and excretory aperture, where a part is
+separated, and the remainder absorbed by the veins for further purposes.
+
+Some of these glands are furnished with long convoluted necks or tubes, as
+the seminal ones, which are curiously seen when injected with quicksilver.
+Others seem to consist of shorter tubes, as that great congeries of glands,
+which constitute the liver, and those of the kidneys. Some have their
+excretory apertures opening into reservoirs, as the urinary and
+gall-bladders. And others on the external body, as those which secrete the
+tears, and perspirable matter.
+
+Another great system of glands, which have very short necks, are the
+capillary vessels; by which the insensible perspiration is secreted on the
+skin; and the mucus of various consistences, which lubricates the
+interstices of the cellular membrane, of the muscular fibres, and of all
+the larger cavities of the body. From the want of a long convolution of
+vessels some have doubted, whether these capillaries should be considered
+as glands, and have been led to conclude, that the perspirable matter
+rather exuded than was secreted. But the fluid of perspiration is not
+simple water, though that part of it, which exhales into the air may be
+such; for there is another part of it, which in a state of health is
+absorbed again; but which, when the absorbents are diseased, remains on the
+surface of the skin, in the form of scurf, or indurated mucus. Another
+thing, which shews their similitude to other glands, is their sensibility
+to certain affections of the mind; as is seen in the deeper colour of the
+skin in the blush of shame, or the greater paleness of it from fear.
+
+III. Another series of glandular vessels is called the absorbent system;
+these open their mouths into all the cavities, and upon all those surfaces
+of the body, where the excretory apertures of the other glands pour out
+their fluids. The mouths of the absorbent system drink up a part or the
+whole of these fluids, and carry them forwards by their living power to
+their respective glands, which are called conglobate glands. There these
+fluids undergo some change, before they pass on into the circulation; but
+if they are very acrid, the conglobate gland swells, and sometimes
+suppurates, as in inoculation of the small-pox, in the plague, and in
+venereal absorptions; at other times the fluid may perhaps continue there,
+till it undergoes some chemical change, that renders it less noxious; or,
+what is more likely, till it is regurgitated by the retrograde motion of
+the gland in spontaneous sweats or diarrhoeas, as disagreeing food is
+vomited from the stomach.
+
+IV. As all the fluids, that pass through these glands, and capillary
+vessels, undergo a chemical change, acquiring new combinations, the matter
+of heat is at the same time given out; this is apparent, since whatever
+increases insensible perspiration, increases the heat of the skin; and when
+the action of these vessels is much increased but for a moment, as in
+blushing, a vivid heat on the skin is the immediate consequence. So when
+great bilious secretions, or those of any other gland, are produced, heat
+is generated in the part in proportion to the quantity of the secretion.
+
+The heat produced on the skin by blushing may be thought by some too sudden
+to be pronounced a chemical effect, as the fermentations or new
+combinations taking place in a fluid is in general a slower process. Yet
+are there many chemical mixtures in which heat is given out as
+instantaneously; as in solutions of metals in acids, or in mixtures of
+essential oils and acids, as of oil of cloves and acid of nitre. So the
+bruised parts of an unripe apple become almost instantaneously sweet; and
+if the chemico-animal process of digestion be stopped for but a moment, as
+by fear, or even by voluntary eructation, a great quantity of air is
+generated, by the fermentation, which instantly succeeds the stop of
+digestion. By the experiments of Dr. Hales it appears, that an apple during
+fermentation gave up above six hundred times its bulk of air; and the
+materials in the stomach are such, and in such a situation, as immediately
+to run into fermentation, when digestion is impeded.
+
+As the blood passes through the small vessels of the lungs, which connect
+the pulmonary artery and vein, it undergoes a change of colour from a dark
+to a light red; which may be termed a chemical change, as it is known to be
+effected by an admixture of oxygene, or vital air; which, according to a
+discovery of Dr. Priestley, passes through the moist membranes, which
+constitute the sides of these vessels. As the blood passes through the
+capillary vessels, and glands, which connect the aorta and its various
+branches with their correspondent veins in the extremities of the body, it
+again loses the bright red colour, and undergoes some new combinations in
+the glands or capillaries, in which the matter of heat is given out from
+the secreted fluids. This process therefore, as well as the process of
+respiration, has some analogy to combustion, as the vital air or oxygene
+seems to become united to some inflammable base, and the matter of heat
+escapes from the new acid, which is thus produced.
+
+V. After the blood has passed these glands and capillaries, and parted with
+whatever they chose to take from it, the remainder is received by the
+veins, which are a set of blood-absorbing vessels in general corresponding
+with the ramifications of the arterial system. At the extremity of the fine
+convolutions of the glands the arterial force ceases; this in respect to
+the capillary vessels, which unite the extremities of the arteries with the
+commencement of the veins, is evident to the eye, on viewing the tail of a
+tadpole by means of a solar, or even by a common microscope, for globules
+of blood are seen to endeavour to pass, and to return again and again,
+before they become absorbed by the mouths of the veins; which returning of
+these globules evinces, that the arterial force behind them has ceased. The
+veins are furnished with valves like the lymphatic absorbents; and the
+great trunks of the veins, and of the lacteals and lymphatics, join
+together before the ingress of their fluids into the left chamber of the
+heart; both which evince, that the blood in the veins, and the lymph and
+chyle in the lacteals and lymphatics, are carried on by a similar force;
+otherwise the stream, which was propelled with a less power, could not
+enter the vessels, which contained the stream propelled with a greater
+power. From whence it appears, that the veins are a system of vessels
+absorbing blood, as the lacteals and lymphatics are a system of vessels
+absorbing chyle and lymph. See Sect. XXVII. 1.
+
+VI. The movements of their adapted fluids in the various vessels of the
+body are carried forwards by the actions of those vessels in consequence of
+two kinds of stimulus, one of which may be compared to a pleasurable
+sensation or desire inducing the vessel to seize, and, as it were, to
+swallow the particles thus selected from the blood; as is done by the
+mouths of the various glands, veins, and other absorbents, which may be
+called glandular appetency. The other kind of stimulus may be compared to
+disagreeable sensation, or aversion, as when the heart has received the
+blood, and is stimulated by it to push it forwards into the arteries; the
+same again stimulates the arteries to contract, and carry forwards the
+blood to their extremities, the glands and capillaries. Thus the mesenteric
+veins absorb the blood from the intestines by glandular appetency, and
+carry it forward to the vena portarum; which acting as an artery contracts
+itself by disagreeable stimulus, and pushes it to its ramified extremities,
+the various glands, which constitute the liver.
+
+It seems probable, that at the beginning of the formation of these vessels
+in the embryon, an agreeable sensation was in reality felt by the glands
+during secretion, as is now felt in the act of swallowing palatable food;
+and that a disagreeable sensation was originally felt by the heart from the
+distention occasioned by the blood, or by its chemical stimulus; but that
+by habit these are all become irritative motions; that is, such motions as
+do not affect the whole system, except when the vessels are diseased by
+inflammation.
+
+       *       *       *       *       *
+
+SECT. XXIV.
+
+OF THE SECRETIONS OF SALIVA, AND OF TEARS, AND OF THE LACRYMAL SACK.
+
+    I. _Secretion of saliva increased by mercury in the blood._ 1. _By the
+    food in the mouth. Dryness of the mouth not from a deficiency of
+    saliva._ 2. _By Sensitive ideas._ 3. _By volition._ 4. _By distasteful
+    substances. It is secreted in a dilute and saline state. It then
+    becomes more viscid._ 5. _By ideas of distasteful substances._ 6. _By
+    nausea._ 7. _By aversion._ 8. _By catenation with stimulating
+    substances in the ear._ II. 1. _Secretion of tears less in sleep. From
+    stimulation of their excretory duct._ 2. _Lacrymal sack is a gland._ 3.
+    _Its uses._ 4. _Tears are secreted, when the nasal duct is stimulated._
+    5. _Or when it is excited by sensation._ 6. _Or by volition._ 7. _The
+    lacrymal sack can regurgitate its contents into the eye._ 8. _More
+    tears are secreted by association with the irritation of the nasal duct
+    of the lacrymal sack, than the puncta lacrymalia can imbibe. Of the
+    gout in the liver and stomach._
+
+I. The salival glands drink up a certain fluid from the circumfluent blood,
+and pour it into the mouth. They are sometimes stimulated into action by
+the blood, that surrounds their origin, or by some part of that
+heterogeneous fluid: for when mercurial salts, or oxydes, are mixed with
+the blood, they stimulate these glands into unnatural exertions; and then
+an unusual quantity of saliva is separated.
+
+1. As the saliva secreted by these glands is most wanted during the
+mastication of our food, it happens, when the terminations of their ducts
+in the mouth are stimulated into action, the salival glands themselves are
+brought into increased action at the same time by association, and separate
+a greater quantity of their juices from the blood; in the same manner as
+tears are produced in greater abundance during the stimulus of the vapour
+of onions, or of any other acrid material in the eye.
+
+The saliva is thus naturally poured into the mouth only during the stimulus
+of our food in mastication; for when there is too great an exhalation of
+the mucilaginous secretion from the membranes, which line the mouth, or too
+great an absorption of it, the mouth becomes dry, though there is no
+deficiency in the quantity of saliva; as in those who sleep with their
+mouths open, and in some fevers.
+
+2. Though during the mastication of our natural food the salival glands are
+excited into action by the stimulus on their excretory ducts, and a due
+quantity of saliva is separated from the blood, and poured into the mouth;
+yet as this mastication of our food is always attended with a degree of
+pleasure; and that pleasurable sensation is also connected with our ideas
+of certain kinds of aliment; it follows, that when these ideas are
+reproduced, the pleasurable sensation arises along with them, and the
+salival glands are excited into action, and fill the mouth with saliva from
+this sensitive association, as is frequently seen in dogs, who slaver at
+the sight of food.
+
+3. We have also a voluntary power over the action of these salival glands,
+for we can at any time produce a flow of saliva into our mouth, and spit
+out, or swallow it at will.
+
+4. If any very acrid material be held in the mouth, as the root of
+pyrethrum, or the leaves of tobacco, the salival glands are stimulated into
+stronger action than is natural, and thence secrete a much larger quantity
+of saliva; which is at the same time more viscid than in its natural state;
+because the lymphatics, that open their mouths into the ducts of the
+salival glands, and on the membranes, which line the mouth, are likewise
+stimulated into stronger action, and absorb the more liquid parts of the
+saliva with greater avidity; and the remainder is left both in greater
+quantity and more viscid.
+
+The increased absorption in the mouth by some stimulating substances, which
+are called astringents, as crab juice, is evident from the instant dryness
+produced in the mouth by a small quantity of them.
+
+As the extremities of the glands are of exquisite tenuity, as appears by
+their difficulty of injection, it was necessary for them to secrete their
+fluids in a very dilute state; and, probably for the purpose of stimulating
+them into action, a quantity of neutral salt is likewise secreted or formed
+by the gland. This aqueous and saline part of all secreted fluids is again
+reabsorbed into the habit. More than half of some secreted fluids is thus
+imbibed from the reservoirs, into which they are poured; as in the urinary
+bladder much more than half of what is secreted by the kidneys becomes
+reabsorbed by the lymphatics, which are thickly dispersed around the neck
+of the bladder. This seems to be the purpose of the urinary bladders of
+fish, as otherwise such a receptacle for the urine could have been of no
+use to an animal immersed in water.
+
+5. The idea of substances disagreeably acrid will also produce a quantity
+of saliva in the mouth; as when we smell very putrid vapours, we are
+induced to spit out our saliva, as if something disagreeable was actually
+upon our palates.
+
+6. When disagreeable food in the stomach produces nausea, a flow of saliva
+is excited in the mouth by association; as efforts to vomit are frequently
+produced by disagreeable drugs in the mouth by the same kind of
+association.
+
+7. A preternatural flow of saliva is likewise sometimes occasioned by a
+disease of the voluntary power; for if we think about our saliva, and
+determine not to swallow it, or not to spit it out, an exertion is produced
+by the will, and more saliva is secreted against our wish; that is, by our
+aversion, which bears the same analogy to desire, as pain does to pleasure;
+as they are only modifications of the same disposition of the sensorium.
+See Class IV. 3. 2. 1.
+
+8. The quantity of saliva may also be increased beyond what is natural, by
+the catenation of the motions of these glands with other motions, or
+sensations, as by an extraneous body in the ear; of which I have known an
+instance; or by the application of stizolobium, siliqua hirsuta, cowhage,
+to the seat of the parotis, as some writers have affirmed.
+
+II. 1. The lacrymal gland drinks up a certain fluid from the circumfluent
+blood, and pours it on the ball of the eye, on the upper part of the
+external corner of the eyelids. Though it may perhaps be stimulated into
+the performance of its natural action by the blood, which surrounds its
+origin, or by some part of that heterogeneous fluid; yet as the tears
+secreted by this gland are more wanted at some times than at others, its
+secretion is variable, like that of the saliva above mentioned, and is
+chiefly produced when its excretory duct is stimulated; for in our common
+sleep there seems to be little or no secretion of tears; though they are
+occasionally produced by our sensations in dreams.
+
+Thus when any extraneous material on the eye-ball, or the dryness of the
+external covering of it, or the coldness of the air, or the acrimony of
+some vapours, as of onions, stimulates the excretory duct of the lacrymal
+gland, it discharges its contents upon the ball; a quicker secretion takes
+place in the gland, and abundant tears succeed, to moisten, clean, and
+lubricate the eye. These by frequent nictitation are diffused over the
+whole ball, and as the external angle of the eye in winking is closed
+sooner than the internal angle, the tears are gradually driven forwards,
+and downwards from the lacrymal gland to the puncta lacrymalia.
+
+2. The lacrymal sack, with its puncta lacrymalia, and its nasal duct, is a
+complete gland; and is singular in this respect, that it neither derives
+its fluid from, nor disgorges it into the circulation. The simplicity of
+the structure of this gland, and both the extremities of it being on the
+surface of the body, makes it well worthy our minuter observation; as the
+actions of more intricate and concealed glands may be better understood
+from their analogy to this.
+
+3. This simple gland consists of two absorbing mouths, a belly, and an
+excretory duct. As the tears are brought to the internal angle of the eye,
+these two mouths drink them up, being stimulated into action by this fluid,
+which they absorb. The belly of the gland, or lacrymal sack, is thus
+filled, in which the saline part of the tears is absorbed, and when the
+other end of the gland, or nasal duct, is stimulated by the dryness, or
+pained by the coldness of the air, or affected by any acrimonious dust or
+vapour in the nostrils, it is excited into action together with the sack,
+and the tears are disgorged upon the membrane, which lines the nostrils;
+where they serve a second purpose to moisten, clean, and lubricate, the
+organ of smell.
+
+4. When the nasal duct of this gland is stimulated by any very acrid
+material, as the powder of tobacco, or volatile spirits, it not only
+disgorges the contents of its belly or receptacle (the lacrymal sack), and
+absorbs hastily all the fluid, that is ready for it in the corner of the
+eye; but by the association of its motions with those of the lacrymal
+gland, it excites that also into increased action, and a large flow of
+tears is poured into the eye.
+
+5. This nasal duct is likewise excited into strong action by sensitive
+ideas, as in grief, or joy, and then also by its associations with the
+lacrymal gland it produces a great flow of tears without any external
+stimulus; as is more fully explained in Sect. XVI. 8. on Instinct.
+
+6. There are some, famous in the arts of exciting compassion, who are said
+to have acquired a voluntary power of producing a flow of tears in the eye;
+which, from what has been said in the section on Instinct above mentioned,
+I should suspect, is performed by acquiring a voluntary power over the
+action of this nasal duct.
+
+7. There is another circumstance well worthy our attention, that when by
+any accident this nasal duct is obstructed, the lacrymal sack, which is the
+belly or receptacle of this gland, by slight pressure of the finger is
+enabled to disgorge its contents again into the eye; perhaps the bile in
+the same manner, when the biliary ducts are obstructed, is returned into
+the blood by the vessels which secrete it?
+
+8. A very important though minute occurrence must here be observed, that
+though the lacrymal gland is only excited into action, when we weep at a
+distressful tale, by its association with this nasal duct, as is more fully
+explained in Sect. XVI. 8; yet the quantity of tears secreted at once is
+more than the puncta lacrymalia can readily absorb; which shews _that the
+motions occasioned by associations are frequently more energetic than the
+original motions, by which they were occasioned_. Which we shall have
+occasion to mention hereafter, to illustrate, why pains frequently exist in
+a part distant from the cause of them, as in the other end of the urethra,
+when a stone stimulates the neck of the bladder. And why inflammations
+frequently arise in parts distant from their cause, as the gutta rosea of
+drinking people, from an inflamed liver.
+
+The inflammation of a part is generally preceded by a torpor or quiescence
+of it; if this exists in any large congeries of glands, as in the liver, or
+any membranous part, as the stomach, pain is produced and chilliness in
+consequence of the torpor of the vessels. In this situation sometimes an
+inflammation of the parts succeeds the torpor; at other times a distant
+more sensible part becomes inflamed; whose actions have previously been
+associated with it; and the torpor of the first part ceases. This I
+apprehend happens, when the gout of the foot succeeds a pain of the biliary
+duct, or of the stomach. Lastly, it sometimes happens, that the pain of
+torpor exists without any consequent inflammation of the affected part, or
+of any distant part associated with it, as in the membranes about the
+temple and eye-brows in hemicrania, and in those pains, which occasion
+convulsions; if this happens to gouty people, when it affects the liver, I
+suppose epileptic fits are produced; and, when it affects the stomach,
+death is the consequence. In these cases the pulse is weak, and the
+extremities cold, and such medicines as stimulate the quiescent parts into
+action, or which induce inflammation in them, or in any distant part, which
+is associated with them, cures the present pain of torpor, and saves the
+patient.
+
+I have twice seen a gouty inflammation of the liver, attended with
+jaundice; the patients after a few days were both of them affected with
+cold fits, like ague-fits, and their feet became affected with gout, and
+the inflammation of their livers ceased. It is probable, that the uneasy
+sensations about the stomach, and indigestion, which precedes gouty
+paroxysms, are generally owing to torpor or slight inflammation of the
+liver, and biliary ducts; but where great pain with continued sickness,
+with feeble pulse, and sensation of cold, affect the stomach in patients
+debilitated by the gout, that it is a torpor of the stomach itself, and
+destroys the patient from the great connexion of that viscus with the vital
+organs. See Sect. XXV. 17.
+
+       *       *       *       *       *
+
+SECT. XXV.
+
+OF THE STOMACH AND INTESTINES.
+
+    1. _Of swallowing our food. Ruminating animals._ 2. _Action of the
+    stomach._ 3. _Action of the intestines. Irritative motions connected
+    with these._ 4. _Effects of repletion._ 5. _Stronger action of the
+    stomach and intestines from more stimulating food._ 6. _Their action
+    inverted by still greater stimuli. Or by disgustful ideas. Or by
+    volition._ 7. _Other glands strengthen or invert their motions by
+    sympathy._ 8. _Vomiting performed by intervals._ 9. _Inversion of the
+    cutaneous absorbents._ 10. _Increased secretion of bile and pancreatic
+    juice._ 11. _Inversion of the lacteals._ 12. _And of the bile-ducts._
+    13. _Case of a cholera._ 14. _Further account of the inversion of
+    lacteals._ 15. _Iliac passions. Valve of the colon._ 16. _Cure of the
+    iliac passion._ 17. _Pain of gall-stone distinguished from pain of the
+    stomach. Gout of the stomach from torpor, from inflammation.
+    Intermitting pulse owing to indigestion. To overdose of foxglove. Weak
+    pulse from emetics. Death from a blow on the stomach. From gout of the
+    stomach._
+
+1. The throat, stomach, and intestines, may be considered as one great
+gland; which like the lacrymal sack above mentioned, neither begins nor
+ends in the circulation. Though the act of masticating our aliment belongs
+to the sensitive class of motions, for the pleasure of its taste induces
+the muscles of the jaw into action; yet the deglutition of it when
+masticated is generally, if not always, an irritative motion, occasioned by
+the application of the food already masticated to the origin of the
+pharinx; in the same manner as we often swallow our spittle without
+attending to it.
+
+The ruminating class of animals have the power to invert the motion of
+their gullet, and of their first stomach, from the stimulus of this
+aliment, when it is a little further prepared; as is their daily practice
+in chewing the cud; and appears to the eye of any one, who attends to them,
+whilst they are employed in this second mastication of their food.
+
+2. When our natural aliment arrives into the stomach, this organ is
+simulated into its proper vermicular action; which beginning at the upper
+orifice of it, and terminating at the lower one, gradually mixes together
+and pushes forwards the digesting materials into the intestine beneath it.
+
+At the same time the glands, that supply the gastric juices, which are
+necessary to promote the chemical part of the process of digestion, are
+stimulated to discharge their contained fluids, and to separate a further
+supply from the blood-vessels: and the lacteals or lymphatics, which open
+their mouths into the stomach, are stimulated into action, and take up some
+part of the digesting materials.
+
+3. The remainder of these digesting materials is carried forwards into the
+upper intestines, and stimulates them into their peristaltic motion similar
+to that of the stomach; which continues gradually to mix the changing
+materials, and pass them along through the valve of the colon to the
+excretory end of this great gland, the sphincter ani.
+
+The digesting materials produce a flow of bile, and of pancreatic juice, as
+they pass along the duodenum, by stimulating the excretory ducts of the
+liver and pancreas, which terminate in that intestine: and other branches
+of the absorbent or lymphatic system, called lacteals, are excited to drink
+up, as it passes, those parts of the digesting materials, that are proper
+for their purpose, by its stimulus on their mouths.
+
+4. When the stomach and intestines are thus filled with their proper food,
+not only the motions of the gastric glands, the pancreas, liver, and
+lacteal vessels, are excited into action; but at the same time the whole
+tribe of irritative motions are exerted with greater energy, a greater
+degree of warmth, colour, plumpness, and moisture, is given to the skin
+from the increased action of those glands called capillary vessels;
+pleasurable sensation is excited, the voluntary motions are less easily
+exerted, and at length suspended; and sleep succeeds, unless it be
+prevented by the stimulus of surrounding objects, or by voluntary exertion,
+or by an acquired habit, which was originally produced by one or other of
+these circumstances, as is explained in Sect. XXI. on Drunkenness.
+
+At this time also, as the blood-vessels become replete with chyle, more
+urine is separated into the bladder, and less of it is reabsorbed; more
+mucus poured into the cellular membranes, and less of it reabsorbed; the
+pulse becomes fuller, and softer, and in general quicker. The reason why
+less urine and cellular mucus is absorbed after a full meal with sufficient
+drink is owing to the blood-vessels being fuller: hence one means to
+promote absorption is to decrease the resistance by emptying the vessels by
+venesection. From this decreased absorption the urine becomes pale as well
+as copious, and the skin appears plump as well as florid.
+
+By daily repetition of these movements they all become connected together,
+and make a diurnal circle of irritative action, and if one of this chain be
+disturbed, the whole is liable to be put into disorder. See Sect. XX. on
+Vertigo.
+
+5. When the stomach and intestines receive a quantity of food, whose
+stimulus is greater than usual, all their motions, and those of the glands
+and lymphatics, are stimulated into stronger action than usual, and perform
+their offices with greater vigour and in less time: such are the effects of
+certain quantities of spice or of vinous spirit.
+
+6. But if the quantity or duration of these stimuli are still further
+increased, the stomach and throat are stimulated into a motion, whose
+direction is contrary to the natural one above described; and they
+regurgitate the materials, which they contain, instead of carrying them
+forwards. This retrograde motion of the stomach may be compared to the
+stretchings of wearied limbs the contrary way, and is well elucidated by
+the following experiment. Look earnestly for a minute or two on an area an
+inch square of pink silk, placed in a strong light, the eye becomes
+fatigued, the colour becomes faint, and at length vanishes, for the
+fatigued eye can no longer be stimulated into direct motions; then on
+closing the eye a green spectrum will appear in it, which is a colour
+directly contrary to pink, and which will appear and disappear repeatedly,
+like the efforts in vomiting. See Section XXIX. 11.
+
+Hence all those drugs, which by their bitter or astringent stimulus
+increase the action of the stomach, as camomile and white vitriol, if their
+quantity is increased above a certain dose become emetics.
+
+These inverted motions of the stomach and throat are generally produced
+from the stimulus of unnatural food, and are attended with the sensation of
+nausea or sickness: but as this sensation is again connected with an idea
+of the distasteful food, which induced it; so an idea of nauseous food will
+also sometimes excite the action of nausea; and that give rise by
+association to the inversion of the motions of the stomach and throat. As
+some, who have had horse-flesh or dogs-flesh given them for beef or mutton,
+are said to have vomited many hours afterwards, when they have been told of
+the imposition.
+
+I have been told of a person, who had gained a voluntary command over these
+inverted motions of the stomach and throat, and supported himself by
+exhibiting this curiosity to the public. At these exhibitions he swallowed
+a pint of red rough gooseberries, and a pint of white smooth ones, brought
+them up in small parcels into his mouth, and restored them separately to
+the spectators, who called for red or white as they pleased, till the whole
+were redelivered.
+
+7. At the same time that these motions of the stomach and throat are
+stimulated into inversion, some of the other irritative motions, that had
+acquired more immediate connexions with the stomach, as those of the
+gastric glands, are excited into stronger action by this association; and
+some other of these motions, which are more easily excited, as those of the
+gastric lymphatics, are inverted by their association with the retrograde
+motions of the stomach, and regurgitate their contents, and thus a greater
+quantity of mucus, and of lymph, or chyle, is poured into the stomach, and
+thrown up along with its contents.
+
+8. These inversions of the motion of the stomach in vomiting are performed
+by intervals, for the same reason that many other motions are reciprocally
+exerted and relaxed; for during the time of exertion the stimulus, or
+sensation, which caused this exertion, is not perceived; but begins to be
+perceived again, as soon as the exertion ceases, and is some time in again
+producing its effect. As explained in Sect. XXXIV. on Volition, where it is
+shewn, that the contractions of the fibres, and the sensation of pain,
+which occasioned that exertion, cannot exist at the same time. The exertion
+ceases from another cause also, which is the exhaustion of the sensorial
+power of the part, and these two causes frequently operate together.
+
+9. At the times of these inverted efforts of the stomach not only the
+lymphatics, which open their mouths into the stomach, but those of the skin
+also, are for a time inverted; for sweats are sometimes pushed out during
+the efforts of vomiting without an increase of heat.
+
+10. But if by a greater stimulus the motions of the stomach are inverted
+still more violently or more permanently, the duodenum has its peristaltic
+motions inverted at the same time by their association with those of the
+stomach; and the bile and pancreatic juice, which it contains, are by the
+inverted motions brought up into the stomach, and discharged along with its
+contents; while a greater quantity of bile and pancreatic juice is poured
+into this intestine; as the glands, that secrete them, are by their
+association with the motions of the intestine excited into stronger action
+than usual.
+
+11. The other intestines are by association excited into more powerful
+action, while the lymphatics, that open their mouths into them, suffer an
+inversion of their motions corresponding with the lymphatics of the
+stomach, and duodenum; which with a part of the abundant secretion of bile
+is carried downwards, and contributes both to stimulate the bowels, and to
+increase the quantity of the evacuations. This inversion of the motion of
+the lymphatics appears from the quantity of chyle, which comes away by
+stools; which is otherwise absorbed as soon as produced, and by the immense
+quantity of thin fluid, which is evacuated along with it.
+
+12. But if the stimulus, which inverts the stomach, be still more powerful,
+or more permanent, it sometimes happens, that the motions of the biliary
+glands, and of their excretory ducts, are at the same time inverted, and
+regurgitate their contained bile into the blood-vessels, as appears by the
+yellow colour of the skin, and of the urine; and it is probable the
+pancreatic secretion may suffer an inversion at the same time, though we
+have yet no mark by which this can be ascertained.
+
+13. Mr. ---- eat two putrid pigeons out of a cold pigeon-pye, and drank
+about a pint of beer and ale along with them, and immediately rode about
+five miles. He was then seized with vomiting, which was after a few periods
+succeeded by purging; these continued alternately for two hours; and the
+purging continued by intervals for six or eight hours longer. During this
+time he could not force himself to drink more than one pint in the whole;
+this great inability to drink was owing to the nausea, or inverted motions
+of the stomach, which the voluntary exertion of swallowing could seldom and
+with difficulty overcome; yet he discharged in the whole at least six
+quarts; whence came this quantity of liquid? First, the contents of the
+stomach were emitted, then of the duodenum, gall-bladder, and pancreas, by
+vomiting. After this the contents of the lower bowels, then the chyle, that
+was in the lacteal vessels, and in the receptacle of chyle, was
+regurgitated into the intestines by a retrograde motion of these vessels.
+And afterwards the mucus deposited in the cellular membrane, and on the
+surface of all the other membranes, seems to have been absorbed; and with
+the fluid absorbed from the air to have been carried up their respective
+lymphatic branches by the increased energy of their natural motions, and
+down the visceral lymphatics, or lacteals, by the inversion of their
+motions.
+
+14. It may be difficult to invent experiments to demonstrate the truth of
+this inversion of some branches of the absorbent system, and increased
+absorption of others, but the analogy of these vessels to the intestinal
+canal, and the symptoms of many diseases, render this opinion more probable
+than many other received opinions of the animal oeconomy.
+
+In the above instance, after the yellow excrement was voided, the fluid
+ceased to have any smell, and appeared like curdled milk, and then a
+thinner fluid, and some mucus, were evacuated; did not these seem to
+partake of the chyle, of the mucous fluid from all the cells of the body,
+and lastly, of the atmospheric moisture? All these facts may be easily
+observed by any one, who takes a brisk purge.
+
+15. Where the stimulus on the stomach, or on some other part of the
+intestinal canal, is still more permanent, not only the lacteal vessels,
+but the whole canal itself, becomes inverted from its associations: this is
+the iliac passion, in which all the fluids mentioned above are thrown up by
+the mouth. At this time the valve in the colon, from the inverted motions
+of that bowel, and the inverted action of this living valve, does not
+prevent the regurgitation of its contents.
+
+The structure of this valve may be represented by a flexile leathern pipe
+standing up from the bottom of a vessel of water: its sides collapse by the
+pressure of the ambient fluid, as a small part of that fluid passes through
+it; but if it has a living power, and by its inverted action keeps itself
+open, it becomes like a rigid pipe, and will admit the whole liquid to
+pass. See Sect. XXIX. 2. 5.
+
+In this case the patient is averse to drink, from the constant inversion of
+the motions of the stomach, and yet many quarts are daily ejected from the
+stomach, which at length smell of excrement, and at last seem to be only a
+thin mucilaginous or aqueous liquor.
+
+From whence is it possible, that this great quantity of fluid for many
+successive days can be supplied, after the cells of the body have given up
+their fluids, but from the atmosphere? When the cutaneous branch of
+absorbents acts with unnatural strength, it is probable the intestinal
+branch has its motions inverted, and thus a fluid is supplied without
+entering the arterial system. Could oiling or painting the skin give a
+check to this disease?
+
+So when the stomach has its motions inverted, the lymphatics of the
+stomach, which are most strictly associated with it, invert their motions
+at the same time. But the more distant branches of lymphatics, which are
+less strictly associated with it, act with increased energy; as the
+cutaneous lymphatics in the cholera, or iliac passion, above described. And
+other irritative motions become decreased, as the pulsations of the
+arteries, from the extra-derivation or exhaustion of the sensorial power.
+
+Sometimes when stronger vomiting takes place the more distant branches of
+the lymphatic system invert their motions with those of the stomach, and
+loose stools are produced, and cold sweats.
+
+So when the lacteals have their motions inverted, as during the operation
+of strong purges, the urinary and cutaneous absorbents have their motions
+increased to supply the want of fluid in the blood, as in great thirst; but
+after a meal with sufficient potation the urine is pale, that is, the
+urinary absorbents act weakly, no supply of water being wanted for the
+blood. And when the intestinal absorbents act too violently, as when too
+great quantities of fluid have been drank, the urinary absorbents invert
+their motions to carry off the superfluity, which is a new circumstance of
+association, and a temporary diabetes supervenes.
+
+16. I have had the opportunity of seeing four patients in the iliac
+passion, where the ejected material smelled and looked like excrement. Two
+of these were so exhausted at the time I saw them, that more blood could
+not be taken from them, and as their pain had ceased, and they continued to
+vomit up every thing which they drank, I suspected that a mortification of
+the bowel had already taken place, and as they were both women advanced in
+life, and a mortification is produced with less preceding pain in old and
+weak people, these both died. The other two, who were both young men, had
+still pain and strength sufficient for further venesection, and they
+neither of them had any appearance of hernia, both recovered by repeated
+bleeding, and a scruple of calomel given to one, and half a dram to the
+other, in very small pills: the usual means of clysters, and purges joined
+with opiates, had been in vain attempted. I have thought an ounce or two of
+crude mercury in less violent diseases of this kind has been of use, by
+contributing to restore its natural motion to some part of the intestinal
+canal, either by its weight or stimulus; and that hence the whole tube
+recovered its usual associations of progressive peristaltic motion. I have
+in three cases seen crude mercury given in small doses, as one or two
+ounces twice a day, have great effect in stopping pertinacious vomitings.
+
+17. Besides the affections above described, the stomach is liable, like
+many other membranes of the body, to torpor without consequent
+inflammation: as happens to the membranes about the head in some cases of
+hemicrania, or in general head-ach. This torpor of the stomach is attended
+with indigestion, and consequent flatulency, and with pain, which is
+usually called the cramp of the stomach, and is relievable by aromatics,
+essential oils, alcohol, or opium.
+
+The intrusion of a gall-stone into the common bile-duct from the
+gall-bladder is sometimes mistaken for a pain of the stomach, as neither of
+them are attended with fever; but in the passage of a gall-stone, the pain
+is confined to a less space, which is exactly where the common bile-duct
+enters the duodenum, as explained in Section XXX. 1. 3. Whereas in this
+gastrodynia the pain is diffused over the whole stomach; and, like other
+diseases from torpor, the pulse is weaker, and the extremities colder, and
+the general debility greater, than in the passage of a gall-stone; for in
+the former the debility is the consequence of the pain, in the latter it is
+the cause of it.
+
+Though the first fits of the gout, I believe, commence with a torpor of the
+liver; and the ball of the toe becomes inflamed instead of the membranes of
+the liver in consequence of this torpor, as a coryza or catarrh frequently
+succeeds a long exposure of the feet to cold, as in snow, or on a moist
+brick-floor; yet in old or exhausted constitutions, which have been long
+habituated to its attacks, it sometimes commences with a torpor of the
+stomach, and is transferable to every membrane of the body. When the gout
+begins with torpor of the stomach, a painful sensation of cold occurs,
+which the patient compares to ice, with weak pulse, cold extremities, and
+sickness; this in its slighter degree is relievable by spice, wine, or
+opium; in its greater degree it is succeeded by sudden death, which is
+owing to the sympathy of the stomach with the heart, as explained below.
+
+If the stomach becomes inflamed in consequence of this gouty torpor of it,
+or in consequence of its sympathy with some other part, the danger is less.
+A sickness and vomiting continues many days, or even weeks, the stomach
+rejecting every thing stimulant, even opium or alcohol, together with much
+viscid mucus; till the inflammation at length ceases, as happens when other
+membranes, as those of the joints, are the seat of gouty inflammation; as
+observed in Sect. XXIV. 2. 8.
+
+The sympathy, or association of motions, between those of the stomach and
+those of the heart, are evinced in many diseases. First, many people are
+occasionally affected with an intermission of their pulse for a few days,
+which then ceases again. In this case there is a stop of the motion of the
+heart, and at the same time a tendency to eructation from the stomach. As
+soon as the patient feels a tendency to the intermission of the motion of
+his heart, if he voluntarily brings up wind from his stomach, the stop of
+the heart does not occur. From hence I conclude that the stop of digestion
+is the primary disease; and that air is instantly generated from the
+aliment, which begins to ferment, if the digestive process is impeded for a
+moment, (see Sect. XXIII. 4.); and that the stop of the heart is in
+consequence of the association of the motions of these viscera, as
+explained in Sect. XXXV. 1. 4.; but if the little air, which is instantly
+generated during the temporary torpor of the stomach, be evacuated, the
+digestion recommences, and the temporary torpor of the heart does not
+follow. One patient, whom I lately saw, and who had been five or six days
+much troubled with this intermission of a pulsation of his heart, and who
+had hemicrania with some fever, was immediately relieved from them all by
+losing ten ounces of blood, which had what is termed an inflammatory crust
+on it.
+
+Another instance of this association between the motions of the stomach and
+heart is evinced by the exhibition of an over dose of foxglove, which
+induces an incessant vomiting, which is attended with very slow, and
+sometimes intermitting pulse.--Which continues in spite of the exhibition
+of wine and opium for two or three days. To the same association must be
+ascribed the weak pulse, which constantly attends the exhibition of emetics
+during their operation. And also the sudden deaths, which have been
+occasioned in boxing by a blow on the stomach; and lastly, the sudden death
+of those, who have been long debilitated by the gout, from the torpor of
+the stomach. See Sect. XXXV. 1. 4.
+
+       *       *       *       *       *
+
+SECT. XXVI.
+
+OF THE CAPILLARY GLANDS AND MEMBRANES.
+
+    I. 1. _The capillary vessels are glands._ 2. _Their excretory ducts.
+    Experiments on the mucus of the intestines, abdomen, cellular membrane,
+    and on the humours of the eye._ 3. _Scurf on the head, cough, catarrh,
+    diarrhoea, gonorrhoea._ 4. _Rheumatism. Gout. Leprosy._ II. 1. _The
+    most minute membranes are unorganized._ 2. _Larger membranes are
+    composed of the ducts of the capillaries, and the mouths of the
+    absorbents._ 3. _Mucilaginous fluid is secreted on their surfaces._
+    III. _Three kinds of rheumatism._
+
+I. 1. The capillary-vessels are like all the other glands except the
+absorbent system, inasmuch as they receive blood from the arteries,
+separate a fluid from it, and return the remainder by the veins.
+
+2. This series of glands is of the most extensive use, as their excretory
+ducts open on the whole external skin forming its perspirative pores, and
+on the internal surfaces of every cavity of the body. Their secretion on
+the skin is termed insensible perspiration, which in health is in part
+reabsorbed by the mouths of the lymphatics, and in part evaporated in the
+air; the secretion on the membranes, which line the larger cavities of the
+body, which have external openings, as the mouth and intestinal canal, is
+termed mucus, but is not however coagulable by heat; and the secretion on
+the membranes of those cavities of the body, which have no external
+openings, is called lymph or water, as in the cavities of the cellular
+membrane, and of the abdomen; this lymph however is coagulable by the heat
+of boiling water. Some mucus nearly as viscid as the white of egg, which
+was discharged by stool, did not coagulate, though I evaporated it to one
+fourth of the quantity, nor did the aqueous and vitreous humours of a
+sheep's eye coagulate by the like experiment: but the serosity from an
+anasarcous leg, and that from the abdomen of a dropsical person, and the
+crystalline humour of a sheep's eye, coagulated in the same heat.
+
+3. When any of these capillary glands are stimulated into greater
+irritative actions, than is natural, they secrete a more copious material;
+and as the mouths of the absorbent system, which open in their vicinity,
+are at the same time stimulated into greater action, the thinner and more
+saline part of the secreted fluid is taken up again; and the remainder is
+not only more copious but also more viscid than natural. This is more or
+less troublesome or noxious according to the importance of the functions of
+the part affected: on the skin and bronchiæ, where this secretion ought
+naturally to evaporate, it becomes so viscid as to adhere to the membrane;
+on the tongue it forms a pellicle, which can with difficulty be scraped
+off; produces the scurf on the heads of many people; and the mucus, which
+is spit up by others in coughing. On the nostrils and fauces, when the
+secretion of these capillary glands is increased, it is termed simple
+catarrh; when in the intestines, a mucous diarrhoea; and in the urethra, or
+vagina, it has the name of gonorrhoea, or fluor albus.
+
+4. When these capillary glands become inflamed, a still more viscid or even
+cretaceous humour is produced upon the surfaces of the membranes, which is
+the cause or the effect of rheumatism, gout, leprosy, and of hard tumours
+of the legs, which are generally termed scorbutic; all which will be
+treated of hereafter.
+
+II. 1. The whole surface of the body, with all its cavities and contents,
+are covered with membrane. It lines every vessel, forms every cell, and
+binds together all the muscular and perhaps the osseous fibres of the body;
+and is itself therefore probably a simpler substance than those fibres. And
+as the containing vessels of the body from the largest to the least are
+thus lined and connected with membranes, it follows that these membranes
+themselves consisted of unorganized materials.
+
+For however small we may conceive the diameters of the minutest vessels of
+the body, which escape our eyes and glasses, yet these vessels must consist
+of coats or sides, which are made up of an unorganized material, and which
+are probably produced from a gluten, which hardens after its production,
+like the silk or web of caterpillars and spiders. Of this material consist
+the membranes, which line the shells of eggs, and the shell itself, both
+which are unorganized, and are formed from mucus, which hardens after it is
+formed, either by the absorption of its more fluid part, or by its uniting
+with some part of the atmosphere. Such is also the production of the shells
+of snails, and of shell-fish, and I suppose of the enamel of the teeth.
+
+2. But though the membranes, that compose the sides of the most minute
+vessels, are in truth unorganized materials, yet the larger membranes,
+which are perceptible to the eye, seem to be composed of an intertexture of
+the mouths of the absorbent system, and of the excretory ducts of the
+capillaries, with their concomitant arteries, veins, and nerves: and from
+this construction it is evident, that these membranes must possess great
+irritability to peculiar stimuli, though they are incapable of any motions,
+that are visible to the naked eye: and daily experience shews us, that in
+their inflamed state they have the greatest sensibility to pain, as in the
+pleurisy and paronychia.
+
+3. On all these membranes a mucilaginous or aqueous fluid is secreted,
+which moistens and lubricates their surfaces, as was explained in Section
+XXIII. 2. Some have doubted, whether this mucus is separated from the blood
+by an appropriated set of glands, or exudes through the membranes, or is an
+abrasion or destruction of the surface of the membrane itself, which is
+continually repaired on the other side of it, but the great analogy between
+the capillary vessels, and the other glands, countenances the former
+opinion; and evinces, that these capillaries are the glands, that secrete
+it; to which we must add, that the blood in passing these capillary vessels
+undergoes a change in its colour from florid to purple, and gives out a
+quantity of heat; from whence, as in other glands, we must conclude that
+something is secreted from it.
+
+III. The seat of rheumatism is in the membranes, or upon them; but there
+are three very distinct diseases, which commonly are confounded under this
+name. First, when a membrane becomes affected with torpor, or inactivity of
+the vessels which compose it, pain and coldness succeed, as in the
+hemicrania, and other head-achs, which are generally termed nervous
+rheumatism; they exist whether the part be at rest or in motion, and are
+generally attended with other marks of debility.
+
+Another rheumatism is said to exist, when inflammation and swelling, as
+well as pain, affect some of the membranes of the joints, as of the ancles,
+wrists, knees, elbows, and sometimes of the ribs. This is accompanied with
+fever, is analogous to pleurisy and other inflammations, and is termed the
+acute rheumatism.
+
+A third disease is called chronic rheumatism, which is distinguished from
+that first mentioned, as in this the pain only affects the patient during
+the motion of the part, and from the second kind of rheumatism above
+described, as it is not attended with quick pulse or inflammation. It is
+generally believed to succeed the acute rheumatism of the same part, and
+that some coagulable lymph, or cretaceous, or calculous material, has been
+left on the membrane; which gives pain, when the muscles move over it, as
+some extraneous body would do, which was too insoluble to be absorbed.
+Hence there is an analogy between this chronic rheumatism and the diseases
+which produce gravel or gout-stones; and it may perhaps receive relief from
+the same remedies, such as aerated sal soda.
+
+       *       *       *       *       *
+
+SECT. XXVII.
+
+OF HÆMORRHAGES.
+
+    I. _The veins are absorbent vessels._ 1. _Hæmorrhages from
+    inflammation. Case of hæmorrhage from the kidney cured by cold bathing.
+    Case of hæmorrhage from the nose cured by cold immersion._ II.
+    _Hæmorrhage from venous paralysis. Of Piles. Black stools. Petechiæ.
+    Consumption. Scurvy of the lungs. Blackness of the face and eyes in
+    epileptic fits. Cure of hæmorrhages from venous inability._
+
+I. As the imbibing mouths of the absorbent system already described open on
+the surface, and into the larger cavities of the body, so there is another
+system of absorbent vessels, which are not commonly esteemed such, I mean
+the veins, which take up the blood from the various glands and capillaries,
+after their proper fluids or secretions have been separated from it.
+
+The veins resemble the other absorbent vessels; as the progression of their
+contents is carried on in the same manner in both, they alike absorb their
+appropriated fluids, and have valves to prevent its regurgitation by the
+accidents of mechanical violence. This appears first, because there is no
+pulsation in the very beginnings of the veins, as is seen by microscopes;
+which must happen, if the blood was carried into them by the actions of the
+arteries. For though the concurrence of various venous streams of blood
+from different distances must prevent any pulsation in the larger branches,
+yet in the very beginnings of all these branches a pulsation must
+unavoidably exist, if the circulation in them was owing to the intermitted
+force of the arteries. Secondly, the venous absorption of blood from the
+penis, and from the teats of female animals after their erection, is still
+more similar to the lymphatic absorption, as it is previously poured into
+cells, where all arterial impulse must cease.
+
+There is an experiment, which seems to evince this venous absorption, which
+consists in the external application of a stimulus to the lips, as of
+vinegar, by which they become instantly pale; that is, the bibulous mouths
+of the veins by this stimulus are excited to absorb the blood faster, than
+it can be supplied by the usual arterial exertion. See Sect. XXIII. 5.
+
+There are two kinds of hæmorrhages frequent in diseases, one is where the
+glandular or capillary action is too powerfully exerted, and propels the
+blood forwards more hastily, than the veins can absorb it; and the other
+is, where the absorbent power of the veins is diminished, or a branch of
+them is become totally paralytic.
+
+1. The former of these cases is known by the heat of the part, and the
+general fever or inflammation that accompanies the hæmorrhage. An
+hæmorrhage from the nose or from the lungs is sometimes a crisis of
+inflammatory diseases, as of the hepatitis and gout, and generally ceases
+spontaneously, when the vessels are considerably emptied. Sometimes the
+hæmorrhage recurs by daily periods accompanying the hot fits of fever, and
+ceasing in the cold fits, or in the intermissions; this is to be cured by
+removing the febrile paroxysms, which will be treated of in their place.
+Otherwise it is cured by venesection, by the internal or external
+preparations of lead, or by the application of cold, with an abstemious
+diet, and diluting liquids, like other inflammations. Which by inducing a
+quiescence on those glandular parts, that are affected, prevents a greater
+quantity of blood from being protruded forwards, than the veins are capable
+of absorbing.
+
+Mr. B---- had an hæmorrhage from his kidney, and parted with not less than
+a pint of blood a day (by conjecture) along with his urine for above a
+fortnight: venesections, mucilages, balsams, preparations of lead, the
+bark, alum, and dragon's blood, opiates, with a large blister on his loins,
+were separately tried, in large doses, to no purpose. He was then directed
+to bathe in a cold spring up to the middle of his body only, the upper part
+being covered, and the hæmorrhage diminished at the first, and ceased at
+the second immersion.
+
+In this case the external capillaries were rendered quiescent by the
+coldness of the water, and thence a less quantity of blood was circulated
+through them; and the internal capillaries, or other glands, became
+quiescent from their irritative associations with the external ones; and
+the hæmorrhage was stopped a sufficient time for the ruptured vessels to
+contract their apertures, or for the blood in those apertures to coagulate.
+
+Mrs. K---- had a continued haemorrhage from her nose for some days; the
+ruptured vessel was not to be reached by plugs up the nostrils, and the
+sensibility of her fauces was such that nothing could be born behind the
+uvula. After repeated venesection, and other common applications, she was
+directed to immerse her whole head into a pail of water, which was made
+colder by the addition of several handfuls of salt, and the hæmorrhage
+immediately ceased, and returned no more; but her pulse continued hard, and
+she was necessitated to lose blood from the arm on the succeeding day.
+
+Query, might not the cold bath instantly stop hæmorrhages from the lungs in
+inflammatory cases?--for the shortness of breath of those, who go suddenly
+into cold water, is not owing to the accumulation of blood in the lungs,
+but to the quiescence of the pulmonary capillaries from association, as
+explained in Section XXXII. 3. 2.
+
+II. The other kind of hæmorrhage is known from its being attended with a
+weak pulse, and other symptoms of general debility, and very frequently
+occurs in those, who have diseased livers, owing to intemperance in the use
+of fermented liquors. These constitutions are shewn to be liable to
+paralysis of the lymphatic absorbents, producing the various kinds of
+dropsies in Section XXIX. 5. Now if any branch of the venous system loses
+its power of absorption, the part swells, and at length bursts and
+discharges the blood, which the capillaries or other glands circulate
+through them.
+
+It sometimes happens that the large external veins of the legs burst, and
+effuse their blood; but this occurs most frequently in the veins of the
+intestines, as the vena portarum is liable to suffer from a schirrus of the
+liver opposing the progression of the blood, which is absorbed from the
+intestines. Hence the piles are a symptom of hepatic obstruction, and hence
+the copious discharges downwards or upwards of a black material, which has
+been called melancholia, or black bile; but is no other than the blood,
+which is probably discharged from the veins of the intestines.
+
+J.F. Meckel, in his Experimenta de Finibus Vasorum, published at Berlin,
+1772, mentions his discovery of a communication of a lymphatic vessel with
+the gastric branch of the vena portarum. It is possible, that when the
+motion of the lymphatic becomes retrograde in some diseases, that blood may
+obtain a passage into it, where it anastomoses with the vein, and thus be
+poured into the intestines. A discharge of blood with the urine sometimes
+attends diabetes, and may have its source in the same manner.
+
+Mr. A----, who had been a hard drinker, and had the gutta rosacea on his
+face and breast, after a stroke of the palsy voided near a quart of a black
+viscid material by stool: on diluting it with water it did not become
+yellow, as it must have done if it had been inspissated bile, but continued
+black like the grounds of coffee.
+
+But any other part of the venous system may become quiescent or totally
+paralytic as well as the veins of the intestines: all which occur more
+frequently in those who have diseased livers, than in any others. Hence
+troublesome bleedings of the nose, or from the lungs with a weak pulse;
+hence hæmorrhages from the kidneys, too great menstruation; and hence the
+oozing of blood from every part of the body, and the petechiæ in those
+fevers, which are termed putrid, and which is erroneously ascribed to the
+thinness of the blood: for the blood in inflammatory diseases is equally
+fluid before it coagulates in the cold air.
+
+Is not that hereditary consumption, which occurs chiefly in dark-eyed
+people about the age of twenty, and commences with slight pulmonary
+hæmorrhages without fever, a disease of this kind?--These hæmorrhages
+frequently begin during sleep, when the irritability of the lungs is not
+sufficient in these patients to carry on the circulation without the
+assistance of volition; for in our waking hours, the motions of the lungs
+are in part voluntary, especially if any difficulty of breathing renders
+the efforts of volition necessary. See Class I. 2. 1. 3. and Class III. 2.
+1. 12. Another species of pulmonary consumption which seems more certainly
+of scrophulous origin is described in the next Section, No. 2.
+
+I have seen two cases of women, of about forty years of age, both of whom
+were seized with quick weak pulse, with difficult respiration, and who spit
+up by coughing much viscid mucus mixed with dark coloured blood. They had
+both large vibices on their limbs, and petechiæ; in one the feet were in
+danger of mortification, in the other the legs were oedematous. To relieve
+the difficult respiration, about six ounces of blood were taken from one of
+them, which to my surprise was sizy, like inflamed blood: they had both
+palpitations or unequal pulsations of the heart. They continued four or
+five weeks with pale and bloated countenances, and did not cease spitting
+phlegm mixed with black blood, and the pulse seldom slower than 130 or 135
+in a minute. This blood, from its dark colour, and from the many vibices
+and petechiæ, seems to have been venous blood; the quickness of the pulse,
+and the irregularity of the motion of the heart, are to be ascribed to
+debility of that part of the system; as the extravasation of blood
+originated from the defect of venous absorption. The approximation of these
+two cases to sea-scurvy is peculiar, and may allow them to be called
+scorbutus pulmonalis. Had these been younger subjects, and the paralysis of
+the veins had only affected the lungs, it is probable the disease would
+have been a pulmonary consumption.
+
+Last week I saw a gentleman of Birmingham, who had for ten days laboured
+under great palpitation of his heart, which was so distinctly felt by the
+hand, as to discountenance the idea of there being a fluid in the
+pericardium. He frequently spit up mucus stained with dark coloured blood,
+his pulse very unequal and very weak, with cold hands and nose. He could
+not lie down at all, and for about ten days past could not sleep a minute
+together, but waked perpetually with great uneasiness. Could those symptoms
+be owing to very extensive adhesions of the lungs? or is this a scorbutus
+pulmonalis? After a few days he suddenly got so much better as to be able
+to sleep many hours at a time by the use of one grain of powder of foxglove
+twice a day, and a grain of opium at night. After a few days longer, the
+bark was exhibited, and the opium continued with some wine; and the
+palpitations of his heart became much relieved, and he recovered his usual
+degree of health, but died suddenly some months afterwards.
+
+In epileptic fits the patients frequently become black in the face, from
+the temporary paralysis of the venous system of this part. I have known two
+instances where the blackness has continued many days. M. P----, who had
+drank intemperately, was seized with the epilepsy when he was in his
+fortieth year; in one of these fits the white part of his eyes was left
+totally black with effused blood; which was attended with no pain or heat,
+and was in a few weeks gradually absorbed, changing colour as is usual with
+vibices from bruises.
+
+The hæmorrhages produced from the inability of the veins to absorb the
+refluent blood, is cured by opium, the preparations of steel, lead, the
+bark, vitriolic acid, and blisters; but these have the effect with much
+more certainty, if a venesection to a few ounces, and a moderate cathartic
+with four or six grains of calomel be premised, where the patient is not
+already too much debilitated; as one great means of promoting the
+absorption of any fluid consists in previously emptying the vessels, which
+are to receive it.
+
+       *       *       *       *       *
+
+SECT. XXVIII.
+
+OF THE PARALYSIS OF THE ABSORBENT SYSTEM.
+
+    I. _Paralysis of the lacteals, atrophy. Distaste to animal food._ II.
+    _Cause of dropsy. Cause of herpes. Scrophula. Mesenteric consumption.
+    Pulmonary consumption. Why ulcers in the lungs are so difficult to
+    heal._
+
+The term paralysis has generally been used to express the loss of voluntary
+motion, as in the hemiplagia, but may with equal propriety be applied to
+express the disobediency of the muscular fibres to the other kinds of
+stimulus; as to those of irritation or sensation.
+
+I. There is a species of atrophy, which has not been well understood; when
+the absorbent vessels of the stomach and intestines have been long inured
+to the stimulus of too much spirituous liquor, they at length, either by
+the too sudden omission of fermented or spirituous potation, or from the
+gradual decay of nature, become in a certain degree paralytic; now it is
+observed in the larger muscles of the body, when one side is paralytic, the
+other is more frequently in motion, owing to the less expenditure of
+sensorial power in the paralytic limbs; so in this case the other part of
+the absorbent system acts with greater force, or with greater perseverance,
+in consequence of the paralysis of the lacteals; and the body becomes
+greatly emaciated in a small time.
+
+I have seen several patients in this disease, of which the following are
+the circumstances. 1. They were men about fifty years of age, and had lived
+freely in respect to fermented liquors. 2. They lost their appetite to
+animal food. 3. They became suddenly emaciated to a great degree. 4. Their
+skins were dry and rough. 5. They coughed and expectorated with difficulty
+a viscid phlegm. 6. The membrane of the tongue was dry and red, and liable
+to become ulcerous.
+
+The inability to digest animal food, and the consequent distaste to it,
+generally precedes the dropsy, and other diseases, which originate from
+spirituous potation. I suppose when the stomach becomes inirritable, that
+there is at the same time a deficiency of gastric acid; hence milk seldom
+agrees with these patients, unless it be previously curdled, as they have
+not sufficient gastric acid to curdle it; and hence vegetable food, which
+is itself acescent, will agree with their stomachs longer than animal food,
+which requires more of the gastric acid for its digestion.
+
+In this disease the skin is dry from the increased absorption of the
+cutaneous lymphatics, the fat is absorbed from the increased absorption of
+the cellular lymphatics, the mucus of the lungs is too viscid to be easily
+spit up by the increased absorption of the thinner parts of it, the
+membrana sneideriana becomes dry, covered with hardened mucus, and at
+length becomes inflamed and full of aphthæ, and either these sloughs, or
+pulmonary ulcers, terminate the scene.
+
+II. The immediate cause of dropsy is the paralysis of some other branches
+of the absorbent system, which are called lymphatics, and which open into
+the larger cavities of the body, or into the cells of the cellular
+membrane; whence those cavities or cells become distended with the fluid,
+which is hourly secreted into them for the purpose of lubricating their
+surfaces. As is more fully explained in No. 5. of the next Section.
+
+As those lymphatic vessels consist generally of a long neck or mouth, which
+drinks up its appropriated fluid, and of a conglobate gland, in which this
+fluid undergoes some change, it happens, that sometimes the mouth of the
+lymphatic, and sometimes the belly or glandular part of it, becomes totally
+or partially paralytic. In the former case, where the mouths of the
+cutaneous lymphatics become torpid or quiescent, the fluid secreted on the
+skin ceases to be absorbed, and erodes the skin by its saline acrimony, and
+produces eruptions termed herpes, the discharge from which is as salt, as
+the tears, which are secreted too fast to be reabsorbed, as in grief, or
+when the puncta lacrymalia are obstructed, and which running down the cheek
+redden and inflame the skin.
+
+When the mouths of the lymphatics, which open on the mucous membrane of the
+nostrils, become torpid, as on walking into the air in a frosty morning;
+the mucus, which continues to be secreted, has not its aqueous and saline
+part reabsorbed, which running over the upper lip inflames it, and has a
+salt taste, if it falls on the tongue.
+
+When the belly, or glandular part of these lymphatics, becomes torpid, the
+fluid absorbed by its mouth stagnates, and forms a tumour in the gland.
+This disease is called the scrophula. If these glands suppurate externally,
+they gradually heal, as those of the neck; if they suppurate without an
+opening on the external habit, as the mesenteric glands, a hectic fever
+ensues, which destroys the patient; if they suppurate in the lungs, a
+pulmonary consumption ensues, which is believed thus to differ from that
+described in the preceding Section, in respect to its seat or proximate
+cause.
+
+It is remarkable, that matter produced by suppuration will lie concealed in
+the body many weeks, or even months, without producing hectic fever; but as
+soon as the wound is opened, so as to admit air to the surface of the
+ulcer, a hectic fever supervenes, even in very few hours, which is probably
+owing to the azotic part of the atmosphere rather than to the oxygene;
+because those medicines, which contain much oxygene, as the calces or
+oxydes of metals, externally applied, greatly contribute to heal ulcers, of
+these are the solutions of lead and mercury, and copper in acids, or their
+precipitates.
+
+Hence when wounds are to be healed by the first intention, as it is called,
+it is necessary carefully to exclude the air from them. Hence we have one
+cause, which prevents pulmonary ulcers from healing, which is their being
+perpetually exposed to the air.
+
+Both the dark-eyed patients, which are affected with pulmonary ulcers from
+deficient venous absorption, as described in Section. XXVII. 2. and the
+light-eyed patients from deficient lymphatic absorption, which we are now
+treating of, have generally large apertures of the iris; these large pupils
+of the eyes are a common mark of want of irritability; and it generally
+happens, that an increase of sensibility, that is, of motions in
+consequence of sensation, attends these constitutions. See Sect. XXXI. 2.
+Whence inflammations may occur in these from stagnated fluids more
+frequently than in those constitutions, which possess more irritability and
+less sensibility.
+
+Great expectations in respect to the cure of consumptions, as well as of
+many other diseases, are produced by the very ingenious exertions of DR.
+BEDDOES; who has established an apparatus for breathing various mixtures of
+airs or gasses, at the hot-wells near Bristol, which well deserves the
+attention of the public.
+
+DR. BEDDOES very ingeniously concludes, from the florid colour of the blood
+of consumptive patients, that it abounds in oxygene; and that the redness
+of their tongues, and lips, and the fine blush of their cheeks shew the
+presence of the same principle, like flesh reddened by nitre. And adds,
+that the circumstance of the consumptions of pregnant women being stopped
+in their progress during pregnancy, at which time their blood may be
+supposed to be in part deprived of its oxygene, by oxygenating the blood of
+the foetus, is a forceable argument in favour of this theory; which must
+soon be confirmed or confuted by his experiments. See Essay on Scurvy,
+Consumption, &c. by Dr. Beddoes. Murray. London. Also Letter to Dr. Darwin,
+by the same. Murray. London.
+
+       *       *       *       *       *
+
+SECT. XXIX.
+
+ON THE RETROGRADE MOTIONS OF THE ABSORBENT SYSTEM.
+
+    I. _Account of the absorbent system._ II. _The valves of the absorbent
+    vessels may suffer their fluids to regurgitate in some diseases._ III.
+    _Communication from the alimentary canal to the bladder by means of the
+    absorbent vessels._ IV. _The phenomena of diabetes explained._ V. 1.
+    _The phenomena of dropsies explained._ 2. _Cases of the use of
+    foxglove._ VI. _Of cold sweats._ VII. _Translations of matter, of
+    chyle, of milk, of urine, operation of purging drugs applied
+    externally._ VIII. _Circumstances by which the fluids, that are effused
+    by the retrograde motions of the absorbent vessels, are distinguished._
+    IX. _Retrograde motions of vegetable juices._ X. _Objections answered._
+    XI. _The causes, which induce the retrograde motions of animal vessels,
+    and the medicines by which the natural motions are restored._
+
+    _N.B. The following Section is a translation of a part of a Latin
+    thesis written by the late Mr. Charles Darwin, which was printed with
+    his prize-dissertation on a criterion between matter and mucus in 1780.
+    Sold by Cadell, London._
+
+I. _Account of the Absorbent System._
+
+1. The absorbent system of vessels in animal bodies consists of several
+branches, differing in respect to their situations, and to the fluids,
+which they absorb.
+
+The intestinal absorbents open their mouths on the internal surfaces of the
+intestines; their office is to drink up the chyle and the other fluids from
+the alimentary canal; and they are termed lacteals, to distinguish them
+from the other absorbent vessels, which have been termed lymphatics.
+
+Those, whose mouths are dispersed on the external skin, imbibe a great
+quantity of water from the atmosphere, and a part of the perspirable
+matter, which does not evaporate, and are termed cutaneous absorbents.
+
+Those, which arise from the internal surface of the bronchia, and which
+imbibe moisture from the atmosphere, and a part of the bronchial mucus, are
+called pulmonary absorbents.
+
+Those, which open their innumerable mouths into the cells of the whole
+cellular membrane; and whose use is to take up the fluid, which is poured
+into those cells, after it has done its office there; may be called
+cellular absorbents.
+
+Those, which arise from the internal surfaces of the membranes, which line
+the larger cavities of the body, as the thorax, abdomen, scrotum,
+pericardium, take up the mucus poured into those cavities; and are
+distinguished by the names of their respective cavities.
+
+Whilst those, which arise from the internal surfaces of the urinary
+bladder, gall-bladder, salivary ducts, or other receptacles of secreted
+fluids, may take their names from those fluids; the thinner parts of which
+it is their office to absorb: as urinary, bilious, or salivary absorbents.
+
+2. Many of these absorbent vessels, both lacteals and lymphatics, like some
+of the veins, are replete with valves: which seem designed to assist the
+progress of their fluids, or at least to prevent their regurgitation; where
+they are subjected to the intermitted pressure of the muscular, or arterial
+actions in their neighbourhood.
+
+These valves do not however appear to be necessary to all the absorbents,
+any more than to all the veins; since they are not found to exist in the
+absorbent system of fish; according to the discoveries of the ingenious,
+and much lamented Mr. Hewson. Philos. Trans. v. 59, Enquiries into the
+Lymph. Syst. p. 94.
+
+3. These absorbent vessels are also furnished with glands, which are called
+conglobate glands; whose use is not at present sufficiently investigated;
+but it is probable that they resemble the conglomerate glands both in
+structure and in use, except that their absorbent mouths are for the
+conveniency of situation placed at a greater distance from the body of the
+gland. The conglomerate glands open their mouths immediately into the
+sanguiferous vessels, which bring the blood, from whence they absorb their
+respective fluids, quite up to the gland: but these conglobate glands
+collect their adapted fluids from very distant membranes, or cysts, by
+means of mouths furnished with long necks for this purpose; and which are
+called lacteals, or lymphatics.
+
+4. The fluids, thus collected from various parts of the body, pass by means
+of the thoracic duct into the left subclavian near the jugular vein; except
+indeed that those collected from the right side of the head and neck, and
+from the right arm, are carried into the right subclavian vein: and
+sometimes even the lymphatics from the right side of the lungs are inserted
+into the right subclavian vein; whilst those of the left side of the head
+open but just into the summit of the thoracic duct.
+
+5. In the absorbent system there are many anastomoses of the vessels, which
+seem of great consequence to the preservation of health. These anastomoses
+are discovered by dissection to be very frequent between the intestinal and
+urinary lymphatics, as mentioned by Mr. Hewson, (Phil. Trans. v. 58.)
+
+6. Nor do all the intestinal absorbents seem to terminate in the thoracic
+duct, as appears from some curious experiments of D. Munro, who gave madder
+to some animals, having previously put a ligature on the thoracic duct, and
+found their bones, and the serum of their blood, coloured red.
+
+II. _The Valves of the Absorbent System may suffer their Fluids to
+regurgitate in some Diseases._
+
+1. The many valves, which occur in the progress of the lymphatic and
+lacteal vessels, would seem insuperable obstacles to the regurgitation of
+their contents. But as these valves are placed in vessels, which are indued
+with life, and are themselves indued with life also; and are very irritable
+into those natural motions, which absorb, or propel the fluids they
+contain; it is possible, in some diseases, where these valves or vessels
+are stimulated into unnatural exertions, or are become paralytic, that
+during the diastole of the part of the vessel to which the valve is
+attached, the valve may not so completely close, as to prevent the relapse
+of the lymph or chyle. This is rendered more probable, by the experiments
+of injecting mercury, or water, or suet, or by blowing air down these
+vessels: all which pass the valves very easily, contrary to the natural
+course of their fluids, when the vessels are thus a little forcibly
+dilated, as mentioned by Dr. Haller, Elem. Physiol. t. iii. s. 4.
+
+"The valves of the thoracic duct are few, some assert they are not more
+than twelve, and that they do not very accurately perform their office, as
+they do not close the whole area of the duct, and thence may permit chyle
+to repass them downwards. In living animals, however, though not always,
+yet more frequently than in the dead, they prevent the chyle from
+returning. The principal of these valves is that, which presides over the
+insertion of the thoracic duct, into the subclavian vein; many have
+believed this also to perform the office of a valve, both to admit the
+chyle into the vein, and to preclude the blood from entering the duct; but
+in my opinion it is scarcely sufficient for this purpose." Haller, Elem.
+Phys. t. vii. p. 226.
+
+2. The mouths of the lymphatics seem to admit water to pass through them
+after death, the inverted way, easier than the natural one; since an
+inverted bladder readily lets out the water with which it is filled; whence
+it may be inferred, that there is no obstacle at the mouths of these
+vessels to prevent the regurgitation of their contained fluids.
+
+I was induced to repeat this experiment, and having accurately tied the
+ureters and neck of a fresh ox's bladder, I made an opening at the fundus
+of it; and then, having turned it inside outwards, filled it half full with
+water, and was surprised to see it empty itself so hastily. I thought the
+experiment more apposite to my purpose by suspending the bladder with its
+neck downwards, as the lymphatics are chiefly spread upon this part of it,
+as shewn by Dr. Watson, Philos. Trans. v. 59. p. 392.
+
+3. In some diseases, as in the diabetes and scrophula, it is probable the
+valves themselves are diseased, and are thence incapable of preventing the
+return of the fluids they should support. Thus the valves of the aorta
+itself have frequently been found schirrous, according to the dissections
+of Mons. Lieutaud, and have given rise to an interrupted pulse, and
+laborious palpitations, by suffering a return of part of the blood into the
+heart. Nor are any parts of the body so liable to schirrosity as the
+lymphatic glands and vessels, insomuch that their schirrosities have
+acquired a distinct name, and been termed scrophula.
+
+4. There are valves in other parts of the body, analogous to those of the
+absorbent system, and which are liable, when diseased, to regurgitate their
+contents: thus the upper and lower orifices of the stomach are closed by
+valves, which, when too great quantities of warm water have been drank with
+a design to promote vomiting, have sometimes resisted the utmost efforts of
+the abdominal muscles, and diaphragm: yet, at other times, the upper valve,
+or cardia, easily permits the evacuation of the contents of the stomach;
+whilst the inferior valve, or pylorus, permits the bile, and other contents
+of the duodenum, to regurgitate into the stomach.
+
+5. The valve of the colon is well adapted to prevent the retrograde motion
+of the excrements; yet, as this valve is possessed of a living power, in
+the iliac passion, either from spasm, or other unnatural exertions, it
+keeps itself open, and either suffers or promotes the retrograde movements
+of the contents of the intestines below; as in ruminating animals the mouth
+of the first stomach seems to be so constructed, as to facilitate or assist
+the regurgitation of the food; the rings of the oesophagus afterwards
+contracting themselves in inverted order. De Haeu, by means of a syringe,
+forced so much water into the rectum intestinum of a dog, that he vomited
+it in a full stream from his mouth; and in the iliac passion above
+mentioned, excrements and clyster are often evacuated by the mouth. See
+Section XXV. 15.
+
+6. The puncta lacrymalia, with the lacrymal sack and nasal duct, compose a
+complete gland, and much resemble the intestinal canal: the puncta
+lacrymalia are absorbent mouths, that take up the tears from the eye, when
+they have done their office there, and convey them into the nostrils; but
+when the nasal duct is obstructed, and the lacrymal sack distended with its
+fluid, on pressure with the finger the mouths of this gland (puncta
+lacrymalia) will readily disgorge the fluid, they had previously absorbed,
+back into the eye.
+
+7. As the capillary vessels receive blood from the arteries, and separating
+the mucus, or perspirable matter from it, convey the remainder back by the
+veins; these capillary vessels are a set of glands, in every respect
+similar to the secretory vessels of the liver, or other large congeries of
+glands. The beginnings of these capillary vessels have frequent anastomoses
+into each other, in which circumstance they are resembled by the lacteals;
+and like the mouths or beginnings of other glands, they are a set of
+absorbent vessels, which drink up the blood which is brought to them by the
+arteries, as the chyle is drank up by the lacteals: for the circulation of
+the blood through the capillaries is proved to be independent of arterial
+impulse; since in the blush of shame, and in partial inflammations, their
+action is increased, without any increase of the motion of the heart.
+
+8. Yet not only the mouths, or beginnings of these anastomosing capillaries
+are frequently seen by microscopes, to regurgitate some particles of blood,
+during the struggles of the animal; but retrograde motion of the blood, in
+the veins of those animals, from the very heart of the extremity of the
+limbs, is observable, by intervals, during the distresses of the dying
+creature. Haller, Elem. Physiol. t. i. p. 216. Now, as the veins have
+perhaps all of them a valve somewhere between their extremities and the
+heart, here is ocular demonstration of the fluids in this diseased
+condition of the animal, repassing through venous valves: and it is hence
+highly probable, from the strictest analogy, that if the course of the
+fluids, in the lymphatic vessels, could be subjected to microscopic
+observation, they would also, in the diseased state of the animal, be seen
+to repass the valves, and the mouths of those vessels, which had previously
+absorbed them, or promoted their progression.
+
+III. _Communication from the Alimentary Canal to the Bladder, by means of
+the Absorbent Vessels._
+
+Many medical philosophers, both ancient and modern, have suspected that
+there was a nearer communication between the stomach and the urinary
+bladder, than that of the circulation: they were led into this opinion from
+the great expedition with which cold water, when drank to excess, passes
+off by the bladder; and from the similarity of the urine, when produced in
+this hasty manner, with the material that was drank.
+
+The former of these circumstances happens perpetually to those who drink
+abundance of cold water, when they are much heated by exercise, and to many
+at the beginning of intoxication.
+
+Of the latter, many instances are recorded by Etmuller, t. xi. p. 716.
+where simple water, wine, and wine with sugar, and emulsions, were returned
+by urine unchanged.
+
+There are other experiments, that seem to demonstrate the existence of
+another passage to the bladder, besides that through the kidneys. Thus Dr.
+Kratzenstein put ligatures on the ureters of a dog, and then emptied the
+bladder by a catheter; yet in a little time the dog drank greedily, and
+made a quantity of water, (Disputat. Morbor. Halleri. t. iv. p. 63.) A
+similar experiment is related in the Philosophical Transactions, with the
+same event, (No. 65, 67, for the year 1670.)
+
+Add to this, that in some morbid cases the urine has continued to pass,
+after the suppuration or total destruction of the kidneys; of which many
+instances are referred to in the Elem. Physiol. t. vii. p. 379. of Dr.
+Haller.
+
+From all which it must be concluded, that some fluids have passed from the
+stomach or abdomen, without having gone through the sanguiferous
+circulation: and as the bladder is supplied with many lymphatics, as
+described by Dr. Watson, in the Philos. Trans. v. 59. p. 392. and as no
+other vessels open into it besides these and the ureters, it seems evident,
+that the unnatural urine, produced as above described, when the ureters
+were tied, or the kidneys obliterated, was carried into the bladder by the
+retrograde motions of the urinary branch of the lymphatic system.
+
+The more certainly to ascertain the existence of another communication
+between the stomach and bladder, besides that of the circulation, the
+following experiment was made, to which I must beg your patient
+attention:--A friend of mine (June 14, 1772) on drinking repeatedly of cold
+small punch, till he began to be intoxicated, made a quantity of colourless
+urine. He then drank about two drams of nitre dissolved in some of the
+punch, and eat about twenty stalks of boiled asparagus: on continuing to
+drink more of the punch, the next urine that he made was quite clear, and
+without smell; but in a little time another quantity was made, which was
+not quite so colourless, and had a strong smell of the asparagus: he then
+lost about four ounces of blood from the arm.
+
+The smell of asparagus was not at all perceptible in the blood, neither
+when fresh taken, nor the next morning, as myself and two others accurately
+attended to; yet this smell was strongly perceived in the urine, which was
+made just before the blood was taken from his arm.
+
+Some bibulous paper, moistened in the serum of this blood, and suffered to
+dry, shewed no signs of nitre by its manner of burning. But some of the
+same paper, moistened in the urine, and dried, on being ignited, evidently
+shewed the presence of nitre. This blood and the urine stood some days
+exposed to the sun in the open air, till they were evaporated to about a
+fourth of their original quantity, and began to stink: the paper, which was
+then moistened with the concentrated urine, shewed the presence of much
+nitre by its manner of burning; whilst that moistened with the blood shewed
+no such appearance at all.
+
+Hence it appears, that certain fluids at the beginning of intoxication,
+find another passage to the bladder besides the long course of the arterial
+circulation; and as the intestinal absorbents are joined with the urinary
+lymphatics by frequent anastomoses, as Hewson has demonstrated; and as
+there is no other road, we may justly conclude, that these fluids pass into
+the bladder by the urinary branch of the lymphatics, which has its motions
+inverted during the diseased state of the animal.
+
+A gentleman, who had been some weeks affected with jaundice, and whose
+urine was in consequence of a very deep yellow, took some cold small punch,
+in which was dissolved about a dram of nitre; he then took repeated
+draughts of the punch, and kept himself in a cool room, till on the
+approach of slight intoxication he made a large quantity of water; this
+water had a slight yellow tinge, as might be expected from a small
+admixture of bile secreted from the kidneys; but if the whole of it had
+passed through the sanguiferous vessels, which were now replete with bile
+(his whole skin being as yellow as gold) would not this urine also, as well
+as that he had made for weeks before, have been of a deep yellow? Paper
+dipped in this water, and dryed, and ignited, shewed evident marks of the
+presence of nitre, when the flame was blown out.
+
+IV. _The Phænomena of the Diabetes explained, and of some Diarrhoeas._
+
+The phenomena of many diseases are only explicable from the retrograde
+motions of some of the branches of the lymphatic system; as the great and
+immediate flow of pale urine in the beginning of drunkenness; in hysteric
+paroxysms; from being exposed to cold air; or to the influence of fear or
+anxiety.
+
+Before we endeavour to illustrate this doctrine, by describing the
+phænomena of these diseases, we must premise one circumstance; that all the
+branches of the lymphatic system have a certain sympathy with each other,
+insomuch that when one branch is stimulated into unusual kinds or
+quantities of motion, some other branch has its motions either increased,
+or decreased, or inverted at the same time. This kind of sympathy can only
+be proved by the concurrent testimony of numerous facts, which will be
+related in the course of the work. I shall only add here, that it is
+probable, that this sympathy does not depend on any communication of
+nervous filaments, but on habit; owing to the various branches of this
+system having frequently been stimulated into action at the same time.
+
+There are a thousand instances of involuntary motions associated in this
+manner; as in the act of vomiting, while the motions of the stomach and
+oesophagus are inverted, the pulsations of the arterial system by a certain
+sympathy become weaker; and when the bowels or kidneys are stimulated by
+poison, a stone, or inflammation, into more violent action; the stomach and
+oesophagus by sympathy invert their motions.
+
+1. When any one drinks a moderate quantity of vinous spirit, the whole
+system acts with more energy by consent with the stomach and intestines, as
+is seen from the glow on the skin, and the increase of strength and
+activity; but when a greater quantity of this inebriating material is
+drank, at the same time that the lacteals are excited into greater action
+to absorb it; it frequently happens, that the urinary branch of absorbents,
+which is connected with the lacteals by many anastomoses, inverts its
+motions, and a great quantity of pale unanimalized urine is discharged. By
+this wise contrivance too much of an unnecessary fluid is prevented from
+entering the circulation--This may be called the drunken diabetes, to
+distinguish it from the other temporary diabetes, which occur in hysteric
+diseases, and from continued fear or anxiety.
+
+2. If this idle ingurgitation of too much vinous spirit be daily practised,
+the urinary branch of absorbents at length gains an habit of inverting its
+motions, whenever the lacteals are much stimulated; and the whole or a
+great part of the chyle is thus daily carried to the bladder without
+entering the circulation, and the body becomes emaciated. This is one kind
+of chronic diabetes, and may be distinguished from the others by the taste
+and appearance of the urine; which is sweet, and the colour of whey, and
+may be termed the chyliferous diabetes.
+
+3. Many children have a similar deposition of chyle in their urine, from
+the irritation of worms in their intestines, which stimulating the mouths
+of the lacteals into unnatural action, the urinary branch of the absorbents
+becomes inverted, and carries part of the chyle to the bladder: part of the
+chyle also has been carried to the iliac and lumbar glands, of which
+instances are recorded by Haller, t. vii. 225. and which can be explained
+on no other theory: but the dissections of the lymphatic system of the
+human body, which have yet been published, are not sufficiently extensive
+for our purpose; yet if we may reason from comparative anatomy, this
+translation of chyle to the bladder is much illustrated by the account
+given of this system of vessels in a turtle, by Mr. Hewson, who observed,
+"That the lacteals near the root of the mesentery anastomose, so as to form
+a net-work, from which several large branches go into some considerable
+lymphatics lying near the spine; and which can be traced almost to the
+anus, and particularly to the kidneys." Philos. Trans. v. 59. p.
+199--Enquiries, p. 74.
+
+4. At the same time that the urinary branch of absorbents, in the beginning
+of diabetes, is excited into inverted action, the cellular branch is
+excited by the sympathy above mentioned, into more energetic action; and
+the fat, that was before deposited, is reabsorbed and thrown into the blood
+vessels; where it floats, and was mistaken for chyle, till the late
+experiments of the ingenious Mr. Hewson demonstrated it to be fat.
+
+This appearance of what was mistaken for chyle in the blood, which was
+drawn from these patients, and the obstructed liver, which very frequently
+accompanies this disease, seems to have led Dr. Mead to suspect the
+diabetes was owing to a defect of sanguification; and that the schirrosity
+of the liver was the original cause of it: but as the schirrhus of the
+liver is most frequently owing to the same causes, that produce the
+diabetes and dropsies; namely, the great use of fermented liquors; there is
+no wonder they should exist together, without being the consequence of each
+other.
+
+5. If the cutaneous branch of absorbents gains a habit of being excited
+into stronger action, and imbibes greater quantities of moisture from the
+atmosphere, at the same time that the urinary branch has its motions
+inverted, another kind of diabetes is formed, which may be termed the
+aqueous diabetes. In this diabetes the cutaneous absorbents frequently
+imbibe an amazing quantity of atmospheric moisture; insomuch that there are
+authentic histories, where many gallons a day, for many weeks together,
+above the quantity that has been drank, have been discharged by urine.
+
+Dr. Keil, in his Medicina Statica, found that he gained eighteen ounces
+from the moist air of one night; and Dr. Percival affirms, that one of his
+hands imbibed, after being well chafed, near an ounce and half of water, in
+a quarter of an hour. (Transact. of the College, London, vol. ii. p. 102.)
+Home's Medic. Facts, p. 2. sect. 3.
+
+The pale urine in hysterical women, or which is produced by fear or
+anxiety, is a temporary complaint of this kind; and it would in reality be
+the same disease, if it was confirmed by habit.
+
+6. The purging stools, and pale urine, occasioned by exposing the naked
+body to cold air, or sprinkling it with cold water, originate from a
+similar cause; for the mouths of the cutaneous lymphatics being suddenly
+exposed to cold become torpid, and cease, or nearly cease, to act; whilst,
+by the sympathy above described, not only the lymphatics of the bladder and
+intestines cease also to absorb the more aqueous and saline part of the
+fluids secreted into them; but it is probable that these lymphatics invert
+their motions, and return the fluids, which were previously absorbed, into
+the intestines and bladder. At the very instant that the body is exposed
+naked to the cold air, an unusual movement is felt in the bowels; as is
+experienced by boys going into the cold bath: this could not occur from an
+obstruction of the perspirable matter, since there is not time, for that to
+be returned to the bowels by the course of the circulation.
+
+There is also a chronic aqueous diarrhoea, in which the atmospheric
+moisture, drank up by the cutaneous and pulmonary lymphatics, is poured
+into the intestines, by the retrograde motions of the lacteals. This
+disease is most similar to the aqueous diabetes, and is frequently
+exchanged for it: a distinct instance of this is recorded by Benningerus,
+Cent. v. Obs. 98. in which an aqueous diarrhoea succeeded an aqueous
+diabetes, and destroyed the patient. There is a curious example of this,
+described by Sympson (De Re Medica)--"A young man (says he) was seized with
+a fever, upon which a diarrhoea came on, with great stupor; and he refused
+to drink any thing, though he was parched up with excessive heat: the
+better to supply him with moisture, I directed his feet to be immersed in
+cold water; immediately I observed a wonderful decrease of water in the
+vessel, and then an impetuous stream of a fluid, scarcely coloured, was
+discharged by stool, like a cataract."
+
+7. There is another kind of diarrhoea, which has been called cæliaca; in
+this disease the chyle, drank up by the lacteals of the small intestines,
+is probably poured into the large intestines, by the retrograde motions of
+their lacteals: as in the chyliferous diabetes, the chyle is poured into
+the bladder, by the retrograde motions of the urinary branch of absorbents.
+
+The chyliferous diabetes, like this chyliferous diarrhoea, produces sudden
+atrophy; since the nourishment, which ought to supply the hourly waste of
+the body, is expelled by the bladder, or rectum: whilst the aqueous
+diabetes, and the aqueous diarrhoea produce excessive thirst; because the
+moisture, which is obtained from the atmosphere, is not conveyed to the
+thoracic receptacle, as it ought to be, but to the bladder, or lower
+intestines; whence the chyle, blood, and whole system of glands, are robbed
+of their proportion of humidity.
+
+8. There is a third species of diabetes, in which the urine is
+mucilaginous, and appears ropy in pouring it from one vessel into another;
+and will sometimes coagulate over the fire. This disease appears by
+intervals, and ceases again, and seems to be occasioned by a previous
+dropsy in some part of the body. When such a collection is reabsorbed, it
+is not always returned into the circulation; but the same irritation that
+stimulates one lymphatic branch to reabsorb the deposited fluid, inverts
+the urinary branch, and pours it into the bladder. Hence this mucilaginous
+diabetes is a cure, or the consequence of a cure, of a worse disease,
+rather than a disease itself.
+
+Dr. Cotunnius gave half an ounce of cream of tartar, every morning, to a
+patient, who had the anasarca; and he voided a great quantity of urine; a
+part of which, put over the fire, coagulated, on the evaporation of half of
+it, so as to look like the white of an egg. De Ischiade Nervos.
+
+This kind of diabetes frequently precedes a dropsy; and has this remarkable
+circumstance attending it, that it generally happens in the night; as
+during the recumbent state of the body, the fluid, that was accumulated in
+the cellular membrane, or in the lungs, is more readily absorbed, as it is
+less impeded by its gravity. I have seen more than one instance of this
+disease. Mr. D. a man in the decline of life, who had long accustomed
+himself to spirituous liquor, had swelled legs, and other symptoms of
+approaching anasarca; about once in a week, or ten days, for several
+months, he was seized, on going to bed, with great general uneasiness,
+which his attendants resembled to an hysteric fit; and which terminated in
+a great discharge of viscid urine; his legs became less swelled, and he
+continued in better health for some days afterwards. I had not the
+opportunity to try if this urine would coagulate over the fire, when part
+of it was evaporated, which I imagine would be the criterion of this kind
+of diabetes; as the mucilaginous fluid deposited in the cells and cysts of
+the body, which have no communication with the external air, seems to
+acquire, by stagnation, this property of coagulation by heat, which the
+secreted mucus of the intestines and bladder do not appear to possess; as I
+have found by experiment: and if any one should suppose this coagulable
+urine was separated from the blood by the kidneys, he may recollect, that
+in the most inflammatory diseases, in which the blood is most replete or
+most ready to part with the coagulable lymph, none of this appears in the
+urine.
+
+9. Different kinds of diabetes require different methods of cure. For the
+first kind, or chyliferous diabetes, after clearing the stomach and
+intestines, by ipecacuanha and rhubarb, to evacuate any acid material,
+which may too powerfully stimulate the mouths of the lacteals, repeated and
+large doses of tincture of cantharides have been much recommended. The
+specific stimulus of this medicine, on the neck of the bladder, is likely
+to excite the numerous absorbent vessels, which are spread on that part,
+into stronger natural actions, and by that means prevent their retrograde
+ones; till, by persisting in the use of the medicine, their natural habits
+of motions might again be established. Another indication of cure, requires
+such medicines, as by lining the intestines with mucilaginous substances,
+or with such as consist of smooth particles, or which chemically destroy
+the acrimony of their contents, may prevent the too great action of the
+intestinal absorbents. For this purpose, I have found the earth
+precipitated from a solution of alum, by means of fixed alcali, given in
+the dose of half a dram every six hours, of great advantage, with a few
+grains of rhubarb, so as to produce a daily evacuation.
+
+The food should consist of materials that have the least stimulus, with
+calcareous water, as of Bristol and Matlock; that the mouths of the
+lacteals may be as little stimulated as is necessary for their proper
+absorption; lest with their greater exertions, should be connected by
+sympathy, the inverted motions of the urinary lymphatics.
+
+The same method may be employed with equal advantage in the aqueous
+diabetes, so great is the sympathy between the skin and the stomach. To
+which, however, some application to the skin might be usefully added; as
+rubbing the patient all over with oil, to prevent the too great action of
+the cutaneous absorbents. I knew an experiment of this kind made upon one
+patient with apparent advantage.
+
+The mucilaginous diabetes will require the same treatment, which is most
+efficacious in the dropsy, and will be described below. I must add, that
+the diet and medicines above mentioned, are strongly recommended by various
+authors, as by Morgan, Willis, Harris, and Etmuller; but more histories of
+the successful treatment of these diseases are wanting to fully ascertain
+the most efficacious methods of cure.
+
+In a letter from Mr. Charles Darwin, dated April 24, 1778, Edinburgh, is
+the subsequent passage:--"A man who had long laboured under a diabetes died
+yesterday in the clinical ward. He had for some time drank four, and passed
+twelve pounds of fluid daily; each pound of urine contained an ounce of
+sugar. He took, without considerable relief, gum kino, sanguis diaconis
+melted with alum, tincture of cantharides, isinglass, gum arabic, crabs
+eyes, spirit of hartshorn, and eat ten or fifteen oysters thrice a day. Dr.
+Home, having read my thesis, bled him, and found that neither the fresh
+blood nor the serum tasted sweet. His body was opened this morning--every
+viscus appeared in a sound and natural state, except that the left kidney
+had a very small pelvis, and that there was a considerable enlargement of
+most of the mesenteric lymphatic glands. I intend to insert this in my
+thesis, as it coincides with the experiment, where some asparagus was eaten
+at the beginning of intoxication, and its smell perceived in the urine,
+though not in the blood."
+
+The following case of chyliferous diabetes is extracted from some letters
+of Mr. Hughes, to whose unremitted care the infirmary at Stafford for many
+years was much indebted. Dated October 10, 1778.
+
+Richard Davis, aged 33, a whitesmith by trade, had drank hard by intervals;
+was much troubled with sweating of his hands, which incommoded him in his
+occupation, but which ceased on his frequently dipping them in lime. About
+seven months ago he began to make large quantities of water; his legs are
+oedematous, his belly tense, and he complains of a rising in his throat,
+like the globus hystericus: he eats twice as much as other people, drinks
+about fourteen pints of small beer a day, besides a pint of ale, some
+milk-porridge, and a bason of broth, and he makes about eighteen pints of
+water a day.
+
+He tried alum, dragon's blood, steel, blue vitriol, and cantharides in
+large quantities, and duly repeated, under the care of Dr. Underhill, but
+without any effect; except that on the day after he omitted the
+cantharides, he made but twelve pints of water, but on the next day this
+good effect ceased again.
+
+November 21.--He made eighteen pints of water, and he now, at Dr. Darwin's
+request, took a grain of opium every four hours, and five grains of aloes
+at night; and had a flannel shirt given him.
+
+22.--Made sixteen pints. 23.--Thirteen pints: drinks less.
+
+24.--Increased the opium to a grain and quarter every four hours: he made
+twelve pints.
+
+25.--Increased the opium to a grain and half: he now makes ten pints; and
+drinks eight pints in a day.
+
+The opium was gradually increased during the next fortnight, till he took
+three grains every four hours, but without any further diminution of his
+water. During the use of the opium he sweat much in the nights, so as to
+have large drops stand on his face and all over him. The quantity of opium
+was then gradually decreased, but not totally omitted, as he continued to
+take about a grain morning and evening.
+
+January 17.--He makes fourteen pints of water a day. Dr. Underhill now
+directed him two scruples of common rosin triturated with as much sugar,
+every six hours; and three grains of opium every night.
+
+19.--Makes fifteen pints of water: sweats at night.
+
+21.--Makes seventeen pints of water; has twitchings of his limbs in a
+morning, and pains of his legs: he now takes a dram of rosin for a dose,
+and continues the opium.
+
+23.--Water more coloured, and reduced to sixteen pints, and he thinks has a
+brackish taste.
+
+26.--Water reduced to fourteen pints.
+
+28.--Water thirteen pints: he continues the opium, and takes four scruples
+of the rosin for a dose.
+
+February 1.--Water twelve pints.
+
+4.--Water eleven pints: twitchings less; takes five scruples for a dose.
+
+8.--Water ten pints: has had many stools.
+
+12.--Appetite less: purges very much.
+
+After this the rosin either purged him, or would not stay on his stomach;
+and he gradually relapsed nearly to his former condition, and in a few
+months sunk under the disease.
+
+October 3, Mr. Hughes evaporated two quarts of the water, and obtained from
+it four ounces and half of a hard and brittle saccharine mass, like treacle
+which had been some time boiled. Four ounces of blood, which he took from
+his arm with design to examine it, had the common appearances, except that
+the serum resembled cheese-whey; and that on the evidence of four persons,
+two of whom did not know what it was they tasted, _the serum had a saltish
+taste_.
+
+From hence it appears, that the saccharine matter, with which the urine of
+these patients so much abounds, does not enter the blood-vessels like the
+nitre and asparagus mentioned above; but that the process of digestion
+resembles the process of the germination of vegetables, or of making barley
+into malt; as the vast quantity of sugar found in the urine must be made
+from the food which he took (which was double that taken by others), and
+from the fourteen pints of small beer which he drank. And, secondly, as the
+serum of the blood was not sweet, the chyle appears to have been conveyed
+to the bladder without entering the circulation of the blood, since so
+large a quantity of sugar, as was found in the urine, namely, twenty ounces
+a day, could not have previously existed in the blood without being
+perceptible to the taste.
+
+November 1. Mr. Hughes dissolved two drams of nitre in a pint of a
+decoction of the roots of asparagus, and added to it two ounces of tincture
+of rhubarb: the patient took a fourth part of this mixture every five
+minutes, till he had taken the whole.--In about half an hour he made
+eighteen ounces of water, which was very manifestly tinged with the
+rhubarb; the smell of asparagus was doubtful.
+
+He then lost four ounces of blood, the serum of which was not so opake as
+that drawn before, but of a yellowish cast, as the serum of the blood
+usually appears.
+
+Paper, dipped three or four times in the tinged urine and dried again, did
+not scintillate when it was set on fire; but when the flame was blown out,
+the fire ran along the paper for half an inch; which, when the same paper
+was unimpregnated, it would not do; nor when the same paper was dipped in
+urine made before he took the nitre, and dried in the same manner.
+
+Paper, dipped in the serum of the blood and dried in the same manner as in
+the urine, did not scintillate when the flame was blown out, but burnt
+exactly in the same manner as the same paper dipped in the serum of blood
+drawn from another person.
+
+This experiment, which is copied from a letter of Mr. Hughes, as well as
+the former, seems to evince the existence of another passage from the
+intestines to the bladder, in this disease, besides that of the
+sanguiferous system; and coincides with the curious experiment related in
+section the third, except that the smell of the asparagus was not here
+perceived, owing perhaps to the roots having been made use of instead of
+the heads.
+
+The rising in the throat of this patient, and the twitchings of his limbs,
+seem to indicate some similarity between the diabetes and the hysteric
+disease, besides the great flow of pale urine, which is common to them
+both.
+
+Perhaps if the mesenteric glands were nicely inspected in the dissections
+of these patients; and if the thoracic duct, and the larger branches of the
+lacteals, and if the lymphatics, which arise from the bladder, were well
+examined by injection, or by the knife, the cause of diabetes might be more
+certainly understood.
+
+The opium alone, and the opium with the rosin, seem much to have served
+this patient, and might probably have effected a cure, if the disease had
+been slighter, or the medicine had been exhibited, before it had been
+confirmed by habit during the seven months it had continued. The increase
+of the quantity of water on beginning the large doses of rosin was probably
+owing to his omitting the morning doses of opium.
+
+V. _The Phænomena of Dropsies explained._
+
+I. Some inebriates have their paroxysms of inebriety terminated by much
+pale urine, or profuse sweats, or vomiting, or stools; others have their
+paroxysms terminated by stupor, or sleep, without the above evacuations.
+
+The former kind of these inebriates have been observed to be more liable to
+diabetes and dropsy; and the latter to gout, gravel, and leprosy. Evoe!
+attend ye bacchanalians! start at this dark train of evils, and, amid your
+immodest jests, and idiot laughter, recollect,
+
+  Quem Deus vult perdere, prius dementat.
+
+In those who are subject to diabetes and dropsy, the absorbent vessels are
+naturally more irritable than in the latter; and by being frequently
+disturbed or inverted by violent stimulus, and by their too great sympathy
+with each other, they become at length either entirely paralytic, or are
+only susceptible of motion from the stimulus of very acrid materials; as
+every part of the body, after having been used to great irritations,
+becomes less affected by smaller ones. Thus we cannot distinguish objects
+in the night, for some time after we come out of a strong light, though the
+iris is presently dilated; and the air of a summer evening appears cold,
+after we have been exposed to the heat of the day.
+
+There are no cells in the body, where dropsy may not be produced, if the
+lymphatics cease to absorb that mucilaginous fluid, which is perpetually
+deposited in them, for the purpose of lubricating their surfaces.
+
+If the lymphatic branch, which opens into the cellular membrane, either
+does its office imperfectly, or not at all; these cells become replete with
+a mucilaginous fluid, which, after it has stagnated some time in the cells,
+will coagulate over the fire; and is erroneously called water. Wherever the
+seat of this disease is, (unless in the lungs or other pendent viscera) the
+mucilaginous liquid above mentioned will subside to the most depending
+parts of the body, as the feet and legs, when those are lower than the head
+and trunk; for all these cells have communications with each other.
+
+When the cellular absorbents are become insensible to their usual
+irritations, it most frequently happens, but not always, that the cutaneous
+branch of absorbents, which is strictly associated with them, suffers the
+like inability. And then, as no water is absorbed from the atmosphere, the
+urine is not only less diluted at the time of its secretion, and
+consequently in less quantity and higher coloured: but great thirst is at
+the same time induced, for as no water is absorbed from the atmosphere to
+dilute the chyle and blood, the lacteals and other absorbent vessels, which
+have not lost their powers, are excited into more constant or more violent
+action, to supply this deficiency; whence the urine becomes still less in
+quantity, and of a deeper colour, and turbid like the yolk of an egg, owing
+to a greater absorption of its thinner parts. From this stronger action of
+those absorbents, which still retain their irritability, the fat is also
+absorbed, and the whole body becomes emaciated. This increased exertion of
+some branches of the lymphatics, while others are totally or partially
+paralytic, is resembled by what constantly occurs in the hemiplagia; when
+the patient has lost the use of the limbs on one side, he is incessantly
+moving those of the other; for the moving power, not having access to the
+paralytic limbs, becomes redundant in those which are not diseased.
+
+The paucity of urine and thirst cannot be explained from a greater quantity
+of mucilaginous fluid being deposited in the cellular membrane: for though
+these symptoms have continued many weeks, or even months, this collection
+frequently does not amount to more than very few pints. Hence also the
+difficulty of promoting copious sweats in anasarca is accounted for, as
+well as the great thirst, paucity of urine, and loss of fat; since, when
+the cutaneous branch of absorbents is paralytic, or nearly so, there is
+already too small a quantity of aqueous fluid in the blood: nor can these
+torpid cutaneous lymphatics be readily excited into retrograde motions.
+
+Hence likewise we understand, why in the ascites, and some other dropsies,
+there is often no thirst, and no paucity of urine; in these cases the
+cutaneous absorbents continue to do their office.
+
+Some have believed, that dropsies were occasioned by the inability of the
+kidneys, from having only observed the paucity of urine; and have thence
+laboured much to obtain diuretic medicines; but it is daily observable,
+that those who die of a total inability to make water, do not become
+dropsical in consequence of it: Fernelius mentions one, who laboured under
+a perfect suppression of urine during twenty days before his death, and yet
+had no symptoms of dropsy. Pathol. 1. vi. c. 8. From the same idea many
+physicians have restrained their patients from drinking, though their
+thirst has been very urgent; and some cases have been published, where this
+cruel regimen has been thought advantageous: but others of nicer
+observation are of opinion, that it has always aggravated the distresses of
+the patient; and though it has abated his swellings, yet by inducing a
+fever it has hastened his dissolution. See Transactions of the College,
+London, vol. ii. p. 235. Cases of Dropsy by Dr. G. Baker.
+
+The cure of anasarca, so far as respects the evacuation of the accumulated
+fluid, coincides with the idea of the retrograde action of the lymphatic
+system. It is well known that vomits, and other drugs, which induce
+sickness or nausea; at the same time that they evacuate the stomach,
+produce a great absorption of the lymph accumulated in the cellular
+membrane. In the operation of a vomit, not only the motions of the stomach
+and duodenum become inverted, but also those of the lymphatics and
+lacteals, which belong to them; whence a great quantity of chyle and lymph
+is perpetually poured into the stomach and intestines, during the
+operation, and evacuated by the mouth. Now at the same time, other branches
+of the lymphatic system, viz. those which open on the cellular membrane,
+are brought into more energetic action, by the sympathy above mentioned,
+and an increase of their absorption is produced.
+
+Hence repeated vomits, and cupreous salts, and small doses of squill or
+foxglove, are so efficacious in this disease. And as drastic purges act
+also by inverting the motions of the lacteals; and thence the other
+branches of lymphatics are induced into more powerful natural action, by
+sympathy, and drink up the fluids from all the cells of the body; and by
+their anastomoses, pour them into the lacteal branches; which, by their
+inverted actions, return them into the intestines; and they are thus
+evacuated from the body:--these purges also are used with success in
+discharging the accumulated fluid in anasarca.
+
+II. The following cases are related with design to ascertain the particular
+kinds of dropsy in which the digitalis purpurea, or common foxglove, is
+preferable to squill, or other evacuants, and were first published in 1780,
+in a pamphlet entitled Experiments on mucilaginous and purulent Matter, &c.
+Cadell. London. Other cases of dropsy, treated with digitalis, were
+afterwards published by Dr. Darwin in the Medical Transactions, vol. iii.
+in which there is a mistake in respect to the dose of the powder of
+foxglove, which should have been from five grains to one, instead of from
+five grains to ten.
+
+_Anasarca of the Lungs._
+
+1. A lady, between forty and fifty years of age, had been indisposed some
+time, was then seized with cough and fever, and afterwards expectorated
+much digested mucus. This expectoration suddenly ceased, and a considerable
+difficulty of breathing supervened, with a pulse very irregular both in
+velocity and strength; she was much distressed at first lying down, and at
+first rising; but after a minute or two bore either of those attitudes with
+ease. She had no pain or numbness in her arms; she had no hectic fever, nor
+any cold shiverings, and the urine was in due quantity, and of the natural
+colour.
+
+The difficulty of breathing was twice considerably relieved by small doses
+of ipecacuanha, which operated upwards and downwards, but recurred in a few
+days: she was then directed a decoction of foxglove, (digitalis purpurea)
+prepared by boiling four ounces of the fresh leaves from two pints of water
+to one pint; to which was added two ounces of vinous spirit: she took three
+large spoonfuls of this mixture every two hours, till she had taken it four
+times; a continued sickness supervened, with frequent vomiting, and a
+copious flow of urine: these evacuations continued at intervals for two or
+three days, and relieved the difficulty of breathing--She had some relapses
+afterwards, which were again relieved by the repetition of the decoction of
+foxglove.
+
+2. A gentleman, about sixty years of age, who had been addicted to an
+immoderate use of fermented liquors, and had been very corpulent, gradually
+lost his strength and flesh, had great difficulty of breathing, with legs
+somewhat swelled, and a very irregular pulse. He was very much distressed
+at first lying down, and at first rising from his bed, yet in a minute or
+two was easy in both those attitudes. He made straw-coloured urine in due
+quantity, and had no pain or numbness of his arms.
+
+He took a large spoonful of the decoction of foxglove, as above, every
+hour, for ten or twelve successive hours, had incessant sickness for about
+two days, and passed a large quantity of urine; upon which his breath
+became quite easy, and the swelling of his legs subsided; but as his whole
+constitution was already sinking from the previous intemperance of his
+life, he did not survive more than three or four months.
+
+_Hydrops Pericardii._
+
+3. A gentleman of temperate life and sedulous application to business,
+between thirty and forty years of age, had long been subject, at intervals,
+to an irregular pulse: a few months ago he became weak, with difficulty of
+breathing, and dry cough. In this situation a physician of eminence
+directed him to abstain from all animal food and fermented liquor, during
+which regimen all his complaints increased; he now became emaciated, and
+totally lost his appetite; his pulse very irregular both in velocity and
+strength; with great difficulty of breathing, and some swelling of his
+legs; yet he could lie down horizontally in his bed, though he got little
+sleep, and passed a due quantity of urine, and of the natural colour: no
+fullness or hardness could be perceived about the region of the liver; and
+he had no pain or numbness in his arms.
+
+One night he had a most profuse sweat all over his body and limbs, which
+quite deluged his bed, and for a day or two somewhat relieved his
+difficulty of breathing, and his pulse became less irregular: this copious
+sweat recurred three or four times at the intervals of five or six days,
+and repeatedly alleviated his symptoms.
+
+He was directed one large spoonful of the above decoction of foxglove every
+hour, till it procured some considerable evacuation: after he had taken it
+eleven successive hours he had a few liquid stools, attended with a great
+flow of urine, which last had a dark tinge, as if mixed with a few drops of
+blood: he continued sick at intervals for two days, but his breath became
+quite easy, and his pulse quite regular, the swelling of his legs
+disappeared, and his appetite and sleep returned.
+
+He then took three grains of white vitriol twice a day, with some bitter
+medicines, and a grain of opium with five grains of rhubarb every night;
+was advised to eat flesh meat, and spice, as his stomach would bear it,
+with small beer, and a few glasses of wine; and had issues made in his
+thighs; and has suffered no relapse.
+
+4. A lady, about fifty years of age, had for some weeks great difficulty of
+breathing, with very irregular pulse, and considerable general debility:
+she could lie down in bed, and the urine was in due quantity and of the
+natural colour, and she had no pain or numbness of her arms.
+
+She took one large spoonful of the above decoction of foxglove every hour,
+for ten or twelve successive hours; was sick, and made a quantity of pale
+urine for about two days, and was quite relieved both of the difficulty of
+breathing, and the irregularity of her pulse. She then took a grain of
+opium, and five grains of rhubarb, every night, night, for many weeks; with
+some slight chalybeate and bitter medicines, and has suffered no relapse.
+
+_Hydrops Thoracis._
+
+5. A tradesman, about fifty years of age, became weak and short of breath,
+especially on increase of motion, with pain in one arm, about the insertion
+of the biceps muscle. He observed he sometimes in the night made an unusual
+quantity of pale water. He took calomel, alum, and peruvian bark, and all
+his symptoms increased: his legs began to swell considerably; his breath
+became more difficult, and he could not lie down in bed; but all this time
+he made a due quantity of straw-coloured water.
+
+The decoction of foxglove was given as in the preceding cases, which
+operated chiefly by purging, and seemed to relieve his breath for a day or
+two; but also seemed to contribute to weaken him.--He became after some
+weeks universally dropsical, and died comatous.
+
+6. A young lady of delicate constitution, with light eyes and hair, and who
+had perhaps lived too abstemiously both in respect to the quantity and
+quality of what she eat and drank, was seized with great difficulty of
+breathing, so as to threaten immediate death. Her extremities were quite
+cold, and her breath felt cold to the back of one's hand. She had no sweat,
+nor could be down for a single moment; and had previously, and at present,
+complained of great weakness and pain and numbness of both her arms; had no
+swelling of her legs, no thirst, water in due quantity and colour. Her
+sister, about a year before, was afflicted with similar symptoms, was
+repeatedly blooded, and died universally dropsical.
+
+A grain of opium was given immediately, and repeated every six hours with
+evident and amazing advantage; afterwards a blister, with chalybeates,
+bitters, and essential oils, were exhibited, but nothing had such eminent
+effect in relieving the difficulty of breathing and coldness of her
+extremities as opium, by the use of which in a few weeks she perfectly
+regained her health, and has suffered no relapse.
+
+_Ascites._
+
+7. A young lady of delicate constitution having been exposed to great fear,
+cold, and fatigue, by the overturn of a chaise in the night, began with
+pain and tumour in the right hypochondrium: in a few months a fluctuation
+was felt throughout the whole abdomen, more distinctly perceptible indeed
+about the region of the stomach; since the integuments of the lower part of
+the abdomen generally become thickened in this disease by a degree of
+anasarca. Her legs were not swelled, no thirst, water in due quantity and
+colour.--She took the foxglove so as to induce sickness and stools, but
+without abating the swelling, and was obliged at length to submit to the
+operation of tapping.
+
+8. A man about sixty-seven, who had long been accustomed to spirituous
+potation, had some time laboured under ascites; his legs somewhat swelled;
+his breath easy in all attitudes; no appetite; great thirst; urine in
+exceedingly small quantity, very deep coloured, and turbid; pulse equal. He
+took the foxglove in such quantity as vomited him, and induced sickness for
+two days; but procured no flow of urine, or diminution of his swelling; but
+was thought to leave him considerably weaker.
+
+9. A corpulent man, accustomed to large potation of fermented liquors, had
+vehement cough, difficult breathing, anasarca of his legs, thighs, and
+hands, and considerable tumour, with evident fluctuation of his abdomen;
+his pulse was equal; his urine in small quantity, of deep colour, and
+turbid. These swellings had been twice considerably abated by drastic
+cathartics. He took three ounces of a decoction of foxglove (made by
+boiling one ounce of the fresh leaves in a pint of water) every three
+hours, for two whole days; it then began to vomit and purge him violently,
+and promoted a great flow of urine; he was by these evacuations completely
+emptied in twelve hours. After two or three months all these symptoms
+returned, and were again relieved by the use of the foxglove; and thus in
+the space of about three years he was about ten times evacuated, and
+continued all that time his usual potations: excepting at first, the
+medicine operated only by urine, and did not appear considerably to weaken
+him--The last time he took it, it had no effect; and a few weeks afterwards
+he vomited a great quantity of blood, and expired.
+
+QUERIES.
+
+1. As the first six of these patients had a due discharge of urine, and of
+the natural colour, was not the feat of the disease confined to some part
+of the thorax, and the swelling of the legs rather a symptom of the
+obstructed circulation of the blood, than of a paralysis of the cellular
+lymphatics of those parts?
+
+2. When the original disease is a general anasarca, do not the cutaneous
+lymphatics always become paralytic at the same time with the cellular ones,
+by their greater sympathy with each other? and hence the paucity of urine,
+and the great thirst, distinguish this kind of dropsy?
+
+3. In the anasarca of the lungs, when the disease is not very great, though
+the patients have considerable difficulty of breathing at their first lying
+down, yet after a minute or two their breath becomes easy again; and the
+same occurs at their first rising. Is not this owing to the time necessary
+for the fluid in the cells of the lungs to change its place, so as the
+least to incommode respiration in the new attitude?
+
+4. In the dropsy of the pericardium does not the patient bear the
+horizontal or perpendicular attitude with equal ease? Does this
+circumstance distinguish the dropsy of the pericardium from that of the
+lungs and of the thorax?
+
+5. Do the universal sweats distinguish the dropsy of the pericardium, or of
+the thorax? and those, which cover the upper parts of the body only, the
+anasarca of the lungs?
+
+6. When in the dropsy of the thorax, the patient endeavours to lie down,
+does not the extravasated fluid compress the upper parts of the bronchia,
+and totally preclude the access of air to every part of the lungs; whilst
+in the perpendicular attitude the inferior parts of the lungs only are
+compressed? Does not something similar to this occur in the anasarca of the
+lungs, when the disease is very great, and thus prevent those patients also
+from lying down?
+
+7. As a principal branch of the fourth cervical nerve of the left side,
+after having joined a branch of the third and of the second cervical
+nerves, descending between the subclavian vein and artery, is received in a
+groove formed for it in the pericardium, and is obliged to make a
+considerable turn outwards to go over the prominent part of it, where the
+point of the heart is lodged, in its course to the diaphragm; and as the
+other phrenic nerve of the right side has a straight course to the
+diaphragm; and as many other considerable branches of this fourth pair of
+cervical nerves are spread on the arms; does not a pain in the left arm
+distinguish a disease of the pericardium, as in the angina pectoris, or in
+the dropsy of the pericardium? and does not a pain or weakness in both arms
+distinguish the dropsy of the thorax?
+
+8. Do not the dropsies of the thorax and pericardium frequently exist
+together, and thus add to the uncertainty and fatality of the disease?
+
+9. Might not the foxglove be serviceable in hydrocephalus internus, in
+hydrocele, and in white swellings of the joints?
+
+VI. _Of cold Sweats._
+
+There have been histories given of chronical immoderate sweatings, which
+bear some analogy to the diabetes. Dr. Willis mentions a lady then living,
+whose sweats where for many years so profuse, that all her bed-clothes were
+not only moistened, but deluged with them every night; and that many
+ounces, and sometimes pints, of this sweat, were received in vessels
+properly placed, as it trickled down her body. He adds, that she had great
+thirst, had taken many medicines, and submitted to various rules of life,
+and changes of climate, but still continued to have these immoderate
+sweats. Pharmac. ration. de sudore anglico.
+
+Dr. Willis has also observed, that the sudor anglicanus which appeared in
+England, in 1483, and continued till 1551, was in some respects similar to
+the diabetes; and as Dr. Caius, who saw this disease, mentions the
+viscidity, as well as the quantity of these sweats, and adds, that the
+extremities were often cold, when the internal parts were burnt up with
+heat and thirst, with great and speedy emaciation and debility: there is
+great reason to believe, that the fluids were absorbed from the cells of
+the body by the cellular and cystic branches of the lymphatics, and poured
+on the skin by the retrograde motions of the cutaneous ones.
+
+Sydenham has recorded, in the stationary fever of the year 1685, the viscid
+sweats flowing from the head, which were probably from the same source as
+those in the sweating plague above mentioned.
+
+It is very common in dropsies of the chest or lungs to have the difficulty
+of breathing relieved by copious sweats, flowing from the head and neck.
+Mr. P. about 50 years of age, had for many weeks been afflicted with
+anasarca of his legs and thighs, attended with difficulty of breathing; and
+had repeatedly been relieved by squill, other bitters, and
+chalybeates.--One night the difficulty of breathing became so great, that
+it was thought he must have expired; but so copious a sweat came out of his
+head and neck, that in a few hours some pints, by estimation, were wiped
+off from those parts, and his breath was for a time relieved. This dyspnoea
+and these sweats recurred at intervals, and after some weeks he ceased to
+exist. The skin of his head and neck felt cold to the hand, and appeared
+pale at the time these sweats flowed so abundantly; which is a proof, that
+they were produced by an inverted motion of the absorbents of those parts:
+for sweats, which are the consequence of an increased action of the
+sanguiferous system, are always attended with a warmth of the skin, greater
+than is natural, and a more florid colour; as the sweats from exercise, or
+those that succeed the cold fits of agues. Can any one explain how these
+partial sweats should relieve the difficulty of breathing in anasarca, but
+by supposing that the pulmonary branch of absorbents drank up the fluid in
+the cavity of the thorax, or in the cells of the lungs, and threw it on the
+skin, by the retrograde motions of the cutaneous branch? for, if we could
+suppose, that the increased action of the cutaneous glands or capillaries
+poured upon the skin this fluid, previously absorbed from the lungs; why is
+not the whole surface of the body covered with sweat? why is not the skin
+warm? Add to this, that the sweats above mentioned were clammy or
+glutinous, which the condensed perspirable matter is not; whence it would
+seem to have been a different fluid from that of common perspiration.
+
+Dr. Dobson, of Liverpool, has given a very ingenious explanation of the
+acid sweats, which he observed in a diabetic patient--he thinks part of the
+chyle is secreted by the skin, and afterwards undergoes an acetous
+fermentation.--Can the chyle get thither, but by an inverted motion of the
+cutaneous lymphatics? in the same manner as it is carried to the bladder,
+by the inverted motions of the urinary lymphatics. Medic. Observat. and
+Enq. London, vol. v.
+
+Are not the cold sweats in some fainting fits, and in dying people, owing
+to an inverted motion of the cutaneous lymphatics? for in these there can
+be no increased arterial or glandular action.
+
+Is the difficulty of breathing, arising from anasarca of the lungs,
+relieved by sweats from the head and neck; whilst that difficulty of
+breathing, which arises from a dropsy of the thorax, or pericardium, is
+never attended with these sweats of the head? and thence can these diseases
+be distinguished from each other? Do the periodic returns of nocturnal
+asthma rise from a temporary dropsy of the lungs, collected during their
+more torpid state in sound deep, and then re-absorbed by the vehement
+efforts of the disordered organs of respiration, and carried off by the
+copious sweats about the head and neck?
+
+More extensive and accurate dissections of the lymphatic system are wanting
+to enable us to unravel these knots of science.
+
+VII. _Translations of Matter, of Chyle, of Milk, of Urine. Operation of
+purging Drugs applied externally._
+
+1. The translations of matter from one part of the body to another, can
+only receive an explanation from the doctrine of the occasional retrograde
+motions of some branches of the lymphatic system: for how can matter,
+absorbed and mixed with the whole mass of blood, be so hastily collected
+again in any one part? and is it not an immutable law, in animal bodies,
+that each gland can secrete no other, but its own proper fluid? which is,
+in part, fabricated in the very gland by an animal process, which it there
+undergoes: of these purulent translations innumerable and very remarkable
+instances are recorded.
+
+2. The chyle, which is seen among the materials thrown up by violent
+vomiting, or in purging stools, can only come thither by its having been
+poured into the bowels by the inverted motions of the lacteals: for our
+aliment is not converted into chyle in the stomach or intestines by a
+chemical process, but is made in the very mouths of the lacteals; or in the
+mesenteric glands; in the same manner as other secreted fluids are made by
+an animal process in their adapted glands.
+
+Here a curious phænomenon in the exhibition of mercury is worth
+explaining:--If a moderate dose of calomel, as six or ten grains, be
+swallowed, and within one or two days a cathartic is given, a salivation is
+prevented: but after three or four days, a salivation having come on,
+repeated purges every day, for a week or two, are required to eliminate the
+mercury from the constitution. For this acrid metallic preparation, being
+absorbed by the mouth of the lacteals, continues, for a time arrested by
+the mesenteric glands, (as the variolous or venereal poisons swell the
+subaxillar or inguinal glands): which, during the operation of a cathartic,
+is returned into the intestines by the inverted action of the lacteals, and
+thus carried out of the system.
+
+Hence we understand the use of vomits or purges, to those who have
+swallowed either contagious or poisonous materials, even though exhibited a
+day or even two days after such accidents; namely, that by the retrograde
+motions of the lacteals and lymphatics, the material still arrested in the
+mesenteric, or other glands, may be eliminated from the body.
+
+3. Many instances of milk and chyle found in ulcers are given by Haller,
+El. Physiol. t. vii. p. 12, 23, which admit of no other explanation than by
+supposing, that the chyle, imbibed by one branch of the absorbent system,
+was carried to the ulcer, by the inverted motions of another branch of the
+same system.
+
+4. Mrs. P. on the second day after delivery, was seized with a violent
+purging, in which, though opiates, mucilages, the bark, and testacea were
+profusely used, continued many days, till at length she recovered. During
+the time of this purging, no milk could be drawn from her breasts; but the
+stools appeared like the curd of milk broken into small pieces. In this
+case, was not the milk taken up from the follicles of the pectoral glands,
+and thrown on the intestines, by a retrogression of the intestinal
+absorbents? for how can we for a moment suspect that the mucous glands of
+the intestines could separate pure milk from the blood? Doctor Smelly has
+observed, that loose stools, mixed with milk, which is curdled in the
+intestines, frequently relieves the turgescency of the breasts of those who
+studiously repel their milk. Cases in Midwifery, 43, No. 2. 1.
+
+5. J.F. Meckel observed in a patient, whose urine was in small quantity and
+high coloured, that a copious sweat under the arm-pits, of a perfectly
+urinous smell, stained the linen; which ceased again when the usual
+quantity of urine was discharged by the urethra. Here we must believe from
+analogy, that the urine was first secreted in the kidneys, then re-absorbed
+by the increased action of the urinary lymphatics, and lastly carried to
+the axillae by the retrograde motions of the lymphatic branches of those
+parts. As in the jaundice it is necessary, that the bile should first be
+secreted by the liver, and re-absorbed into the circulation, to produce the
+yellowness of the skin; as was formerly demonstrated by the late Dr. Munro,
+(Edin. Medical Essays) and if in this patient the urine had been
+re-absorbed into the mass of blood, as the bile in the jaundice, why was it
+not detected in other parts of the body, as well as in the arm-pits?
+
+6. Cathartic and vermifuge medicines applied externally to the abdomen,
+seem to be taken up by the cutaneous branch of lymphatics, and poured on
+the intestines by the retrograde motions of the lacteals, without having
+passed the circulation.
+
+For when the drastic purges are taken by the mouth, they excite the
+lacteals of the intestines into retrograde motions, as appears from the
+chyle, which is found coagulated among the fæces, as was shewn above,
+(sect. 2 and 4.) And as the cutaneous lymphatics are joined with the
+lacteals of the intestines, by frequent anastomoses; it would be more
+extraordinary, when a strong purging drug, absorbed by the skin, is carried
+to the anastomosing branches of the lacteals unchanged, if it should not
+excite them into retrograde action as efficaciously, as if it was taken by
+the mouth, and mixed with the food of the stomach.
+
+VIII. _Circumstances by which the Fluids, that are effused by the
+retrograde Motions of the absorbent Vessels, are distinguished._
+
+1. We frequently observe an unusual quantity of mucus or other fluids in
+some diseases, although the action of the glands, by which those fluids are
+separated from the blood, is not unusually increased; but when the power of
+absorption alone is diminished. Thus the catarrhal humour from the nostrils
+of some, who ride in frosty weather; and the tears, which run down the
+cheeks of those, who have an obstruction of the puncta lacrymalia; and the
+ichor of those phagedenic ulcers, which are not attended with inflammation,
+are all instances of this circumstance.
+
+These fluids however are easily distinguished from others by their
+abounding in ammoniacal or muriatic salts; whence they inflame the
+circumjacent skin: thus in the catarrh the upper lip becomes red and
+swelled from the acrimony of the mucus, and patients complain of the
+saltness of its taste. The eyes and cheeks are red with the corrosive
+tears, and the ichor of some herpetic eruptions erodes far and wide the
+contiguous parts, and is pungently salt to the taste, as some patients have
+informed me.
+
+Whilst, on the contrary, those fluids, which are effused by the retrograde
+action of the lymphatics, are for the most part mild and innocent; as
+water, chyle, and the natural mucus: or they take their properties from the
+materials previously absorbed, as in the coloured or vinous urine, or that
+scented with asparagus, described before.
+
+2. Whenever the secretion of any fluid is increased, there is at the same
+time an increased heat in the part; for the secreted fluid, as the bile,
+did not previously exist in the mass of blood, but a new combination is
+produced in the gland. Now as solutions are attended with cold, so
+combinations are attended with heat; and it is probable the sum of the heat
+given out by all the secreted fluids of animal bodies may be the cause of
+their general heat above that of the atmosphere.
+
+Hence the fluids derived from increased secretions are readily
+distinguished from those originating from the retrograde motions of the
+lymphatics: thus an increase of heat either in the diseased parts, or
+diffused over the whole body, is perceptible, when copious bilious stools
+are consequent to an inflamed liver; or a copious mucous salivation from
+the inflammatory angina.
+
+3. When any secreted fluid is produced in an unusual quantity, and at the
+same time the power of absorption is increased in equal proportion, not
+only the heat of the gland becomes more intense, but the secreted fluid
+becomes thicker and milder, its thinner and saline parts being re-absorbed:
+and these are distinguishable both by their greater consistence, and by
+their heat, from the fluids, which are effused by the retrograde motions of
+the lymphatics; as is observable towards the termination of gonorrhoea,
+catarrh, chincough, and in those ulcers, which are said to abound with
+laudable pus.
+
+4. When chyle is observed in stools, or among the materials ejected by
+vomit, we may be confident it must have been brought thither by the
+retrograde motions of the lacteals; for chyle does not previously exist
+amid the contents of the intestines, but is made in the very mouths of the
+lacteals, as was before explained.
+
+5. When chyle, milk, or other extraneous fluids are found in the urinary
+bladder, or in any other excretory receptacle of a gland; no one can for a
+moment believe, that these have been collected from the mass of blood by a
+morbid secretion, as it contradicts all analogy.
+
+                  ---- Aurea duræ
+  Mala ferant quercus? Narcisco floreat alnus?
+  Pinguia corticibus sudent electra myricæ?--VIRGIL.
+
+IX. _Retrograde Motions of Vegetable juices._
+
+There are besides some motions of the sap in vegetables, which bear analogy
+to our present subject; and as the vegetable tribes are by many
+philosophers held to be inferior animals, it may be a matter of curiosity
+at least to observe, that their absorbent vessels seem evidently, at times,
+to be capable of a retrograde motion. Mr. Perault cut off a forked branch
+of a tree, with the leaves on; and inverting one of the forks into a vessel
+of water, observed, that the leaves on the other branch continued green
+much longer than those of a similar branch, cut off from the same tree;
+which shews, that the water from the vessel was carried up one part of the
+forked branch, by the retrograde motion of its vessels, and supplied
+nutriment some time to the other part of the branch, which was out of the
+water. And the celebrated Dr. Hales found, by numerous very accurate
+experiments, that the sap of trees rose upwards during the warmer hours of
+the day, and in part descended again during the cooler ones. Vegetable
+Statics.
+
+It is well known that the branches of willows, and of many other trees,
+will either take root in the earth or engraft on other trees, so as to have
+their natural direction inverted, and yet flourish with vigour.
+
+Dr. Hope has also made this pleasing experiment, after the manner of
+Hales--he has placed a forked branch, cut from one tree, erect between two
+others; then cutting off a part of the bark from one fork applied it to a
+similar branch of one of the trees in its vicinity; and the same of the
+other fork; so that a tree is seen to grow suspended in the air, between
+two other trees; which supply their softer friend with due nourishment.
+
+  Miranturque novas frondes, et non sua poma.
+
+All these experiments clearly evince, that the juices of vegetables can
+occasionally pass either upwards or downwards in their absorbent system of
+vessels.
+
+X. _Objections answered._
+
+The following experiment, at first view, would seem to invalidate this
+opinion of the retrograde motions of the lymphatic vessels, in some
+diseases.
+
+About a gallon of milk having been giving to an hungry swine, he was
+suffered to live about an hour, and was then killed by a stroke or two on
+his head with an axe.--On opening his belly the lacteals were well seen
+filled with chyle; on irritating many of the branches of them with a knife,
+they did not appear to empty themselves hastily; but they did however carry
+forwards their contents in a little time.
+
+I then passed a ligature round several branches of lacteals, and irritated
+them much with a knife beneath the ligature, but could not make them
+regurgitate their contained fluid into the bowels.
+
+I am not indeed certain, that the nerve was not at the same time included
+in the ligature, and thus the lymphatic rendered unirritable or lifeless;
+but this however is certain, that it is not any quantity of any stimulus,
+which induces the vessels of animal bodies to revert their motions; but a
+certain quantity of a certain stimulus, as appears from wounds in the
+stomach, which do not produce vomiting; and wounds of the intestines, which
+do not produce the cholera morbus.
+
+At Nottingham, a few years ago, two shoemakers quarrelled, and one of them
+with a knife, which they use in their occupation, stabbed his companion
+about the region of the stomach. On opening the abdomen of the wounded man
+after his death the food and medicines he had taken were in part found in
+the cavity of the belly, on the outside of the bowels; and there was a
+wound about half an inch long at the bottom of the stomach; which I suppose
+was distended with liquor and food at the time of the accident; and thence
+was more liable to be injured at its bottom: but during the whole time he
+lived, which was about ten days, he had no efforts to vomit, nor ever even
+complained of being sick at the stomach! Other cases similar to this are
+mentioned in the philosophical transactions.
+
+Thus, if you vellicate the throat with a feather, nausea is produced; if
+you wound it with a penknife, pain is induced, but not sickness. So if the
+soles of the feet of children or their armpits are tickled, convulsive
+laughter is excited, which ceases the moment the hand is applied, so as to
+rub them more forcibly.
+
+The experiment therefore above related upon the lacteals of a dead pig,
+which were included in a strict ligature, proves nothing; as it is not the
+quantity, but the kind of stimulus, which excites the lymphatic vessels
+into retrograde motion.
+
+XI. _The Causes which induce the retrograde Motions of animal Vessels; and
+the Medicines by which the natural Motions are restored._
+
+1. Such is the construction of animal bodies, that all their parts, which
+are subjected to less stimuli than nature designed, perform their functions
+with less accuracy: thus, when too watery or too acescent food is taken
+into the stomach, indigestion, and flatulency, and heartburn succeed.
+
+2. Another law of irritation, connate with our existence, is, that all
+those parts of the body, which have previously been exposed to too great a
+quantity of such stimuli, as strongly affect them, become for some time
+afterwards disobedient to the natural quantity of their adapted
+stimuli.--Thus the eye is incapable of seeing objects in an obscure room,
+though the iris is quite dilated, after having been exposed to the meridian
+sun.
+
+3. There is a third law of irritation, that all the parts of our bodies,
+which have been lately subjected to less stimulus, than they have been
+accustomed to, when they are exposed to their usual quantity of stimulus,
+are excited into more energetic motions: thus when we come from a dusky
+cavern into the glare of daylight, our eyes are dazzled; and after emerging
+from the cold bath, the skin becomes warm and red.
+
+4. There is a fourth law of irritation, that all the parts of our bodies,
+which are subjected to still stronger stimuli for a length of time, become
+torpid, and refuse to obey even these stronger stimuli; and thence do their
+offices very imperfectly.--Thus, if any one looks earnestly for some
+minutes on an area, an inch diameter, of red silk, placed on a sheet of
+white paper, the image of the silk will gradually become pale, and at
+length totally vanish.
+
+5. Nor is it the nerves of sense alone, as the optic and auditory nerves,
+that thus become torpid, when the stimulus is withdrawn or their
+irritability decreased; but the motive muscles, when they are deprived of
+their natural stimuli, or of their irritability, become torpid and
+paralytic; as is seen in the tremulous hand of the drunkard in a morning;
+and in the awkward step of age.
+
+The hollow muscles also, of which the various vessels of the body are
+constructed, when they are deprived of their natural stimuli, or of their
+due degree of irritability, not only become tremulous, as the arterial
+pulsations of dying people; but also frequently invert their motions, as in
+vomiting, in hysteric suffocations, and diabetes above described.
+
+I must beg your patient attention, for a few moments whilst I endeavour to
+explain, how the retrograde actions of our hollow muscles are the
+consequence of their debility; as the tremulous actions of the solid
+muscles are the consequence of their debility. When, through fatigue, a
+muscle can act no longer; the antagonist muscles, either by their inanimate
+elasticity, or by their animal action, draw the limb into a contrary
+direction: in the solid muscles, as those of locomotion, their actions are
+associated in tribes, which have been accustomed to synchronous action
+only; hence when they are fatigued, only a single contrary effort takes
+place; which is either tremulous, when the fatigued muscles are again
+immediately brought into action; or it is a pandiculation, or stretching,
+where they are not immediately again brought into action.
+
+Now the motions of the hollow muscles, as they in general propel a fluid
+along their cavities, are associated in trains, which have been accustomed
+to successive actions: hence when one ring of such a muscle is fatigued
+from its too great debility, and is brought into retrograde action, the
+next ring from its association falls successively into retrograde action;
+and so on throughout the whole canal. See Sect. XXV. 6.
+
+6. But as the retrograde motions of the stomach, oesophagus, and fauces in
+vomiting are, as it were, apparent to the eye; we shall consider this
+operation more minutely, that the similar operations in the more recondite
+parts of our system may be easier understood.
+
+From certain nauseous ideas of the mind, from an ungrateful taste in the
+mouth, or from foetid smells, vomiting is sometimes instantly excited; or
+even from a stroke on the head, or from the vibratory motions of a ship;
+all which originate from association, or sympathy. See Sect. XX. on
+Vertigo.
+
+But when the stomach is subjected to a less stimulus than is natural,
+according to the first law of irritation mentioned above, its motions
+become disturbed, as in hunger; first pain is produced, then sickness, and
+at length vain efforts to vomit, as many authors inform us.
+
+But when a great quantity of wine, or of opium, is swallowed, the
+retrograde motions of the stomach do not occur till after several minutes,
+or even hours; for when the power of so strong a stimulus ceases, according
+to the second law of irritation, mentioned above, the peristaltic motions
+become tremulous, and at length retrograde; as is well known to the
+drunkard, who on the next morning has sickness and vomitings.
+
+When a still greater quantity of wine, or of opium, or when nauseous
+vegetables, or strong bitters, or metallic salts, are taken into the
+stomach, they quickly induce vomiting; though all these in less doses
+excite the stomach into more energetic action, and strengthen the
+digestion; as the flowers of chamomile, and the vitriol of zinc: for,
+according to the fourth law of irritation, the stomach will not long be
+obedient to a stimulus so much greater than is natural; but its action
+becomes first tremulous and then retrograde.
+
+7. When the motions of any vessels become retrograde, less heat of the body
+is produced; for in paroxysms of vomiting, of hysteric affections, of
+diabetes, of asthma, the extremities of the body are cold: hence we may
+conclude, that these symptoms arise from the debility of the parts in
+action; for an increase of muscular action is always attended with increase
+of heat.
+
+8. But as animal debility is owing to defect of stimulus, or to defect of
+irritability, as shewn above, the method of cure is easily deduced: when
+the vascular muscles are not excited into their due action by the natural
+stimuli, we should exhibit those medicines, which possess a still greater
+degree of stimulus; amongst these are the foetids, the volatiles,
+aromatics, bitters, metallic salts, opiates, wine, which indeed should be
+given in small doses, and frequently repeated. To these should be added
+constant, but moderate exercise, cheerfulness of mind, and change of
+country to a warmer climate; and perhaps occasionally the external stimulus
+of blisters.
+
+It is also frequently useful to diminish the quantity of natural stimulus
+for a short time, by which afterwards the irritability of the system
+becomes increased; according to the third law of irritation
+above-mentioned, hence the use of baths somewhat colder than animal heat,
+and of equitation in the open air.
+
+_The catalogue of diseases owing to the retrograde motions of lymphatics is
+here omitted, as it will appear in the second volume of this work. The
+following is the conclusion to this thesis of_ Mr. CHARLES DARWIN.
+
+Thus have I endeavoured in a concise manner to explain the numerous
+diseases, which deduce their origin from the inverted motions of the hollow
+muscles of our bodies: and it is probable, that Saint Vitus's dance, and
+the stammering of speech, originate from a similar, inverted order of the
+associated motions of some of the solid muscles; which, as it is foreign to
+my present purpose, I shall not here discuss.
+
+I beg, illustrious professors, and ingenious fellow-students, that you will
+recollect how difficult a talk I have attempted, to evince the retrograde
+motions of the lymphatic vessels, when the vessels themselves for so many
+ages escaped the eyes and glasses of philosophers: and if you are not yet
+convinced of the truth of this theory, hold, I entreat you, your minds in
+suspense, till ANATOMY draws her sword with happier omens, cuts asunder the
+knots, which entangle PHYSIOLOGY; and, like an augur inspecting the
+immolated victim, announces to mankind the wisdom of HEAVEN.
+
+       *       *       *       *       *
+
+SECT. XXX.
+
+PARALYSIS OF THE LIVER AND KIDNEYS.
+
+    I. 1._Bile-ducts less irritable after having been stimulated much._ 2.
+    _Jaundice from paralysis of the bile-ducts cured by electric shocks._
+    3. _From bile-stones. Experiments on bile-stones. Oil vomit._ 4. _Palsy
+    of the liver, two cases._ 5. _Schirrosity of the liver._ 6. _Large
+    livers of geese._ II. _Paralysis of the kidneys._ III. _Story of
+    Prometheus._
+
+I. 1. From the ingurgitation of spirituous liquors into the stomach and
+duodenum, the termination of the common bile-duct in that bowel becomes
+stimulated into unnatural action, and a greater quantity of bile is
+produced from all the secretory vessels of the liver, by the association of
+their motions with those of their excretory ducts; as has been explained in
+Section XXIV. and XXV. but as all parts of the body, that have been
+affected with stronger stimuli for any length of time, become less
+susceptible of motion, from their natural weaker stimuli, it follows, that
+the motions of the secretory vessels, and in consequence the secretion of
+bile, is less than is natural during the intervals of sobriety. 2. If this
+ingurgitation of spirituous liquors has been daily continued in
+considerable quantity, and is then suddenly intermitted, a languor or
+paralysis of the common bile-duct is induced; the bile is prevented from
+being poured into the intestines; and as the bilious absorbents are
+stimulated into stronger action by its accumulation, and by the acrimony or
+viscidity, which it acquires by delay, it is absorbed, and carried to the
+receptacle of the chyle; or otherwise the secretory vessels of the liver,
+by the above-mentioned stimulus, invert their motions, and regurgitate
+their contents into the blood, as sometimes happens to the tears in the
+lachrymal sack, see Sect. XXIV. 2. 7. and one kind of jaundice is brought
+on.
+
+There is reason to believe, that the bile is most frequently returned into
+the circulation by the inverted motions of these hepatic glands, for the
+bile does not seem liable to be absorbed by the lymphatics, for it soaks
+through the gall-ducts, and is frequently found in the cellular membrane.
+This kind of jaundice is not generally attended with pain, neither at the
+extremity of the bile-duct, where it enters the duodenum, nor on the region
+of the gall-bladder.
+
+Mr. S. a gentleman between 40 and 50 years of age, had had the jaundice
+about six weeks, without pain, sickness, or fever; and had taken emetics,
+cathartics, mercurials, bitters, chalybeates, essential oil, and ether,
+without apparent advantage. On a supposition that the obstruction of the
+bile might be owing to the paralysis, or torpid action of the common
+bile-duct, and the stimulants taken into the stomach seeming to have no
+effect, I directed half a score smart electric shocks from a coated bottle,
+which held about a quart, to be passed through the liver, and along the
+course of the common gall-duct, as near as could be guessed, and on that
+very day the stools became yellow; he continued the electric shocks a few
+days more, and his skin gradually became clear.
+
+3. The bilious vomiting and purging, that affects some people by intervals
+of a few weeks, is a less degree of this disease; the bile-duct is less
+irritable than natural, and hence the bile becomes accumulated in the
+gall-bladder, and hepatic ducts, till by its quantity, acrimony or
+viscidity, a greater degree of irritation is produced, and it is suddenly
+evacuated, or lastly from the absorption of the more liquid parts of the
+bile, the remainder becomes inspissated, and chrystallizes into masses too
+large to pass, and forms another kind of jaundice, where the bile-duct is
+not quite paralytic, or has regained its irritability.
+
+This disease is attended with much pain, which at first is felt at the pit
+of the stomach, exactly in the centre of the body, where the bile-duct
+enters the duodenum; afterwards, when the size of the bile-stones increase,
+it is also felt on the right side, where the gall-bladder is situated. The
+former pain at the pit of the stomach recurs by intervals, as the
+bile-stone is pushed against the neck of the duct; like the paroxysms of
+the stone in the urinary bladder, the other is a more dull and constant
+pain.
+
+Where these bile-stones are too large to pass, and the bile-ducts possess
+their sensibility, this becomes a very painful and hopeless disease. I made
+the following experiments with a view to their chemical solution.
+
+Some fragments of the same bile-stone were put into the weak spirit of
+marine salt, which is sold in the shops, and into solution of mild alcali;
+and into a solution of caustic alcali; and into oil of turpentine; without
+their being dissolved. All these mixtures were after some time put into a
+heat of boiling water, and then the oil of turpentine dissolved its
+fragments of bile-stone, but no alteration was produced upon those in the
+other liquids except some change of their colour.
+
+Some fragments of the same bile-stone were put into vitriolic æther, and
+were quickly dissolved without additional heat. Might not æther mixed with
+yolk of egg or with honey be given advantageously in bilious concretions?
+
+I have in two instances seen from 30 to 50 bile-stones come away by stool,
+about the size of large peas, after having given six grains of calomel in
+the evening, and four ounces of oil of almonds or olives on the succeeding
+morning. I have also given half a pint of good olive or almond oil as an
+emetic during the painful fit, and repeated it in half an hour, if the
+first did not operate, with frequent good effect.
+
+4. Another disease of the liver, which I have several times observed,
+consists in the inability or paralysis of the secretory vessels. This
+disease has generally the same cause as the preceding one, the too frequent
+potation of spirituous liquors, or the too sudden omission of them, after
+the habit is confined; and is greater or less in proportion, as the whole
+or a part of the liver is affected, and as the inability or paralysis is
+more or less complete.
+
+This palsy of the liver is known from these symptoms, the patients have
+generally passed the meridian of life, have drank fermented liquors daily,
+but perhaps not been opprobrious drunkards; they lose their appetite, then
+their flesh and strength diminish in consequence, there appears no bile in
+their stools, nor in their urine, nor is any hardness or swelling
+perceptible on the region of the liver. But what is peculiar to this
+disease, and distinguishes it from all others at the first glance of the
+eye, is the bombycinous colour of the skin, which, like that of full-grown
+silkworms, has a degree of transparency with a yellow tint not greater than
+is natural to the serum of the blood.
+
+Mr. C. and Mr. B. both very strong men, between 50 and 60 years of age, who
+had drank ale at their meals instead of small beer, but were not reputed
+hard-drinkers, suddenly became weak, lost their appetite, flesh, and
+strength, with all the symptoms above enumerated, and died in about two
+months from the beginning of their malady. Mr. C. became anasarcous a few
+days before his death, and Mr. B. had frequent and great hæmorrhages from
+an issue, and some parts of his mouth, a few days before his death. In both
+these cases calomel, bitters and chalybeates were repeatedly used without
+effect.
+
+One of the patients described above, Mr. C, was by trade a plumber; both of
+them could digest no food, and died apparently for want of blood. Might not
+the transfusion of blood be used in these cases with advantage?
+
+5. When the paralysis of the hepatic glands is less complete, or less
+universal, a schirrosity of some part of the liver is induced; for the
+secretory vessels retaining some of their living power take up a fluid from
+the circulation, without being sufficiently irritable to carry it forwards
+to their excretory ducts; hence the body, or receptacle of each gland,
+becomes inflated, and this distension increases, till by its very great
+stimulus inflammation is produced, or till those parts of the viscus become
+totally paralytic. This disease is distinguishable from the foregoing by
+the palpable hardness or largeness of the liver; and as the hepatic glands
+are not totally paralytic, or the whole liver not affected, some bile
+continues to be made. The inflammations of this viscus, consequent to the
+schirrosity of it, belong to the diseases of the sensitive motions, and
+will be treated of hereafter.
+
+6. The ancients are said to have possessed an art of increasing the livers
+of geese to a size greater than the remainder of the goose. Martial. l. 13.
+epig. 58.--This is said to have been done by fat and figs. Horace, l. 2.
+sat. 8.--Juvenal sets these large livers before an epicure as a great
+rarity. Sat. 5. l. 114; and Persius, sat. 6. l. 71. Pliny says these large
+goose-livers were soaked in mulled milk, that is, I suppose, milk mixed
+with honey and wine; and adds, "that it is uncertain whether Scipio
+Metellus, of consular dignity, or M. Sestius, a Roman knight, was the great
+discoverer of this excellent dish." A modern traveller, I believe Mr.
+Brydone, asserts that the art of enlarging the livers of geese still exists
+in Sicily; and it is to be lamented that he did not import it into his
+native country, as some method of affecting the human liver might perhaps
+have been collected from it; besides the honour he might have acquired in
+improving our giblet pies.
+
+Our wiser caupones, I am told, know how to fatten their fowls, as well as
+their geese, for the London markets, by mixing gin instead of figs and fat
+with their food; by which they are said to become sleepy, and to fatten
+apace, and probably acquire enlarged livers; as the swine are asserted to
+do, which are fed on the sediments of barrels in the distilleries; and
+which so frequently obtains in those, who ingurgitate much ale, or wine, or
+drams.
+
+II. The irritative diseases of the kidneys, pancreas, spleen, and other
+glands, are analogous to those of the liver above described, differing only
+in the consequences attending their inability to action. For instance, when
+the secretory vessels of the kidneys become disobedient to the stimulus of
+the passing current of blood, no urine is separated or produced by them;
+their excretory mouths become filled with concreted mucus, or calculus
+matter, and in eight or ten days stupor and death supervenes in consequence
+of the retention of the feculent part of the blood.
+
+This disease in a slighter degree, or when only a part of the kidney is
+affected, is succeeded by partial inflammation of the kidney in consequence
+of previous torpor. In that case greater actions of the secretory vessels
+occur, and the nucleus of gravel is formed by the inflamed mucous membranes
+of the tubuli uriniferi, as farther explained in its place.
+
+This torpor, or paralysis of the secretory vessels of the kidneys, like
+that of the liver, owes its origin to their being previously habituated to
+too great stimulus; which in this country is generally owing to the alcohol
+contained in ale or wine; and hence must be registered amongst the diseases
+owing to inebriety; though it may be caused by whatever occasionally
+inflames the kidney; as too violent riding on horseback, or the cold from a
+damp bed, or by sleeping on the cold ground; or perhaps by drinking in
+general too little aqueous fluids.
+
+III. I shall conclude this section on the diseases of the liver induced by
+spirituous liquors, with the well known story of Prometheus, which seems
+indeed to have been invented by physicians in those ancient times, when all
+things were clothed in hieroglyphic, or in fable. Prometheus was painted as
+stealing fire from heaven, which might well represent the inflammable
+spirit produced by fermentation; which may be said to animate or enliven
+the man of clay: whence the conquests of Bacchus, as well as the temporary
+mirth and noise of his devotees. But the after punishment of those, who
+steal this accursed fire, is a vulture gnawing the liver; and well
+allegorises the poor inebriate lingering for years under painful hepatic
+diseases. When the expediency of laying a further tax on the distillation
+of spirituous liquors from grain was canvassed before the House of Commons
+some years ago, it was said of the distillers, with great truth, "_They
+take the bread from the people, and convert it into poison!_" Yet is this
+manufactory of disease permitted to continue, as appears by its paying into
+the treasury above 900,000l. near a million of money annually. And thus,
+under the names of rum, brandy, gin, whisky, usquebaugh, wine, cyder, beer,
+and porter, alcohol is become the bane of the Christian world, as opium of
+the Mahometan.
+
+          Evoe! parce, liber?
+  Parce, gravi metuende thirso!--Hor.
+
+       *       *       *       *       *
+
+SECT. XXXI.
+
+OF TEMPERAMENTS.
+
+    I. _The temperament of decreased irritability known by weak pulse,
+    large pupils of the eyes, cold extremities. Are generally supposed to
+    be too irritable. Bear pain better than labour. Natives of
+    North-America contrasted with those upon the coast of Africa. Narrow
+    and broad shouldered people. Irritable constitutions bear labour better
+    than pain._ II. _Temperament of increased sensibility. Liable to
+    intoxication, to inflammation, hæmoptoe, gutta serena, enthusiasm,
+    delirium, reverie. These constitutions are indolent to voluntary
+    exertions, and dull to irritations. The natives of South-America, and
+    brute animals of this temperament._ III. _Of increased voluntarity;
+    these are subject to locked jaw, convulsions, epilepsy, mania. Are very
+    active, bear cold, hunger, fatigue. Are suited to great exertions. This
+    temperament distinguishes mankind from other animals._ IV. _Of
+    increased association. These have great memories, are liable to quartan
+    agues, and stronger sympathies of parts with each other._ V. _Change of
+    temperaments into one another._
+
+Antient writers have spoken much of temperaments, but without sufficient
+precision. By temperament of the system should be meant a permanent
+predisposition to certain classes of diseases: without this definition a
+temporary predisposition to every distinct malady might be termed a
+temperament. There are four kinds of constitution, which permanently
+deviate from good health, and are perhaps sufficiently marked to be
+distinguished from each other, and constitute the temperaments or
+predispositions to the irritative, sensitive, voluntary, and associate
+classes of diseases.
+
+I. _The Temperament of decreased Irritability._
+
+The diseases, which are caused by irritation, most frequently originate
+from the defect of it; for those, which are immediately owing to the excess
+of it, as the hot fits of fever, are generally occasioned by an
+accumulation of sensorial power in consequence of a previous defect of
+irritation, as in the preceding cold fits of fever. Whereas the diseases,
+which are caused by sensation and volition, most frequently originate from
+the excess of those sensorial powers, as will be explained below.
+
+The temperament of decreased irritability appears from the following
+circumstances, which shew that the muscular fibres or organs of sense are
+liable to become torpid or quiescent from less defect of stimulation than
+is productive of torpor or quiescence in other constitutions.
+
+1. The first is the weak pulse, which in some constitutions is at the same
+time quick. 2. The next most marked criterion of this temperament is the
+largeness of the aperture of the iris, or pupil of the eye, which has been
+reckoned by some a beautiful feature in the female countenance, as an
+indication of delicacy, but to an experienced observer it is an indication
+of debility, and is therefore a defect, not an excellence. The third most
+marked circumstance in this constitution is, that the extremities, as the
+hands and feet, or nose and ears, are liable to become cold and pale in
+situations in respect to warmth, where those of greater strength are not
+affected. Those of this temperament are subject to hysteric affections,
+nervous fevers, hydrocephalus, scrophula, and consumption, and to all other
+diseases of debility.
+
+Those, who possess this kind of constitution, are popularly supposed to be
+more irritable than is natural, but are in reality less so.
+
+This mistake has arisen from their generally having a greater quickness of
+pulse, as explained in Sect. XII. 1. 4. XII. 3. 3.; but this frequency of
+pulse is not necessary to the temperament, like the debility of it.
+
+Persons of this temperament are frequently found amongst the softer sex,
+and amongst narrow-shouldered men; who are said to bear labour worse, and
+pain better than others. This last circumstance is supposed to have
+prevented the natives of North America from having been made slaves by the
+Europeans. They are a narrow-shouldered race of people, and will rather
+expire under the lash, than be made to labour. Some nations of Asia have
+small hands, as may be seen by the handles of their scymetars; which with
+their narrow shoulders shew, that they have not been accustomed to so great
+labour with their hands and arms, as the European nations in agriculture,
+and those on the coasts of Africa in swimming and rowing. Dr. Maningham, a
+popular accoucheur in the beginning of this century, observes in his
+aphorisms, that broad-shouldered men procreate broad-shouldered children.
+Now as labour strengthens the muscles employed, and increases their bulk,
+it would seem that a few generations of labour or of indolence may in this
+respect change the form and temperament of the body.
+
+On the contrary, those who are happily possessed of a great degree of
+irritability, bear labour better than pain; and are strong, active, and
+ingenious. But there is not properly a temperament of increased
+irritability tending to disease, because an increased quantity of
+irritative motions generally induces an increase of pleasure or pain, as in
+intoxication, or inflammation; and then the new motions are the immediate
+consequences of increased sensation, not of increased irritation; which
+have hence been so perpetually confounded with each other.
+
+II. _Temperament of Sensibility._
+
+There is not properly a temperament, or predisposition to disease, from
+decreased sensibility, since irritability and not sensibility is
+immediately necessary to bodily health. Hence it is the excess of sensation
+alone, as it is the defect of irritation, that most frequently produces
+disease. This temperament of increased sensibility is known from the
+increased activity of all those motions of the organs of sense and muscles,
+which are exerted in consequence of pleasure or pain, as in the beginning
+of drunkenness, and in inflammatory fever. Hence those of this constitution
+are liable to inflammatory diseases, as hepatitis; and to that kind of
+consumption which is hereditary, and commences with slight repeated
+hæmoptoe. They have high-coloured lips, frequently dark hair and dark eyes
+with large pupils, and are in that case subject to gutta serena. They are
+liable to enthusiasm, delirium, and reverie. In this last circumstance they
+are liable to start at the clapping of a door; because the more intent any
+one is on the passing current of his ideas, the greater surprise he
+experiences on their being dissevered by some external violence, as
+explained in Sect. XIX. on reverie.
+
+As in these constitutions more than the natural quantities of sensitive
+motions are produced by the increased quantity of sensation existing in the
+habit, it follows, that the irritative motions will be performed in some
+degree with less energy, owing to the great expenditure of sensorial power
+on the sensitive ones. Hence those of this temperament do not attend to
+slight stimulations, as explained in Sect. XIX. But when a stimulus is so
+great as to excite sensation, it produces greater sensitive actions of the
+system than in others; such as delirium or inflammation. Hence they are
+liable to be absent in company; sit or lie long in one posture; and in
+winter have the skin of their legs burnt into various colours by the fire.
+Hence also they are fearful of pain; covet music and sleep; and delight in
+poetry and romance.
+
+As the motions in consequence of sensation are more than natural, it also
+happens from the greater expenditure of sensorial power on them, that the
+voluntary motions are less easily exerted. Hence the subjects of this
+temperament are indolent in respect to all voluntary exertions, whether of
+mind or body.
+
+A race of people of this description seems to have been found by the
+Spaniards in the islands of America, where they first landed, ten of whom
+are said not to have consumed more food than one Spaniard, nor to have been
+capable of more than one tenth of the exertion of a Spaniard. Robertson's
+History.--In a state similar to this the greatest part of the animal world
+pass their lives, between sleep or inactive reverie, except when they are
+excited by the call of hunger.
+
+III. _The Temperament of increased Voluntarity._
+
+Those of this constitution differ from both the last mentioned in this,
+that the pain, which gradually subsides in the first, and is productive of
+inflammation or delirium in the second, is in this succeeded by the
+exertion of the muscles or ideas, which are most frequently connected with
+volition; and they are thence subject to locked jaw, convulsions, epilepsy,
+and mania, as explained in Sect. XXXIV. Those of this temperament attend to
+the slightest irritations or sensations, and immediately exert themselves
+to obtain or avoid the objects of them; they can at the same time bear cold
+and hunger better than others, of which Charles the Twelfth of Sweden was
+an instance. They are suited and generally prompted to all great exertions
+of genius or labour, as their desires are more extensive and more vehement,
+and their powers of attention and of labour greater. It is this facility of
+voluntary exertion, which distinguishes men from brutes, and which has made
+them lords of the creation.
+
+IV. _The Temperament of increased Association._
+
+This constitution consists in the too great facility, with which the
+fibrous motions acquire habits of association, and by which these
+associations become proportionably stronger than in those of the other
+temperaments. Those of this temperament are slow in voluntary exertions, or
+in those dependent on sensation, or on irritation. Hence great memories
+have been said to be attended with less sense and less imagination from
+Aristotle down to the present time; for by the word memory these writers
+only understood the unmeaning repetition of words or numbers in the order
+they were received, without any voluntary efforts of the mind.
+
+In this temperament those associations of motions, which are commonly
+termed sympathies, act with greater certainty and energy, as those between
+disturbed vision and the inversion of the motion of the stomach, as in
+sea-sickness; and the pains in the shoulder from hepatic inflammation. Add
+to this, that the catenated circles of actions are of greater extent than
+in the other constitutions. Thus if a strong vomit or cathartic be
+exhibited in this temperament, a smaller quantity will produce as great an
+effect, if it be given some weeks afterwards; whereas in other temperaments
+this is only to be expected, if it be exhibited in a few days after the
+first dose. Hence quartan agues are formed in those of this temperament, as
+explained in Section XXXII. on diseases from irritation, and other
+intermittents are liable to recur from slight causes many weeks after they
+have been cured by the bark.
+
+V. The first of these temperaments differs from the standard of health from
+defect, and the others from excess of sensorial power; but it sometimes
+happens that the same individual, from the changes introduced into his
+habit by the different seasons of the year, modes or periods of life, or by
+accidental diseases, passes from one of these temperaments to another. Thus
+a long use of too much fermented liquor produces the temperament of
+increased sensibility; great indolence and solitude that of decreased
+irritability; and want of the necessaries of life that of increased
+voluntarity.
+
+       *       *       *       *       *
+
+SECT. XXXII.
+
+DISEASES OF IRRITATION.
+
+    I. _Irritative fevers with strong pulse. With weak pulse. Symptoms of
+    fever, Their source._ II. 1. _Quick pulse is owing to decreased
+    irritability_. 2. _Not in sleep or in apoplexy._ 3. _From inanition.
+    Owing to deficiency of sensorial power._ III. 1. _Causes of fever. From
+    defect of heat. Heat from secretions. Pain of cold in the loins and
+    forehead._ 2. _Great expense of sensorial power in the vital motions.
+    Immersion in cold water. Succeeding glow of heat. Difficult respiration
+    in cold bathing explained. Why the cold bath invigorates. Bracing and
+    relaxation are mechanical terms._ 3. _Uses of cold bathing. Uses of
+    cold air in fevers._ 4. _Ague fits from cold air. Whence their
+    periodical returns._ IV. _Defect of distention a cause of fever.
+    Deficiency of blood. Transfusion of blood._ V. 1. _Defect of momentum
+    of the blood from mechanic stimuli. 2. Air injected into the
+    blood-vessels._ 3. _Exercise increases the momentum of the blood._ 4.
+    _Sometimes bleeding increases the momentum of it._ VI. _Influence of
+    the sun and moon on diseases. The chemical stimulus of the blood.
+    Menstruation obeys the lunations. Queries._ VII. _Quiesence of large
+    glands a cause of fever. Swelling of the præcordia._ VIII. _Other
+    causes of quiescence, as hunger, bad air, fear, anxiety._ IX. 1.
+    _Symptoms of the cold fit._ 2. _Of the hot fit._ 3. _Second cold fit
+    why._ 4. _Inflammation introduced, or delirium, or stupor._ X.
+    _Recapitulation. Fever not an effort of nature to relieve herself.
+    Doctrine of spasm._
+
+I. When the contractile sides of the heart and arteries perform a greater
+number of pulsations in a given time, and move through a greater area at
+each pulsation, whether these motions are occasioned by the stimulus of the
+acrimony or quantity of the blood, or by their association with other
+irritative motions, or by the increased irritability of the arterial
+system, that is, by an increased quantity of sensorial power, one kind of
+fever is produced; which may be called Synocha irritativa, or Febris
+irritativa pulsu forti, or irritative fever with strong pulse.
+
+When the contractile sides of the heart and arteries perform a greater
+number of pulsations in a given time, but move through a much less area at
+each pulsation, whether these motions are occasioned by defect of their
+natural stimuli, or by the defect of other irritative motions with which
+they are associated, or from the inirritability of the arterial system,
+that is, from a decreased quantity of sensorial power, another kind of
+fever arises; which may be termed, Typhus irritativus, or Febris irritativa
+pulsu debili, or irritative fever with weak pulse. The former of these
+fevers is the synocha of nosologists, and the latter the typhus mitior, or
+nervous fever. In the former there appears to be an increase of sensorial
+power, in the latter a deficiency of it; which is shewn to be the immediate
+cause of strength and weakness, as defined in Sect. XII. 1. 3.
+
+It should be added, that a temporary quantity of strength or debility may
+be induced by the defect or excess of stimulus above what is natural; and
+that in the same fever _debility always exists during the cold fit, though
+strength does not always exist during the hot fit._
+
+These fevers are always connected with, and generally induced by, the
+disordered irritative motions of the organs of sense, or of the intestinal
+canal, or of the glandular system, or of the absorbent system; and hence
+are always complicated with some or many of these disordered motions, which
+are termed the symptoms of the fever, and which compose the great variety
+in these diseases.
+
+The irritative fevers both with strong and with weak pulse, as well as the
+sensitive fevers with strong and with weak pulse, which are to be described
+in the next section, are liable to periodical remissions, and then they
+take the name of intermittent fevers, and are distinguished by the
+periodical times of their access.
+
+II. For the better illustration of the phenomena of irritative fevers we
+must refer the reader to the circumstances of irritation explained in Sect.
+XII. and shall commence this intricate subject by speaking of the quick
+pulse, and proceed by considering many of the causes, which either
+separately or in combination most frequently produce the cold fits of
+fevers.
+
+1. If the arteries are dilated but to half their usual diameters, though
+they contract twice as frequently in a given time, they will circulate only
+half their usual quantity of blood: for as they are cylinders, the blood
+which they contain must be as the squares of their diameters. Hence when
+the pulse becomes quicker and smaller in the same proportion, the heart and
+arteries act with less energy than in their natural state. See Sect. XII.
+1. 4.
+
+That this quick small pulse is owing to want of irritability, appears,
+first, because it attends other symptoms of want of irritability; and,
+secondly, because on the application of a stimulus greater than usual, it
+becomes slower and larger. Thus in cold fits of agues, in hysteric
+palpitations of the heart, and when the body is much exhausted by
+hæmorrhages, or by fatigue, as well as in nervous fevers, the pulse becomes
+quick and small; and secondly, in all those cases if an increase of
+stimulus be added, by giving a little wine or opium; the quick small pulse
+becomes slower and larger, as any one may easily experience on himself, by
+counting his pulse after drinking one or two glasses of wine, when he is
+faint from hunger or fatigue.
+
+Now nothing can so strongly evince that this quick small pulse is owing to
+defect of irritability, than that an additional stimulus, above what is
+natural, makes it become slower and larger immediately: for what is meant
+by a defect of irritability, but that the arteries and heart are not
+excited into their usual exertions by their usual quantity of stimulus? but
+if you increase the quantity of stimulus, and they immediately act with
+their usual energy, this proves their previous want of their natural degree
+of irritability. Thus the trembling hands of drunkards in a morning become
+steady, and acquire strength to perform their usual offices, by the
+accustomed stimulus of a glass or two of brandy.
+
+2. In sleep and in apoplexy the pulse becomes slower, which is not owing to
+defect of irritability, for it is at the same time larger; and thence the
+quantity of the circulation is rather increased than diminished. In these
+cases the organs of sense are closed, and the voluntary power is suspended,
+while the motions dependent on internal irritations, as those of digestion
+and secretion, are carried on with more than their usual vigour; which has
+led superficial observers to confound these cases with those arising from
+want of irritability. Thus if you lift up the eyelid of an apoplectic
+patient, who is not actually dying, the iris will, as usual, contract
+itself, as this motion is associated with the stimulus of light; but it is
+not so in the last stages of nervous fevers, where the pupil of the eye
+continues expanded in the broad day-light: in the former case there is a
+want of voluntary power, in the latter a want of irritability.
+
+Hence also those constitutions which are deficient in quantity of
+irritability, and which possess too great sensibility, as during the pain
+of hunger, of hysteric spasms, or nervous headachs, are generally supposed
+to have too much irritability; and opium, which in its due dose is a most
+powerful stimulant, is erroneously called a sedative; because by increasing
+the irritative motions it decreases the pains arising from defect of them.
+
+Why the pulse should become quicker both from an increase of irritation, as
+in the synocha irritativa, or irritative fever with strong pulse; and from
+the decrease of it, as in the typhus irritativus, or irritative fever with
+weak pulse; seems paradoxical. The former circumstance needs no
+illustration; since if the stimulus of the blood, or the irritability of
+the sanguiferous system be increased, and the strength of the patient not
+diminished, it is plain that the motions must be performed quicker and
+stronger.
+
+In the latter circumstance the weakness of the muscular power of the heart
+is soon over-balanced by the elasticity of the coats of the arteries, which
+they possess besides a muscular power of contraction; and hence the
+arteries are distended to less than their usual diameters. The heart being
+thus stopped, when it is but half emptied, begins sooner to dilate again;
+and the arteries being dilated to less than their usual diameters, begin so
+much sooner to contract themselves; insomuch, that in the last stages of
+fevers with weakness the frequency of pulsation of the heart and arteries
+becomes doubled; which, however, is never the case in fevers with strength,
+in which they seldom exceed 118 or 120 pulsations in a minute. It must be
+added, that in these cases, while the pulse is very small and very quick,
+the heart often feels large, and labouring to one's hand; which coincides
+with the above explanation, shewing that it does not completely empty
+itself.
+
+3. In cases however of debility from paucity of blood, as in animals which
+are bleeding to death in the slaughter-house, the quick pulsations of the
+heart and arteries may be owing to their not being distended to more than
+half their usual diastole; and in consequence they must contract sooner, or
+more frequently, in a given time. As weak people are liable to a deficient
+quantity of blood, this cause may occasionally contribute to quicken the
+pulse in fevers with debility, which may be known by applying one's hand
+upon the heart as above; but the principal cause I suppose to consist in
+the diminution of sensorial power. When a muscle contains, or is supplied
+with but little sensorial power, its contraction soon ceases, and in
+consequence may soon recur, as is seen in the trembling hands of people
+weakened by age or by drunkenness. See Sect. XII. 1. 4. XII. 3. 4.
+
+It may nevertheless frequently happen, that both the deficiency of
+stimulus, as where the quantity of blood is lessened (as described in No.
+4. of this section), and the deficiency of sensorial power, as in those of
+the temperament of irritability, described in Sect. XXXI. occur at the same
+time; which will thus add to the quickness of the pulse and to the danger
+of the disease.
+
+III. 1. A certain degree of heat is necessary to muscular motion, and is,
+in consequence, essential to life. This is observed in those animals and
+insects which pass the cold season in a torpid state, and which revive on
+being warmed by the fire. This necessary stimulus of heat has two sources;
+one from the fluid atmosphere of heat, in which all things are immersed,
+and the other from the internal combinations of the particles, which form
+the various fluids, which are produced in the extensive systems of the
+glands. When either the external heat, which surrounds us, or the internal
+production of it, becomes lessened to a certain degree, the pain of cold is
+perceived.
+
+This pain of cold is experienced most sensibly by our teeth, when ice is
+held in the mouth; or by our whole system after having been previously
+accustomed to much warmth. It is probable, that this pain does not arise
+from the mechanical or chemical effects of a deficiency of heat; but that,
+like the organs of sense by which we perceive hunger and thirst, this sense
+of heat suffers pain, when the stimulus of its object is wanting to excite
+the irritative motions of the organ; that is, when the sensorial power
+becomes too much accumulated in the quiescent fibres. See Sect. XII. 5. 3.
+For as the peristaltic motions of the stomach are lessened, when the pain
+of hunger is great, so the action of the cutaneous capillaries are lessened
+during the pain of cold; as appears by the paleness of the skin, as
+explained in Sect. XIV. 6. on the production of ideas.
+
+The pain in the small of the back and forehead in the cold fits of the
+ague, in nervous hemicrania, and in hysteric paroxysms, when all the
+irritative motions are much impaired, seems to arise from this cause; the
+vessels of these membranes or muscles become torpid by their irritative
+associations with other parts of the body, and thence produce less of their
+accustomed secretions, and in consequence less heat is evolved, and they
+experience the pain of cold; which coldness may often be felt by the hand
+applied upon the affected part.
+
+2. The importance of a greater or less deduction of heat from the system
+will be more easy to comprehend, if we first consider the great expense of
+sensorial power used in carrying on the vital motions; that is, which
+circulates, absorbs, secretes, aerates, and elaborates the whole mass of
+fluids with unceasing assiduity. The sensorial power, or spirit of
+animation, used in giving perpetual and strong motion to the heart, which
+overcomes the elasticity and vis inertiæ of the whole arterial system; next
+the expense of sensorial power in moving with great force and velocity the
+innumerable trunks and ramifications of the arterial system; the expense of
+sensorial power in circulating the whole mass of blood through the long and
+intricate intortions of the very fine vessels, which compose the glands and
+capillaries; then the expense of sensorial power in the exertions of the
+absorbent extremities of all the lacteals, and of all the lymphatics, which
+open their mouths on the external surface of the skin, and on the internal
+surfaces of every cell or interstice of the body; then the expense of
+sensorial power in the venous absorption, by which the blood is received
+from the capillary vessels, or glands, where the arterial power ceases, and
+is drank up, and returned to the heart; next the expense of sensorial power
+used by the muscles of respiration in their office of perpetually expanding
+the bronchia, or air-vessels, of the lungs; and lastly in the unceasing
+peristaltic motions of the stomach and whole system of intestines, and in
+all the secretions of bile, gastric juice, mucus, perspirable matter, and
+the various excretions from the system. If we consider the ceaseless
+expense of sensorial power thus perpetually employed, it will appear to be
+much greater in a day than all the voluntary exertions of our muscles and
+organs of sense consume in a week; and all this without any sensible
+fatigue! Now, if but a part of these vital motions are impeded, or totally
+stopped for but a short time, we gain an idea, that there must be a great
+accumulation of sensorial power; as its production in these organs, which
+are subject to perpetual activity, is continued during their quiescence,
+and is in consequence accumulated.
+
+While, on the contrary, where those vital organs act too forcibly by
+increase of stimulus without a proportionally-increased production of
+sensorial power in the brain, it is evident, that a great deficiency of
+action, that is torpor, must soon follow, as in fevers; whereas the
+locomotive muscles, which act only by intervals, are neither liable to so
+great accumulation of sensorial power during their times of inactivity, nor
+to so great an exhaustion of it during their times of action.
+
+Thus, on going into a very cold bath, suppose at 33 degrees of heat on
+Fahrenheit's scale, the action of the subcutaneous capillaries, or glands,
+and of the mouths of the cutaneous absorbents is diminished, or ceases for
+a time. Hence less or no blood passes these capillaries, and paleness
+succeeds. But soon after emerging from the bath, a more florid colour and a
+greater degree of heat is generated on the skin than was possessed before
+immersion; for the capillary glands, after this quiescent state, occasioned
+by the want of stimulus, become more irritable than usual to their natural
+stimuli, owing to the accumulation of sensorial power, and hence a greater
+quantity of blood is transmitted through them, and a greater secretion of
+perspirable matter; and, in consequence, a greater degree of heat succeeds.
+During the continuance in cold water the breath is cold, and the act of
+respiration quick and laborious; which have generally been ascribed to the
+obstruction of the circulating fluid by a spasm of the cutaneous vessels,
+and by a consequent accumulation of blood in the lungs, occasioned by the
+pressure as well as by the coldness of the water. This is not a
+satisfactory account of this curious phænomenon, since at this time the
+whole circulation is less, as appears from the smallness of the pulse and
+coldness of the breath; which shew that less blood passes through the lungs
+in a given time; the same laborious breathing immediately occurs when the
+paleness of the skin is produced by fear, where no external cold or
+pressure are applied.
+
+The minute vessels of the bronchia, through which the blood passes from the
+arterial to the venal system, and which correspond with the cutaneous
+capillaries, have frequently been exposed to cold air, and become quiescent
+along with those of the skin; and hence their motions are so associated
+together, that when one is affected either with quiescence or exertion, the
+other sympathizes with it, according to the laws of irritative association.
+See Sect. XXVII. 1. on hæmorrhages.
+
+Besides the quiescence of the minute vessels of the lungs, there are many
+other systems of vessels which become torpid from their irritative
+associations with those of the skin, as the absorbents of the bladder and
+intestines; whence an evacuation of pale urine occurs, when the naked skin
+is exposed only to the coldness of the atmosphere; and sprinkling the naked
+body with cold water is known to remove even pertinacious constipation of
+the bowels. From the quiescence of such extensive systems of vessels as the
+glands and capillaries of the skin, and the minute vessels of the lungs,
+with their various absorbent series of vessels, a great accumulation of
+sensorial powers is occasioned; part of which is again expended in the
+increased exertion of all these vessels, with an universal glow of heat in
+consequence of this exertion, and the remainder of it adds vigour to both
+the vital and voluntary exertions of the whole day.
+
+If the activity of the subcutaneous vessels, and of those with which their
+actions are associated, was too great before cold immersion, as in the hot
+days of summer, and by that means the sensorial power was previously
+diminished, we see the cause why the cold bath gives such present strength;
+namely, by stopping the unnecessary activity of the subcutaneous vessels,
+and thus preventing the too great exhaustion of sensorial power; which, in
+metaphorical language, has been called _bracing_ the system: which is,
+however, a mechanical term, only applicable to drums, or musical strings:
+as on the contrary the word _relaxation_, when applied to living animal
+bodies, can only mean too small a quantity of stimulus, or too small a
+quantity of sensorial power; as explained in Sect. XII. 1.
+
+3. This experiment of cold bathing presents us with a simple fever-fit; for
+the pulse is weak, small, and quick during the cold immersion; and becomes
+strong, full, and quick during the subsequent glow of heat; till in a few
+minutes these symptoms subside, and the temporary fever ceases.
+
+In those constitutions where the degree of inirritability, or of debility,
+is greater than natural, the coldness and paleness of the skin with the
+quick and weak pulse continue a long time after the patient leaves the
+bath; and the subsequent heat approaches by unequal flushings, and he feels
+himself disordered for many hours. Hence the bathing in a cold spring of
+water, where the heat is but forty-eight degrees on Fahrenheit's
+thermometer, much disagrees with those of weak or inirritable habits of
+body; who possess so little sensorial power, that they cannot without
+injury bear to have it diminished even for a short time; but who can
+nevertheless bear the more temperate coldness of Buxton bath, which is
+about eighty degrees of heat, and which strengthens them, and makes them by
+habit less liable to great quiescence from small variations of cold, and
+thence less liable to be disordered by the unavoidable accidents of life.
+Hence it appears, why people of these inirritable constitutions, which is
+another expression for sensorial deficiency, are often much injured by
+bathing in a cold spring of water; and why they should continue but a very
+short time in baths, which are colder than their bodies; and should
+gradually increase both the degree of coldness of the water, and the time
+of their continuance in it, if they would obtain salutary effects from cold
+immersions. See Sect. XII. 2. 1.
+
+On the other hand, in all cases where the heat of the external surface of
+the body, or of the internal surface of the lungs, is greater than natural,
+the use of exposure to cool air may be deduced. In fever-fits attended with
+strength, that is with great quantity of sensorial power, it removes the
+additional stimulus of heat from the surfaces above mentioned, and thus
+prevents their excess of useless motion; and in fever-fits attended with
+debility, that is with a deficiency of the quantity of sensorial power, it
+prevents the great and dangerous waste of sensorial power expended in the
+unnecessary increase of the actions of the glands and capillaries of the
+skin and lungs.
+
+4. In the same manner, when any one is long exposed to very cold air, a
+quiescence is produced of the cutaneous and pulmonary capillaries and
+absorbents, owing to the deficiency of their usual stimulus of heat; and
+this quiescence of so great a quantity of vessels affects, by irritative
+association, the whole absorbent and glandular system, which becomes in a
+greater or less degree quiescent, and a cold fit of fever is produced.
+
+If the deficiency of the stimulus of heat is very great, the quiescence
+becomes so general as to extinguish life, as in those who are frozen to
+death.
+
+If the deficiency of heat be in less degree, but yet so great as in some
+measure to disorder the system, and should occur the succeeding day, it
+will induce a greater degree of quiescence than before, from its acting in
+concurrence with the period of the diurnal circle of actions, explained in
+Sect. XXXVI. Hence from a small beginning a greater and greater degree of
+quiescence may be induced, till a complete fever-fit is formed; and which
+will continue to recur at the periods by which it was produced. See Sect.
+XVII. 3. 6.
+
+If the degree of quiescence occasioned by defect of the stimulus of heat be
+very great, it will recur a second time by a slighter cause, than that
+which first induced it. If the cause, which induces the second fit of
+quiescence, recurs the succeeding day, the quotidian fever is produced; if
+not till the alternate day, the tertian fever; and if not till after
+seventy-two hours from the first fit of quiescence, the quartan fever is
+formed. This last kind of fever recurs less frequently than the other, as
+it is a disease only of those of the temperament of associability, as
+mentioned in Sect. XXXI.; for in other constitutions the capability of
+forming a habit ceases, before the new cause of quiescence is again
+applied, if that does not occur sooner than in seventy-two hours.
+
+And hence those fevers, whose cause is from cold air of the night or
+morning, are more liable to observe the solar day in their periods; while
+those from other causes frequently observe the lunar day in their periods,
+their paroxysms returning near an hour later every day, as explained in
+Sect. XXXVI.
+
+IV. Another frequent cause of the cold fits of fever is the defect of the
+stimulus of distention. The whole arterial system would appear, by the
+experiments of Haller, to be irritable by no other stimulus, and the
+motions of the heart and alimentary canal are certainly in some measure
+dependant on the same cause. See Sect. XIV. 7. Hence there can be no
+wonder, that the diminution of distention should frequently induce the
+quiescence, which constitutes the beginning of fever-fits.
+
+Monsieur Leiutaud has judiciously mentioned the deficiency of the quantity
+of blood amongst the causes of diseases, which he says is frequently
+evident in dissections: fevers are hence brought on by great hæmorrhages,
+diarrhoeas, or other evacuations; or from the continued use of diet, which
+contains but little nourishment; or from the exhaustion occasioned by
+violent fatigue, or by those chronic diseases in which the digestion is
+much impaired; as where the stomach has been long affected with the gout or
+schirrus; or in the paralysis of the liver, as described in Sect. XXX.
+Hence a paroxysm of gout is liable to recur on bleeding or purging; as the
+torpor of some viscus, which precedes the inflammation of the foot, is thus
+induced by the want of the stimulus of distention. And hence the
+extremities of the body, as the nose and fingers, are more liable to become
+cold, when we have long abstained from food; and hence the pulse is
+increased both in strength and velocity above the natural standard after a
+full meal by the stimulus of distention.
+
+However, this stimulus of distention, like the stimulus of heat above
+described, though it contributes much to the due action not only of the
+heart, arteries, and alimentary canal, but seems necessary to the proper
+secretion of all the various glands; yet perhaps it is not the sole cause
+of any of these numerous motions: for as the lacteals, cutaneous
+absorbents, and the various glands appear to be stimulated into action by
+the peculiar pungency of the fluids they absorb, so in the intestinal canal
+the pungency of the digesting aliment, or the acrimony of the fæces, seem
+to contribute, as well as their bulk, to promote the peristaltic motions;
+and in the arterial system, the momentum of the particles of the
+circulating blood, and their acrimony, stimulate the arteries, as well as
+the distention occasioned by it. Where the pulse is small this defect of
+distention is present, and contributes much to produce the febris
+irritativa pulsu debili, or irritative fever with weak pulse, called by
+modern writers nervous fever, as a predisponent cause. See Sect. XII. 1. 4.
+Might not the transfusion of blood, suppose of four ounces daily from a
+strong man, or other healthful animal, as a sheep or an ass, be used in the
+early state of nervous or putrid fevers with great prospect of success?
+
+V. 1. The defect of the momentum of the particles of the circulating blood
+is another cause of the quiescence, with which the cold fits of fever
+commence. This stimulus of the momentum of the progressive particles of the
+blood does not act over the whole body like those of heat and distention
+above described, but is confined to the arterial system; and differs from
+the stimulus of the distention of the blood, as much as the vibration of
+the air does from the currents of it. Thus are the different organs of our
+bodies stimulated by four different mechanic properties of the external
+world: the sense of touch by the pressure of solid bodies so as to
+distinguish their figure; the muscular system by the distention, which they
+occasion; the internal surface of the arteries, by the momentum of their
+moving particles; and the auditory nerves, by the vibration of them: and
+these four mechanic properties are as different from each other as the
+various chemical ones, which are adapted to the numerous glands, and to the
+other organs of sense.
+
+2. The momentum of the progressive particles of blood is compounded of
+their velocity and their quantity of matter: hence whatever circumstances
+diminish either of these without proportionally increasing the other, and
+without superadding either of the general stimuli of heat or distention,
+will tend to produce a quiescence of the arterial system, and from thence
+of all the other irritative motions, which are connected with it.
+
+Hence in all those constitutions or diseases where the blood contains a
+greater proportion of serum, which is the lightest part of its composition,
+the pulsations of the arteries are weaker, as in nervous fevers, chlorosis,
+and hysteric complaints; for in these cases the momentum of the progressive
+particles of blood is less: and hence, where the denser parts of its
+composition abound, as the red part of it, or the coagulable lymph, the
+arterial pulsations are stronger; as in those of robust health, and in
+inflammatory diseases.
+
+That this stimulus of the momentum of the particles of the circulating
+fluid is of the greatest consequence to the arterial action, appears from
+the experiment of injecting air into the blood vessels, which seems to
+destroy animal life from the want of this stimulus of momentum; for the
+distention of the arteries is not diminished by it, it possesses no
+corrosive acrimony, and is less liable to repass the valves than the blood
+itself; since air-valves in all machinery require much less accuracy of
+construction than those which are opposed to water.
+
+3. One method of increasing the velocity of the blood, and in consequence
+the momentum of its particles, is by the exercise of the body, or by the
+friction of its surface: so, on the contrary, too great indolence
+contributes to decrease this stimulus of the momentum of the particles of
+the circulating blood, and thus tends to induce quiescence; as is seen in
+hysteric cases, and chlorosis, and the other diseases of sedentary people.
+
+4. The velocity of the particles of the blood in certain circumstances is
+increased by venesection, which, by removing a part of it, diminishes the
+resistance to the motion of the other part, and hence the momentum of the
+particles of it is increased. This may be easily understood by considering
+it in the extreme, since, if the resistance was greatly increased, so as to
+overcome the propelling power, there could be no velocity, and in
+consequence no momentum at all. From this circumstance arises that curious
+phænomenon, the truth of which I have been more than once witness to, that
+venesection will often instantaneously relieve those nervous pains, which
+attend the cold periods of hysteric, asthmatic, or epileptic diseases; and
+that even where large doses of opium have been in vain exhibited. In these
+cases the pulse becomes stronger after the bleeding, and the extremities
+regain their natural warmth; and an opiate then given acts with much more
+certain effect.
+
+VI. There is another cause, which seems occasionally to induce quiescence
+into some part of our system, I mean the influence of the sun and moon; the
+attraction of these luminaries, by decreasing the gravity of the particles
+of the blood, cannot affect their momentum, as their vis inertiæ remains
+the same; but it may nevertheless produce some chemical change in them,
+because whatever affects the general attractions of the particles of matter
+may be supposed from analogy to affect their specific attractions or
+affinities: and thus the stimulus of the particles of blood may be
+diminished, though not their momentum. As the tides of the sea obey the
+southing and northing of the moon (allowing for the time necessary for
+their motion, and the obstructions of the shores), it is probable, that
+there are also atmospheric tides on both sides of the earth, which to the
+inhabitants of another planet might so deflect the light as to resemble the
+ring of Saturn. Now as these tides of water, or of air, are raised by the
+diminution of their gravity, it follows, that their pressure on the surface
+of the earth is no greater than the pressure of the other parts of the
+ocean, or of the atmosphere, where no such tides exist; and therefore that
+they cannot affect the mercury in the barometer. In the same manner, the
+gravity of all other terrestrial bodies is diminished at the times of the
+southing and northing of the moon, and that in a greater degree when this
+coincides with the southing and northing of the sun, and this in a still
+greater degree about the times of the equinoxes. This decrease of the
+gravity of all bodies during the time the moon passes our zenith or nadir
+might possibly be shewn by the slower vibrations of a pendulum, compared
+with a spring clock, or with astronomical observation. Since a pendulum of
+a certain length moves slower at the line than near the poles, because the
+gravity being diminished and the vis inertiæ continuing the same, the
+motive power is less, but the resistance to be overcome continues the same.
+The combined powers of the lunar and solar attraction is estimated by Sir
+Isaac Newton not to exceed one 7,868,850th part of the power of
+gravitation, which seems indeed but a small circumstance to produce any
+considerable effect on the weight of sublunary bodies, and yet this is
+sufficient to raise the tides at the equator above ten feet high; and if it
+be considered, what small impulses of other bodies produce their effects on
+the organs of sense adapted to the perception of them, as of vibration on
+the auditory nerves, we shall cease to to be surprised, that so minute a
+diminution in the gravity of the particles of blood should so far affect
+their chemical changes, or their stimulating quality, as, joined with other
+causes, sometimes to produce the beginnings of diseases.
+
+Add to this, that if the lunar influence produces a very small degree of
+quiescence at first, and if that recurs at certain periods even with less
+power to produce quiescence than at first, yet the quiescence will daily
+increase by the acquired habit acting at the same time, till at length so
+great a degree of quiescence is induced as to produce phrensy, canine
+madness, epilepsy, hysteric pains or cold fits of fever, instances of many
+of which are to be found in Dr. Mead's work on this subject. The solar
+influence also appears daily in several diseases; but as darkness, silence,
+sleep, and our periodical meals mark the parts of the solar circle of
+actions, it is sometimes dubious to which of these the periodical returns
+of these diseases are to be ascribed.
+
+As far as I have been able to observe, the periods of inflammatory diseases
+observe the solar day; as the gout and rheumatism have their greatest
+quiescence about noon and midnight, and their exacerbations some hours
+after; as they have more frequently their immediate cause from cold air,
+inanition, or fatigue, than from the effects of lunations: whilst the cold
+fits of hysteric patients, and those in nervous fevers, more frequently
+occur twice a day, later by near half an hour each time, according to the
+lunar day; whilst some fits of intermittents, which are undisturbed by
+medicines, return at regular solar periods, and others at lunar ones; which
+may, probably, be owing to the difference of the periods of those external
+circumstances of cold, inanition, or lunation, which immediately caused
+them.
+
+We must, however, observe, that the periods of quiescence and exacerbation
+in diseases do not always commence at the times of the syzygies or
+quadratures of the moon and sun, or at the times of their passing the
+zenith or nadir; but as it is probable, that the stimulus of the particles
+of the circumfluent blood is gradually diminished from the time of the
+quadratures to that of the syzygies, the quiescence may commence at any
+hour, when co-operating with other causes of quiescence, it becomes great
+enough to produce a disease: afterwards it will continue to recur at the
+same period of the lunar or solar influence; the same cause operating
+conjointly with the acquired habit, that is with the catenation of this new
+motion with the dissevered links of the lunar or solar circles of animal
+action.
+
+In this manner the periods of menstruation obey the lunar month with great
+exactness in healthy patients (and perhaps the venereal orgasm in brute
+animals does the same), yet these periods do not commence either at the
+syzygies or quadratures of the lunations, but at whatever time of the lunar
+periods they begin, they observe the same in their returns till some
+greater cause disturbs them.
+
+Hence, though the best way to calculate the time of the expected returns of
+the paroxysms of periodical diseases is to count the number of hours
+between the commencement of the two preceding fits, yet the following
+observations may be worth attending to, when we endeavour to prevent the
+returns of maniacal or epileptic diseases; whose periods (at the beginning
+of them especially) frequently observe the syzygies of the moon and sun,
+and particularly about the equinox.
+
+The greatest of the two tides happening in every revolution of the moon, is
+that when the moon approaches nearest to the zenith or nadir; for this
+reason, while the sun is in the northern signs, that is during the vernal
+and summer months, the greater of the two diurnal tides in our latitude is
+that, when the moon is above the horizon; and when the sun is in the
+southern signs, or during the autumnal and winter months, the greater tide
+is that, which arises when the moon is below the horizon: and as the sun
+approaches somewhat nearer the earth in winter than in summer, the greatest
+equinoctial tides are observed to be a little before the vernal equinox,
+and a little after the autumnal one.
+
+Do not the cold periods of lunar diseases commence a few hours before the
+southing of the moon during the vernal and summer months, and before the
+northing of the moon during the autumnal and winter months? Do not palsies
+and apoplexies, which occur about the equinoxes, happen a few days before
+the vernal equinoctial lunation, and after the autumnal one? Are not the
+periods of those diurnal diseases more obstinate, that commence many hours
+before the southing or northing of the moon, than of those which commence
+at those times? Are not those palsies and apoplexies more dangerous which
+commence many days before the syzygies of the moon, than those which happen
+at those times? See Sect. XXXVI. on the periods of diseases.
+
+VII. Another very frequent cause of the cold fit of fever is the quiescence
+of some of those large congeries of glands, which compose the liver,
+spleen, or pancreas; one or more of which are frequently so enlarged in the
+autumnal intermittents as to be perceptible to the touch externally, and
+are called by the vulgar ague-cakes. As these glands are stimulated into
+action by the specific pungency of the fluids, which they absorb, the
+general cause of their quiescence seems to be the too great insipidity of
+the fluids of the body, co-operating perhaps at the same time with other
+general causes of quiescence.
+
+Hence, in marshy countries at cold seasons, which have succeeded hot ones,
+and amongst those, who have lived on innutritious and unstimulating diet,
+these agues are most frequent. The enlargement of these quiescent viscera,
+and the swelling of the præcordia in many other fevers, is, most probably,
+owing to the same cause; which may consist in a general deficiency of the
+production of sensorial power, as well as in the diminished stimulation of
+the fluids; and when the quiescence of so great a number of glands, as
+constitute one of those large viscera, commences, all the other irritative
+motions are affected by their connection with it, and the cold fit of fever
+is produced.
+
+VIII. There are many other causes, which produce quiescence of some part of
+the animal system, as fatigue, hunger, thirst, bad diet, disappointed love,
+unwholesome air, exhaustion from evacuations, and many others; but the last
+cause, that we shall mention, as frequently productive of cold fits of
+fever, is fear or anxiety of mind. The pains, which we are first and most
+generally acquainted with, have been produced by defect of some stimulus;
+thus, soon after our nativity we become acquainted with the pain from the
+coldness of the air, from the want of respiration, and from the want of
+food. Now all these pains occasioned by defect of stimulus are attended
+with quiescence of the organ, and at the same time with a greater or less
+degree of quiescence of other parts of the system: thus, if we even endure
+the pain of hunger so as to miss one meal instead of our daily habit of
+repletion, not only the peristaltic motions of the stomach and bowels are
+diminished, but we are more liable to coldness of our extremities, as of
+our noses, and ears, and feet, than at other times.
+
+Now, as fear is originally excited by our having experienced pain, and is
+itself a painful affection, the same quiescence of other fibrous motions
+accompany it, as have been most frequently connected with this kind of
+pain, as explained in Sect. XVI. 8. 1. as the coldness and paleness of the
+skin, trembling, difficult respiration, indigestion, and other symptoms,
+which contribute to form the cold fit of fevers. Anxiety is fear continued
+through a longer time, and, by producing chronical torpor of the system,
+extinguishes life slowly, by what is commonly termed a broken heart.
+
+IX. 1. We now step forwards to consider the other symptoms in consequence
+of the quiescence which begins the fits of fever. If by any of the
+circumstances before described, or by two or more of them acting at the
+same time, a great degree of quiescence is induced on any considerable part
+of the circle of irritative motions, the whole class of them is more or
+less disturbed by their irritative associations. If this torpor be
+occasioned by a deficient supply of sensorial power, and happens to any of
+those parts of the system, which are accustomed to perpetual activity, as
+the vital motions, the torpor increases rapidly, because of the great
+expenditure of sensorial power by the incessant activity of those parts of
+the system, as shewn in No. 3. 2. of this Section. Hence a deficiency of
+all the secretions succeeds, and as animal heat is produced in proportion
+to the quantity of those secretions, the coldness of the skin is the first
+circumstance, which is attended to. Dr. Martin asserts, that some parts of
+his body were warmer than natural in the cold fit of fever; but it is
+certain, that those, which are uncovered, as the fingers, and nose, and
+ears, are much colder to the touch, and paler in appearance. It is
+possible, that his experiments were made at the beginning of the subsequent
+hot fits; which commence with partial distributions of heat, owing to some
+parts of the body regaining their natural irritability sooner than others.
+
+From the quiescence of the anastomosing capillaries a paleness of the skin
+succeeds, and a less secretion of the perspirable matter; from the
+quiescence of the pulmonary capillaries a difficulty of respiration arises;
+and from the quiescence of the other glands less bile, less gastric and
+pancreatic juice, are secreted into the stomach and intestines, and less
+mucus and saliva are poured into the mouth; whence arises the dry tongue,
+costiveness, dry ulcers, and paucity of urine. From the quiescence of the
+absorbent system arises the great thirst, as less moisture is absorbed from
+the atmosphere. The absorption from the atmosphere was observed by Dr.
+Lyster to amount to eighteen ounces in one night, above what he had at the
+same time insensibly perspired. See Langrish. On the same account the urine
+is pale, though in small quantity, for the thinner part is not absorbed
+from it; and when repeated ague-fits continue long, the legs swell from the
+diminished absorption of the cellular absorbents.
+
+From the quiescence of the intestinal canal a loss of appetite and
+flatulencies proceed. From the partial quiescence of the glandular viscera
+a swelling and tension about the præcordia becomes sensible to the touch;
+which is occasioned by the delay of the fluids from the defect of venous or
+lymphatic absorption. The pain of the forehead, and of the limbs, and of
+the small of the back, arises from the quiescence of the membranous fascia,
+or muscles of those parts, in the same manner as the skin becomes painful,
+when the vessels, of which it is composed, become quiescent from cold. The
+trembling in consequence of the pain of coldness, the restlessness, and the
+yawning, and stretching of the limbs, together with the shuddering, or
+rigours, are convulsive motions; and will be explained amongst the diseases
+of volition; Sect. XXXIV.
+
+Sickness and vomiting is a frequent symptom in the beginnings of
+fever-fits, the muscular fibres of the stomach share the general torpor and
+debility of the system; their motions become first lessened, and then stop,
+and then become retrograde; for the act of vomiting, like the globus
+hystericus and the borborigmi of hypochondriasis, is always a symptom of
+debility, either from want of stimulus, as in hunger; or from want of
+sensorial power, as after intoxication; or from sympathy with some other
+torpid irritative motions, as in the cold fits of ague. See Sect. XII. 5.
+5. XXIX. 11. and XXXV. 1. 3. where this act of vomiting is further
+explained.
+
+The small pulse, which is said by some writers to be slow at the
+commencement of ague-fits, and which is frequently trembling and
+intermittent, is owing to the quiescence of the heart and arterial system,
+and to the resistance opposed to the circulating fluid from the inactivity
+of all the glands and capillaries. The great weakness and inability to
+voluntary motions, with the insensibility of the extremities, are owing to
+the general quiescence of the whole moving system; or, perhaps, simply to
+the deficient production of sensorial power.
+
+If all these symptoms are further increased, the quiescence of all the
+muscles, including the heart and arteries, becomes complete, and death
+ensues. This is, most probably, the case of those who are starved to death
+with cold, and of those who are said to die in Holland from long skaiting
+on their frozen canals.
+
+2. As soon as this general quiescence of the system ceases, either by the
+diminution of the cause, or by the accumulation of sensorial power, (as in
+syncope, Sect. XII. 7. 1.) which is the natural consequence of previous
+quiescence, the hot fit commences. Every gland of the body is now
+stimulated into stronger action than is natural, as its irritability is
+increased by accumulation of sensorial power during its late quiescence, a
+superabundance of all the secretions is produced, and an increase of heat
+in consequence of the increase of these secretions. The skin becomes red,
+and the perspiration great, owing to the increased action of the
+capillaries during the hot part of the paroxysm. The secretion of
+perspirable matter is perhaps greater during the hot fit than in the
+sweating fit which follows; but as the absorption of it also is greater, it
+does not stand on the skin in visible drops: add to this, that the
+evaporation of it also is greater, from the increased heat of the skin. But
+at the decline of the hot fit, as the mouths of the absorbents of the skin
+are exposed to the cooler air, or bed-clothes, these vessels sooner lose
+their increased activity, and cease to absorb more than their natural
+quantity: but the secerning vessels for some time longer, being kept warm
+by the circulating blood, continue to pour out an increased quantity of
+perspirable matter, which now stands on the skin in large visible drops;
+the exhalation of it also being lessened by the greater coolness of the
+skin, as well as its absorption by the diminished action of the lymphatics.
+See Class I. 1. 2. 3.
+
+The increased secretion of bile and of other fluids poured into the
+intestines frequently induce a purging at the decline of the hot fit; for
+as the external absorbent vessels have their mouths exposed to the cold
+air, as above mentioned, they cease to be excited into unnatural activity
+sooner than the secretory vessels, whose mouths are exposed to the warmth
+of the blood: now, as the internal absorbents sympathize with the external
+ones, these also, which during the hot fit drank up the thinner part of the
+bile, or of other secreted fluids, lose their increased activity before the
+gland loses its increased activity, at the decline of the hot fit; and the
+loose dejections are produced from the same cause, that the increased
+perspiration stands on the surface of the skin, from the increased
+absorption ceasing sooner than the increased secretion.
+
+The urine during the cold fit is in small quantity and pale, both from a
+deficiency of the secretion and a deficiency of the absorption.
+
+During the hot fit it is in its usual quantity, but very high coloured and
+turbid, because a greater quantity had been secreted by the increased
+action of the kidnies, and also a greater quantity of its more aqueous part
+had been absorbed from it in the bladder by the increased action of the
+absorbents; and lastly, at the decline of the hot fit it is in large
+quantity and less coloured, or turbid, because the absorbent vessels of the
+bladder, as observed above, lose their increased action by sympathy with
+the cutaneous ones sooner than the secretory vessels of the kidnies lose
+their increased activity. Hence the quantity of the sediment, and the
+colour of the urine, in fevers, depend much on the quantity secreted by the
+kidnies, and the quantity absorbed from it again in the bladder: the kinds
+of sediment, as the lateritious, purulent, mucous, or bloody sediments,
+depend on other causes. It should be observed, that if the sweating be
+increased by the heat of the room, or of the bed-clothes, that a paucity of
+turbid urine will continue to be produced, as the absorbents of the bladder
+will have their activity increased by their sympathy with the vessels of
+the skin, for the purpose of supplying the fluid expended in perspiration.
+
+The pulse becomes strong and full owing to the increased irritability of
+the heart and arteries, from the accumulation of sensorial power during
+their quiescence, and to the quickness of the return of the blood from the
+various glands and capillaries. This increased action of all the secretory
+vessels does not occur very suddenly, nor universally at the same time. The
+heat seems to begin about the center, and to be diffused from thence
+irregularly to the other parts of the system. This may be owing to the
+situation of the parts which first became quiescent and caused the
+fever-fit, especially when a hardness or tumour about the præcordia can be
+felt by the hand; and hence this part, in whatever viscus it is seated,
+might be the first to regain its natural or increased irritability.
+
+3. It must be here noted, that, by the increased quantity of heat, and of
+the impulse of the blood at the commencement of the hot fit, a great
+increase of stimulus is induced, and is now added to the increased
+irritability of the system, which was occasioned by its previous
+quiescence. This additional stimulus of heat and momentum of the blood
+augments the violence of the movements of the arterial and glandular system
+in an increasing ratio. These violent exertions still producing more heat
+and greater momentum of the moving fluids, till at length the sensoral
+power becomes wasted by this great stimulus beneath its natural quantity,
+and predisposes the system to a second cold fit.
+
+At length all these unnatural exertions spontaneously subside with the
+increased irritability that produced them; and which was itself produced by
+the preceding quiescence, in the same manner as the eye, on coming from
+darkness into day-light, in a little time ceases to be dazzled and pained,
+and gradually recovers its natural degree of irritability.
+
+4. But if the increase of irritability, and the consequent increase of the
+stimulus of heat and momentum, produce more violent exertions than those
+above described; great pain arises in some part of the moving system, as in
+the membranes of the brain, pleura, or joints; and new motions of the
+vessels are produced in consequence of this pain, which are called
+inflammation; or delirium or stupor arises; as explained in Sect. XXI. and
+XXXIII.: for the immediate effect is the same, whether the great energy of
+the moving organs arises from an increase of stimulus or an increase of
+irritability; though in the former case the waste of sensorial power leads
+to debility, and in the latter to health.
+
+_Recapitulation._
+
+X. Those muscles, which are less frequently exerted, and whose actions are
+interrupted by sleep, acquire less accumulation of sensorial power during
+their quiescent state, as the muscles of locomotion. In these muscles after
+great exertion, that is, after great exhaustion of sensorial power, the
+pain of fatigue ensues; and during rest there is a renovation of the
+natural quantity of sensorial power; but where the rest, or quiescence of
+the muscle, is long continued, a quantity of sensorial power becomes
+accumulated beyond what is necessary; as appears by the uneasiness
+occasioned by want of exercise; and which in young animals is one cause
+exciting them into action, as is seen in the play of puppies and kittens.
+
+But when those muscles, which are habituated to perpetual actions, as those
+of the stomach by the stimulus of food, those of the vessels of the skin by
+the stimulus of heat, and those which constitute the arteries and glands by
+the stimulus of the blood, become for a time quiescent, from the want of
+their appropriated stimuli, or by their associations with other quiescent
+parts of the system; a greater accumulation of sensorial power is acquired
+during their quiescence, and a greater or quicker exhaustion of it is
+produced during their increased action.
+
+This accumulation of sensorial power from deficient action, if it happens
+to the stomach from want of food, occasions the pain of hunger; if it
+happens to the vessels of the skin from want of heat, it occasions the pain
+of cold; and if to the arterial system from the want of its adapted
+stimuli, many disagreeable sensations are occasioned, such as are
+experienced in the cold fits of intermittent fevers, and are as various, as
+there are glands or membranes in the system, and are generally termed
+universal uneasiness.
+
+When the quiescence of the arterial system is not owing to defect of
+stimulus as above, but to the defective quantity of sensorial power, as in
+the commencement of nervous fever, or irritative fever with weak pulse, a
+great torpor of this system is quickly induced; because both the irritation
+from the stimulus of the blood, and the association of the vascular motions
+with each other, continue to excite the arteries into action, and thence
+quickly exhaust the ill-supplied vascular muscles; for to rest is death;
+and therefore those vascular muscles continue to proceed, though with
+feebler action, to the extreme of weariness or faintness: while nothing
+similar to this affects the locomotive muscles, whose actions are generally
+caused by volition, and not much subject either to irritation or to other
+kinds of associations besides the voluntary ones, except indeed when they
+are excited by the lash of slavery.
+
+In these vascular muscles, which are subject to perpetual action, and
+thence liable to great accumulation of sensorial power during their
+quiescence from want of stimulus, a great increase of activity occurs,
+either from the renewal of their accustomed stimulus, or even from much
+less quantities of stimulus than usual. This increase of action constitutes
+the hot fit of fever, which is attended with various increased secretions,
+with great concomitant heat, and general uneasiness. The uneasiness
+attending this hot paroxysm of fever, or fit of exertion, is very different
+from that, which attends the previous cold fit, or fit of quiescence, and
+is frequently the cause of inflammation, as in pleurisy, which is treated
+of in the next section.
+
+A similar effect occurs after the quiescence of our organs of sense; those
+which are not subject to perpetual action, as the taste and smell, are less
+liable to an exuberant accumulation of sensorial power after their having
+for a time been inactive; but the eye, which is in perpetual action during
+the day, becomes dazzled, and liable to inflammation after a temporary
+quiescence.
+
+Where the previous quiescence has been owing to a defect of sensorial
+power, and not to a defect of stimulus, as in the irritative fever with
+weak pulse, a similar increase of activity of the arterial system succeeds,
+either from the usual stimulus of the blood, or from a stimulus less than
+usual; but as there is in general in these cases of fever with weak pulse a
+deficiency of the quantity of the blood, the pulse in the hot fit is weaker
+than in health, though it is stronger than in the cold fit, as explained in
+No. 2. of this section. But at the same time in those fevers, where the
+defect of irritation is owing to the defect of the quantity of sensorial
+power, as well as to the defect of stimulus, another circumstance occurs;
+which consists in the partial distribution of it, as appears in partial
+flushings, as of the face or bosom, while the extremities are cold; and in
+the increase of particular secretions, as of bile, saliva, insensible
+perspiration, with great heat of the skin, or with partial sweats, or
+diarrhoea.
+
+There are also many uneasy sensations attending these increased actions,
+which, like those belonging to the hot fit of fever with strong pulse, are
+frequently followed by inflammation, as in scarlet fever; which
+inflammation is nevertheless accompanied with a pulse weaker, though
+quicker, than the pulse during the remission or intermission of the
+paroxysms, though stronger than that of the previous cold fit.
+
+From hence I conclude, that both the cold and hot fits of fever are
+necessary consequences of the perpetual and incessant action of the
+arterial and glandular system; since those muscular fibres and those organs
+of sense, which are most frequently exerted, become necessarily most
+affected both with defect and accumulation of sensorial power: and that
+hence _fever-fits are not an effort of nature to relieve herself_, and that
+therefore they should always be prevented or diminished as much as
+possible, by any means which decrease the general or partial vascular
+actions, when they are greater, or by increasing them when they are less
+than in health, as described in Sect. XII. 6. 1.
+
+Thus have I endeavoured to explain, and I hope to the satisfaction of the
+candid and patient reader, the principal symptoms or circumstances of fever
+without the introduction of the supernatural power of spasm. To the
+arguments in favour of the doctrine of spasm it may be sufficient to reply,
+that in the evolution of medical as well as of dramatic catastrophe,
+
+  Nec Deus intersit, nisi dignus vindice nodus inciderit.--HOR.
+
+       *       *       *       *       *
+
+SECT. XXXIII.
+
+DISEASES OF SENSATION.
+
+    I. 1. _Motions excited by sensation. Digestion. Generation. Pleasure of
+    existence. Hypochondriacism._ 2. _Pain introduced. Sensitive fevers of
+    two kinds._ 3. _Two sensorial powers exerted in sensitive fevers. Size
+    of the blood. Nervous fevers distinguished from putrid ones. The septic
+    and antiseptic theory._ 4. _Two kinds of delirium._ 5. _Other animals
+    are less liable to delirium, cannot receive our contagious diseases,
+    and are less liable to madness._ II. 1. _Sensitive motions generated._
+    2. _Inflammation explained._ 3. _Its remote causes from excess of
+    irritation, or of irritability, not from those pains which are owing to
+    defect of irritation. New vessels produced, and much heat._ 4.
+    _Purulent matter secreted._ 5. _Contagion explained._ 6. _Received but
+    once._ 7. _If common matter be contagious?_ 8. _Why some contagions are
+    received but once._ 9. _Why others may be received frequently.
+    Contagions of small-pox and measles do not act at the same times. Two
+    cases of such patients._ 10. _The blood from patients in the small-pox
+    will not infect others. Cases of children thus inoculated. The
+    variolous contagion is not received into the blood. It acts by
+    sensitive association between the stomach and skin._ III. 1.
+    _Absorption of solids and fluids._ 2. _Art of healing ulcers._ 3.
+    _Mortification attended with less pain in weak people._
+
+I. 1. As many motions of the body are excited and continued by irritations,
+so others require, either conjunctly with these, or separately, the
+pleasurable or painful sensations, for the purpose of producing them with
+due energy. Amongst these the business of digestion supplies us with an
+instance: if the food, which we swallow, is not attended with agreeable
+sensation, it digests less perfectly; and if very disagreeable sensation
+accompanies it, such as a nauseous idea, or very disgustful taste, the
+digestion becomes impeded; or retrograde motions of the stomach and
+oesophagus succeed, and the food is ejected.
+
+The business of generation depends so much on agreeable sensation, that,
+where the object is disgustful, neither voluntary exertion nor irritation
+can effect the purpose; which is also liable to be interrupted by the pain
+of fear or bashfulness.
+
+Besides the pleasure, which attends the irritations produced by the objects
+of lust and hunger, there seems to be a sum of pleasurable affection
+accompanying the various secretions of the numerous glands, which
+constitute the pleasure of life, in contradistinction to the tedium vitæ.
+This quantity or sum of pleasurable affection, seems to contribute to the
+due or energetic performance of the whole moveable system, as well that of
+the heart and arteries, as of digestion and of absorption; since without
+the due quantity of pleasurable sensation, flatulency and hypochondriacism
+affect the intestines, and a languor seizes the arterial pulsations and
+secretions; as occurs in great and continued anxiety of the mind.
+
+2. Besides the febrile motions occasioned by irritation, described in Sect.
+XXXII. and termed irritative fever, it frequently happens that pain is
+excited by the violence of the fibrous contractions; and other new motions
+are then superadded, in consequence of sensation, which we shall term
+febris sensitiva, or sensitive fever. It must be observed, that most
+irritative fevers begin with a decreased exertion of irritation, owing to
+defect of stimulus; but that on the contrary the sensitive fevers, or
+inflammations, generally begin with the increased exertion of sensation, as
+mentioned in Sect. XXXI. on temperaments: for though the cold fit, which
+introduces inflammation, commences with decreased irritation, yet the
+inflammation itself commences in the hot fit during the increase of
+sensation. Thus a common pustule, or phlegmon, in a part of little
+sensibility does not excite an inflammatory fever; but if the stomach,
+intestines, or the tender substance beneath the nails, be injured, great
+sensation is produced, and the whole system is thrown into that kind of
+exertion, which constitutes inflammation.
+
+These sensitive fevers, like the irritative ones, resolve themselves into
+those with arterial strength, and those with arterial debility, that is
+with excess or defect of sensorial power; these may be termed the febris
+sensitiva pulsu forti, sensitive fever with strong pulse, which is the
+synocha, or inflammatory fever; and the febris sensitiva pulsu debili,
+sensitive fever with weak pulse, which is the typhus gravior, or putrid
+fever of some writers.
+
+3. The inflammatory fevers, which are here termed sensitive fevers with
+strong pulse, are generally attended with some topical inflammation, as
+pleurisy, peripneumony, or rheumatism, which distinguishes them from
+irritative fevers with strong pulse. The pulse is strong, quick, and full;
+for in this fever there is great irritation, as well as great sensation,
+employed in moving the arterial system. The size, or coagulable lymph,
+which appears on the blood, is probably an increased secretion from the
+inflamed internal lining of the whole arterial system, the thinner part
+being taken away by the increased absorption of the inflamed lymphatics.
+
+The sensitive fevers with weak pulse, which are termed putrid or malignant
+fevers, are distinguished from irritative fevers with weak pulse, called
+nervous fevers, described in the last section, as the former consist of
+inflammation joined with debility, and the latter of debility alone. Hence
+there is greater heat and more florid colour of the skin in the former,
+with petechiæ, or purple spots, and aphthæ, or sloughs in the throat, and
+generally with previous contagion.
+
+When animal matter dies, as a slough in the throat, or the mortified part
+of a carbuncle, if it be kept moist and warm, as during its abhesion to a
+living body, it will soon putrify. This, and the origin of contagion from
+putrid animal substances, seem to have given rise to the septic and
+antiseptic theory of these fevers.
+
+The matter in pustules and ulcers is thus liable to become putrid, and to
+produce microscopic animalcula; the urine, if too long retained, may also
+gain a putrescent smell, as well as the alvine feces; but some writers have
+gone so far as to believe, that the blood itself in these fevers has smelt
+putrid, when drawn from the arm of the patient: but this seems not well
+founded; since a single particle of putrid matter taken into the blood can
+produce fever, how can we conceive that the whole mass could continue a
+minute in a putrid state without destroying life? Add to this, that putrid
+animal substances give up air, as in gangrenes; and that hence if the blood
+was putrid, air should be given out, which in the blood-vessels is known to
+occasion immediate death.
+
+In these sensitive fevers with strong pulse (or inflammations) there are
+two sensorial faculties concerned in producing the disease, viz. irritation
+and sensation; and hence, as their combined action is more violent, the
+general quantity of sensorial power becomes further exhausted during the
+exacerbation, and the system more rapidly weakened than in irritative fever
+with strong pulse; where the spirit of animation is weakened by but one
+mode of its exertion: so that this febris sensitiva pulsu forti (or
+inflammatory fever,) may be considered as the febris irritativa pulsu
+forti, with the addition of inflammation; and the febris sensitiva pulsu
+debili (or malignant fever) may be considered as the febris irritativa
+pulsu debili (or nervous fever), with the addition of inflammation.
+
+4. In these putrid or malignant fevers a deficiency of irritability
+accompanies the increase of sensibility; and by this waste of sensorial
+power by the excess of sensation, which was already too small, arises the
+delirium and stupor which so perpetually attend these inflammatory fevers
+with arterial debility. In these cases the voluntary power first ceases to
+act from deficiency of sensorial spirit; and the stimuli from external
+bodies have no effect on the exhausted sensorial power, and a delirium like
+a dream is the consequence. At length the internal stimuli cease to excite
+sufficient irritation, and the secretions are either not produced at all,
+or too parsimonious in quantity. Amongst these the secretion of the brain,
+or production of the sensorial power, becomes deficient, till at last all
+sensorial power ceases, except what is just necessary to perform the vital
+motions, and a stupor succeeds; which is thus owing to the same cause as
+the preceding delirium exerted in a greater degree.
+
+This kind of delirium is owing to a suspension of volition, and to the
+disobedience of the senses to external stimuli, and is always occasioned by
+great debility, or paucity of sensorial power; it is therefore a bad sign
+at the end of inflammatory fevers, which had previous arterial strength, as
+rheumatism, or pleurisy, as it shews the presence of great exhaustion of
+sensorial power in a system, which having lately been exposed to great
+excitement, is not so liable to be stimulated into its healthy action,
+either by additional stimulus of food and medicines, or by the accumulation
+of sensorial power during its present torpor. In inflammatory fevers with
+debility, as those termed putrid fevers, delirium is sometimes, as well as
+stupor, rather a favourable sign; as less sensorial power is wasted during
+its continuance (see Class II. 1. 6. 8.), and the constitution not having
+been previously exposed to excess of stimulation, is more liable to be
+excited after previous quiescence.
+
+When the sum of general pleasurable sensation becomes too great, another
+kind of delirium supervenes, and the ideas thus excited are mistaken for
+the irritations of external objects: such a delirium is produced for a time
+by intoxicating drugs, as fermented liquors, or opium: a permanent delirium
+of this kind is sometimes induced by the pleasures of inordinate vanity, or
+by the enthusiastic hopes of heaven. In these cases the power of volition
+is incapable of exertion, and in a great degree the external senses become
+incapable of perceiving their adapted stimuli, because the whole sensorial
+power is employed or expended on the ideas excited by pleasurable
+sensation.
+
+This kind of delirium is distinguished from that which attends the fevers
+above mentioned from its not being accompanied with general debility, but
+simply with excess of pleasurable sensation; and is therefore in some
+measure allied to madness or to reverie; it differs from the delirium of
+dreams, as in this the power of volition is not totally suspended, nor are
+the senses precluded from external stimulation; there is therefore a degree
+of consistency, in this kind of delirium, and a degree of attention to
+external objects, neither of which exist in the delirium of fevers or in
+dreams.
+
+5. It would appear, that the vascular system of other animals are less
+liable to be put into action by their general sum of pleasurable or painful
+sensation; and that the trains of their ideas, and the muscular motions
+usually associated with them, are less powerfully connected than in the
+human system. For other animals neither weep, nor smile, nor laugh; and are
+hence seldom subject to delirium, as treated of in Sect. XVI. on Instinct.
+Now as our epidemic and contagious diseases are probably produced by
+disagreeable sensation, and not simply by irritation; there appears a
+reason, why brute animals are less liable to epidemic or contagious
+diseases; and secondly, why none of our contagions, as the small-pox or
+measles, can be communicated to them, though one of theirs, viz. the
+hydrophobia, as well as many of their poisons, as those of snakes and of in
+insects, communicate their deleterious or painful effects to mankind.
+
+Where the quantity of general painful sensation is too great in the system,
+inordinate voluntary exertions are produced either of our ideas, as in
+melancholy and madness, or of our muscles, as in convulsion. From these
+maladies also brute animals are much more exempt than mankind, owing to
+their greater inaptitude to voluntary exertion, as mentioned in Sect. XVI.
+on Instinct.
+
+II. 1. When any moving organ is excited into such violent motions, that a
+quantity of pleasurable or painful sensation is produced, it frequently
+happens (but not always) that new motions of the affected organ are
+generated in consequence of the pain or pleasure, which are termed
+inflammation.
+
+These new motions are of a peculiar kind, tending to distend the old, and
+to produce new fibres, and thence to elongate the straight muscles, which
+serve locomotion, and to form new vessels at the extremities or sides of
+the vascular muscles.
+
+2. Thus the pleasurable sensations produce an enlargement of the nipples of
+nurses, of the papillæ of the tongue, of the penis, and probably produce
+the growth of the body from its embryon state to its maturity; whilst the
+new motions in consequence of painful sensation, with the growth of the
+fibres or vessels, which they occasion, are termed inflammation.
+
+Hence when the straight muscles are inflamed, part of their tendons at each
+extremity gain new life and sensibility, and thus the muscle is for a time
+elongated; and inflamed bones become soft, vascular, and sensible. Thus new
+vessels shoot over the cornea of inflamed eyes, and into scirrhous tumours,
+when they become inflamed; and hence all inflamed parts grow together by
+intermixture, and inosculation of the new and old vessels.
+
+The heat is occasioned from the increased secretions either of mucus, or of
+the fibres, which produce or elongate the vessels. The red colour is owing
+to the pellucidity of the newly formed vessels, and as the arterial parts
+of them are probably formed before their correspondent venous parts.
+
+3. These new motions are excited either from the increased quantity of
+sensation in consequence of greater fibrous contractions, or from increased
+sensibility, that is, from the increased quantity of sensorial power in the
+moving organ. Hence they are induced by great external stimuli, as by
+wounds, broken bones; and by acrid or infectious materials; or by common
+stimuli on those organs, which have been some time quiescent; as the usual
+light of the day inflames the eyes of those, who have been confined in
+dungeons; and the warmth of a common fire inflames those, who have been
+previously exposed to much cold.
+
+But these new motions are never generated by that pain, which arises from
+defect of stimulus, as from hunger, thirst, cold, or inanition, with all
+those pains, which are termed nervous. Where these pains exist, the motions
+of the affected part are lessened; and if inflammation succeeds, it is in
+some distant parts; as coughs are caused by coldness and moisture being
+long applied to the feet; or it is in consequence of the renewal of the
+stimulus, as of heat or food, which excites our organs into stronger action
+after their temporary quiescence; as kibed heels after walking in snow.
+
+4. But when these new motions of the vascular muscles are exerted with
+greater violence, and these vessels are either elongated too much or too
+hastily, a new material is secreted from their extremities, which is of
+various kinds according to the peculiar animal motions of this new kind of
+gland, which secretes it; such is the pus laudabile or common matter, the
+variolous matter, venereal matter, catarrhous matter, and many others.
+
+5. These matters are the product of an animal process; they are secreted or
+produced from the blood by certain diseased motions of the extremities of
+the blood-vessels, and are on that account all of them contagious; for if a
+portion of any of these matters is transmitted into the circulation, or
+perhaps only inserted into the skin, or beneath the cuticle of an healthy
+person, its stimulus in a certain time produces the same kind of morbid
+motions, by which itself was produced; and hence a similar kind is
+generated. See Sect. XXXIX. 6. 1.
+
+6. It is remarkable, that many of these contagious matters are capable of
+producing a similar disease but once; as the small-pox and measles; and I
+suppose this is true of all those contagious diseases, which are
+spontaneously cured by nature in a certain time; for if the body was
+capable of receiving the disease a second time, the patient must
+perpetually infect himself by the very matter, which he has himself
+produced, and is lodged about him; and hence he could never become free
+from the disease. Something similar to this is seen in the secondary fever
+of the confluent small-pox; there is a great absorption of variolous
+matter, a very minute part of which would give the genuine small-pox to
+another person; but here it only stimulates the system into common fever;
+like that which common puss, or any other acrid material might occasion.
+
+7. In the pulmonary consumption, where common matter is daily absorbed, an
+irritative fever only, without new inflammation, is generally produced;
+which is terminated like other irritative fevers by sweats, or loose
+stools. Hence it does not appear, that this absorbed matter always acts as
+a contagious material producing fresh inflammation or new abscesses. Though
+there is reason to believe, that the first time any common matter is
+absorbed, it has this effect, but not the second time, like the variolous
+matter above mentioned.
+
+This accounts for the opinion, that the pulmonary consumption is sometimes
+infectious, which opinion was held by the ancients, and continues in Italy
+at present; and I have myself seen three or four instances, where a husband
+and wife, who have slept together, and have thus much received each other's
+breath, who have infected each other, and both died in consequence of the
+original taint of only one of them. This also accounts for the abscesses in
+various parts of the body, that are sometimes produced after the inoculated
+small-pox is terminated; for this second absorption of variolous matter
+acts like common matter, and produces only irritative fever in those
+children, whose constitutions have already experienced the absorption of
+common matter; and inflammation with a tendency to produce new abscesses in
+those, whose constitutions have not experienced the absorptions of common
+matter.
+
+It is probable, that more certain proofs might have been found to shew,
+that common matter is infectious the first time it is absorbed, tending to
+produce similar abscesses, but not the second time of its absorption, if
+this subject had been attended to.
+
+8. These contagious diseases are very numerous, as the plague, small-pox,
+chicken-pox, measles, scarlet-fever, pemphigus, catarrh, chincough,
+venereal disease, itch, trichoma, tinea. The infectious material does not
+seem to be dissolved by the air, but only mixed with it perhaps in fine
+powder, which soon subsides; since many of these contagions can only be
+received by actual contact; and others of them only at small distances from
+the infected person; as is evident from many persons having been near
+patients of the small-pox without acquiring the disease.
+
+The reason, why many of these diseases are received but once, and others
+repeatedly, is not well understood; it appears to me, that the constitution
+becomes so accustomed to the stimuli of these infectious materials, by
+having once experienced them, that though irritative motions, as hectic
+fevers, may again be produced by them, yet no sensation, and in consequence
+no general inflammation succeeds; as disagreeable smells or tastes by habit
+cease to be perceived; they continue indeed to excite irritative ideas on
+the organs of sense, but these are not succeeded by sensation.
+
+There are many irritative motions, which were at first succeeded by
+sensation, but which by frequent repetition cease to excite sensation, as
+explained in Sect. XX. on Vertigo. And, that this circumstance exists in
+respect to infectious matter appears from a known fact; that nurses, who
+have had the small-pox, are liable to experience small ulcers on their arms
+by the contact of variolous matter in lifting their patients; and that when
+patients, who have formerly had the small-pox have been inoculated in the
+arm, a phlegmon, or inflamed sore, has succeeded, but no subsequent fever.
+Which shews, that the contagious matter of the small-pox has not lost its
+power of stimulating the part it is applied to, but that the general system
+is not affected in consequence. See Section XII. 7. 6. XIX. 9.
+
+9. From the accounts of the plague, virulent catarrh, and putrid dysentery,
+it seems uncertain, whether these diseases are experienced more than once;
+but the venereal disease and itch are doubtless repeatedly infectious; and
+as these diseases are never cured spontaneously, but require medicines,
+which act without apparent operation, some have suspected, that the
+contagious material produces similar matter rather by a chemical change of
+the fluids, than by an animal process; and that the specific medicines
+destroy their virus by chemically combining with it. This opinion is
+successfully combated by Mr. Hunter, in his Treatise on Venereal Disease,
+Part I. c. i.
+
+But this opinion wants the support of analogy, as there is no known process
+in animal bodies, which is purely chemical, not even digestion; nor can any
+of these matters be produced by chemical processes. Add to this, that it is
+probable, that the insects, observed in the pustules of the itch, and in
+the stools of dysenteric patients, are the consequences, and not the causes
+of these diseases. And that the specific medicines, which cure the itch and
+lues venerea, as brimstone and mercury, act only by increasing the
+absorption of the matter in the ulcuscles of those diseases, and thence
+disposing them to heal; which would otherwise continue to spread.
+
+Why the venereal disease, and itch, and tenia, or scald head, are
+repeatedly contagious, while those contagions attended with fever can be
+received but once, seems to depend on their being rather local diseases
+than universal ones, and are hence not attended with fever, except the
+purulent fever in their last stages, when the patient is destroyed by them.
+On this account the whole of the system does not become habituated to these
+morbid actions, so as to cease to be affected with sensation by a
+repetition of the contagion. Thus the contagious matter of the venereal
+disease, and of the tenia, affects the lymphatic glands, as the inquinal
+glands, and those about the roots of the hair and neck, where it is
+arrested, but does not seem to affect the blood-vessels, since no fever
+ensues.
+
+Hence it would appear, that these kinds of contagion are propagated not by
+means of the circulation, but by sympathy of distant parts with each other;
+since if a distant part, as the palate, should be excited by sensitive
+association into the same kind of motions, as the parts originally affected
+by the contact of infectious matter; that distant part will produce the
+same kind of infectious matter; for every secretion from the blood is
+formed from it by the peculiar motions of the fine extremities of the
+gland, which secretes it; the various secreted fluids, as the bile, saliva,
+gastric juice, not previously existing, as such, in the blood-vessels.
+
+And this peculiar sympathy between the genitals and the throat, owing to
+sensitive association, appears not only in the production of venereal
+ulcers in the throat, but in variety of other instances, as in the mumps,
+in the hydrophobia, some coughs, strangulation, the production of the
+beard, change of voice at puberty. Which are further described in Class IV.
+1. 2. 7.
+
+To evince that the production of such large quantities of contagious
+matter, as are seen in some variolous patients, so as to cover the whole
+skin almost with pustules, does not arise from any chemical fermentation in
+the blood, but that it is owing to morbid motions of the fine extremities
+of the capillaries, or glands, whether these be ruptured or not, appears
+from the quantity of this matter always corresponding with the quantity of
+the fever; that is, with the violent exertions of those glands and
+capillaries, which are the terminations of the arterial system.
+
+The truth of this theory is evinced further by a circumstance observed by
+Mr. J. Hunter, in his Treatise on Venereal Disease; that in a patient, who
+was inoculated for the small-pox, and who appeared afterwards to have been
+previously infested with the measles, the progress of the small-pox was
+delayed till the measles had run their course, and that then the small-pox
+went through its usual periods.
+
+Two similar cases fell under my care, which I shall here relate, as it
+confirms that of Mr. Hunter, and contributes to illustrate this part of the
+theory of contagious diseases. I have transcribed the particulars from a
+letter of Mr. Lightwood of Yoxal, the surgeon who daily attended them, and
+at my request, after I had seen them, kept a kind of journal of their
+cases.
+
+Miss H. and Miss L. two sisters, the one about four and the other about
+three years old, were inoculated Feb. 7, 1791. On the 10th there was a
+redness on both arms discernible by a glass. On the 11th their arms were so
+much inflamed as to leave no doubt of the infection having taken place. On
+the 12th less appearance of inflammation on their arms. In the evening Miss
+L. had an eruption, which resembled the measles. On the 12th the eruption
+on Miss L. was very full on the face and breast, like the measles, with
+considerable fever. It was now known, that the measles were in a farm house
+in the neighbourhood. Miss H.'s arm less inflamed than yesterday. On the
+14th Miss L.'s fever great, and the eruption universal. The arm appears to
+be healed. Miss H.'s arm somewhat redder. They were now put into separate
+rooms. On the 15th Miss L.'s arms as yesterday. Eruption continues. Miss
+H.'s arms have varied but little. 16th, the eruptions on Miss L. are dying
+away, her fever gone. Begins to have a little redness in one arm at the
+place of inoculation. Miss H.'s arms get redder, but she has no appearance
+of complaint. 20th, Miss L.'s arms have advanced slowly till this day, and
+now a few pustules appear. Miss H.'s arm has made little progress from the
+16th to this day, and now she has some fever. 21st, Miss L. as yesterday.
+Miss H. has much inflammation, and an increase of the red circle on one arm
+to the size of half a crown, and had much fever at night, with fetid
+breath. 22d, Miss L.'s pustules continue advancing. Miss H.'s inflammation
+of her arm and red circle increases. A few red spots appear in different
+parts with some degree of fever this morning, 23d. Miss L. has a larger
+crop of pustules. Miss H. has small pustules and great inflammation of her
+arms, with but one pustule likely to suppurate. After this day they
+gradually got well, and the pustules disappeared.
+
+In one of these cases the measles went through their common course with
+milder symptoms than usual, and in the other the measly contagion seemed
+just sufficient to stop the progress of variolous contagion, but without
+itself throwing the constitution into any disorder. At the same time both
+the measles and small-pox seem to have been rendered milder. Does not this
+give an idea, that if they were both inoculated at the same time, that
+neither of them might affect the patient?
+
+From these cases I contend, that the contagious matter of these diseases
+does not affect the constitution by a fermentation, or chemical change of
+the blood, because then they must have proceeded together, and have
+produced a third something, not exactly similar to either of them: but that
+they produce new motions of the cutaneous terminations of the
+blood-vessels, which for a time proceed daily with increasing activity,
+like some paroxysms of fever, till they at length secrete or form a similar
+poison by these unnatural actions.
+
+Now as in the measles one kind of unnatural motion takes place, and in the
+small-pox another kind, it is easy to conceive, that these different kinds
+of morbid motions cannot exist together; and therefore, that that which has
+first begun will continue till the system becomes habituated to the
+stimulus which occasions it, and has ceased to be thrown into action by it;
+and then the other kind of stimulus will in its turn produce fever, and new
+kinds of motions peculiar to itself.
+
+10. On further considering the action of contagious matter, since the
+former part of this work was sent to the press; where I have asserted, in
+Sect. XXII. 3. 3. that it is probable, that the variolous matter is
+diffused through the blood; I prevailed on my friend Mr. Power, surgeon at
+Bosworth in Leicestershire to try, whether the small-pox could be
+inoculated by using the blood of a variolous patient instead of the matter
+from the pustules; as I thought such an experiment might throw some light
+at least on this interesting subject. The following is an extract from his
+letter:--
+
+"March 11, 1793. I inoculated two children, who had not had the small-pox,
+with blood; which was taken from a patient on the second day after the
+eruption commenced, and before it was completed. And at the same time I
+inoculated myself with blood from the same person, in order to compare the
+appearances, which might arise in a person liable to receive the infection,
+and in one not liable to receive it. On the same day I inoculated four
+other children liable to receive the infection with blood taken from
+another person on the fourth day after the commencement of the eruption.
+The patients from whom the blood was taken had the disease mildly, but had
+the most pustules of any I could select from twenty inoculated patients;
+and as much of the blood was insinuated under the cuticle as I could
+introduce by elevating the skin without drawing blood; and three or four
+such punctures were made in each of their arms, and the blood was used in
+its fluid state.
+
+"As the appearances in all these patients, as well as in myself, were
+similar, I shall only mention them in general terms. March 13. A slight
+subcuticular discoloration, with rather a livid appearance, without
+soreness or pain, was visible in them all, as well as in my own hand. 15.
+The discoloration somewhat less, without pain or soreness. Some patients
+inoculated on the same day with variolous matter have considerable
+inflammation. 17. The discoloration is quite gone in them all, and from my
+own hand, a dry mark only remaining. And they were all inoculated on the
+18th, with variolous matter, which produced the disease in them all."
+
+Mr. Power afterwards observes, that, as the patients from whom the blood
+was taken had the disease mildly, it may be supposed, that though the
+contagious matter might be mixed with the blood, it might still be in too
+dilute a state to convey the infection; but adds at the same time, that he
+has diluted recent matter with at least five times its quantity of water,
+and which has still given the infection; though he has sometimes diluted it
+so far as to fail.
+
+The following experiments were instituted at my request by my friend Mr.
+Hadley, surgeon in Derby, to ascertain whether the blood of a person in the
+small-pox be capable of communicating the disease. "Experiment 1st. October
+18th, 1793. I took some blood from a vein in the arm of a person who had
+the small-pox, on the second day of the eruption, and introduced a small
+quantity of it immediately with the point of a lancet between the scars and
+true skin of the right arm of a boy nine years old in two or three
+different places; the other arm was inoculated with variolous matter at the
+same time.
+
+"19th. The punctured parts of the right arm were surrounded with some
+degree of subcuticular inflammation. 20th. The inflammation more
+considerable, with a slight degree of itching, but no pain upon pressure.
+21st. Upon examining the arm this day with a lens I found the inflammation
+less extensive, and the redness changing to a deep yellow or orange-colour,
+22d. Inflammation nearly gone. 23d. Nothing remained, except a slight
+discoloration and a little scurfy appearance on the punctures. At the same
+time the inflammation of the arm inoculated with variolous matter was
+increasing fast, and he had the disease mildly at the usual time.
+
+"Experiment 2d. I inoculated another child at the same time and in the same
+manner, with blood taken on the first day of the eruption; but as the
+appearance and effects were similar to those in the preceding experiment, I
+shall not relate them minutely.
+
+"Experiment 3d. October 20th. Blood was taken from a person who had the
+small-pox, on the third day of the eruption, and on the sixth from the
+commencement of the eruptive fever. I introduced some of it in its fluid
+state into both arms of a boy seven years old.
+
+21st. There appeared to be some inflammation under the cuticle, where the
+punctures were made. 22d. Inflammation more considerable. 23d. On this day
+the inflammation was somewhat greater, and the cuticle rather elevated.
+
+"24th. Inflammation much less, and only a brown or orange-colour remained.
+25th. Scarcely any discoloration left. On this day he was inoculated with
+variolous matter, the progress of the infection went on in the usual way,
+and he had the small-pox very favourably.
+
+"At this time I was requested to inoculate a young person, who was thought
+to have had the small-pox, but his parents were not quite certain; in one
+arm I introduced variolous matter, and in the other blood, taken as in
+experiment 3d. On the second day after the operation, the punctured parts
+were inflamed, though I think the arm in which I had inserted variolous
+matter was rather more so than the other. On the third the inflammation was
+increased, and looked much the same as in the preceding experiment. 4th.
+The inflammation was much diminished, and on the 5th almost gone. He was
+exposed at the same time to the natural infection, but has continued
+perfectly well.
+
+"I have frequently observed (and believe most practitioners have done the
+same), that if variolous matter be inserted in the arm of a person who has
+previously had the small-pox, that the inflammation on the second or third
+days is much greater, than if they had not had the disease, but on the
+fourth or fifth it disappears.
+
+"On the 23d I introduced blood into the arms of three more children, taken
+on the third and fourth days of the eruption. The appearances were much the
+same as mentioned in experiments first and third. They were afterwards
+inoculated with variolous matter, and had the disease in the regular way.
+
+"The above experiments were made with blood taken from a small vein in the
+hand or foot of three or four different patients, whom I had at that time
+under inoculation. They were selected from 160, as having the greatest
+number of pustules. The part was washed with warm water before the blood
+was taken, to prevent the possibility of any matter being mixed with it
+from the surface."
+
+Shall we conclude from hence, that the variolous matter never enters the
+blood-vessels? but that the morbid motions of the vessels of the skin
+around the insertion of it continue to increase in a larger and larger
+circle for six or seven days; that then their quantity of morbid action
+becomes great enough to produce a fever-fit, and to affect the stomach by
+association of motions? and finally, that a second association of motions
+is produced between the stomach and the other parts of the skin, inducing
+them into morbid actions similar to those of the circle round the insertion
+of the variolous matter? Many more experiments and observations are
+required before this important question can be satisfactorily answered.
+
+It may be adduced, that as the matter inserted into the skin of the arm
+frequently swells the lymphatic in the axilla, that in that circumstance it
+seems to be there arrested in its progress, and cannot be imagined to enter
+the blood by that lymphatic gland till the swelling of it subsides. Some
+other phænomena of the disease are more easily reconcileable to this theory
+of sympathetic motions than to that of absorption; as the time taken up
+between the insertion of the matter, and the operation of it on the system,
+as mentioned above. For the circle around the insertion is seen to
+increase, and to inflame; and I believe, undergoes a kind of diurnal
+paroxysm of torpor and paleness with a succeeding increase of action and
+colour, like a topical fever-fit. Whereas if the matter is conceived to
+circulate for six or seven days with the blood, without producing disorder,
+it ought to be rendered milder, or the blood-vessels more familiarized to
+its acrimony.
+
+It is much easier to conceive from this doctrine of associated or
+sympathetic motions of distant parts of the system, how it happens, that
+the variolous infection can be received but once, as before explained; than
+by supposing, that a change is effected in the mass of blood by any kind of
+fermentative process.
+
+The curious circumstance of the two contagions of small-pox and measles not
+acting at the same time, but one of them resting or suspending its action
+till that of the other ceases, may be much easier explained from
+sympathetic or associated actions of the infected part with other parts of
+the system, than it can from supposing the two contagions to enter the
+circulation.
+
+The skin of the face is subject to more frequent vicissitudes of heat and
+cold, from its exposure to the open air, and is in consequence more liable
+to sensitive association with the stomach than any other part of the
+surface of the body, because their actions have been more frequently thus
+associated. Thus in a surfeit from drinking cold water, when a person is
+very hot and fatigued, an eruption is liable to appear on the face in
+consequence of this sympathy. In the same manner the rosy eruption on the
+faces of drunkards more probably arises from the sympathy of the face with
+the stomach, rather than between the face and the liver, as is generally
+supposed.
+
+This sympathy between the stomach and the skin of the face is apparent in
+the eruption of the small-pox; since, where the disease is in considerable
+quantity, the eruption on the face first succeeds the sickness of the
+stomach. In the natural disease the stomach seems to be frequently
+primarily affected, either alone or along with the tonsils, as the matter
+seems to be only diffused in the air, and by being mixed with the saliva,
+or mucus of the tonsils, to be swallowed into the stomach.
+
+After some days the irritative circles of motions become disordered by this
+new stimulus, which acts upon the mucus lining of the stomach; and
+sickness, vertigo, and a diurnal fever succeed. These disordered irritative
+motions become daily increased for two or three days, and then by their
+increased action certain sensitive motions, or inflammation, is produced,
+and at the next cold fit of fever, when the stomach recovers from its
+torpor, an inflammation of the external skin is formed in points (which
+afterwards suppurate), by sensitive association, in the same manner as a
+cough is produced in consequence of exposing the feet to cold, as described
+in Sect. XXV. 17. and Class IV. 2. I. 7. If the inoculated skin of the arm,
+as far as it appears inflamed, was to be cut out, or destroyed by caustic,
+before the fever commenced, as suppose on the fourth day after inoculation,
+would this prevent the disease? as it is supposed to prevent the
+hydrophobia.
+
+III. 1. Where the new vessels, and enlarged old ones, which constitute
+inflammation, are not so hastily distended as to burst, and form a new kind
+of gland for the secretion of matter, as above mentioned; if such
+circumstances happen as diminish the painful sensation, the tendency to
+growth ceases, and by and by an absorption commences, not only of the
+superabundant quantity of fluids deposited in the inflamed part, but of the
+solids likewise, and this even of the hardest kind.
+
+Thus during the growth of the second set of teeth in children, the roots of
+the first set are totally absorbed, till at length nothing of them remains
+but the crown; though a few weeks before, if they are drawn immaturely,
+their roots are found complete. Similar to this Mr. Hunter has observed,
+that where a dead piece of bone is to exfoliate, or to separate from a
+living one, that the dead part does not putrify, but remains perfectly
+sound, while the surface of the living part of the bone, which is in
+contact with the dead part, becomes absorbed, and thus effects its
+separation. Med. Comment. Edinb. V. 1. 425. In the same manner the
+calcareous matter of gouty concretions, the coagulable lymph deposited on
+inflamed membranes in rheumatism and extravasated blood become absorbed;
+which are all as solid and as indissoluble materials as the new vessels
+produced in inflammation.
+
+This absorption of the new vessels and deposited fluids of inflamed parts
+is called resolution: it is produced by first using such internal means as
+decrease the pain of the part, and in consequence its new motions, as
+repeated bleeding, cathartics, diluent potations, and warm bath.
+
+After the vessels are thus emptied, and the absorption of the new vessels
+and deposited fluids is evidently begun, it is much promoted by stimulating
+the part externally by solutions of lead, or other metals, and internally
+by the bark, and small doses of opium. Hence when an ophthalmy begins to
+become paler, any acrid eye-water, as a solution of six grains of white
+vitriol in an ounce of water, hastens the absorption, and clears the eye in
+a very short time. But the same application used a few days sooner would
+have increased the inflammation. Hence after evacuation opium in small
+doses may contribute to promote the absorption of fluids deposited on the
+brain, as observed by Mr. Bromfield in his treatise of surgery.
+
+2. Where an abscess is formed by the rupture of these new vessels, the
+violence of inflammation ceases, and a new gland separates a material
+called pus: at the same time a less degree of inflammation produces new
+vessels called vulgarly proud flesh; which, if no bandage confines its
+growth, nor any other circumstance promotes absorption in the wound, would
+rise to a great height above the usual size of the part.
+
+Hence the art of healing ulcers consists in producing a tendency to
+absorption in the wound greater than the deposition. Thus when an
+ill-conditioned ulcer separates a copious and thin discharge, by the use of
+any stimulus, as of salts of lead, or mercury, or copper externally
+applied, the discharge becomes diminished in quantity, and becomes thicker,
+as the thinner parts are first absorbed.
+
+But nothing so much contributes to increase the absorption in a wound as
+covering the whole limb above the sore with a bandage, which should be
+spread with some plaster, as with emplastrum de minio, to prevent it from
+slipping. By this artificial tightness of the skin, the arterial pulsations
+act with double their usual power in promoting the ascending current of the
+fluid in the valvular lymphatics.
+
+Internally the absorption from ulcers should be promoted first by
+evacuation, then by opium, bark, mercury, steel.
+
+3. Where the inflammation proceeds with greater violence or rapidity, that
+is, when by the painful sensation a more inordinate activity of the organ
+is produced, and by this great activity an additional quantity of painful
+sensation follows in an increasing ratio, till the whole of the sensorial
+power, or spirit of animation, in the part becomes exhausted, a
+mortification ensues, as in a carbuncle, in inflammations of the bowels, in
+the extremities of old people, or in the limbs of those who are brought
+near a fire after having been much benumbed with cold. And from hence it
+appears, why weak people are more subject to mortification than strong
+ones, and why in weak persons less pain will produce mortification, namely,
+because the sensorial power is sooner exhausted by any excess of activity.
+I remember seeing a gentleman who had the preceding day travelled two
+stages in a chaise with what he termed a bearable pain in his bowels; which
+when I saw him had ceased rather suddenly, and without a passage through
+him; his pulse was then weak, though not very quick; but as nothing which
+he swallowed would continue in his stomach many minutes, I concluded that
+the bowel was mortified; he died on the next day. It is usual for patients
+sinking under the small-pox with mortified pustules, and with purple spots
+intermixed, to complain of no pain, but to say they are pretty well to the
+last moment.
+
+_Recapitulation._
+
+IV. When the motions of any part of the system, in consequence of previous
+torpor, are performed with more energy than in the irritative fevers, a
+disagreeable sensation is produced, and new actions of some part of the
+system commence in consequence of this sensation conjointly with the
+irritation: which motions constitute inflammation. If the fever be attended
+with a strong pulse, as in pleurisy, or rheumatism, it is termed synocha
+sensitiva, or sensitive fever with strong pulse; which is usually termed
+inflammatory fever. If it be attended with weak pulse, it is termed typhus
+sensitivus, or sensitive fever with weak pulse, or typhus gravior, or
+putrid malignant fever.
+
+The synocha sensitiva, or sensitive fever with strong pulse, is generally
+attended with some topical inflammation, as in peripneumony, hepatitis, and
+is accompanied with much coagulable lymph, or size; which rises to the
+surface of the blood, when taken into a bason, as it cools; and which is
+believed to be the increased mucous secretion from the coats of the
+arteries, inspissated by a greater absorption of its aqueous and saline
+part, and perhaps changed by its delay in the circulation.
+
+The typhus sensitivus, or sensitive fever with weak pulse, is frequently
+attended with delirium, which is caused by the deficiency of the quantity
+of sensorial power, and with variety of cutaneous eruptions.
+
+Inflammation is caused by the pains occasioned by excess of action, and not
+by those pains which are occasioned by defect of action. These morbid
+actions, which are thus produced by two sensorial powers, viz. by
+irritation and sensation, secrete new living fibres, which elongate the old
+vessels, or form new ones, and at the same time much heat is evolved from
+these combinations. By the rupture of these vessels, or by a new
+construction of their apertures, purulent matters are secreted of various
+kinds; which are infectious the first time they are applied to the skin
+beneath the cuticle, or swallowed with the saliva into the stomach. This
+contagion acts not by its being absorbed into the circulation, but by the
+sympathies, or associated actions, between the part first stimulated by the
+contagious matter and the other parts of the system. Thus in the natural
+small-pox the contagion is swallowed with the saliva, and by its stimulus
+inflames the stomach; this variolous inflammation of the stomach increases
+every day, like the circle round the puncture of an inoculated arm, till it
+becomes great enough to disorder the circles of irritative and sensitive
+motions, and thus produces fever-fits, with sickness and vomiting. Lastly,
+after the cold paroxysm, or fit of torpor, of the stomach has increased for
+two or three successive days, an inflammation of the skin commences in
+points; which generally first appear upon the face, as the associated
+actions between the skin of the face and that of the stomach have been more
+frequently exerted together than those of any other parts of the external
+surface.
+
+Contagious matters, as those of the measles and small-pox, do not act upon
+the system at the same time; but the progress of that which was last
+received is delayed, till the action of the former infection ceases. All
+kinds of matter, even that from common ulcers, are probably contagious the
+first time they are inserted beneath the cuticle or swallowed into the
+stomach; that is, as they were formed by certain morbid actions of the
+extremities of the vessels, they have the power to excite similar morbid
+actions in the extremities of other vessels, to which they are applied; and
+these by sympathy, or associations of motion, excite similar morbid actions
+in distant parts of the system, without entering the circulation; and hence
+the blood of a patient in the small-pox will not give that disease by
+inoculation to others.
+
+When the new fibres or vessels become again absorbed into the circulation,
+the inflammation ceases; which is promoted, after sufficient evacuations,
+by external stimulants and bandages: but where the action of the vessels is
+very great, a mortification of the part is liable to ensue, owing to the
+exhaustion of sensorial power; which however occurs in weak people without
+much pain, and without very violent previous inflammation; and, like
+partial paralysis, may be esteemed one mode of natural death of old people,
+a part dying before the whole.
+
+       *       *       *       *       *
+
+SECT. XXXIV.
+
+DISEASES OF VOLITION.
+
+    I. 1. _Volition defined. Motions termed involuntary are caused by
+    volition. Desires opposed to each other. Deliberation. Ass between two
+    hay-cocks. Saliva swallowed against one's desire. Voluntary motions
+    distinguished from those associated with sensitive motions._ 2. _Pains
+    from excess, and from defect of motion. No pain is felt during vehement
+    voluntary exertion; as in cold fits of ague, labour-pains, strangury,
+    tenesmus, vomiting, restlessness in fevers, convulsion of a wounded
+    muscle._ 3. _Of holding the breath and screaming in pain; why swine and
+    dogs cry out in pain, and not sheep and horses. Of grinning and biting
+    in pain; why mad animals bite others._ 4. _Epileptic convulsions
+    explained, why the fits begin with quivering of the under jaw, biting
+    the tongue, and setting the teeth; why the convulsive motions are
+    alternately relaxed. The phenomenon of laughter explained. Why children
+    cannot tickle themselves. How some have died from immoderate laughter._
+    5. _Of cataleptic spasms, of the locked jaw, of painful cramps._ 6.
+    _Syncope explained. Why no external objects are perceived in syncope._
+    7. _Of palsy and apoplexy from violent exertions. Case of Mrs. Scot.
+    From dancing, scating, swimming. Case of Mr. Nairn. Why palsies are not
+    always immediately preceded by violent exertions. Palsy and epilepsy
+    from diseased livers. Why the right arm more frequently paralytic than
+    the left. How paralytic limbs regain their motions._ II. _Diseases of
+    the sensual motions from excess or defect of voluntary exertion._ 1.
+    _Madness._ 2. _Distinguished from delirium._ 3. _Why mankind more
+    liable to insanity than brutes._ 4. _Suspicion. Want of shame, and of
+    cleanliness._ 5. _They bear cold, hunger, and fatigue. Charles XII. of
+    Sweden._ 6. _Pleasureable delirium, and insanity. Child riding on a
+    stick. Pains of martyrdom not felt._ 7. _Dropsy._ 8. _Inflammation
+    cured by insanity._ III. 1. _Pain relieved by reverie. Reverie is an
+    exertion of voluntary and sensitive motions._ 2. _Case of reverie._ 3.
+    _Lady supposed to have two souls._ 4. _Methods of relieving pain._
+
+I. 1. Before we commence this Section on Diseased Voluntary Motions, it may
+be necessary to premise, that the word volition is not used in this work
+exactly in its common acceptation. Volition is said in Section V. to bear
+the same analogy to desire and aversion, which sensation does to pleasure
+and pain. And hence that, when desire or aversion produces any action of
+the muscular fibres, or of the organs of sense, they are termed volition;
+and the actions produced in consequence are termed voluntary actions.
+Whence it appears, that motions of our muscles or ideas may be produced in
+consequence of desire or aversion without our having the power to prevent
+them, and yet these motions may be termed voluntary, according to our
+definition of the word; though in common language they would be called
+involuntary.
+
+The objects of desire and aversion are generally at a distance, whereas
+those of pleasure and pain are immediately acting upon our organs. Hence,
+before desire or aversion are exerted, so as to cause any actions, there is
+generally time for deliberation; which consists in discovering the means to
+obtain the object of desire, or to avoid the object of aversion; or in
+examining the good or bad consequences, which may result from them. In this
+case it is evident, that we have a power to delay the proposed action, or
+to perform it; and this power of choosing, whether we shall act or not, is
+in common language expressed by the word volition, or will. Whereas in this
+work the word volition means simply the active state of the sensorial
+faculty in producing motion in consequence of desire or aversion: whether
+we have the power of restraining that action, or not; that is, whether we
+exert any actions in consequence of opposite desires or aversions, or not.
+
+For if the objects of desire or aversion are present, there is no necessity
+to investigate or compare the _means_ of obtaining them, nor do we always
+deliberate about their consequences; that is, no deliberation necessarily
+intervenes, and in consequence the power of choosing to act or not is not
+exerted. It is probable, that this twofold use of the word volition in all
+languages has confounded the metaphysicians, who have disputed about free
+will and necessity. Whereas from the above analysis it would appear, that
+during our sleep, we use no voluntary exertions at all; and in our waking
+hours, that they are the consequence of desire or aversion.
+
+To will is to act in consequence of desire; but to desire means to desire
+something, even if that something be only to become free from the pain,
+which causes the desire; for to desire nothing is not to desire; the word
+desire, therefore, includes both the action and the object or motive; for
+the object and motive of desire are the same thing. Hence to desire without
+an object, that is, without a motive, is a solecism in language. As if one
+should ask, if you could eat without food, or breathe without air.
+
+From this account of volition it appears, that convulsions of the muscles,
+as in epileptic fits, may in the common sense of that word be termed
+involuntary; because no deliberation is interposed between the desire or
+aversion and the consequent action; but in the sense of the word, as above
+defined, they belong to the class of voluntary motions, as delivered in
+Vol. II. Class III. If this use of the word be discordant to the ear of the
+reader, the term morbid voluntary motions, or motions in consequence of
+aversion, may be substituted in its stead.
+
+If a person has a desire to be cured of the ague, and has at the same time
+an aversion (or contrary desire) to swallowing an ounce of Peruvian bark;
+he balances desire against desire, or aversion against aversion; and thus
+he acquires the power of choosing, which is the common acceptation of the
+word _willing_. But in the cold fit of ague, after having discovered that
+the act of shuddering, or exerting the subcutaneous muscles, relieves the
+pain of cold; he immediately exerts this act of volition, and shudders, as
+soon as the pain and consequent aversion return, without any deliberation
+intervening; yet is this act, as well as that of swallowing an ounce of the
+bark, caused by volition; and that even though he endeavours in vain to
+prevent it by a weaker contrary volition. This recalls to our minds the
+story of the hungry ass between two hay-stacks, where the two desires are
+supposed so exactly to counteract each other, that he goes to neither of
+the stacks, but perishes by want. Now as two equal and opposite desires are
+thus supposed to balance each other, and prevent all action, it follows,
+that if one of these hay-stacks was suddenly removed, that the ass would
+irresistibly be hurried to the other, which in the common use of the word
+might be called an involuntary act; but which, in our acceptation of it,
+would be classed amongst voluntary actions, as above explained.
+
+Hence to deliberate is to compare opposing desires or aversions, and that
+which is the most interesting at length prevails, and produces action.
+Similar to this, where two pains oppose each other, the stronger or more
+interesting one produces action; as in pleurisy the pain from suffocation
+would produce expansion of the lungs, but the pain occasioned by extending
+the inflamed membrane, which lines the chest, opposes this expansion, and
+one or the other alternately prevails.
+
+When any one moves his hand quickly near another person's eyes, the
+eye-lids instantly close; this act in common language is termed
+involuntary, as we have not time to deliberate or to exert any contrary
+desire or aversion, but in this work it would be termed a voluntary act,
+because it is caused by the faculty of volition, and after a few trials the
+nictitation can be prevented by a contrary or opposing volition.
+
+The power of opposing volitions is best exemplified in the story of Mutius
+Scævola, who is said to have thrust his hand into the fire before Porcenna,
+and to have suffered it to be consumed for having failed him in his attempt
+on the life of that general. Here the aversion for the loss of same, or the
+unsatisfied desire to serve his country, the two prevalent enthusiasms at
+that time, were more powerful than the desire of withdrawing his hand,
+which must be occasioned by the pain of combustion; of these opposing
+volitions
+
+  Vincit amor patriæ, laudumque immensa cupido.
+
+If any one is told not to swallow his saliva for a minute, he soon swallows
+it contrary to his will, in the common sense of that word; but this also is
+a voluntary action, as it is performed by the faculty of volition, and is
+thus to be understood. When the power of volition is exerted on any of our
+senses, they become more acute, as in our attempts to hear small noises in
+the night. As explained in Section XIX. 6. Hence by our attention to the
+fauces from our desire not to swallow our saliva; the fauces become more
+sensible; and the stimulus of the saliva is followed by greater sensation,
+and consequent desire of swallowing it. So that the desire or volition in
+consequence of the increased sensation of the saliva is more powerful, than
+the previous desire not to swallow it. See Vol. II. Deglutitio invita. In
+the same manner if a modest man wishes not to want to make water, when he
+is confined with ladies in a coach or an assembly-room; that very act of
+volition induces the circumstance, which he wishes to avoid, as above
+explained; insomuch that I once saw a partial insanity, which might be
+called a voluntary diabetes, which was occasioned by the fear (and
+consequent aversion) of not being able to make water at all.
+
+It is further necessary to observe here, to prevent any confusion of
+voluntary, with sensitive, or associate motions, that in all the instances
+of violent efforts to relieve pain, those efforts are at first voluntary
+exertions; but after they have been frequently repeated for the purpose of
+relieving certain pains, they become associated with those pains, and cease
+at those times to be subservient to the will; as in coughing, sneezing, and
+strangury. Of these motions those which contribute to remove or dislodge
+the offending cause, as the actions of the abdominal muscles in parturition
+or in vomiting, though they were originally excited by volition, are in
+this work termed sensitive motions; but those actions of the muscles or
+organs of sense, which do not contribute to remove the offending cause, as
+in general convulsions or in madness, are in this work termed voluntary
+motions, or motions in consequence of aversion, though in common language
+they are called involuntary ones. Those sensitive unrestrainable actions,
+which contribute to remove the cause of pain are uniformly and invariably
+exerted, as in coughing or sneezing; but those motions which are exerted in
+consequence of aversion without contributing to remove the painful cause,
+but only to prevent the sensation of it, as in epileptic, or cataleptic
+fits, are not uniformly and invariably exerted, but change from one set of
+muscles to another, as will be further explained; and may by this criterion
+also be distinguished from the former.
+
+At the same time those motions, which are excited by perpetual stimulus, or
+by association with each other, or immediately by pleasureable or painful
+sensation, may properly be termed involuntary motions, as those of the
+heart and arteries; as the faculty of volition seldom affects those, except
+when it exists in unnatural quantity, as in maniacal people.
+
+2. It was observed in Section XIV. on the Production of Ideas, that those
+parts of the system, which are usually termed the organs of sense, are
+liable to be excited into pain by the excess of the stimulus of those
+objects, which are by nature adapted to affect them; as of too great light,
+sound, or pressure. But that these organs receive no pain from the defect
+or absence of these stimuli, as in darkness or silence. But that our other
+organs of perception, which have generally been called appetites, as of
+hunger, thirst, want of heat, want of fresh air, are liable to be affected
+with pain by the defect, as well as by the excess of their appropriated
+stimuli.
+
+This excess or defect of stimulus is however to be considered only as the
+remote cause of the pain, the immediate cause being the excess or defect of
+the natural action of the affected part, according to Sect. IV. 5. Hence
+all the pains of the body may be divided into those from excess of motion,
+and those from defect of motion; which distinction is of great importance
+in the knowledge and the cure of many diseases. For as the pains from
+excess of motion either gradually subside, or are in general succeeded by
+inflammation; so those from defect of motion either gradually subside, or
+are in general succeeded by convulsion, or madness. These pains are easily
+distinguishable from each other by this circumstance, that the former are
+attended with heat of the pained part, or of the whole body; whereas the
+latter exists without increase of heat in the pained part, and is generally
+attended with coldness of the extremities of the body; which is the true
+criterion of what have been called nervous pains.
+
+Thus when any acrid material, as snuff or lime, falls into the eye, pain
+and inflammation and heat are produced from the excess of stimulus; but
+violent hunger, hemicrania, or the clavus hystericus, are attended with
+coldness of the extremities, and defect of circulation. When we are exposed
+to great cold, the pain we experience from the deficiency of heat is
+attended with a quiescence of the motions of the vascular system; so that
+no inflammation is produced, but a great desire of heat, and a tremulous
+motion of the subcutaneous muscles, which is properly a convulsion in
+consequence of this pain from defect of the stimulus of heat.
+
+It was before mentioned, that as sensation consists in certain movements of
+the sensorium, beginning at some of the extremities of it, and propagated
+to the central parts of it; so volition consists of certain other movements
+of the sensorium, commencing in the central parts of it, and propagated to
+some of its extremities. This idea of these two great powers of motion in
+the animal machine is confirmed from observing, that they never exist in a
+great degree or universally at the same time; for while we strongly exert
+our voluntary motions, we cease to feel the pains or uneasinesses, which
+occasioned us to exert them.
+
+Hence during the time of fighting with fists or swords no pain is felt by
+the combatants, till they cease to exert themselves. Thus in the beginning
+of ague-fits the painful sensation of cold is diminished, while the patient
+exerts himself in the shivering and gnashing of his teeth. He then ceases
+to exert himself, and the pain of cold returns; and he is thus perpetually
+induced to reiterate these exertions, from which he experiences a temporary
+relief. The same occurs in labour-pains, the exertion of the parturient
+woman relieves the violence of the pains for a time, which recur again soon
+after she has ceased to use those exertions. The same is true in many other
+painful diseases, as in the strangury, tenesmus, and the efforts of
+vomiting; all these disagreeable sensations are diminished or removed for a
+time by the various exertions they occasion, and recur alternately with
+those exertions.
+
+The restlessness in some fevers is an almost perpetual exertion of this
+kind, excited to relieve some disagreeable sensations; the reciprocal
+opposite exertions of a wounded worm, the alternate emprosthotonos and
+opisthotonos of some spasmodic diseases, and the intervals of all
+convulsions, from whatever cause, seem to be owing to this circumstance of
+the laws of animation; that great or universal exertion cannot exist at the
+same time with great or universal sensation, though they can exist
+reciprocally; which is probably resolvable into the more general law, that
+the whole sensorial power being expended in one mode of exertion, there is
+none to spare for any other. Whence syncope, or temporary apoplexy,
+succeeds to epileptic convulsions.
+
+3. Hence when any violent pain afflicts us, of which we can neither avoid
+nor remove the cause, we soon learn to endeavour to alleviate it, by
+exerting some violent voluntary effort, as mentioned above; and are
+naturally induced to use those muscles for this purpose, which have been in
+the early periods of our lives most frequently or most powerfully exerted.
+
+Now the first muscles, which infants use most frequently, are those of
+respiration; and on this account we gain a habit of holding our breath, at
+the same time that we use great efforts to exclude it, for this purpose of
+alleviating unavoidable pain; or we press out our breath through a small
+aperture of the larynx, and scream violently, when the pain is greater than
+is relievable by the former mode of exertion. Thus children scream to
+relieve any pain either of body or mind, as from anger, or fear of being
+beaten.
+
+Hence it is curious to observe, that those animals, who have more
+frequently exerted their muscles of respiration violently, as in talking,
+barking, or grunting, as children, dogs, hogs, scream much more, when they
+are in pain, than those other animals, who use little or no language in
+their common modes of life; as horses, sheep, and cows.
+
+The next most frequent or most powerful efforts, which infants are first
+tempted to produce, are those with the muscles in biting hard substances;
+indeed the exertion of these muscles is very powerful in common
+mastication, as appears from the pain we receive, if a bit of bone is
+unexpectedly found amongst our softer food; and further appears from their
+acting to so great mechanical disadvantage, particularly when we bite with
+the incisores, or canine teeth; which are first formed, and thence are
+first used to violent exertion.
+
+Hence when a person is in great pain, the cause of which he cannot remove,
+he sets his teeth firmly together, or bites some substance between them
+with great vehemence, as another mode of violent exertion to produce a
+temporary relief. Thus we have a proverb where no help can be had in pain,
+"to grin and abide;" and the tortures of hell are said to be attended with
+"gnashing of teeth."
+
+Hence in violent spasmodic pains I have seen people bite not only their
+tongues, but their arms or fingers, or those of the attendants, or any
+object which was near them; and also strike, pinch, or tear, others or
+themselves, particularly the part of their own body, which is painful at
+the time. Soldiers, who die of painful wounds in battle, are said in Homer
+to bite the ground. Thus also in the bellon, or colica saturnina, the
+patients are said to bite their own flesh, and dogs in this disease to bite
+up the ground they lie upon. It is probable that the great endeavours to
+bite in mad dogs, and the violence of other mad animals, is owing to the
+same cause.
+
+4. If the efforts of our voluntary motions are exerted with still greater
+energy for the relief of some disagreeable sensation, convulsions are
+produced; as the various kinds of epilepsy, and in some hysteric paroxysms.
+In all these diseases a pain, or disagreeable sensation is produced,
+frequently by worms, or acidity in the bowels, or by a diseased nerve in
+the side, or head, or by the pain of a diseased liver.
+
+In some constitutions a more intolerable degree of pain is produced in some
+part at a distance from the cause by sensitive association, as before
+explained; these pains in such constitutions arise to so great a degree,
+that I verily believe no artificial tortures could equal some, which I have
+witnessed; and am confident life would not have long been preserved, unless
+they had been soon diminished or removed by the universal convulsion of the
+voluntary motions, or by temporary madness.
+
+In some of the unfortunate patients I have observed, the pain has risen to
+an inexpressible degree, as above described, before the convulsions have
+supervened; and which were preceded by screaming, and grinning; in others,
+as in the common epilepsy, the convulsion has immediately succeeded the
+commencement of the disagreeable sensations; and as a stupor frequently
+succeeds the convulsions, they only seemed to remember that a pain at the
+stomach preceded the fit, or some other uneasy feel; or more frequently
+retained no memory at all of the immediate cause of the paroxysm. But even
+in this kind of epilepsy, where the patient does not recollect any
+preceding pain, the paroxysms generally are preceded by a quivering motion
+of the under jaw, with a biting of the tongue; the teeth afterwards become
+pressed together with vehemence, and the eyes are then convulsed, before
+the commencement of the universal convulsion; which are all efforts to
+relieve pain.
+
+The reason why these convulsive motions are alternately exerted and
+remitted was mentioned above, and in Sect. XII. 1. 3. when the exertions
+are such as give a temporary relief to the pain, which excites them, they
+cease for a time, till the pain is again perceived; and then new exertions
+are produced for its relief. We see daily examples of this in the loud
+reiterated laughter of some people; the pleasureable sensation, which
+excites this laughter, arises for a time so high as to change its name and
+become painful: the convulsive motions of the respiratory muscles relieve
+the pain for a time; we are, however, unwilling to lose the pleasure, and
+presently put a stop to this exertion, and immediately the pleasure recurs,
+and again as instantly rises into pain. All of us have felt the pain of
+immoderate laughter; children have been tickled into convulsions of the
+whole body; and others have died in the act of laughing; probably from a
+paralysis succeeding the long continued actions of the muscles of
+respiration.
+
+Hence we learn the reason, why children, who are so easily excited to laugh
+by the tickling of other people's fingers, cannot tickle themselves into
+laughter. The exertion of their hands in the endeavour to tickle themselves
+prevents the necessity of any exertion of the respiratory muscles to
+relieve the excess of pleasurable affection. See Sect. XVII. 3. 5.
+
+Chrysippus is recorded to have died laughing, when an ass was invited to
+sup with him. The same is related of one of the popes, who, when he was
+ill, saw a tame monkey at his bedside put on the holy thiara. Hall. Phys.
+T. III. p. 306.
+
+There are instances of epilepsy being produced by laughing recorded by Van
+Swieten, T. III. 402 and 308. And it is well known, that many people have
+died instantaneously from the painful excess of joy, which probably might
+have been prevented by the exertions of laughter.
+
+Every combination of ideas, which we attend to, occasions pain or pleasure;
+those which occasion pleasure, furnish either social or selfish pleasure,
+either malicious or friendly, or lascivious, or sublime pleasure; that is,
+they give us pleasure mixed with other emotions, or they give us unmixed
+pleasure, without occasioning any other emotions or exertions at the same
+time. This unmixed pleasure, if it be great, becomes painful, like all
+other animal motions from stimuli of every kind; and if no other exertions
+are occasioned at the same time, we use the exertion of laughter to relieve
+this pain. Hence laughter is occasioned by such wit as excites simple
+pleasure without any other emotion, such as pity, love, reverence. For
+sublime ideas are mixed with admiration, beautiful ones with love, new ones
+with surprise; and these exertions of our ideas prevent the action of
+laughter from being necessary to relieve the painful pleasure above
+described. Whence laughable wit consists of frivolous ideas, without
+connections of any consequence, such as puns on words, or on phrases,
+incongruous junctions of ideas; on which account laughter is so frequent in
+children.
+
+Unmixed pleasure less than that, which causes laughter, causes sleep, as in
+singing children to sleep, or in slight intoxication from wine or food. See
+Sect. XVIII. 12.
+
+5. If the pains, or disagreeable sensations, above described do not obtain
+a temporary relief from these convulsive exertions of the muscles, those
+convulsive exertions continue without remission, and one kind of catalepsy
+is produced. Thus when a nerve or tendon produces great pain by its being
+inflamed or wounded, the patient sets his teeth firmly together, and grins
+violently, to diminish the pain; and if the pain is not relieved by this
+exertion, no relaxation of the maxillary muscles takes place, as in the
+convulsions above described, but the jaws remain firmly fixed together.
+This locked jaw is the most frequent instance of cataleptic spasm, because
+we are more inclined to exert the muscles subservient to mastication from
+their early obedience to violent efforts of volition.
+
+But in the case related in Sect. XIX. on Reverie, the cataleptic lady had
+pain in her upper teeth; and pressing one of her hands vehemently against
+her cheek-bone to diminish this pain, it remained in that attitude for
+about half an hour twice a day, till the painful paroxysm was over.
+
+I have this very day seen a young lady in this disease, (with which she has
+frequently been afflicted,) she began to-day with violent pain shooting
+from one side of the forehead to the occiput, and after various struggles
+lay on the bed with her fingers and wrists bent and stiff for about two
+hours; in other respects she seemed in a syncope with a natural pulse. She
+then had intervals of pain and of spasm, and took three grains of opium
+every hour till she had taken nine grains, before the pains and spasm
+ceased.
+
+There is, however, another species of fixed spasm, which differs from the
+former, as the pain exists in the contracted muscle, and would seem rather
+to be the consequence than the cause of the contraction, as in the cramp in
+the calf of the leg, and in many other parts of the body.
+
+In these spasms it should seem, that the muscle itself is first thrown into
+contraction by some disagreeable sensation, as of cold; and that then the
+violent pain is produced by the great contraction of the muscular fibres
+extending its own tendons, which are said to be sensible to extension only;
+and is further explained in Sect. XVIII. 15.
+
+6. Many instances have been given in this work, where after violent motions
+excited by irritation, the organ has become quiescent to less, and even to
+the great irritation, which induced it into violent motion; as after
+looking long at the sun or any bright colour, they cease to be seen; and
+after removing from bright day-light into a gloomy room, the eye cannot at
+first perceive the objects, which stimulate it less. Similar to this is the
+syncope, which succeeds after the violent exertions of our voluntary
+motions, as after epileptic fits, for the power of volition acts in this
+case as the stimulus in the other. This syncope is a temporary palsy, or
+apoplexy, which ceases after a time, the muscles recovering their power of
+being excited into action by the efforts of volition; as the eye in the
+circumstance above mentioned recovers in a little time its power of seeing
+objects in a gloomy room; which were invisible immediately after coming out
+of a stronger light. This is owing to an accumulation of sensorial power
+during the inaction of those fibres, which were before accustomed to
+perpetual exertions, as explained in Sect. XII. 7. 1. A slighter degree of
+this disease is experienced by every one after great fatigue, when the
+muscles gain such inability to further action, that we are obliged to rest
+them for a while, or to summon a greater power of volition to continue
+their motions.
+
+In all the syncopes, which I have seen induced after convulsive fits, the
+pulse has continued natural, though the organs of sense, as well as the
+locomotive muscles, have ceased to perform their functions; for it is
+necessary for the perception of objects, that the external organs of sense
+should be properly excited by the voluntary power, as the eye-lids must be
+open, and perhaps the muscles of the eye put into action to distend, and
+thence give greater pellucidity to the cornea, which in syncope, as in
+death, appears flat and less transparent.
+
+The tympanum of the ear also seems to require a voluntary exertion of its
+muscles, to gain its due tension, and it is probable the other external
+organs of sense require a similar voluntary exertion to adapt them to the
+distinct perception of objects. Hence in syncope as in sleep, as the power
+of volition is suspended, no external objects are perceived. See Sect.
+XVIII. 5. During the time which the patient lies in a fainting fit, the
+spirit of animation becomes accumulated; and hence the muscles in a while
+become irritable by their usual stimulation, and the fainting fit ceases.
+See Sect. XII. 7. 1.
+
+7. If the exertion of the voluntary motions has been still more energetic,
+the quiescence, which succeeds, is so complete, that they cannot again be
+excited into action by the efforts of the will. In this manner the palsy,
+and apoplexy (which is an universal palsy) are frequently produced after
+convulsions, or other violent exertions; of this I shall add a few
+instances.
+
+Platernus mentions some, who have died apoplectic from violent exertions in
+dancing; and Dr. Mead, in his Essay on Poisons, records a patient in the
+hydrophobia, who at one effort broke the cords which bound him, and at the
+same instant expired. And it is probable, that those, who have expired from
+immoderate laughter, have died from this paralysis consequent to violent
+exertion. Mrs. Scott of Stafford was walking in her garden in perfect
+health with her neighbour Mrs. ----; the latter accidentally fell into a
+muddy rivulet, and tried in vain to disengage herself by the assistance of
+Mrs. Scott's hand. Mrs. Scott exerted her utmost power for many minutes,
+first to assist her friend, and next to prevent herself from being pulled
+into the morass, as her distressed companion would not disengage her hand.
+After other assistance was procured by their united screams, Mrs. Scott
+walked to a chair about twenty yards from the brook, and was seized with an
+apoplectic stroke: which continued many days, and terminated in a total
+loss of her right arm, and her speech; neither of which she ever after
+perfectly recovered.
+
+It is said, that many people in Holland have died after skating too long or
+too violently on their frozen canals; it is probable the death of these,
+and of others, who have died suddenly in swimming, has been owing to this
+great quiescence or paralysis; which has succeeded very violent exertions,
+added to the concomitant cold, which has had greater effect after the
+sufferers had been heated and exhausted by previous exercise.
+
+I remember a young man of the name of Nairne at Cambridge, who walking on
+the edge of a barge fell into the river. His cousin and fellow-student of
+the same name, knowing the other could not swim, plunged into the water
+after him, caught him by his clothes, and approaching the bank by a
+vehement exertion propelled him safe to the land, but that instant, seized,
+as was supposed, by the cramp, or paralysis, sunk to rise no more. The
+reason why the cramp of the muscles, which compose the calf of the leg, is
+so liable to affect swimmers, is, because these muscles have very weak
+antagonists, and are in walking generally elongated again after their
+contraction by the weight of the body on the ball of the toe, which is very
+much greater than the resistance of the water in swimming. See Section
+XVIII. 15.
+
+It does not follow that every apoplectic or paralytic attack is immediately
+preceded by vehement exertion; the quiescence, which succeeds exertion, and
+which is not so great as to be termed paralysis, frequently recurs
+afterwards at certain periods; and by other causes of quiescence, occurring
+with those periods, as was explained in treating of the paroxysms of
+intermitting fevers; the quiescence at length, becomes so great as to be
+incapable of again being removed by the efforts of volition, and complete
+paralysis is formed. See Section XXXII. 3. 2.
+
+Many of the paralytic patients, whom I have seen, have evidently had
+diseased livers from the too frequent potation of spirituous liquors; some
+of them have had the gutta rosea on their faces and breasts; which has in
+some degree receded either spontaneously, or by the use of external
+remedies, and the paralytic stroke has succeeded; and as in several
+persons, who have drank much vinous spirits, I have observed epileptic fits
+to commence at about forty or fifty years of age, without any hereditary
+taint, from the stimulus, as I believed, of a diseased liver; I was induced
+to ascribe many paralytic cases to the same source; which were not
+evidently the effect of age, or of unacquired debility. And the account
+given before of dropsies, which very frequently are owing to a paralysis of
+the absorbent system, and are generally attendant on free drinkers of
+spirituous liquors, confirmed me in this opinion.
+
+The disagreeable irritation of a diseased liver produces exertions and
+consequent quiescence; these by the accidental concurrence of other causes
+of quiescence, as cold, solar or lunar periods, inanition, the want of
+their usual portion of spirit of wine, at length produces paralysis.
+
+This is further confirmed by observing, that the muscles, we most
+frequently, or most powerfully exert, are most liable to palsy; as those of
+the voice and of articulation, and of those paralytics which I have seen, a
+much greater proportion have lost the use of their right arm; which is so
+much more generally exerted than the left.
+
+I cannot dismiss this subject without observing, that after a paralytic
+stroke, if the vital powers are not much injured, that the patient has all
+the movements of the affected limb to learn over again, just as in early
+infancy; the limb is first moved by the irritation of its muscles, as in
+stretching, (of which a case was related in Section VII. 1. 3.) or by the
+electric concussion; afterwards it becomes obedient to sensation, as in
+violent danger or fear; and lastly, the muscles become again associated
+with volition, and gradually acquire their usual habits of acting together.
+
+Another phænomenon in palsies is, that when the limbs of one side are
+disabled, those of the other are in perpetual motion. This can only be
+explained from conceiving that the power of motion, whatever it is, or
+wherever it resides, and which is capable of being exhausted by fatigue,
+and accumulated in rest, is now less expended, whilst one half of the body
+is capable of receiving its usual proportion of it, and is hence derived
+with greater ease or in greater abundance into the limbs, which remain
+unaffected.
+
+II. 1. The excess or defect of voluntary exertion produces similar effects
+upon the sensual motions, or ideas of the mind, as those already mentioned
+upon the muscular fibres. Thus when any violent pain, arising from the
+defect of some peculiar stimulus, exists either in the muscular or sensual
+systems of fibres, and which cannot be removed by acquiring the defective
+stimulus; as in some constitutions convulsions of the muscles are produced
+to procure a temporary relief, so in other constitutions vehement voluntary
+exertions of the ideas of the mind are produced for the same purpose; for
+during this exertion, like that of the muscles, the pain either vanishes or
+is diminished: this violent exertion constitutes madness; and in many cases
+I have seen the madness take place, and the convulsions cease, and
+reciprocally the madness cease, and the convulsions supervene. See Section
+III. 5. 8.
+
+2. Madness is distinguishable from delirium, as in the latter the patient
+knows not the place where he resides, nor the persons of his friends or
+attendants, nor is conscious of any external objects, except when spoken to
+with a louder voice, or stimulated with unusual force, and even then he
+soon relapses into a state of inattention to every thing about him. Whilst
+in the former he is perfectly sensible to every thing external, but has the
+voluntary powers of his mind intensely exerted on some particular object of
+his desire or aversion, he harbours in his thoughts a suspicion of all
+mankind, lest they should counteract his designs; and while he keeps his
+intentions, and the motives of his actions profoundly secret; he is
+perpetually studying the means of acquiring the object of his wish, or of
+preventing or revenging the injuries he suspects.
+
+3. A late French philosopher, Mr. Helvetius, has deduced almost all our
+actions from this principle of their relieving us from the ennui or tædium
+vitæ; and true it is, that our desires or aversions are the motives of all
+our voluntary actions; and human nature seems to excel other animals in the
+more facil use of this voluntary power, and on that account is more liable
+to insanity than other animals. But in mania this violent exertion of
+volition is expended on mistaken objects, and would not be relieved, though
+we were to gain or escape the objects, that excite it. Thus I have seen two
+instances of madmen, who conceived that they had the itch, and several have
+believed they had the venereal infection, without in reality having a
+symptom of either of them. They have been perpetually thinking upon this
+subject, and some of them were in vain salivated with design of convincing
+them to the contrary.
+
+4. In the minds of mad people those volitions alone exist, which are
+unmixed with sensation; immoderate suspicion is generally the first
+symptom, and want of shame, and want of delicacy about cleanliness.
+Suspicion is a voluntary exertion of the mind arising from the pain of
+fear, which it is exerted to relieve: shame is the name of a peculiar
+disagreeable sensation, see Fable of the Bees, and delicacy about
+cleanliness arises from another disagreeable sensation. And therefore are
+not found in the minds of maniacs, which are employed solely in voluntary
+exertions. Hence the most modest women in this disease walk naked amongst
+men without any kind of concern, use obscene discourse, and have no
+delicacy about their natural evacuations.
+
+5. Nor are maniacal people more attentive to their natural appetites, or to
+the irritations which surround them, except as far as may respect their
+suspicions or designs; for the violent and perpetual exertions of their
+voluntary powers of mind prevents their perception of almost every other
+object, either of irritation or of sensation. Hence it is that they bear
+cold, hunger, and fatigue, with much greater pertinacity than in their
+sober hours, and are less injured by them in respect to their general
+health. Thus it is asserted by historians, that Charles the Twelfth of
+Sweden slept on the snow, wrapped only in his cloak, at the siege of
+Frederickstad, and bore extremes of cold and hunger, and fatigue, under
+which numbers of his soldiers perished; because the king was insane with
+ambition, but the soldier had no such powerful stimulus to preserve his
+system from debility and death.
+
+6. Besides the insanities arising from exertions in consequence of pain,
+there is also a pleasurable insanity, as well as a pleasurable delirium; as
+the insanity of personal vanity, and that of religious fanaticism. When
+agreeable ideas excite into motion the sensorial power of sensation, and
+this again causes other trains of agreeable ideas, a constant stream of
+pleasurable ideas succeeds, and produces pleasurable delirium. So when the
+sensorial power of volition excites agreeable ideas, and the pleasure thus
+produced excites more volition in its turn, a constant flow of agreeable
+voluntary ideas succeeds; which when thus exerted in the extreme
+constitutes insanity.
+
+Thus when our muscular actions are excited by our sensations of pleasure,
+it is termed play; when they are excited by our volition, it is termed
+work; and the former of these is attended with less fatigue, because the
+muscular actions in play produce in their turn more pleasurable sensation;
+which again has the property of producing more muscular action. An
+agreeable instance of this I saw this morning. A little boy, who was tired
+with walking, begged of his papa to carry him. "Here," says the reverend
+doctor, "ride upon my gold-headed cane;" and the pleased child, putting it
+between his legs, gallopped away with delight, and complained no more of
+his fatigue. Here the aid of another sensorial power, that of pleasurable
+sensation, superadded vigour to the exertion of exhausted volition. Which
+could otherwise only have been excited by additional pain, as by the lash
+of slavery. On this account where the whole sensorial power has been
+exerted on the contemplation of the promised joys of heaven, the saints of
+all persecuted religions have borne the tortures of martyrdom with
+otherwise unaccountable firmness.
+
+7. There are some diseases, which obtain at least a temporary relief from
+the exertions of insanity; many instances of dropsies being thus for a time
+cured are recorded. An elderly woman labouring with ascites I twice saw
+relieved for some weeks by insanity, the dropsy ceased for several weeks,
+and recurred again alternating with the insanity. A man afflicted with
+difficult respiration on lying down, with very irregular pulse, and
+oedematous legs, whom I saw this day, has for above a week been much
+relieved in respect to all those symptoms by the accession of insanity,
+which is shewn by inordinate suspicion, and great anger.
+
+In cases of common temporary anger the increased action of the arterial
+system is seen by the red skin, and increased pulse, with the immediate
+increase of muscular activity. A friend of mine, when he was painfully
+fatigued by riding on horseback, was accustomed to call up ideas into his
+mind, which used to excite his anger or indignation, and thus for a time at
+least relieved the pain of fatigue. By this temporary insanity, the effect
+of the voluntary power upon the whole of his system was increased; as in
+the cases of dropsy above mentioned, it would appear, that the increased
+action of the voluntary faculty of the sensorium affected the absorbent
+system, as well as the secerning one.
+
+8. In respect to relieving inflammatory pains, and removing fever, I have
+seen many instances, as mentioned in Sect. XII. 2. 4. One lady, whom I
+attended, had twice at some years interval a locked jaw, which relieved a
+pain on her sternum with peripneumony. Two other ladies I saw, who towards
+the end of violent peripneumony, in which they frequently lost blood, were
+at length cured by insanity supervening. In the former the increased
+voluntary exertion of the muscles of the jaw, in the latter that of the
+organs of sense, removed the disease; that is, the disagreeable sensation,
+which had produced the inflammation, now excited the voluntary power, and
+these new voluntary exertions employed or expended the superabundant
+sensorial power, which had previously been exerted on the arterial system,
+and caused inflammation.
+
+Another case, which I think worth relating, was of a young man about
+twenty; he had laboured under an irritative fever with debility for three
+or four weeks, with very quick and very feeble pulse, and other usual
+symptoms of that species of typhus, but at this time complained much and
+frequently of pain of his legs and feet. When those who attended him were
+nearly in despair of his recovery, I observed with pleasure an insanity of
+mind supervene: which was totally different from delirium, as he knew his
+friends, calling them by their names, and the room in which he lay, but
+became violently suspicious of his attendants, and calumniated with
+vehement oaths his tender mother, who sat weeping by his bed. On this his
+pulse became slower and firmer, but the quickness did not for some time
+intirely cease, and he gradually recovered. In this case the introduction
+of an increased quantity of the power of volition gave vigour to those
+movements of the system, which are generally only actuated by the power of
+irritation, and of association.
+
+Another case I recollect of a young man, about twenty-five, who had the
+scarlet-fever, with very quick pulse, and an universal eruption on his
+skin, and was not without reason esteemed to be in great danger of his
+life. After a few days an insanity supervened, which his friends mistook
+for delirium, and he gradually recovered, and the cuticle peeled off. From
+these and a few other cases I have always esteemed insanity to be a
+favourable sign in fevers, and have cautiously distinguished it from
+delirium.
+
+III. Another mode of mental exertion to relieve pain, is by producing a
+train of ideas not only by the efforts of volition, as in insanity; but by
+those of sensation likewise, as in delirium and sleep. This mental effort
+is termed reverie, or somnambulation, and is described more at large in
+Sect. XIX. on that subject. But I shall here relate another case of that
+wonderful disease, which fell yesterday under my eye, and to which I have
+seen many analogous alienations of mind, though not exactly similar in all
+circumstances. But as all of them either began or terminated with pain or
+convulsion, there can be no doubt but that they are of epileptic origin,
+and constitute another mode of mental exertion to relieve some painful
+sensation.
+
+1. Master A. about nine years old, had been seized at seven every morning
+for ten days with uncommon fits, and had had slight returns in the
+afternoon. They were supposed to originate from worms, and had been in vain
+attempted to be removed by vermifuge purges. As his fit was expected at
+seven yesterday morning, I saw him before that hour; he was asleep, seemed
+free from pain, and his pulse natural. About seven he began to complain of
+pain about his navel, or more to the left side, and in a few minutes had
+exertions of his arms and legs like swimming. He then for half an hour
+hunted a pack of hounds; as appeared by his hallooing, and calling the dogs
+by their names, and discoursing with the attendants of the chase,
+describing exactly a day of hunting, which (I was informed) he had
+witnessed a year before, going through all the most minute circumstances of
+it; calling to people, who were then present, and lamenting the absence of
+others, who were then also absent. After this scene he imitated, as he lay
+in bed, some of the plays of boys, as swimming and jumping. He then sung an
+English and then an Italian song; part of which with his eyes open, and
+part with them closed, but could not be awakened or excited by any
+violence, which it was proper to use.
+
+After about an hour he came suddenly to himself with apparent surprise, and
+seemed quite ignorant of any part of what had passed, and after being
+apparently well for half an hour, he suddenly fell into a great stupor,
+with slower pulse than natural, and a slow moaning respiration, in which he
+continued about another half hour, and then recovered.
+
+The sequel of this disease was favourable; he was directed one grain of
+opium at six every morning, and then to rise out of bed; at half past six
+he was directed fifteen drops of laudanum in a glass of wine and water. The
+first day the paroxysm became shorter, and less violent. The dose of opium
+was increased to one-half more, and in three or four days the fits left
+him. The bark and filings of iron were also exhibited twice a day; and I
+believe the complaint returned no more.
+
+2. In this paroxysm it must be observed, that he began with pain, and ended
+with stupor, in both circumstances resembling a fit of epilepsy. And that
+therefore the exertions both of mind and body, both the voluntary ones, and
+those immediately excited by pleasurable sensation, were exertions to
+relieve pain.
+
+The hunting scene appeared to be rather an act of memory than of
+imagination, and was therefore rather a voluntary exertion, though attended
+with the pleasurable eagerness, which was the consequence of those ideas
+recalled by recollection, and not the cause of them.
+
+These ideas thus voluntarily recollected were succeeded by sensations of
+pleasure, though his senses were unaffected by the stimuli of visible or
+audible objects; or so weakly excited by them as not to produce sensation
+or attention. And the pleasure thus excited by volition produced other
+ideas and other motions in consequence of the sensorial power of sensation.
+Whence the mixed catenations of voluntary and sensitive ideas and muscular
+motions in reverie; which, like every other kind of vehement exertion,
+contribute to relieve pain, by expending a large quantity of sensorial
+power.
+
+Those fits generally commence during sleep, from whence I suppose they have
+been thought to have some connection with sleep, and have thence been
+termed Somnambulism; but their commencement during sleep is owing to our
+increased excitability by internal sensations at that time, as explained in
+Sect. XVIII. 14. and 15., and not to any similitude between reverie and
+sleep.
+
+3. I was once concerned for a very elegant and ingenious young lady, who
+had a reverie on alternate days, which continued nearly the whole day; and
+as in her days of disease she took up the same kind of ideas, which she had
+conversed about on the alternate day before, and could recollect nothing of
+them on her well-day; she appeared to her friends to possess two minds.
+This case also was of epileptic kind, and was cured, with some relapses, by
+opium administered before the commencement of the paroxysm.
+
+4. Whence it appears, that the methods of relieving inflammatory pains, is
+by removing all stimulus, as by venesection, cool air, mucilaginous diet,
+aqueous potation, silence, darkness.
+
+The methods of relieving pains from defect of stimulus is by supplying the
+peculiar stimulus required, as of food, or warmth.
+
+And the general method of relieving pain is by exciting into action some
+great part of the system for the purpose of expending a part of the
+sensorial power. This is done either by exertion of the voluntary ideas and
+muscles, as in insanity and convulsion; or by exerting both voluntary and
+sensitive motions, as in reverie; or by exciting the irritative motions by
+wine or opium internally, and by the warm bath or blisters externally; or
+lastly, by exciting the sensitive ideas by good news, affecting stories, or
+agreeable passions.
+
+       *       *       *       *       *
+
+SECT. XXXV.
+
+DISEASES OF ASSOCIATION.
+
+    I. 1. _Sympathy or consent of parts. Primary and secondary parts of an
+    associated train of motions reciprocally affect each other. Parts of
+    irritative trains of motion affect each other in four ways. Sympathies
+    of the skin and stomach. Flushing of the face after a meal. Eruption of
+    the small-pox on the face. Chilness after a meal._ 2. _Vertigo from
+    intoxication._ 3. _Absorption from the lungs and pericardium by
+    emetics. In vomiting the actions of the stomach are decreased, not
+    increased. Digestion strengthened after an emetic. Vomiting from
+    deficiency of sensorial power._ 4. _Dyspnoea from cold bathing. Slow
+    pulse from digitalis. Death from gout in the stomach._ II. 1. _Primary
+    and secondary parts of sensitive associations affect each other. Pain
+    from gall-stone, from urinary stone, Hemicrania. Painful epilepsy._ 2.
+    _Gout and red face from inflamed liver. Shingles from inflamed kidney._
+    3. _Coryza from cold applied to the feet. Pleurisy. Hepatitis._ 4.
+    _Pain of shoulders from inflamed liver._ III. _Diseases from the
+    associations of ideas._
+
+I. 1. Many synchronous and successive motions of our muscular fibres, and
+of our organs of sense, or ideas, become associated so as to form
+indissoluble tribes or trains of action, as shewn in Section X. on
+Associate Motions. Some constitutions more easily establish these
+associations, whether by voluntary, sensitive, or irritative repetitions,
+and some more easily lose them again, as shewn in Section XXXI. on
+Temperaments.
+
+When the beginning of such a train of actions becomes by any means
+disordered, the succeeding part is liable to become disturbed in
+consequence, and this is commonly termed sympathy or consent of parts by
+the writers of medicine. For the more clear understanding of these
+sympathies we must consider a tribe or train of actions as divided into two
+parts, and call one of them the primary or original motions, and the other
+the secondary or sympathetic ones.
+
+The primary and secondary parts of a train of irritative actions may
+reciprocally affect each other in four different manners. 1. They may both
+be exerted with greater energy than natural. 2. The former may act with
+greater, and the latter with less energy. 3. The former may act with less,
+and the latter with greater energy. 4. They may both act with less energy
+than natural. I shall now give an example of each kind of these modes of
+action, and endeavour to shew, that though the primary and secondary parts
+of these trains or tribes of motion are connected by irritative
+association, or their previous habits of acting together, as described in
+Sect. XX. on Vertigo. Yet that their acting with similar or dissimilar
+degrees of energy, depends on the greater or less quantity of sensorial
+power, which the primary part of the train expends in its exertions.
+
+The actions of the stomach constitute so important a part of the
+associations of both irritative and sensitive motions, that it is said to
+sympathize with almost every part of the body; the first example, which I
+shall adduce to shew that both the primary and secondary parts of a train
+of irritative associations of motion act with increased energy, is taken
+from the consent of the skin with this organ. When the action of the fibres
+of the stomach is increased, as by the stimulus of a full meal, the
+exertions of the cutaneous arteries of the face become increased by their
+irritative associations with those of the stomach, and a glow or flushing
+of the face succeeds. For the small vessels of the skin of the face having
+been more accustomed to the varieties of action, from their frequent
+exposure to various degrees of cold and heat become more easily excited
+into increased action, than those of the covered parts of our bodies, and
+thus act with more energy from their irritative or sensitive associations
+with the stomach. On this account in small-pox the eruption in consequence
+of the previous affection of the stomach breaks out a day sooner on the
+face than on the hands, and two days sooner than on the trunk, and recedes
+in similar times after maturation.
+
+But secondly, in weaker constitutions, that is, in those who possess less
+sensorial power, so much of it is expended in the increased actions of the
+fibres of the stomach excited by the stimulus of a meal, that a sense of
+chilness succeeds instead of the universal glow above mentioned; and thus
+the secondary part of the associated train of motions is diminished in
+energy, in consequence of the increased activity of the primary part of it.
+
+2. Another instance of a similar kind, where the secondary part of the
+train acts with less energy in consequence of the greater exertions of the
+primary part, is the vertigo attending intoxication; in this circumstance
+so much sensorial power is expended on the stomach, and on its nearest or
+more strongly associated motions, as those of the subcutaneous vessels, and
+probably of the membranes of some internal viscera, that the irritative
+motions of the retina become imperfectly exerted from deficiency of
+sensorial power, as explained in Sect. XX. and XXI. 3. on Vertigo and on
+Drunkenness, and hence the staggering inebriate cannot completely balance
+himself by such indistinct vision.
+
+3. An instance of the third circumstance, where the primary part of a train
+of irritative motions acts with less, and the secondary part with greater
+energy, may be observed by making the following experiment. If a person
+lies with his arms and shoulders out of bed, till they become cold, a
+temporary coryza or catarrh is produced; so that the passage of the
+nostrils becomes totally obstructed; at least this happens to many people;
+and then on covering the arms and shoulders, till they become warm, the
+passage of the nostrils ceases again to be obstructed, and a quantity of
+mucus is discharged from them. In this case the quiescence of the vessels
+of the skin of the arms and shoulders, occasioned by exposure to cold air,
+produces by irritative association an increased action of the vessels of
+the membrane of the nostrils; and the accumulation of sensorial power
+during the torpor of the arms and shoulders is thus expended in producing a
+temporary coryza or catarrh.
+
+Another instance may be adduced from the sympathy or consent of the motions
+of the stomach with other more distant links of the very extensive tribes
+or trains of irritative motions associated with them, described in Sect.
+XX. on Vertigo. When the actions of the fibres of the stomach are
+diminished or inverted, the actions of the absorbent vessels, which take up
+the mucus from the lungs, pericardium, and other cells of the body, become
+increased, and absorb the fluids accumulated in them with greater avidity,
+as appears from the exhibition of foxglove, antimony, or other emetics in
+cases of anasarca, attended with unequal pulse and difficult respiration.
+
+That the act of nausea and vomiting is a decreased exertion of the fibres
+of the stomach may be thus deduced; when an emetic medicine is
+administered, it produces the pain of sickness, as a disagreeable taste in
+the mouth produces the pain of nausea; these pains, like that of hunger, or
+of cold, or like those, which are usually termed nervous, as the head-ach
+or hemicrania, do not excite the organ into greater action; but in this
+case I imagine the pains of sickness or of nausea counteract or destroy the
+pleasurable sensation, which seems necessary to digestion, as shewn in
+Sect. XXXIII. 1. 1. The peristaltic motions of the fibres of the stomach
+become enfeebled by the want of this stimulus of pleasurable sensation, and
+in consequence stop for a time, and then become inverted; for they cannot
+become inverted without being previously stopped. Now that this inversion
+of the trains of motion of the fibres of the stomach is owing to the
+deficiency of pleasurable sensation is evinced from this circumstance, that
+a nauseous idea excited by words will produce vomiting as effectually us a
+nauseous drug.
+
+Hence it appears, that the act of nausea or vomiting expends less sensorial
+power than the usual peristaltic motions of the stomach in the digestion of
+our aliment; and that hence there is a greater quantity of sensorial power
+becomes accumulated in the fibres of the stomach, and more of it in
+consequence to spare for the action of those parts of the system, which are
+thus associated with the stomach, as of the whole absorbent series of
+vessels, and which are at the same time excited by their usual stimuli.
+
+From this we can understand, how after the operation of an emetic the
+stomach becomes more irritable and sensible to the stimulus, and the
+pleasure of food; since as the sensorial power becomes accumulated during
+the nausea and vomiting, the digestive power is afterwards exerted more
+forceably for a time. It should, however, be here remarked, that though
+vomiting is in general produced by the defect of this stimulus of
+pleasurable sensation, as when a nauseous drug is administered; yet in long
+continued vomiting, as in sea-sickness, or from habitual dram-drinking, it
+arises from deficiency of sensorial power, which in the former case is
+exhausted by the increased exertion of the irritative ideas of vision, and
+in the latter by the frequent application of an unnatural stimulus.
+
+4. An example of the fourth circumstance above mentioned, where both the
+primary and secondary parts of a train of motions proceed with energy less
+than natural, may be observed in the dyspnoea, which occurs in going into a
+very cold bath, and which has been described and explained in Sect. XXXII.
+3. 2.
+
+And by the increased debility of the pulsations of the heart and arteries
+during the operation of an emetic. Secondly, from the slowness and
+intermission of the pulsations of the heart from the incessant efforts to
+vomit occasioned by an overdose of digitalis. And thirdly, from the total
+stoppage of the motions of the heart, or death, in consequence of the
+torpor of the stomach, when affected with the commencement or cold paroxysm
+of the gout. See Sect. XXV. 17.
+
+II. 1. The primary and secondary parts of the trains of sensitive
+association reciprocally affect each other in different manners. 1. The
+increased sensation of the primary part may cease, when that of the
+secondary part commences. 2. The increased action of the primary part may
+cease, when that of the secondary part commences. 3. The primary part may
+have increased sensation, and the secondary part increased action. 4. The
+primary part may have increased action, and the secondary part increased
+sensation.
+
+Examples of the first mode, where the increased sensation of the primary
+part of a train of sensitive association ceases, when that of the secondary
+part commences, are not unfrequent; as this is the general origin of those
+pains, which continue some time without being attended with inflammation,
+such as the pain at the pit of the stomach from a stone at the neck of the
+gall-bladder, and the pain of strangury in the glans penis from a stone at
+the neck of the urinary bladder. In both these cases the part, which is
+affected secondarily, is believed to be much more sensible than the part
+primarily affected, as described in the catalogue of diseases, Class II. 1.
+1. 11. and IV. 2. 2. 2. and IV. 2. 2. 4.
+
+The hemicrania, or nervous headach, as it is called, when it originates
+from a decaying tooth, is another disease of this kind; as the pain of the
+carious tooth always ceases, when the pain over one eye and temple
+commences. And it is probable, that the violent pains, which induce
+convulsions in painful epilepsies, are produced in the same manner, from a
+more sensible part sympathizing with a diseased one of less sensibility.
+See Catalogue of Diseases, Class IV. 2. 2. 8. and III. 1. 1. 6.
+
+The last tooth, or dens sapientiæ, of the upper jaw most frequently decays
+first, and is liable to produce pain over the eye and temple of that side.
+The last tooth of the under-jaw is also liable to produce a similar
+hemicrania, when it begins to decay. When a tooth in the upper-jaw is the
+cause of the headach, a slighter pain is sometimes perceived on the
+cheek-bone. And when a tooth in the lower-jaw is the cause of headach, a
+pain sometimes affects the tendons of the muscles of the neck, which are
+attached near the jaws. But the clavus hystericus, or pain about the middle
+of the parietal bone on one side of the head, I have seen produced by the
+second of the molares, or grinders, of the under-jaw; of which I shall
+relate the following case. See Class IV. 2. 2. 8.
+
+Mrs. ----, about 30 years of age, was seized with great pain about the
+middle of the right parietal bone, which had continued a whole day before I
+saw her, and was so violent as to threaten to occasion convulsions. Not
+being able to detect a decaying tooth, or a tender one, by examination with
+my eye, or by striking them with a tea-spoon, and fearing bad consequences
+from her tendency to convulsion, I advised her to extract the last tooth of
+the under-jaw on the affected side; which was done without any good effect.
+She was then directed to lose blood, and to take a brisk cathartic; and
+after that had operated, about 60 drops of laudanum were given her, with
+large doses of bark; by which the pain was removed. In about a fortnight
+she took a cathartic medicine by ill advice, and the pain returned with
+greater violence in the same place; and, before I could arrive, as she
+lived 30 miles from me, she suffered a paralytic stroke; which affected her
+limbs and her face on one side, and relieved the pain of her head.
+
+About a year afterwards I was again called to her on account of a pain as
+violent as before exactly on the same part of the other parietal bone. On
+examining her mouth I found the second molaris of the under-jaw on the side
+before affected was now decayed, and concluded, that this tooth had
+occasioned the stroke of the palsy by the pain and consequent exertion it
+had caused. On this account I earnestly entreated her to allow the sound
+molaris of the same jaw opposite to the decayed one to be extracted; which
+was forthwith done, and the pain of her head immediately ceased, to the
+astonishment of her attendants.
+
+In the cases above related of the pain existing in a part distant from the
+seat of the disease, the pain is owing to defect of the usual motions of
+the painful part. This appears from the coldness, paleness, and emptiness
+of the affected vessels, or of the extremities of the body in general, and
+from there being no tendency to inflammation. The increased action of the
+primary part of these associated motions, as of the hepatic termination of
+the bile-duct; from the stimulus of a gall-stone, or of the interior
+termination of the urethra from the stimulus of a stone in the bladder, or
+lastly, of a decaying tooth in hemicrania, deprives the secondary part of
+these associated motions, namely, the exterior terminations of the
+bile-duct or urethra, or the pained membranes of the head in hemicrania, of
+their natural share of sensorial power: and hence the secondary parts of
+these sensitive trains of association become pained from the deficiency of
+their usual motions, which is accompanied with deficiency of secretions and
+of heat. See Sect. IV. 5. XII. 5. 3. XXXIV. 1.
+
+Why does the pain of the primary part of the association cease, when that
+of the secondary part commences? This is a question of intricacy, but
+perhaps not inexplicable. The pain of the primary part of these associated
+trains of motion was owing to too great stimulus, as of the stone at the
+neck of the bladder, and was consequently caused by too great action of the
+pained part. This greater action than natural of the primary part of these
+associated motions, by employing or expending the sensorial power of
+irritation belonging to the whole associated train of motions, occasioned
+torpor, and consequent pain in the secondary part of the associated train;
+which was possessed of greater sensibility than the primary part of it. Now
+the great pain of the secondary part of the train, as soon as it commences,
+employs or expends the sensorial power of sensation belonging to the whole
+associated train of motions; and in consequence the motions of the primary
+part, though increased by the stimulus of an extraneous body, cease to be
+accompanied with pain or sensation.
+
+If this mode of reasoning be just it explains a curious fact, why when two
+parts of the body are strongly stimulated, the pain is felt only in one of
+them, though it is possible by voluntary attention it may be alternately
+perceived in them both. In the same manner, when two new ideas are
+presented to us from the stimulus of external bodies, we attend to but one
+of them at a time. In other words, when one set of fibres, whether of the
+muscles or organs of sense, contract so strongly as to excite much
+sensation; another set of fibres contracting more weakly do not excite
+sensation at all, because the sensorial power of sensation is pre-occupied
+by the first set of fibres. So we cannot will more than one effect at once,
+though by associations previously formed we can move many fibres in
+combination.
+
+Thus in the instances above related, the termination of the bile duct in
+the duodenum, and the exterior extremity of the urethra, are more sensible
+than their other terminations. When these parts are deprived of their usual
+motions by deficiency of sensorial power, as above explained, they become
+painful according to law the fifth in Section IV. and the less pain
+originally excited by the stimulus of concreted bile, or of a stone at
+their other extremities ceases to be perceived. Afterwards, however, when
+the concretions of bile, or the stone on the urinary bladder, become more
+numerous or larger, the pain from their increased stimulus becomes greater
+than the associated pain; and is then felt at the neck of the gall bladder
+or urinary bladder; and the pain of the glans penis, or at the pit of the
+stomach, ceases to be perceived.
+
+2. Examples of the second mode, where the increased action of the primary
+part of a train of sensitive association ceases, when that of the secondary
+part commences, are also not unfrequent; as this is the usual manner of the
+translation of inflammations from internal to external parts of the system,
+such as when an inflammation of the liver or stomach is translated to the
+membranes of the foot, and forms the gout; or to the skin of the face, and
+forms the rosy drop; or when an inflammation of the membranes of the
+kidneys is translated to the skin of the loins, and forms one kind of
+herpes, called shingles; in these cases by whatever cause the original
+inflammation may have been produced, as the secondary part of the train of
+sensitive association is more sensible, it becomes exerted with greater
+violence than the first part of it; and by both its increased pain, and the
+increased motion of its fibres, so far diminishes or exhausts the sensorial
+power of sensation; that the primary part of the train being less sensible
+ceases both to feel pain, and to act with unnatural energy.
+
+3. Examples of the third mode, where the primary part of a train of
+sensitive association of motions may experience increased sensation, and
+the secondary part increased action, are likewise not unfrequent; as it is
+in this manner that most inflammations commence. Thus, after standing some
+time in snow, the feet become affected with the pain of cold, and a common
+coryza, or inflammation of the membrane of the nostrils, succeeds. It is
+probable that the internal inflammations, as pleurisies, or hepatitis,
+which are produced after the cold paroxysm of fever, originate in the same
+manner from the sympathy of those parts with some others, which were
+previously pained from quiescence; as happens to various parts of the
+system during the cold fits of fevers. In these cases it would seem, that
+the sensorial power of sensation becomes accumulated during the pain of
+cold, as the torpor of the vessels occasioned by the defect of heat
+contributes to the increase or accumulation of the sensorial power of
+irritation, and that both these become exerted on some internal part, which
+was not rendered torpid by the cold which affected the external parts, nor
+by its association with them; or which sooner recovered its sensibility.
+This requires further consideration.
+
+4. An example of the fourth mode, or where the primary part of a sensitive
+association of motions may have increased action, and the secondary part
+increased sensation, may be taken from the pain of the shoulder, which
+attends inflammation of the membranes of the liver, see Class IV. 2. 2. 9.;
+in this circumstance so much sensorial power seems to be expended in the
+violent actions and sensations of the inflamed membranes of the liver, that
+the membranes associated with them become quiescent to their usual stimuli,
+and painful in consequence.
+
+There may be other modes in which the primary and secondary parts of the
+trains of associated sensitive motions may reciprocally affect each other,
+as may be seen by looking over Class IV. in the catalogue of diseases; all
+which may probably be resolved into the plus and minus of sensorial power,
+but we have not yet had sufficient observations made upon them with a view
+to this doctrine.
+
+III. The associated trains of our ideas may have sympathies, and their
+primary and secondary parts affect each other in some manner similar to
+those above described; and may thus occasion various curious phenomena not
+yet adverted to, besides those explained in the Sections on Dreams,
+Reveries, Vertigo, and Drunkenness; and may thus disturb the deductions of
+our reasonings, as well as the streams of our imaginations; present us with
+false degrees of fear, attach unfounded value to trivial circumstances;
+give occasion to our early prejudices and antipathies; and thus embarrass
+the happiness of our lives. A copious and curious harvest might be reaped
+from this province of science, in which, however, I shall not at present
+wield my sickle.
+
+       *       *       *       *       *
+
+SECT. XXXVI.
+
+OF THE PERIODS OF DISEASES.
+
+    I. _Muscles excited by volition soon cease to contract, or by
+    sensation, or by irritation, owing to the exhaustion of sensorial
+    power. Muscles subjected to less stimulus have their sensorial power
+    accumulated. Hence the periods of some fevers. Want of irritability
+    after intoxication._ II. 1. _Natural actions catenated with daily
+    habits of life._ 2. _With solar periods. Periods of sleep. Of
+    evacuating the bowels._ 3. _Natural actions catenated with lunar
+    periods. Menstruation. Venereal orgasm of animals. Barrenness._ III.
+    _Periods of diseased animal actions from stated returns of nocturnal
+    cold, from solar and lunar influence. Periods of diurnal fever, hectic
+    fever, quotidian, tertian, quartan fever. Periods of gout, pleurisy, of
+    fevers with arterial debility, and with arterial strength, Periods of
+    rhaphania, of nervous cough, hemicrania, arterial hæmorrhages,
+    hæmorrhoids, hæmoptoe, epilepsy, palsy, apoplexy, madness._ IV.
+    _Critical days depend on lunar periods. Lunar periods in the small
+    pox._
+
+I. If any of our muscles be made to contract violently by the power of
+volition, as those of the fingers, when any one hangs by his hands on a
+swing, fatigue soon ensues; and the muscles cease to act owing to the
+temporary exhaustion of the spirit of animation; as soon as this is again
+accumulated in the muscles, they are ready to contract again by the efforts
+of volition.
+
+Those violent muscular actions induced by pain become in the same manner
+intermitted and recurrent; as in labour-pains, vomiting, tenesmus,
+strangury; owing likewise to the temporary exhaustion of the spirit of
+animation, as above mentioned.
+
+When any stimulus continues long to act with unnatural violence, so as to
+produce too energetic action of any of our moving organs, those motions
+soon cease, though the stimulus continues to act; as in looking long on a
+bright object, as on an inch-square of red silk laid on white paper in the
+sunshine. See Plate I. in Sect. III. 1.
+
+On the contrary, where less of the stimulus of volition, sensation, or
+irritation, have been applied to a muscle than usual; there appears to be
+an accumulation of the spirit of animation in the moving organ; by which it
+is liable to act with greater energy from less quantity of stimulus, than
+was previously necessary to excite it into so great action; as after having
+been immersed in snow the cutaneous vessels of our hands are excited into
+stronger action by the stimulus of a less degree of heat, than would
+previously have produced that effect.
+
+From hence the periods of some fever-fits may take their origin, either
+simply, or by their accidental coincidence with lunar and solar periods, or
+with the diurnal periods of heat and cold, to be treated of below; for
+during the cold fit at the commencement of a fever, from whatever cause
+that cold fit may have been induced, it follows, 1. That the spirit of
+animation must become accumulated in the parts, which exert during this
+cold fit less than their natural quantity of action. 2. If the cause
+producing the cold fit does not increase, or becomes diminished; the parts
+before benumbed or inactive become now excitable by smaller stimulus, and
+are thence thrown into more violent action than is natural; that is a hot
+fit succeeds the cold one. 3. By the energetic action of the system during
+the hot fit, if it continues long, an exhaustion of the spirit of animation
+takes place; and another cold fit is liable to succeed, from the moving
+system not being excitable into action from its usual stimulus. This
+inirritability of the system from a too great previous stimulus, and
+consequent exhaustion of sensorial power, is the cause of the general
+debility, and sickness, and head-ach, some hours after intoxication. And
+hence we see one of the causes of the periods of fever-fits; which however
+are frequently combined with the periods of our diurnal habits, or of heat
+and cold, or of solar or lunar periods.
+
+When besides the tendency to quiescence occasioned by the expenditure of
+sensorial power during the hot fit of fever, some other cause of torpor, as
+the solar or lunar periods, is necessary to the introduction of a second
+cold fit; the fever becomes of the intermittent kind; that is, there is a
+space of time intervenes between the end of the hot fit, and the
+commencement of the next cold one. But where no exteriour cause is
+necessary to the introduction of the second cold fit; no such interval of
+health intervenes; but the second cold fit commences, as soon as the
+sensorial power is sufficiently exhausted by the hot fit; and the fever
+becomes continual.
+
+II. 1. The following are natural animal actions, which are frequently
+catenated with our daily habits of life, as well as excited by their
+natural irritations. The periods of hunger and thirst become catenated with
+certain portions of time, or degrees of exhaustion, or other diurnal habits
+of life. And if the pain of hunger be not relieved by taking food at the
+usual time, it is liable to cease till the next period of time or other
+habits recur; this is not only true in respect to our general desire of
+food, but the kinds of it also are governed by this periodical habit;
+insomuch that beer taken to breakfast will disturb the digestion of those,
+who have been accustomed to tea; and tea taken at dinner will disagree with
+those, who have been accustomed to beer. Whence it happens, that those, who
+have weak stomachs, will be able to digest more food, if they take their
+meals at regular hours; because they have both the stimulus of the aliment
+they take, and the periodical habit, to assist their digestion.
+
+The periods of emptying the bladder are not only dependent on the acrimony
+or distention of the water in it, but are frequently catenated with
+external cold applied to the skin, as in cold bathing, or washing the
+hands; or with other habits of life, as many are accustomed to empty the
+bladder before going to bed, or into the house after a journey, and this
+whether it be full or not.
+
+Our times of respiration are not only governed by the stimulus of the blood
+in the lungs, or our desire of fresh air, but also by our attention to the
+hourly objects before us. Hence when a person is earnestly contemplating an
+idea of grief, he forgets to breathe, till the sensation in his lungs
+becomes very urgent; and then a sigh succeeds for the purpose of more
+forceably pushing forwards the blood, which is accumulated in the lungs.
+
+Our times of respiration are also frequently governed in part by our want
+of a steady support for the actions of our arms, and hands, as in threading
+a needle, or hewing wood, or in swimming; when we are intent upon these
+objects, we breathe at the intervals of the exertion of the pectoral
+muscles.
+
+2. The following natural animal actions are influenced by solar periods.
+The periods of sleep and of waking depend much on the solar period, for we
+are inclined to sleep at a certain hour, and to awake at a certain hour,
+whether we have had more or less fatigue during the day, if within certain
+limits; and are liable to wake at a certain hour, whether we went to bed
+earlier or later, within certain limits. Hence it appears, that those who
+complain of want of sleep, will be liable to sleep better or longer, if
+they accustom themselves to go to rest, and to rise, at certain hours.
+
+The periods of evacuating the bowels are generally connected with some part
+of the solar day, as well as with the acrimony or distention occasioned by
+the feces. Hence one method of correcting costiveness is by endeavouring to
+establish a habit of evacuation at a certain hour of the day, as
+recommended by Mr. Locke, which may be accomplished by using daily
+voluntary efforts at those times, joined with the usual stimulus of the
+material to be evacuated.
+
+3. The following natural animal actions are connected with lunar periods.
+1. The periods of female menstruation are connected with lunar periods to
+great exactness, in some instances even to a few hours. These do not
+commence or terminate at the full or change, or at any other particular
+part of the lunation, but after they have commenced at any part of it, they
+continue to recur at that part with great regularity, unless disturbed by
+some violent circumstance, as explained in Sect. XXXII. No. 6. their return
+is immediately caused by deficient venous absorption, which is owing to the
+want of the stimulus, designed by nature, of amatorial copulation, or of
+the growing fetus. When the catamenia returns sooner than the period of
+lunation, it shows a tendency of the constitution to inirritability; that
+is to debility, or deficiency of sensorial power, and is to be relieved by
+small doses of steel and opium.
+
+The venereal orgasm of birds and quadrupeds seems to commence, or return
+about the most powerful lunations at the vernal or autumnal equinoxes; but
+if it be disappointed of its object, it is said to recur at monthly
+periods; in this respect resembling the female catamenia. Whence it is
+believed, that women are more liable to become pregnant at or about the
+time of their catamenia, than at the intermediate times; and on this
+account they are seldom much mistaken in their reckoning of nine lunar
+periods from the last menstruation; the inattention to this may sometimes
+have been the cause of supposed barrenness, and is therefore worth the
+observation of those, who wish to have children.
+
+III. We now come to the periods of diseased animal actions. The periods of
+fever-fits, which depend on the stated returns of nocturnal cold, are
+discussed in Sect. XXXII. 3. Those, which originate or recur at solar or
+lunar periods, are also explained in Section XXXII. 6. These we shall here
+enumerate; observing, however, that it is not more surprising, that the
+influence of the varying attractions of the sun and moon, should raise the
+ocean into mountains, than that it should affect the nice sensibilities of
+animal bodies; though the manner of its operation on them is difficult to
+be understood. It is probable however, that as this influence gradually
+lessens during the course of the day, or of the lunation, or of the year,
+some actions of our system become less and less; till at length a total
+quiescence of some part is induced; which is the commencement of the
+paroxysms of fever, of menstruation, of pain with decreased action of the
+affected organ, and of consequent convulsion.
+
+1. A diurnal fever in some weak people is distinctly observed to come on
+towards evening, and to cease with a moist skin early in the morning,
+obeying the solar periods. Persons of weak constitutions are liable to get
+into better spirits at the access of the hot fit of this evening fever; and
+are thence inclined to sit up late; which by further enfeebling them
+increases the disease; whence they lose their strength and their colour.
+
+2. The periods of hectic fever, supposed to arise from absorption of
+matter, obeys the diurnal periods like the above, having the exacerbescence
+towards evening, and its remission early in the morning, with sweats, or
+diarrhoea, or urine with white sediment.
+
+3. The periods of quotidian fever are either catenated with solar time, and
+return at the intervals of twenty-four hours; or with lunar time, recurring
+at the intervals of about twenty-five hours. There is great use in knowing
+with what circumstances the periodical return or new morbid motions are
+conjoined, as the most effectual times of exhibiting the proper medicines
+are thus determined. So if the torpor, which ushers in an ague fit, is
+catenated with the lunar day: it is known, when the bark or opium must be
+given, so as to exert its principal effect about the time of the expected
+return. Solid opium should be given about an hour before the expected cold
+fit; liquid opium and wine about half an hour; the bark repeatedly for six
+or eight hours previous to the expected return.
+
+4. The periods of tertian fevers, reckoned from the commencement of one
+cold fit to the commencement of the next cold fit, recur with solar
+intervals of forty-eight hours, or with lunar ones of about fifty hours.
+When these of recurrence begin one or two hours earlier than the solar
+period, it shews, that the torpor or cold fit is produced by less external
+influence; and therefore that it is more liable to degenerate into a fever
+with only remissions; so when menstruation recurs sooner than the period of
+lunation, it shews a tendency of the habit to torpor of inirritability.
+
+5. The periods of quartan fevers return at solar intervals of seventy-two
+hours, or at lunar ones of about seventy-four hours and an half. This kind
+of ague appears most in moist cold autumns, and in cold countries replete
+with marshes. It is attended with greater debility, and its cold access
+more difficult to prevent. For where there is previously a deficiency of
+sensorial power, the constitution is liable to run into greater torpor from
+any further diminution of it; two ounces of bark and some steel should be
+given on the day before the return of the cold paroxysm, and a pint of wine
+by degrees a few hours before its return, and thirty drops of laudanum one
+hour before the expected cold fit.
+
+6. The periods of the gout generally commence about an hour before
+sun-rise, which is usually the coldest part of the twenty-four hours. The
+greater periods of the gout seem also to observe the solar influence,
+returning about the same season of the year.
+
+7. The periods of the pleurisy recur with exacerbation of the pain and
+fever about sun-set, at which time venesection is of most service. The same
+may be observed of the inflammatory rheumatism, and other fevers with
+arterial strength, which seem to obey solar periods; and those with
+debility seem to obey lunar ones.
+
+8. The periods of fevers with arterial debility seem to obey the lunar day,
+having their access daily nearly an hour later; and have sometimes two
+accesses in a day, resembling the lunar effects upon the tides.
+
+9. The periods of rhaphania, or convulsions of the limbs from rheumatic
+pains, seem to be connected with solar influence, returning at nearly the
+same hour for weeks together, unless disturbed by the exhibition of
+powerful doses of opium.
+
+So the periods of Tussis ferina, or violent cough with slow pulse, called
+nervous cough, recurs by solar periods. Five grains of opium, given at the
+time the cough commenced disturbed the period, from seven in the evening to
+eleven, at which time it regularly returned for some days, during which
+time the opium was gradually omitted. Then 120 drops of laudanum were given
+an hour before the access of the cough, and it totally ceased. The laudanum
+was continued a fortnight, and then gradually discontinued.
+
+10. The periods of hemicrania, and of painful epilepsy, are liable to obey
+lunar periods, both in their diurnal returns, and in their greater periods
+of weeks, but are also induced by other exciting causes.
+
+11. The periods of arterial hæmorrhages seem to return at solar periods
+about the same hour of the evening or morning. Perhaps the venous
+hæmorrhages obey the lunar periods, as the catamenia, and hæmorrhoids.
+
+12. The periods of the hæmorrhoids, or piles, in some recur monthly, in
+others only at the greater lunar influence about the equinoxes.
+
+13. The periods of hæmoptoe sometimes obey solar influence, recurring early
+in the morning for several days; and sometimes lunar periods, recurring
+monthly; and sometimes depend on our hours of sleep. See Class I. 2. 1. 9.
+
+14. Many of the first periods of epileptic fits obey the monthly lunation
+with some degree of accuracy; others recur only at the most powerful
+lunations before the vernal equinox, and after the autumnal one; but when
+the constitution has gained a habit of relieving disagreeable sensations by
+this kind of exertion, the fit recurs from any slight cause.
+
+15. The attack of palsy and apoplexy are known to recur with great
+frequency about the equinoxes.
+
+16. There are numerous instances of the effect of the lunations upon the
+periods of insanity, whence the name of lunatic has been given to those
+afflicted with this disease.
+
+IV. The critical days, in which fevers are supposed to terminate, have
+employed the attention of medical philosophers from the days of Hippocrates
+to the present time. In whatever part of a lunation a fever commences,
+which owes either its whole cause to solar and lunar influence, or to this
+in conjunction with other causes; it would seem, that the effect would be
+the greatest at the full and new moon, as the tides rise highest at those
+times, and would be the least at the quadratures; thus if a fever-fit
+should commence at the new or full moon, occasioned by the solar and lunar
+attraction diminishing some chemical affinity of the particles of blood,
+and thence decreasing their stimulus on our sanguiferous system, as
+mentioned in Sect. XXXII. 6. this effect will daily decrease for the first
+seven days, and will then increase till about the fourteenth day, and will
+again decrease till about the twenty-first day, and increase again till the
+end of the lunation. If a fever-fit from the above cause should commence on
+the seventh day after either lunation, the reverse of the above
+circumstances would happen. Now it is probable, that those fevers, whose
+crisis or terminations are influenced by lunations, may begin at one or
+other of the above times, namely at the changes or quadratures; though
+sufficient observations have not been made to ascertain this circumstance.
+Hence I conclude, that the small-pox and measles have their critical days,
+not governed by the times required for certain chemical changes in the
+blood, which affect or alter the stimulus of the contagious matter, but
+from the daily increasing or decreasing effect of this lunar link of
+catenation, as explained in Section XVII. 3. 3. And as other fevers
+terminate most frequently about the seventh, fourteenth, twenty-first, or
+about the end of four weeks, when no medical assistance has disturbed their
+periods, I conclude, that these crises, or terminations, are governed by
+periods of the lunations; though we are still ignorant of their manner of
+operation.
+
+In the distinct small-pox the vestiges of lunation are very apparent, after
+inoculation a quarter of a lunation precedes the commencement of the fever,
+another quarter terminates with the complete eruption, another quarter with
+the complete maturation, and another quarter terminates the complete
+absorption of a material now rendered inoffensive to the constitution.
+
+       *       *       *       *       *
+
+SECT. XXXVII.
+
+OF DIGESTION, SECRETION, NUTRITION.
+
+    I. _Crystals increase by the greater attraction of their sides.
+    Accretion by chemical precipitations, by welding, by pressure, by
+    agglutination._ II. _Hunger, digestion, why it cannot be imitated out
+    of the body. Lacteals absorb by animal selection or appetency._ III.
+    _The glands and pores absorb nutritious particles by animal selection.
+    Organic particles of Buffon. Nutrition applied at the time of
+    elongation of fibres. Like inflammation._ IV. _It seems easier to have
+    preserved animals than to reproduce them. Old age and death from
+    inirritability. Three causes of this. Original fibres of the organs of
+    sense and muscles unchanged._ V. _Art of producing long life._
+
+I. The larger crystals of saline bodies may be conceived to arise from the
+combination of smaller crystals of the same form, owing to the greater
+attractions of their sides than of their angles. Thus if four cubes were
+floating in a fluid, whose friction or resistance is nothing, it is certain
+the sides of these cubes would attract each other stronger than their
+angles; and hence that these four smaller cubes would so arrange themselves
+as to produce one larger one.
+
+There are other means of chemical accretion, such as the depositions of
+dissolved calcareous or siliceous particles, as are seen in the formation
+of the stalactites of limestone in Derbyshire, or of calcedone in Cornwall.
+Other means of adhesion are produced by heat and pressure, as in the
+welding of iron-bars; and other means by simple pressure, as in forcing two
+pieces of caoutchou, or elastic gum, to adhere; and lastly, by the
+agglutination of a third substance penetrating the pores of the other two,
+as in the agglutination of wood by means of animal gluten. Though the
+ultimate particles of animal bodies are held together during life, as well
+as after death, by their specific attraction of cohesion, like all other
+matter; yet it does not appear, that their original organization was
+produced by chemical laws, and their production and increase must therefore
+only be looked for from the laws of animation.
+
+II. When the pain of hunger requires relief, certain parts of the material
+world, which surround us, when applied to our palates, excite into action
+the muscles of deglutition; and the material is swallowed into the stomach.
+Here the new aliment becomes mixed with certain animal fluids, and
+undergoes a chemical process, termed digestion; which however chemistry has
+not yet learnt to imitate out of the bodies of living animals or
+vegetables. This process seems very similar to the saccharine process in
+the lobes of farinaceous seeds, as of barley, when it begins to germinate;
+except that, along with the sugar, oil and mucilage are also produced;
+which form the chyle of animals, which is very similar to their milk.
+
+The reason, I imagine, why this chyle-making, or saccharine process, has
+not yet been imitated by chemical operations, is owing to the materials
+being in such a situation in respect to warmth, moisture, and motion; that
+they will immediately change into the vinous or acetous fermentation;
+except the new sugar be absorbed by the numerous lacteal or lymphatic
+vessels, as soon as it is produced; which is not easy to imitate in the
+laboratory.
+
+These lacteal vessels have mouths, which are irritated into action by the
+stimulus of the fluid, which surrounds them; and by animal selection, or
+appetency, they absorb such part of the fluid as is agreeable to their
+palate; those parts, for instance, which are already converted into chyle,
+before they have time to undergo another change by a vinous or acetous
+fermentation. This animal absorption of fluid is almost visible to the
+naked eye in the action of the puncta lacrymalia; which imbibe the tears
+from the eye, and discharge them again into the nostrils.
+
+III. The arteries constitute another reservoir of a changeful fluid; from
+which, after its recent oxygenation in the lungs, a further animal
+selection of various fluids is absorbed by the numerous glands; these
+select their respective fluids from the blood, which is perpetually
+undergoing a chemical change; but the selection by these glands, like that
+of the lacteals, which open their mouths into the digesting aliment in the
+stomach, is from animal appetency, not from chemical affinity; secretion
+cannot therefore be imitated in the laboratory, as it consists in a
+selection of part of a fluid during the chemical change of that fluid.
+
+The mouths of the lacteals, and lymphatics, and the ultimate terminations
+of the glands, are finer than can easily be conceived; yet it is probable,
+that the pores, or interstices of the parts, or coats, which constitute
+these ultimate vessels, may still have greater tenuity; and that these
+pores from the above analogy must posses a similar power of irritability,
+and absorb by their living energy the particles of fluid adapted to their
+purposes, whether to replace the parts abraded or dissolved, or to elongate
+and enlarge themselves. Not only every kind of gland is thus endued with
+its peculiar appetency, and selects the material agreeable to its taste
+from the blood, but every individual pore acquires by animal selection the
+material, which it wants; and thus nutrition seems to be performed in a
+manner so similar to secretion; that they only differ in the one retaining,
+and the other parting again with the particles, which they have selected
+from the blood.
+
+This way of accounting for nutrition from stimulus, and the consequent
+animal selection of particles, is much more analogous to other phenomena of
+the animal microcosm, than by having recourse to the microscopic
+animalcula, or organic particles of Buffon, and Needham; which being
+already compounded must themselves require nutritive particles to continue
+their own existence. And must be liable to undergo a change by our
+digestive or secretory organs; otherwise mankind would soon resemble by
+their theory the animals, which they feed upon. He, who is nourished by
+beef or venison, would in time become horned; and he, who feeds on pork or
+bacon, would gain a nose proper for rooting into the earth, as well as for
+the perception of odours.
+
+The whole animal system may be considered as consisting of the extremities
+of the nerves, or of having been produced from them; if we except perhaps
+the medullary part of the brain residing in the head and spine, and in the
+trunks of the nerves. These extremities of the nerves are either of those
+of locomotion, which are termed muscular fibres; or of those of sensation,
+which constitute the immediate organs of sense, and which have also their
+peculiar motions. Now as the fibres, which constitute the bones and
+membranes, possessed originally sensation and motion; and are liable again
+to possess them, when they become inflamed; it follows, that those were,
+when first formed, appendages to the nerves of sensation or locomotion, or
+were formed from them. And that hence all these solid parts of the body, as
+they have originally consisted of extremities of nerves, require an
+apposition of nutritive particles of a similar kind, contrary to the
+opinion of Buffon and Needham above recited.
+
+Lastly, as all these filaments have possessed, or do possess, the power of
+contraction, and of consequent inertion or elongation; it seems probable,
+that the nutritive particles are applied during their times of elongation;
+when their original constituent particles are removed to a greater distance
+from each other. For each muscular or sensual fibre may be considered as a
+row or string of beads; which approach, when in contraction, and recede
+during its rest or elongation; and our daily experience shews us, that
+great action emaciates the system, and that it is repaired during rest.
+
+Something like this is seen out of the body; for if a hair, or a single
+untwisted fibre of flax or silk, be soaked in water; it becomes longer and
+thicker by the water, which is absorbed into its pores. Now if a hair could
+be supposed to be thus immersed in a solution of particles similar to
+those, which compose it; one may imagine, that it might be thus increased
+in weight and magnitude; as the particles of oak-bark increase the
+substance of the hides of beasts in the process of making leather. I
+mention these not as philosophic analogies, but as similes to facilitate
+our ideas, how an accretion of parts may be effected by animal appetences,
+or selections, in a manner somewhat similar to mechanical or chemical
+attractions.
+
+If those new particles of matter, previously prepared by digestion and
+sanguification, only supply the places of those, which have been abraded by
+the actions of the system, it is properly termed nutrition. If they are
+applied to the extremities of the nervous fibrils, or in such quantity as
+to increase the length or crassitude of them, the body becomes at the same
+time enlarged, and its growth is increased, as well as its deficiences
+repaired.
+
+In this last case something more than a simple apposition or selection of
+particles seems to be necessary; as many parts of the system during its
+growth are caused to recede from those, with which they were before in
+contact; as the ends of the bones, or cartilages, recede from each other,
+as their growth advances: this process resembles inflammation, as appears
+in ophthalmy, or in the production of new flesh in ulcers, where old
+vessels are enlarged, and new ones produced; and like that is attended with
+sensation. In this situation the vessels become distended with blood, and
+acquire greater sensibility, and may thus be compared to the erection of
+the penis, or of the nipples of the breasts of women; while new particles
+become added at the same time; as in the process of nutrition above
+described.
+
+When only the natural growth of the various parts of the body are produced,
+a pleasurable sensation attends it, as in youth, and perhaps in those, who
+are in the progress of becoming fat. When an unnatural growth is the
+consequence, as in inflammatory diseases, a painful sensation attends the
+enlargement of the system.
+
+IV. This apposition of new parts, as the old ones disappear, selected from
+the aliment we take, first enlarges and strengthens our bodies for twenty
+years, for another twenty years it keeps us in health and vigour, and adds
+strength and solidity to the system; and then gradually ceases to nourish
+us properly, and for another twenty years we gradually sink into decay, and
+finally cease to act, and to exist.
+
+On considering this subject one should have imagined at first view, that it
+might have been easier for nature to have supported her progeny for ever in
+health and life, than to have perpetually reproduced them by the wonderful
+and mysterious process of generation. But it seems our bodies by long habit
+cease to obey the stimulus of the aliment, which should support us. After
+we have acquired our height and solidity we make no more new parts, and the
+system obeys the irritations, sensations, volitions; and associations,
+with, less and less energy, till the whole sinks into inaction.
+
+Three causes may conspire to render our nerves less excitable, which have
+been already mentioned, 1. If a stimulus be greater than natural, it
+produces too great an exertion of the stimulated organ, and in consequence
+exhausts the spirit of animation; and the moving organ ceases to act, even
+though the stimulus be continued. And though rest will recruit this
+exhaustion, yet some degree of permanent injury remains, as is evident
+after exposing the eyes long to too strong a light. 2. If excitations
+weaker than natural be applied, so as not to excite the organ into action,
+(as when small doses of aloe or rhubarb are exhibited,) they may be
+gradually increased, without exciting the organ into action; which will
+thus acquire a habit of disobedience to the stimulus; thus by increasing
+the dose by degrees, great quantities of opium or wine may be taken without
+intoxication. See Sect. XII. 3. 1.
+
+3. Another mode, by which life is gradually undermined, is when irritative
+motions continue to be produced in consequence of stimulus, but are not
+succeeded by sensation; hence the stimulus of contagious matter is not
+capable of producing fever a second time, because it is not succeeded by
+sensation. See Sect. XII. 3. 6. And hence, owing to the want of the general
+pleasurable sensation, which ought to attend digestion and glandular
+secretion, an irksomeness of life ensues; and, where this is in greater
+excess, the melancholy of old age occurs, with torpor or debility.
+
+From hence I conclude, that it is probable that the fibrillæ, or moving
+filaments at the extremities of the nerves of sense, and the fibres which
+constitute the muscles (which are perhaps the only parts of the system that
+are endued with contractile life) are not changed, as we advance in years,
+like the other parts of the body; but only enlarged or elongated with our
+growth; and in consequence they become less and less excitable into action.
+Whence, instead of gradually changing the old animal, the generation of a
+totally new one becomes necessary with undiminished excitability; which
+many years will continue to acquire new parts, or new solidity, and then
+losing its excitability in time, perish like its parent.
+
+V. From this idea the art of preserving long health and life may be
+deduced; which must consist in using no greater stimulus, whether of the
+quantity or kind of our food and drink, or of external circumstances, such
+as heat, and exercise, and wakefulness, than is sufficient to preserve us
+in vigour; and gradually, as we grow old to increase the stimulus of our
+aliment, as the irritability of our system increases.
+
+The debilitating effects ascribed by the poet MARTIAL to the excessive use
+of warm bathing in Italy, may with equal propriety be applied to the warm
+rooms of England; which, with the general excessive stimulus of spirituous
+or fermented liquors, and in some instances of immoderate venery,
+contribute to shorten our lives.
+
+  _Balnea, vina, venus, corrumpunt corpora nostra_,
+  _At faciunt vitam balnea, vina, venus!_
+
+  Wine, women, warmth, against our lives combine;
+  But what is life without warmth, women, wine!
+
+       *       *       *       *       *
+
+SECT. XXXVIII.
+
+OF THE OXYGENATION OF THE BLOOD IN THE LUNGS, AND IN THE PLACENTA.
+
+    I. _Blood absorbs oxygene from the air, whence phosphoric acid changes
+    its colour, gives out heat, and some phlogistic material, and acquires
+    an ethereal spirit, which is dissipated in fibrous motion._ II. _The
+    placenta is a pulmonary organ like the gills of fish. Oxygenation of
+    the blood from air, from water, by lungs, by gills, by the placenta;
+    necessity of this oxygenation to quadrupeds, to fish, to the foetus in
+    utero. Placental vessels inserted into the arteries of the mother. Use
+    of cotyledons in cows. Why quadrupeds have not sanguiferous lochia.
+    Oxygenation of the chick in the egg, of feeds._ III. _The liquor amnii
+    is not excrementitious. It is nutritious. It is found in the esophagus
+    and stomach, and forms the meconium. Monstrous births without heads.
+    Question of Dr. Harvey._
+
+I. From the recent discoveries of many ingenious philosophers it appears,
+that during respiration the blood imbibes the vital part of the air, called
+oxygene, through the membranes of the lungs; and that hence respiration may
+be aptly compared to a slow combustion. As in combustion the oxygene of the
+atmosphere unites with some phlogistic or inflammable body, and forms an
+acid (as in the production of vitriolic acid from sulphur, or carbonic acid
+from charcoal,) giving out at the same time a quantity of the matter of
+heat; so in respiration the oxygene of the air unites with the phlogistic
+part of the blood, and probably produces phosphoric or animal acid,
+changing the colour of the blood from a dark to a bright red; and probably
+some of the matter of heat is at the same time given out according to the
+theory of Dr. Crawford. But as the evolution of heat attends almost all
+chemical combinations, it is probable, that it also attends the secretions
+of the various fluids from the blood; and that the constant combinations or
+productions of new fluids by means of the glands constitute the more
+general source of animal heat; this seems evinced by the universal
+evolution of the matter of heat in the blush of shame or of anger; in which
+at the same time an increased secretion of the perspirable matter occurs;
+and the partial evolution of it from topical inflammations, as in gout or
+rheumatism, in which there is a secretion of new blood-vessels.
+
+Some medical philosophers have ascribed the heat of animal bodies to the
+friction of the particles of the blood against the sides of the vessels.
+But no perceptible heat has ever been produced by the agitation of water,
+or oil, or quicksilver, or other fluids; except those fluids have undergone
+at the same time some chemical change, as in agitating milk or wine, till
+they become sour.
+
+Besides the supposed production of phosphoric acid, and change of colour of
+the blood, and the production of carbonic acid, there would appear to be
+something of a more subtile nature perpetually acquired from the
+atmosphere; which is too fine to be long contained in animal vessels, and
+therefore requires perpetual renovation; and without which life cannot
+continue longer than a minute or two; this ethereal fluid is probably
+secreted from the blood by the brain, and perpetually dissipated in the
+actions of the muscles and organs of sense.
+
+That the blood acquires something from the air, which is immediately
+necessary to life, appears from an experiment of Dr. Hare (Philos.
+Transact. abridged, Vol. III. p. 239.) who found, "that birds, mice, &c.
+would live as long again in a vessel, where he had crowded in double the
+quantity of air by a condensing engine, than they did when confined in air
+of the common density." Whereas if some kind of deleterious vapour only was
+exhaled from the blood in respiration; the air, when condensed into half
+its compass, could not be supposed to receive so much of it.
+
+II. Sir Edward Hulse, a physician of reputation at the beginning of the
+present century, was of opinion, that the placenta was a respiratory organ,
+like the gills of fish; and not an organ to supply nutriment to the foetus;
+as mentioned in Derham's Physico-theology. Many other physicians seem to
+have espoused the same opinion, as noticed by Haller. Elem. Physiologiæ, T.
+1. Dr. Gipson published a defence of this theory in the Medical Essays of
+Edinburgh, Vol. I. and II. which doctrine is there controverted at large by
+the late Alexander Monro; and since that time the general opinion has been,
+that the placenta is an organ of nutrition only, owing perhaps rather to
+the authority of so great a name, than to the validity of the arguments
+adduced in its support. The subject has lately been resumed by Dr. James
+Jeffray, and by Dr. Forester French, in their inaugural dissertations at
+Edinburgh and at Cambridge; who have defended the contrary opinion in an
+able and ingenious manner; and from whose Theses I have extracted many of
+the following remarks.
+
+First, by the late discoveries of Dr. Priestley, M. Lavoisier, and other
+philosophers, it appears, that the basis of atmospherical air, called
+oxygene, is received by the blood through the membranes of the lungs; and
+that by this addition the colour of the blood is changed from a dark to a
+light red. Secondly, that water possesses oxygene also as a part of its
+composition, and contains air likewise in its pores; whence the blood of
+fish receives oxygene from the water, or from the air it contains, by means
+of their gills, in the same manner as the blood is oxygenated in the lungs
+of air-breathing animals; it changes its colour at the same time from a
+dark to a light red in the vessels of their gills, which constitute a
+pulmonary organ adapted to the medium in which they live. Thirdly, that the
+placenta consists of arteries carrying the blood to its extremities, and a
+vein bringing it back, resembling exactly in structure the lungs and gills
+above mentioned; and that the blood changes its colour from a dark to a
+light red in passing through these vessels.
+
+This analogy between the lungs and gills of animals, and the placenta of
+the fetus, extends through a great variety of other circumstances; thus
+air-breathing creatures and fish can live but a few minutes without air or
+water; or when they are confined in such air or water, as has been spoiled
+by their own respiration; the same happens to the fetus, which, as soon as
+the placenta is separated from the uterus, must either expand its lungs,
+and receive air, or die. Hence from the structure, as well as the use of
+the placenta, it appears to be a respiratory organ, like the gills of fish,
+by which the blood in the fetus becomes oxygenated.
+
+From the terminations of the placental vessels not being observed to bleed
+after being torn from the uterus, while those of the uterus effuse a great
+quantity of florid arterial blood, the terminations of the placental
+vessels would seem to be inserted into the arterial ones of the mother; and
+to receive oxygenation from the passing currents of her blood through their
+coats or membranes; which oxygenation is proved by the change of the colour
+of the blood from dark to light red in its passage from the placental
+arteries to the placental vein.
+
+The curious structure of the cavities or lacunæ of the placenta,
+demonstrated by Mr. J. Hunter, explain this circumstance. That ingenious
+philosopher has shewn, that there are numerous cavities of lacunæ formed on
+that side of the placenta, which is in contact with the uterus; those
+cavities or cells are filled with blood from the maternal arteries, which
+open into them; which blood is again taken up by the maternal veins, and is
+thus perpetually changed. While the terminations of the placental arteries
+and veins are spread in fine reticulation on the sides of these cells. And
+thus, as the growing fetus requires greater oxygenation, an apparatus is
+produced resembling exactly the air-cells of the lungs.
+
+In cows, and other ruminating animals, the internal surface of the uterus
+is unequal like hollow cups, which have been called cotyledons; and into
+these cavities the prominencies of the numerous placentas, with which the
+fetus of those animals is furnished, are inserted, and strictly adhere;
+though they may be extracted without effusion of blood. These inequalities
+of the uterus, and the numerous placentas in consequence, seem to be
+designed for the purpose of expanding a greater surface for the
+terminations of the placental vessels for the purpose of receiving
+oxygenation from the uterine ones; as the progeny of this class of animals
+are more completely formed before their nativity, than that of the
+carnivorous classes, and must thence in the latter weeks of pregnancy
+require greater oxygenation. Thus calves and lambs can walk about in a few
+minutes after their birth; while puppies and kittens remain many days
+without opening their eyes. And though on the separation of the cotyledons
+of ruminating animals no blood is effused, yet this is owing clearly to the
+greater power of contraction of their uterine lacunæ or alveoli. See
+Medical Essays, Vol. V. page 144. And from the same cause they are not
+liable to a sanguiferous menstruation.
+
+The necessity of the oxygenation of the blood in the fetus is farther
+illustrated by the analogy of the chick in the egg; which appears to have
+its blood oxygenated at the extremities of the vessels surrounding the
+yolk; which are spread on the air-bag at the broad end of the egg, and may
+absorb oxygene through that moist membrane from the air confined behind it;
+and which is shewn by experiments in the exhausted receiver to be
+changeable though the shell.
+
+This analogy may even be extended to the growing seeds of vegetables; which
+were shewn by Mr. Scheele to require a renovation of the air over the
+water, in which they were confined. Many vegetable seeds are surrounded
+with air in their pods or receptacles, as peas, the fruit of staphylea, and
+lichnis vesicaria; but it is probable, that those seeds, after they are
+shed, as well as the spawn of fish, by the situation of the former on or
+near the moist and aerated surface of the earth, and of the latter in the
+ever-changing and ventilated water, may not be in need of an apparatus for
+the oxygenation of their first blood, before the leaves of one, and the
+gills of the other, are produced for this purpose.
+
+III. 1. There are many arguments, besides the strict analogy between the
+liquor amnii and the albumen ovi, which shew the former to be a nutritive
+fluid; and that the fetus in the latter months of pregnancy takes it into
+its stomach; and that in consequence the placenta is produced for some
+other important purpose.
+
+First, that the liquor amnii is not an excrementitious fluid is evinced,
+because it is found in greater quantity, when the fetus is young,
+decreasing after a certain period till birth. Haller asserts, "that in some
+animals but a small quantity of this fluid remains at the birth. In the
+eggs of hens it is consumed on the eighteenth day, so that at the exclusion
+of the chick scarcely any remains. In rabbits before birth there is none."
+Elem. Physiol. Had this been an excrementitious fluid, the contrary would
+probably have occurred. Secondly, the skin of the fetus is covered with a
+whitish crust or pellicle, which would seem to preclude any idea of the
+liquor amnii being produced by any exsudation of perspirable matter. And it
+cannot consist of urine, because in brute animals the urachus passes from
+the bladder to the alantois for the express purpose of carrying off that
+fluid; which however in the human fetus seems to be retained in the
+distended bladder, as the feces are accumulated in the bowels of all
+animals.
+
+2. The nutritious quality of the liquid, which surrounds the fetus, appears
+from the following considerations. 1. It is coagulable by heat, by nitrous
+acid, and by spirit of wine, like milk, serum of blood, and other fluids,
+which daily experience evinces to be nutritious. 2. It has a saltish taste
+according to the accurate Baron Haller, not unlike the whey of milk, which
+it even resembles in smell. 3. The white of the egg which constitutes the
+food of the chick, is shewn to be nutritious by our daily experience;
+besides the experiment of its nutritious effects mentioned by Dr. Fordyce
+in his late Treatise on Digestion, p. 178; who adds, that it much resembles
+the essential parts of the serum of blood.
+
+3. A fluid similar to the fluid, with which the fetus is surrounded, except
+what little change may be produced by a beginning digestion, is found in
+the stomach of the fetus; and the white of the egg is found, in the same
+manner in the stomach of the chick.
+
+Numerous hairs, similar to those of its skin, are perpetually found among
+the contents of the stomach in new-born calves; which must therefore have
+licked themselves before their nativity. Blasii Anatom. See Sect. XVI. 2.
+on Instinct.
+
+The chick in the egg is seen gently to move in its surrounding fluid, and
+to open and shut its mouth alternately. The same has been observed in
+puppies. Haller's El. Phys. I. 8. p. 201.
+
+A column of ice has been seen to reach down the oesophagus from the mouth
+to the stomach in a frozen fetus; and this ice was the liquor amnii frozen.
+
+The meconium, or first fæces, in the bowels of new-born infants evince,
+that something has been digested; and what could this be but the liquor
+amnii together with the recrements of the gastric juice and gall, which
+were necessary for its digestion?
+
+There have been recorded some monstrous births of animals without heads,
+and consequently without mouths, which seem to have been delivered on
+doubtful authority, or from inaccurate observation. There are two of such
+monstrous productions however better attested; one of a human fetus,
+mentioned by Gipson in the Scots Medical Essays; which having the gula
+impervious was furnished with an aperture into the wind-pipe, which
+communicated below into the gullet; by means of which the liquor amnii
+might be taken into the stomach before nativity without danger of
+suffocation, while the fetus had no occasion to breathe. The other
+monstrous fetus is described by Vander Wiel, who asserts, that he saw a
+monstrous lamb, which had no mouth; but instead of it was furnished with an
+opening in the lower part of the neck into the stomach. Both these
+instances evidently favour the doctrine of the fetus being nourished by the
+mouth; as otherwise there had been no necessity for new or unnatural
+apertures into the stomach, when the natural ones were deficient?
+
+From these facts and observations we may safely infer, that the fetus in
+the womb is nourished by the fluid which surrounds it; which during the
+first period of gestation is absorbed by the naked lacteals; and is
+afterwards swallowed into the stomach and bowels, when these organs are
+perfected; and lastly that the placenta is an organ for the purpose of
+giving due oxygenation to the blood of the fetus; which is more necessary,
+or at least more frequently necessary, than even the supply of food.
+
+The question of the great Harvey becomes thus easily answered. "Why is not
+the fetus in the womb suffocated for want of air, when it remains there
+even to the tenth month without respiration: yet if it be born in the
+seventh or eighth month, and has once respired, it becomes immediately
+suffocated for want of air, if its respiration be obstructed?"
+
+For further information on this subject, the reader is referred to the
+Tentamen Medicum of Dr. Jeffray, printed at Edinburgh in 1786. And it is
+hoped that Dr. French will some time give his theses on this subject to the
+public.
+
+       *       *       *       *       *
+
+SECT. XXXIX.
+
+OF GENERATION.
+
+  Felix, qui causas altà caligine mersas
+  Pandit, et evolvit tenuissima vincula rerum.
+
+    I. _Habits of acting and feeling of individuals attend the soul into a
+    future life, and attend the new embryon at the time of its production.
+    The new speck of entity absorbs nutriment, and receives oxygene.
+    Spreads the terminations of its vessels on cells, which communicate
+    with the arteries of the uterus; sometimes with those of the
+    peritoneum. Afterwards it swallows the liquor amnii, which it produces
+    by its irritation from the uterus, or peritoneum. Like insects in the
+    heads of calves and sheep. Why the white of egg is of two
+    consistencies. Why nothing is found in quadrupeds similar to the yolk,
+    nor in most vegetable seeds._ II. 1. _Eggs of frogs and fish
+    impregnated out of their bodies. Eggs of fowls which are not
+    fecundated, contain only the nutriment for the embryon. The embryon is
+    produced by the male, and the nutriment by the female. Animalcula in
+    semine. Profusion of nature's births._ 2. _Vegetables viviparous. Buds
+    and bulbs have each a father but no mother. Vessels of the leaf and bud
+    inosculate. The paternal offspring exactly resembles the parent._ 3.
+    _Insects impregnated for six generations. Polypus branches like buds.
+    Creeping roots. Viviparous flowers. Tænia, volvox. Eve from Adam's rib.
+    Semen not a stimulus to the egg._ III. 1. _Embryons not originally
+    created within other embryons. Organized matter is not so minute._ 2.
+    _All the parts of the embryon are not formed in the male parent. Crabs
+    produce their legs, worms produce their heads and tails. In wens,
+    cancers, and inflammations, new vessels are formed. Mules partake of
+    the forms of both parents. Hair and nails grow by elongation, not by
+    distention._ 3. _Organic particles of Buffon._ IV. 1. _Rudiment of the
+    embryon a simple living filament, becomes a living ring, and then a
+    living tube._ 2. _It acquires irritabilities, and sensibilities with
+    new organizations, as in wounded snails, polypi, moths, gnats,
+    tadpoles. Hence new parts are acquired by addition not by distention._
+    3. _All parts of the body grow if not confined._ 4. _Fetuses deficient
+    at their extremities, or have a duplicature of parts. Monstrous births.
+    Double parts of vegetables._ 5. _Mules cannot be formed by distention
+    of the seminal ens._ 6. _Families of animals from a mixture of their
+    orders. Mules imperfect._ 7. _Animal appetency like chemical affinity.
+    Vis fabricatrix and medicatrix of nature._ 8. _The changes of animals
+    before and after nativity. Similarity of their structure. Changes in
+    them from lust, hunger, and danger. All warm-blooded animals derived
+    from one living filament. Cold-blooded animals, insects, worms,
+    vegetables, derived also from one living filament. Male animals have
+    teats. Male pigeon gives milk. The world itself generated. The cause of
+    causes. A state of probation and responsibility._ V. 1. _Efficient
+    cause of the colours of birds eggs, and of hair and feathers, which
+    become white in snowy countries. Imagination of the female colours the
+    egg. Ideas or motions of the retina imitated by the extremities of the
+    nerves of touch, or rete mucosum._ 2. _Nutriment supplied by the female
+    of three kinds. Her imagination can only affect the first kind. Mules
+    how produced, and mulattoes. Organs of reproduction why deficient in
+    mules. Eggs with double yolks._ VI. 1. _Various secretions produced by
+    the extremities of the vessels, as in the glands. Contagious matter.
+    Many glands affected by pleasurable ideas, as those which secrete the
+    semen._ 2. _Snails and worms are hermaphrodite, yet cannot impregnate
+    themselves. Final cause of this._ 3. _The imagination of the male forms
+    the sex. Ideas, or motions of the nerves of vision or of touch, are
+    imitated by the ultimate extremities of the glands of the testes, which
+    mark the sex. This effect of the imagination belongs only to the male.
+    The sex of the embryon is not owing to accident._ 4. _Causes of the
+    changes in animals from imagination as in monsters. From the male. From
+    the female._ 5. _Miscarriages from fear._ 6. _Power of the imagination
+    of the male over the colour, form, and sex of the progeny. An instance
+    of._ 7. _Act of generation accompanied with ideas of the male or female
+    form. Art of begetting beautiful children of either sex._ VII.
+    _Recapitulation._ VIII. _Conclusion. Of cause and effect. The atomic
+    philosophy leads to a first cause._
+
+I. The ingenious Dr. Hartley in his work on man, and some other
+philosophers, have been of opinion, that our immortal part acquires during
+this life certain habits of action or of sentiment, which become for ever
+indissoluble, continuing after death in a future state of existence; and
+add, that if these habits are of the malevolent kind, they must render the
+possessor miserable even in heaven. I would apply this ingenious idea to
+the generation or production of the embryon, or new animal, which partakes
+so much of the form and propensities of the parent.
+
+Owing to the imperfection of language the offspring is termed a _new_
+animal, but is in truth a branch or elongation of the parent; since a part
+of the embryon-animal is, or was, a part of the parent; and therefore in
+strict language it cannot be said to be entirely _new_ at the time of its
+production; and therefore it may retain some of the habits of the
+parent-system.
+
+At the earliest period of its existence the embryon, as secreted from the
+blood of the male, would seem to consist of a living filament with certain
+capabilities of irritation, sensation, volition, and association; and also
+with some acquired habits or propensities peculiar to the parent: the
+former of these are in common with other animals; the latter seem to
+distinguish or produce the kind of animal, whether man or quadruped, with
+the similarity of feature or form to the parent. It is difficult to be
+conceived, that a living entity can be separated or produced from the blood
+by the action of a gland; and which shall afterwards become an animal
+similar to that in whose vessels it is formed; even though we should
+suppose with some modern theorists, that the blood is alive; yet every
+other hypothesis concerning generation rests on principles still more
+difficult to our comprehension.
+
+At the time of procreation this speck of entity is received into an
+appropriated nidus, in which it must acquire two circumstances necessary to
+its life and growth; one of these is food or sustenance, which is to be
+received by the absorbent mouths of its vessels; and the other is that part
+of atmospherical air, or of water, which by the new chemistry is termed
+oxygene, and which affects the blood by passing through the coats of the
+vessels which contain it. The fluid surrounding the embryon in its new
+habitation, which is called liquor amnii, supplies it with nourishment; and
+as some air cannot but be introduced into the uterus along with a new
+embryon, it would seem that this same fluid would for a short time, suppose
+for a few hours, supply likewise a sufficient quantity of the oxygene for
+its immediate existence.
+
+On this account the vegetable impregnation of aquatic plants is performed
+in the air; and it is probable that the honey-cup or nectary of vegetables
+requires to be open to the air, that the anthers and stigmas of the flower
+may have food of a more oxygenated kind than the common vegetable
+sap-juice.
+
+On the introduction of this primordium of entity into the uterus the
+irritation of the liquor amnii, which surrounds it, excites the absorbent
+mouths of the new vessels into action; they drink up a part of it, and a
+pleasurable sensation accompanies this new action; at the same time the
+chemical affinity of the oxygene acts through the vessels of the rubescent
+blood; and a previous want, or disagreeable sensation, is relieved by this
+process.
+
+As the want of this oxygenation of the blood is perpetual, (as appears from
+the incessant necessity of breathing by lungs or gills,) the vessels become
+extended by the efforts of pain or desire to seek this necessary object of
+oxygenation, and to remove the disagreeable sensation, which that want
+occasions. At the same time new particles of matter are absorbed, or
+applied to these extended vessels, and they become permanently elongated,
+as the fluid in contact with them soon loses the oxygenous part, which it
+at first possessed, which was owing to the introduction of air along with
+the embryon. These new blood-vessels approach the sides of the uterus, and
+penetrate with their fine terminations into the vessels of the mother; or
+adhere to them, acquiring oxygene through their coats from the passing
+currents of the arterial blood of the mother. See Sect. XXXVIII. 2.
+
+This attachment of the placental vessels to the internal side of the uterus
+by their own proper efforts appears further illustrated by the many
+instances of extra-uterine fetuses, which have thus attached or inserted
+their vessels into the peritoneum; or on the viscera, exactly in the same
+manner as they naturally insert or attach them to the uterus.
+
+The absorbent vessels of the embryon continue to drink up nourishment from
+the fluid in which they swim, or liquor amnii; and which at first needs no
+previous digestive preparation; but which, when the whole apparatus of
+digestion becomes complete, is swallowed by the mouth into the stomach, and
+being mixed with saliva, gastric juice, bile, pancreatic juice, and mucus
+of the intestines, becomes digested, and leaves a recrement, which produces
+the first feces of the infant, called meconium.
+
+The liquor amnii is secreted into the uterus, as the fetus requires it, and
+may probably be produced by the irritation of the fetus as an extraneous
+body; since a similar fluid is acquired from the peritoneum in cases of
+extra-uterine gestation. The young caterpillars of the gadfly placed in the
+skins of cows, and the young of the ichneumon-fly placed in the backs of
+the caterpillars on cabbages, seem to produce their nourishment by their
+irritating the sides of their nidus. A vegetable secretion and concretion
+is thus produced on oak-leaves by the gall-insect, and by the cynips in the
+bedeguar of the rose; and by the young grasshopper on many plants, by which
+the animal surrounds itself with froth. But in no circumstance is
+extra-uterine gestation so exactly resembled as by the eggs of a fly, which
+are deposited in the frontal sinus of sheep and calves. These eggs float in
+some ounces of fluid collected in a thin pellicle or hydatide. This bag of
+fluid compresses the optic nerve on one side, by which the vision being
+less distinct in that eye, the animal turns in perpetual circles towards
+the side affected, in order to get a more accurate view of objects; for the
+same reason as in squinting the affected eye is turned away from the object
+contemplated. Sheep in the warm months keep their noses close to the ground
+to prevent this fly from so readily getting into their nostrils.
+
+The liquor amnii is secreted into the womb as it is required, not only in
+respect to quantity, but, as the digestive powers of the fetus become
+formed, this fluid becomes of a different consistence and quality, till it
+is exchanged for milk after nativity. Haller. Physiol. V. 1. In the egg the
+white part, which is analogous to the liquor amnii of quadrupeds, consists
+of two distinct parts; one of which is more viscid, and probably more
+difficult of digestion, and more nutritive than the other; and this latter
+is used in the last week of incubation. The yolk of the egg is a still
+stronger or more nutritive fluid, which is drawn up into the bowels of the
+chick just at its exclusion from the shell, and serves it for nourishment
+for a day or two, till it is able to digest, and has learnt to choose the
+harder seeds or grains, which are to afford it sustenance. Nothing
+analogous to this yolk is found in the fetus of lactiferous animals, as the
+milk is another nutritive fluid ready prepared for the young progeny.
+
+The yolk therefore is not necessary to the spawn of fish, the eggs of
+insects, or for the seeds of vegetables; as their embryons have probably
+their food presented to them as soon as they are excluded from their
+shells, or have extended their roots. Whence it happens that some insects
+produce a living progeny in the spring and summer, and eggs in the autumn;
+and some vegetables have living roots or buds produced in the place of
+seeds, as the polygonum viviparum, and magical onions. See Botanic Garden,
+p. 11. art. anthoxanthum.
+
+There seems however to be a reservoir of nutriment prepared for some seeds
+besides their cotyledons or seed-leaves, which may be supposed in some
+measure analogous to the yolk of the egg. Such are the saccharine juices of
+apples, grapes and other fruits, which supply nutrition to the seeds after
+they fall on the ground. And such is the milky juice in the centre of the
+cocoa-nut, and part of the kernel of it; the same I suppose of all other
+monocotyledon seeds, as of the palms, grasses, and lilies.
+
+II. 1. The process of generation is still involved in impenetrable
+obscurity, conjectures may nevertheless be formed concerning some of its
+circumstances. First, the eggs of fish and frogs are impregnated, after
+they leave the body of the female; because they are deposited in a fluid,
+and are not therefore covered with a hard shell. It is however remarkable,
+that neither frogs nor fish will part with their spawn without the presence
+of the male; on which account female carp and gold-fish in small ponds,
+where there are no males, frequently die from the distention of their
+growing spawn. 2. The eggs of fowls, which are laid without being
+impregnated, are seen to contain only the yolk and white, which are
+evidently the food or sustenance for the future chick. 3. As the
+cicatricula of these eggs is given by the cock, and is evidently the
+rudiment of the new animal; we may conclude, that the embryon is produced
+by the male, and the proper food and nidus by the female. For if the female
+be supposed to form an equal part of the embryon, why should she form the
+whole of the apparatus for nutriment and for oxygenation? the male in many
+animals is larger, stronger, and digests more food than the female, and
+therefore should contribute as much or more towards the reproduction of the
+species; but if he contributes only half the embryon and none of the
+apparatus for sustenance and oxygenation, the division is unequal; the
+strength of the male, and his consumption of food are too great for the
+effect, compared with that of the female, which is contrary to the usual
+course of nature.
+
+In objection to this theory of generation it may be said, if the animalcula
+in femine, as seen by the microscope, be all of them rudiments of
+homunculi, when but one of them can find a nidus, what a waste nature has
+made of her productions? I do not assert that these moving particles,
+visible by the microscope, are homunciones; perhaps they may be the
+creatures of stagnation or putridity, or perhaps no creatures at all; but
+if they are supposed to be rudiments of homunculi, or embryons, such a
+profusion of them corresponds with the general efforts of nature to provide
+for the continuance of her species of animals. Every individual tree
+produces innumerable seeds, and every individual fish innumerable spawn, in
+such inconceivable abundance as would in a short space of time crowd the
+earth and ocean with inhabitants; and these are much more perfect animals
+than the animalcula in femine can be supposed to be, and perish in
+uncounted millions. This argument only shews, that the productions of
+nature are governed by general laws; and that by a wise superfluity of
+provision she has ensured their continuance.
+
+2. That the embryon is secreted or produced by the male, and not by the
+conjunction of fluids from both male and female, appears from the analogy
+of vegetable seeds. In the large flowers, as the tulip, there is no
+similarity of apparatus between the anthers and the stigma: the seed is
+produced according to the observations of Spallanzani long before the
+flowers open, and in consequence long before it can be impregnated, like
+the egg in the pullet. And after the prolific dust is shed on the stigma,
+the seed becomes coagulated in one point first, like the cicatricula of the
+impregnated egg. See Botanic Garden, Part I. additional note 38. Now in
+these simple products of nature, if the female contributed to produce the
+new embryon equally with the male, there would probably have been some
+visible similarity of parts for this purpose, besides those necessary for
+the nidus and sustenance of the new progeny. Besides in many flowers the
+males are more numerous than the females, or than the separate uterine
+cells in their germs, which would shew, that the office of the male was at
+least as important as that of the female; whereas if the female, besides
+producing the egg or seed, was to produce an equal part of the embryon, the
+office of reproduction would be unequally divided between them.
+
+Add to this, that in the most simple kind of vegetable reproduction, I mean
+the buds of trees, which are their viviparous offspring, the leaf is
+evidently the parent of the bud, which rises in its bosom, according to the
+observation of Linnaeus. This leaf consists of absorbent vessels, and
+pulmonary ones, to obtain its nutriment, and to impregnate it with oxygene.
+This simple piece of living organization is also furnished with a power of
+reproduction; and as the new offspring is thus supported adhering to its
+father, it needs no mother to supply it with a nidus, and nutriment, and
+oxygenation; and hence no female leaf has existence.
+
+I conceive that the vessels between the bud and the leaf communicate or
+inosculate; and that the bud is thus served with vegetable blood, that is,
+with both nutriment and oxygenation, till the death of the parent-leaf in
+autumn. And in this respect it differs from the fetus of viviparous
+animals. Secondly, that then the bark-vessels belonging to the dead-leaf,
+and in which I suppose a kind of manna to have been deposited, become now
+the placental vessels, if they may be so called, of the new bud. From the
+vernal sap thus produced of one sugar-maple-tree in New-York and in
+Pennsylvania, five or six pounds of good sugar may be made annually without
+destroying the tree. Account of maple-sugar by B. Rushes. London, Phillips.
+(See Botanic Garden, Part I. additional note on vegetable placentation.)
+
+These vessels, when the warmth of the vernal sun hatches the young bud,
+serve it with a saccharine nutriment, till it acquires leaves of its own,
+and shoots a new system of absorbents down the bark and root of the tree,
+just as the farinaceous or oily matter in seeds, and the saccharine matter
+in fruits, serve their embryons with nutriment, till they acquire leaves
+and roots. This analogy is as forceable in so obscure a subject, as it is
+curious, and may in large buds, as of the horse-chesnut, be almost seen by
+the naked eye; if with a penknife the remaining rudiment of the last year's
+leaf, and of the new bud in its bosom, be cut away slice by slice. The
+seven ribs of the last year's leaf will be seen to have arisen from the
+pith in seven distinct points making a curve; and the new bud to have been
+produced in their centre, and to have pierced the alburnum and cortex, and
+grown without the assistance of a mother. A similar process may be seen on
+dissecting a tulip-root in winter; the leaves, which inclosed the last
+year's flower-stalk, were not necessary for the flower; but each of these
+was the father of a new bud, which may be now found at its base; and which,
+as it adheres to the parent, required no mother.
+
+This paternal offspring of vegetables, I mean their buds and bulbs, is
+attended with a very curious circumstance; and that is, that they exactly
+resemble their parents, as is observable in grafting fruit-trees, and in
+propagating flower-roots; whereas the seminal offspring of plants, being
+supplied with nutriment by the mother, is liable to perpetual variation.
+Thus also in the vegetable class dioicia, where the male flowers are
+produced on one tree, and the female ones on another; the buds of the male
+trees uniformly produce either male flowers, or other buds similar to
+themselves; and the buds of the female trees produce either female flowers,
+or other buds similar to themselves; whereas the seeds of these trees
+produce either male or female plants. From this analogy of the production
+of vegetable buds without a mother, I contend that the mother does not
+contribute to the formation of the living ens in animal generation, but is
+necessary only for supplying its nutriment and oxygenation.
+
+There is another vegetable fact published by M. Koelreuter, which he calls
+"a complete metamorphosis of one natural species of plants into another,"
+which shews, that in seeds as well as in buds, the embryon proceeds from
+the male parent, though the form of the subsequent mature plant is in part
+dependant on the female. M. Koelreuter impregnated a stigma of the
+nicotiana rustica with the farina of the nicotiana paniculata, and obtained
+prolific seeds from it. With the plants which sprung from these seeds, he
+repeated the experiment, impregnating them with the farina of the nicotiana
+paniculata. As the mule plants which he thus produced were prolific, he
+continued to impregnate them for many generations with the farina of the
+nicotiana paniculata, and they became more and more like the male parent,
+till he at length obtained six plants in every respect perfectly similar to
+the nicotiana paniculata; and in no respect resembling their female parent
+the nicotiana rustica. _Blumenbach_ on Generation.
+
+3. It is probable that the insects, which are said to require but one
+impregnation for six generations, as the aphis (see Amenit. Academ.)
+produce their progeny in the manner above described, that is, without a
+mother, and not without a father; and thus experience a lucina sine
+concubitu. Those who have attended to the habits of the polypus, which is
+found in the stagnant water of our ditches in July, affirm, that the young
+ones branch out from the side of the parent like the buds of trees, and
+after a time separate themselves from them. This is so analogous to the
+manner in which the buds of trees appear to be produced, that these polypi
+may be considered as all male animals, producing embryons, which require no
+mother to supply them with a nidus, or with nutriment, and oxygenation.
+
+This lateral or lineal generation of plants, not only obtains in the buds
+of trees, which continue to adhere to them, but is beautifully seen in the
+wires of knot-grass, polygonum aviculare, and in those of strawberries,
+fragaria vesca. In these an elongated creeping bud is protruded, and, where
+it touches the ground, takes root, and produces a new plant derived from
+its father, from which it acquires both nutriment and oxygenation; and in
+consequence needs no maternal apparatus for these purposes. In viviparous
+flowers, as those of allium magicum, and polygonum viviparum, the anthers
+and the stigmas become effete and perish; and the lateral or paternal
+offspring succeeds instead of seeds, which adhere till they are
+sufficiently mature, and then fall upon the ground, and take root like
+other bulbs.
+
+The lateral production of plants by wires, while each new plant is thus
+chained to its parent, and continues to put forth another and another, as
+the wire creeps onward on the ground, is exactly resembled by the
+tape-worm, or tænia, so often found in the bowels, stretching itself in a
+chain quite from the stomach to the rectum. Linnæus asserts, "that it grows
+old at one extremity, while it continues to generate young ones at the
+other, proceeding ad infinitum, like a root of grass. The separate joints
+are called gourd-worms, and propagate new joints like the parent without
+end, each joint being furnished with its proper mouth, and organs of
+digestion." Systema naturæ. Vermes tenia. In this animal there evidently
+appears a power of reproduction without any maternal apparatus for the
+purpose of supplying nutriment and oxygenation to the embryon, as it
+remains attached to its father till its maturity. The volvox globator,
+which is a transparent animal, is said by Linnæus to bear within it sons
+and grand-sons to the fifth generation. These are probably living fetuses,
+produced by the father, of different degrees of maturity, to be detruded at
+different periods of time, like the unimpregnated eggs of various sizes,
+which are found in poultry; and as they are produced without any known
+copulation, contribute to evince, that the living embryon in other orders
+of animals is formed by the male-parent, and not by the mother, as one
+parent has the power to produce it.
+
+This idea of the reproduction of animals from a single living filament of
+their fathers, appears to have been shadowed or allegorized in the curious
+account in sacred writ of the formation of Eve from a rib of Adam.
+
+From all these analogies I conclude, that the embryon is produced solely by
+the male, and that the female supplies it with a proper nidus, with
+sustenance, and with oxygenation; and that the idea of the semen of the
+male constituting only a stimulus to the egg of the female, exciting it
+into life, (as held by some philosophers) has no support from experiment or
+analogy.
+
+III. 1. Many ingenious philosophers have found so great difficulty in
+conceiving the manner of the reproduction of animals, that they have
+supposed all the numerous progeny, to have existed in miniature in the
+animal originally created; and that these infinitely minute forms are only
+evolved or distended, as the embryon increases in the womb. This idea,
+besides its being unsupported by any analogy we are acquainted with,
+ascribes a greater tenuity to organized matter, than we can readily admit;
+as these included embryons are supposed each of them to consist of the
+various and complicate parts of animal bodies: they must possess a much
+greater degree of minuteness, than that which was ascribed to the devils
+that tempted St. Anthony; of whom 20,000 were said to have been able to
+dance a saraband on the point of the finest needle without incommoding each
+other.
+
+2. Others have supposed, that all the parts of the embryon are formed in
+the male, previous to its being deposited in the egg or uterus; and that it
+is then only to have its parts evolved or distended as mentioned above; but
+this is only to get rid of one difficulty by proposing another equally
+incomprehensible: they found it difficult to conceive, how the embryon
+could be formed in the uterus or egg, and therefore wished it to be formed
+before it came thither. In answer to both these doctrines it may be
+observed, 1st, that some animals, as the crab-fish, can reproduce a whole
+limb, as a leg which has been broken off; others, as worms and snails, can
+reproduce a head, or a tail, when either of them has been cut away; and
+that hence in these animals at least a part can be formed anew, which
+cannot be supposed to have existed previously in miniature.
+
+Secondly, there are new parts or new vessels produced in many diseases, as
+on the cornea of the eye in ophthalmy, in wens and cancers, which cannot be
+supposed to have had a prototype or original miniature in the embryon.
+
+Thirdly, how could mule-animals be produced, which partake of the forms of
+both the parents, if the original embryon was a miniature existing in the
+semen of the male parent? if an embryon of the male ass was only expanded,
+no resemblance to the mare could exist in the mule.
+
+This mistaken idea of the extension of parts seems to have had its rise
+from the mature man resembling the general form of the fetus; and from
+thence it was believed, that the parts of the fetus were distended into the
+man; whereas they have increased 100 times in weight, as well as 100 times
+in size; now no one will call the additional 99 parts a distention of the
+original one part in respect to weight. Thus the uterus during pregnancy is
+greatly enlarged in thickness and solidity as well as in capacity, and
+hence must have acquired this additional size by accretion of new parts,
+not by an extension of the old ones; the familiar act of blowing up the
+bladder of an animal recently slaughtered has led our imaginations to apply
+this idea of distention to the increase of size from natural growth; which
+however must be owing to the apposition of new parts; as it is evinced from
+the increase of weight along with the increase of dimension; and is even
+visible to our eyes in the elongation of our hair from the colour of its
+ends; or when it has been dyed on the head; and in the growth of our nails
+from the specks sometimes observable on them; and in the increase of the
+white crescent at their roots, and in the growth of new flesh in wounds,
+which consists of new nerves as well as of new blood-vessels.
+
+3. Lastly, Mr. Buffon has with great ingenuity imagined the existence of
+certain organic particles, which are supposed to be partly alive, and
+partly mechanic springs. The latter of these were discovered by Mr. Needham
+in the milt or male organ of a species of cuttle fish, called calmar; the
+former, or living animalcula, are found in both male and female secretions,
+in the infusions of seeds, as of pepper, in the jelly of roasted veal, and
+in all other animal and vegetable substances. These organic particles he
+supposes to exist in the spermatic fluids of both sexes, and that they are
+derived thither from every part of the body, and must therefore resemble,
+as he supposes, the parts from whence they are derived. These organic
+particles he believes to be in constant activity, till they become mixed in
+the womb, and then they instantly join and produce an embryon or fetus
+similar to the two parents.
+
+Many objections might be adduced to this fanciful theory, I shall only
+mention two. First, that it is analogous to no known animal laws. And
+secondly, that as these fluids, replete with organic particles derived both
+from the male and female organs, are supposed to be similar; there is no
+reason why the mother should not produce a female embryon without the
+assistance of the male, and realize the lucina sine concubitu.
+
+IV. 1. I conceive the primordium, or rudiment of the embryon, as secreted
+from the blood of the parent, to consist of a simple living filament as a
+muscular fibre; which I suppose to be an extremity of a nerve of
+loco-motion, as a fibre of the retina is an extremity of a nerve of
+sensation; as for instance one of the fibrils, which compose the mouth of
+an absorbent vessel; I suppose this living filament, of whatever form it
+may be, whether sphere, cube, or cylinder, to be endued with the capability
+of being excited into action by certain kinds of stimulus. By the stimulus
+of the surrounding fluid, in which it is received from the male, it may
+bend into a ring; and thus form the beginning of a tube. Such moving
+filaments, and such rings, are described by those, who have attended to
+microscopic animalcula. This living ring may now embrace or absorb a
+nutritive particle of the fluid, in which it swims; and by drawing it into
+its pores, or joining it by compression to its extremities, may increase
+its own length or crassitude; and by degrees the living ring may become a
+living tube.
+
+2. With this new organization, or accretion of parts, new kinds of
+irritability may commence; for so long as there was but one living organ,
+it could only be supposed to possess irritability; since sensibility may be
+conceived to be an extension of the effect of irritability over the rest of
+the system. These new kinds of irritability and of sensibility in
+consequence of new organization, appear from variety of facts in the more
+mature animal; thus the formation of the testes, and consequent secretion
+of the semen, occasion the passion of lust; the lungs must be previously
+formed before their exertions to obtain fresh air can exist; the throat or
+oesophagus must be formed previous to the sensation or appetites of hunger
+and thirst; one of which seems to reside at the upper end, and the other at
+the lower end of that canal.
+
+Thus also the glans penis, when it is distended with blood, acquires a new
+sensibility, and a new appetency. The same occurs to the nipples of the
+breasts of female animals, when they are distended with blood, they acquire
+the new appetency of giving milk. So inflamed tendons and membranes, and
+even bones, acquire new sensations; and the parts of mutilated animals, as
+of wounded snails, and polypi, and crabs, are reproduced; and at the same
+time acquire sensations adapted to their situations. Thus when the head of
+a snail is reproduced after decollation with a sharp rasor, those curious
+telescopic eyes are also reproduced, and acquire their sensibility to
+light, as well as their adapted muscles for retraction on the approach of
+injury.
+
+With every new change, therefore, of organic form, or addition of organic
+parts, I suppose a new kind of irritability or of sensibility to be
+produced; such varieties of irritability or of sensibility exist in our
+adult state in the glands; every one of which is furnished with an
+irritability, or a taste, or appetency, and a consequent mode of action
+peculiar to itself.
+
+In this manner I conceive the vessels of the jaws to produce those of the
+teeth, those of the fingers to produce the nails, those of the skin to
+produce the hair; in the same manner as afterwards about the age of puberty
+the beard and other great changes in the form of the body, and disposition
+of the mind, are produced in consequence of the new secretion of semen; for
+if the animal is deprived of this secretion those changes do not take
+place. These changes I conceive to be formed not by elongation or
+distention of primeval stamina, but by apposition of parts; as the mature
+crab-fish, when deprived of a limb, in a certain space of time has power to
+regenerate it; and the tadpole puts forth its feet long after its exclusion
+from the spawn; and the caterpillar in changing into a butterfly acquires a
+new form, with new powers, new sensations, and new desires.
+
+The natural history of butterflies, and moths, and beetles, and gnats, is
+full of curiosity; some of them pass many months, and others even years, in
+their caterpillar or grub state; they then rest many weeks without food,
+suspended in the air, buried in the earth, or submersed in water; and
+change themselves during this time into an animal apparently of a different
+nature; the stomachs of some of them, which before digested vegetable
+leaves or roots, now only digest honey; they have acquired wings for the
+purpose of seeking this new food, and a long proboscis to collect it from
+flowers, and I suppose a sense of smell to detect the secret places in
+flowers, where it is formed. The moths, which fly by night, have a much
+longer proboscis rolled up under their chins like a watch spring; which
+they extend to collect the honey from flowers in their sleeping state; when
+they are closed, and the nectaries in consequence more difficult to be
+plundered. The beetle kind are furnished with an external covering of a
+hard material to their wings, that they may occasionally again make holes
+in the earth, in which they passed the former state of their existence.
+
+But what most of all distinguishes these new animals is, that they are new
+furnished with the powers of reproduction; and that they now differ from
+each other in sex, which does not appear in their caterpillar or grub
+state. In some of them the change from a caterpillar into a butterfly or
+moth seems to be accomplished for the sole purpose of their propagation;
+since they immediately die after this is finished, and take no food in the
+interim, as the silk-worm in this climate; though it is possible, it might
+take honey as food, if it was presented to it. For in general it would
+seem, that food of a more stimulating kind, the honey of vegetables instead
+of their leaves, was necessary for the purpose of the seminal reproduction
+of these animals, exactly similar to what happens in vegetables; in these
+the juices of the earth are sufficient for their purpose of reproduction by
+buds or bulbs; in which the new plant seems to be formed by irritative
+motions, like the growth of their other parts, as their leaves or roots;
+but for the purpose of seminal or amatorial reproduction, where sensation
+is required, a more stimulating food becomes necessary for the anther, and
+stigma; and this food is honey; as explained in Sect. XIII. on Vegetable
+Animation.
+
+The gnat and the tadpole resemble each other in their change from natant
+animals with gills into aerial animals with lungs; and in their change of
+the element in which they live; and probably of the food, with which they
+are supported; and lastly, with their acquiring in their new state the
+difference of sex, and the organs of seminal or amatorial reproduction.
+While the polypus, who is their companion in their former state of life,
+not being allowed to change his form and element, can only propagate like
+vegetable buds by the same kind of irritative motions, which produces the
+growth of his own body, without the seminal or amatorial propagation, which
+requires sensation; and which in gnats and tadpoles seems to require a
+change both of food and of respiration.
+
+From hence I conclude, that with the acquisition of new parts, new
+sensations, and new desires, as well as new powers, are produced; and this
+by accretion to the old ones, and not by distention of them. And finally,
+that the most essential parts of the system, as the brain for the purpose
+of distributing the power of life, and the placenta for the purpose of
+oxygenating the blood, and the additional absorbent vessels for the purpose
+of acquiring aliment, are first formed by the irritations above mentioned,
+and by the pleasurable sensations attending those irritations, and by the
+exertions in consequence of painful sensations, similar to those of hunger
+and suffocation. After these an apparatus of limbs for future uses, or for
+the purpose of moving the body in its present natant state, and of lungs
+for future respiration, and of testes for future reproduction, are formed
+by the irritations and sensations, and consequent exertions of the parts
+previously existing, and to which the new parts are to be attached.
+
+3. In confirmation of these ideas it may be observed, that all the parts of
+the body endeavour to grow, or to make additional parts to themselves
+throughout our lives; but are restrained by the parts immediately
+containing them; thus, if the skin be taken away, the fleshy parts beneath
+soon shoot out new granulations, called by the vulgar proud flesh. If the
+periosteum be removed, a similar growth commences from the bone. Now in the
+case of the imperfect embryon, the containing or confining parts are not
+yet supposed to be formed, and hence there is nothing to restrain its
+growth.
+
+4. By the parts of the embryon being thus produced by new apportions, many
+phenomena both of animal and vegetable productions receive an easier
+explanation; such as that many fetuses are deficient at the extremities, as
+in a finger or a toe, or in the end of the tongue, or in what is called a
+hare-lip with deficiency of the palate. For if there should be a deficiency
+in the quantity of the first nutritive particles laid up in the egg for the
+reception of the first living filament, the extreme parts, as being last
+formed, must shew this deficiency by their being imperfect.
+
+This idea of the growth of the embryon accords also with the production of
+some monstrous births, which consist of a duplicature of the limbs, as
+chickens with four legs; which could not occur, if the fetus was formed by
+the distention of an original stamen, or miniature. For if there should be
+a superfluity of the first nutritive particles laid up in the egg for the
+first living filament; it is easy to conceive, that a duplicature of some
+parts may be formed. And that such superfluous nourishment sometimes
+exists, is evinced by the double yolks in some eggs, which I suppose were
+thus formed previous to their impregnation by the exuberant nutriment of
+the hen.
+
+This idea is confirmed by the analogy of the monsters in the vegetable
+world also; in which a duplicate or triplicate production of various parts
+of the flower is observable, as a triple nectary in some columbines, and a
+triple petal in some primroses; and which are supposed to be produced by
+abundant nourishment.
+
+5. If the embryon be received into a fluid, whose stimulus is different in
+some degree from the natural, as in the production of mule-animals, the new
+irritabilities or sensibilities acquired by the increasing or growing
+organized parts may differ, and thence produce parts not similar to the
+father, but of a kind belonging in part to the mother; and thus, though the
+original stamen or living ens was derived totally from the father, yet new
+irritabilities or sensibilities being excited, a change of form
+corresponding with them will be produced. Nor could the production of mules
+exist, if the stamen or miniature of all the parts of the embryon is
+previously formed in the male semen, and is only distended by nourishment
+in the female uterus. Whereas this difficulty ceases, if the embryon be
+supposed to consist of a living filament, which acquires or makes new parts
+with new irritabilities, as it advances in its growth.
+
+The form, solidity, and colour, of the particles of nutriment laid up for
+the reception of the first living filament, as well as their peculiar kind
+of stimulus, may contribute to produce a difference in the form, solidity,
+and colour of the fetus, so as to resemble the mother, as it advances in
+life. This also may especially happen during the first state of the
+existence of the embryon, before it has acquired organs, which can change
+these first nutritive particles, as explained in No. 5. 2. of this Section.
+And as these nutritive particles are supposed to be similar to those, which
+are formed for her own nutrition, it follows that the fetus should so far
+resemble the mother.
+
+This explains, why hereditary diseases may be derived either from the male
+or female parent, as well as the peculiar form of either of their bodies.
+Some of these hereditary diseases are simply owing to a deficient activity
+of a part of the system, as of the absorbent vessels, which open into the
+cells or cavities of the body, and thus occasion dropsies. Others are at
+the same time owing to an increase of sensation, as in scrophula and
+consumption; in these the obstruction of the fluids is first caused by the
+inirritability of the vessels, and the inflammation and ulcers which
+succeed, are caused by the consequent increase of sensation in the
+obstructed part. Other hereditary diseases, as the epilepsy, and other
+convulsions, consist in too great voluntary exertions in consequence of
+disagreeable sensation in some particular diseased part. Now as the pains,
+which occasion these convulsions, are owing to defect of the action of the
+diseased part, as shewn in Sect. XXXIV. it is plain, that all these
+hereditary diseases may have their origin either from defective
+irritability derived from the father, or from deficiency of the stimulus of
+the nutriment derived from the mother. In either case the effect would be
+similar; as a scrophulous race is frequently produced among the poor from
+the deficient stimulus of bad diet, or of hunger; and among the rich, by a
+deficient irritability from their having been long accustomed to too great
+stimulus, as of vinous spirit.
+
+6. From this account of reproduction it appears, that all animals have a
+similar origin, viz. from a single living filament; and that the difference
+of their forms and qualities has arisen only from the different
+irritabilities and sensibilities, or voluntarities, or associabilities, of
+this original living filament; and perhaps in some degree from the
+different forms of the particles of the fluids, by which it has been at
+first stimulated into activity. And that from hence, as Linnæus has
+conjectured in respect to the vegetable world, it is not impossible, but
+the great variety of species of animals, which now tenant the earth, may
+have had their origin from the mixture of a few natural orders. And that
+those animal and vegetable mules, which could continue their species, have
+done so, and constitute the numerous families of animals and vegetables
+which now exist; and that those mules, which were produced with imperfect
+organs of generation, perished without reproduction, according to the
+observation of Aristotle; and are the animals, which we now call mules. See
+Botanic Garden, Part II. Note on Dianthus.
+
+Such a promiscuous intercourse of animals is said to exist at this day in
+New South Wales by Captain Hunter. And that not only amongst the quadrupeds
+and birds of different kinds, but even amongst the fish, and, as he
+believes, amongst the vegetables. He speaks of an animal between the
+opossum and the kangaroo, from the size of a sheep to that of a rat. Many
+fish seemed to partake of the shark; some with a shark's head and
+shoulders, and the hind part of a shark; others with a shark's head and the
+body of a mullet; and some with a shark's head and the flat body of a
+sting-ray. Many birds partake of the parrot; some have the head, neck, and
+bill of a parrot, with long straight feet and legs; others with legs and
+feet of a parrot, with head and neck of a sea gull. Voyage to South Wales
+by Captain John Hunter, p. 68.
+
+7. All animals therefore, I contend, have a similar cause of their
+organization, originating from a single living filament, endued indeed with
+different kinds of irritabilities and sensibilities, or of animal
+appetencies; which exist in every gland, and in every moving organ of the
+body, and are as essential to living organization as chemical affinities
+are to certain combinations of inanimate matter.
+
+If I might be indulged to make a simile in a philosophical work, I should
+say, that the animal appetencies are not only perhaps less numerous
+originally than the chemical affinities; but that like these latter, they
+change with every new combination; thus vital air and azote, when combined,
+produce nitrous acid; which now acquires the property of dissolving silver;
+so with every new additional part to the embryon, as of the throat or
+lungs, I suppose a new animal appetency to be produced.
+
+In this early formation of the embryon from the irritabilities,
+sensibilities, and associabilities, and consequent appetencies, the faculty
+of volition can scarcely be supposed to have had its birth. For about what
+can the fetus deliberate, when it has no choice of objects? But in the more
+advanced state of the fetus, it evidently possesses volition; as it
+frequently changes its attitude, though it seems to sleep the greatest part
+of its time; and afterwards the power of volition contributes to change or
+alter many parts of the body during its growth to manhood, by our early
+modes of exertion in the various departments of life. All these faculties
+then constitute the vis fabricatrix, and the vis conservatrix, as well as
+the vis medicatrix of nature, so much spoken of, but so little understood
+by philosophers.
+
+8. When we revolve in our minds, first, the great changes, which we see
+naturally produced in animals after their nativity, as in the production of
+the butterfly with painted wings from the crawling caterpillar; or of the
+respiring frog from the subnatant tadpole; from the feminine boy to the
+bearded man, and from the infant girl to the lactescent woman; both which
+changes may be prevented by certain mutilations of the glands necessary to
+reproduction.
+
+Secondly, when we think over the great changes introduced into various
+animals by artificial or accidental cultivation, as in horses, which we
+have exercised for the different purposes of strength or swiftness, in
+carrying burthens or in running races; or in dogs, which have been
+cultivated for strength and courage, as the bull-dog; or for acuteness of
+his sense or smell, as the hound and spaniel; or for the swiftness of his
+foot, as the greyhound; or for his swimming in the water, or for drawing
+snow-sledges, as the rough-haired dogs of the north; or lastly, as a
+play-dog for children, as the lap-dog; with the changes of the forms of the
+cattle, which have been domesticated from the greatest antiquity, as
+camels, and sheep; which have undergone so total a transformation, that we
+are now ignorant from what species of wild animals they had their origin.
+Add to these the great changes of shape and colour, which we daily see
+produced in smaller animals from our domestication of them, as rabbits, or
+pigeons; or from the difference of climates and even of seasons; thus the
+sheep of warm climates are covered with hair instead of wool; and the hares
+and partridges of the latitudes, which are long buried in snow, become
+white during the winter months; add to these the various changes produced
+in the forms of mankind, by their early modes of exertion; or by the
+diseases occasioned by their habits of life; both of which became
+hereditary, and that through many generations. Those who labour at the
+anvil, the oar, or the loom, as well as those who carry sedan-chairs, or
+who have been educated to dance upon the rope, are distinguishable by the
+shape of their limbs; and the diseases occasioned by intoxication deform
+the countenance with leprous eruptions, or the body with tumid viscera, or
+the joints with knots and distortions.
+
+Thirdly, when we enumerate the great changes produced in the species of
+animals before their nativity; these are such as resemble the form or
+colour of their parents, which have been altered by the cultivation or
+accidents above related, and are thus continued to their posterity. Or they
+are changes produced by the mixture of species as in mules; or changes
+produced probably by the exuberance of nourishment supplied to the fetus,
+as in monstrous births with additional limbs; many of these enormities of
+shape are propagated, and continued as a variety at least, if not as a new
+species of animal. I have seen a breed of cats with an additional claw on
+every foot; of poultry also with an additional claw, and with wings to
+their feet; and of others without rumps. Mr. Buffon mentions a breed of
+dogs without tails, which are common at Rome and at Naples, which he
+supposes to have been produced by a custom long established of cutting
+their tails close off. There are many kinds of pigeons, admired for their
+peculiarities, which are monsters thus produced and propagated. And to
+these must be added, the changes produced by the imagination of the male
+parent, as will be treated of more at large in No. VI. of this Section.
+
+When we consider all these changes of animal form, and innumerable others,
+which may be collected from the books of natural history; we cannot but be
+convinced, that the fetus or embryon is formed by apposition of new parts,
+and not by the distention of a primordial nest of germs, included one
+within another, like the cups of a conjurer.
+
+Fourthly, when we revolve in our minds the great similarity of structure,
+which obtains in all the warm-blooded animals, as well quadrupeds, birds,
+and amphibious animals, as in mankind; from the mouse and bat to the
+elephant and whale; one is led to conclude, that they have alike been
+produced from a similar living filament. In some this filament in its
+advance to maturity has acquired hands and fingers, with a fine sense of
+touch, as in mankind. In others it has acquired claws or talons, as in
+tygers and eagles. In others, toes with an intervening web, or membrane, as
+in seals and geese. In others it has acquired cloven hoofs, as in cows and
+swine; and whole hoofs in others, as in the horse. While in the bird kind
+this original living filament has put forth wings instead of arms or legs,
+and feathers instead of hair. In some it has protruded horns on the
+forehead instead of teeth in the fore part of the upper jaw; in others
+tushes instead of horns; and in others beaks instead of either. And all
+this exactly as is daily seen in the transmutations of the tadpole, which
+acquires legs and lungs, when he wants them; and loses his tail, when it is
+no longer of service to him.
+
+Fifthly, from their first rudiment, or primordium, to the termination of
+their lives, all animals undergo perpetual transformations; which are in
+part produced by their own exertions in consequence of their desires and
+aversions, of their pleasures and their pains, or of irritations, or of
+associations; and many of these acquired forms or propensities are
+transmitted to their posterity. See Sect. XXXI. 1.
+
+As air and water are supplied to animals in sufficient profusion, the three
+great objects of desire, which have changed the forms of many animals by
+their exertions to gratify them, are those of lust, hunger, and security. A
+great want of one part of the animal world has consisted in the desire of
+the exclusive possession of the females; and these have acquired weapons to
+combat each other for this purpose, as the very thick, shield-like, horny
+skin on the shoulder of the boar is a defence only against animals of his
+own species, who strike obliquely upwards, nor are his tushes for other
+purposes, except to defend himself, as he is not naturally a carnivorous
+animal. So the horns of the stag are sharp to offend his adversary, but are
+branched for the purpose of parrying or receiving the thrusts of horns
+similar to his own, and have therefore been formed for the purpose of
+combating other stags for the exclusive possession of the females; who are
+observed, like the ladies in the times of chivalry, to attend the car of
+the victor.
+
+The birds, which do not carry food to their young, and do not therefore
+marry, are armed with spurs for the purpose of fighting for the exclusive
+possession of the females, as cocks and quails. It is certain that these
+weapons are not provided for their defence against other adversaries,
+because the females of these species are without this armour. The final
+cause of this contest amongst the males seems to be, that the strongest and
+most active animal should propagate the species, which should thence become
+improved.
+
+Another great want consists in the means of procuring food, which has
+diversified the forms of all species of animals. Thus the nose of the swine
+has become hard for the purpose of turning up the soil in search of insects
+and of roots. The trunk of the elephant is an elongation of the nose for
+the purpose of pulling down the branches of trees for his food, and for
+taking up water without bending his knees. Beasts of prey have acquired
+strong jaws or talons. Cattle have acquired a rough tongue and a rough
+palate to pull off the blades of grass, as cows and sheep. Some birds have
+acquired harder beaks to crack nuts, as the parrot. Others have acquired
+beaks adapted to break the harder seeds, as sparrows. Others for the softer
+seeds of flowers, or the buds of trees, as the finches. Other birds have
+acquired long beaks to penetrate the moister soils in search of insects or
+roots, as woodcocks; and others broad ones to filtrate the water of lakes,
+and to retain aquatic insects. All which seem to have been gradually
+produced during many generations by the perpetual endeavour of the
+creatures to supply the want of food, and to have been delivered to their
+posterity with constant improvement of them for the purposes required.
+
+The third great want amongst animals is that of security, which seems much
+to have diversified the forms of their bodies and the colour of them; these
+consist in the means of escaping other animals more powerful than
+themselves. Hence some animals have acquired wings instead of legs, as the
+smaller birds, for the purpose of escape. Others great length of fin, or of
+membrane, as the flying fish, and the bat. Others great swiftness of foot,
+as the hare. Others have acquired hard or armed shells, as the tortoise and
+the echinus marinus.
+
+Mr. Osbeck, a pupil of Linnæus, mentions the American frog fish, Lophius
+Histrio, which inhabits the large floating islands of sea-weed about the
+Cape of Good Hope, and has fulcra resembling leaves, that the fishes of
+prey may mistake it for the sea-weed, which it inhabits. Voyage to China,
+p. 113.
+
+The contrivances for the purposes of security extend even to vegetables, as
+is seen in the wonderful and various means of their concealing or defending
+their honey from insects, and their seeds from birds. On the other hand
+swiftness of wing has been acquired by hawks and swallows to pursue their
+prey; and a proboscis of admirable structure has been acquired by the bee,
+the moth, and the humming bird, for the purpose of plundering the nectaries
+of flowers. All which seem to have been formed by the original living
+filament, excited into action by the necessities of the creatures, which
+possess them, and on which their existence depends.
+
+From thus meditating on the great similarity of the structure of the
+warm-blooded animals, and at the same time of the great changes they
+undergo both before and after their nativity; and by considering in how
+minute a portion of time many of the changes of animals above described
+have been produced; would it be too bold to imagine, that in the great
+length of time, since the earth began to exist, perhaps millions of ages
+before the commencement of the history of mankind, would it be too bold to
+imagine, that all warm-blooded animals have arisen from one living
+filament, which THE GREAT FIRST CAUSE endued with animality, with the power
+of acquiring new parts, attended with new propensities, directed by
+irritations, sensations, volitions, and associations; and thus possessing
+the faculty of continuing to improve by its own inherent activity, and of
+delivering down those improvements by generation to its posterity, world
+without end!
+
+Sixthly, The cold-blooded animals, as the fish-tribes, which are furnished
+with but one ventricle of the heart, and with gills instead of lungs, and
+with fins instead of feet or wings, bear a great similarity to each other;
+but they differ, nevertheless, so much in their general structure from the
+warm-blooded animals, that it may not seem probable at first view, that the
+same living filament could have given origin to this kingdom of animals, as
+to the former. Yet are there some creatures, which unite or partake of both
+these orders of animation, as the whales and seals; and more particularly
+the frog, who changes from an aquatic animal furnished with gills to an
+aerial one furnished with lungs.
+
+The numerous tribes of insects without wings, from the spider to the
+scorpion, from the flea to the lobster; or with wings, from the gnat and
+the ant to the wasp and the dragon-fly, differ so totally from each other,
+and from the red-blooded classes above described, both in the forms of
+their bodies, and their modes of life; besides the organ of sense, which
+they seem to possess in their antennæ or horns, to which it has been
+thought by some naturalists, that other creatures have nothing similar;
+that it can scarcely be supposed that this nation of animals could have
+been produced by the same kind of living filament, as the red-blooded
+classes above mentioned. And yet the changes which many of them undergo in
+their early state to that of their maturity, are as different, as one
+animal can be from another. As those of the gnat, which passes his early
+state in water, and then stretching out his new wings, and expanding his
+new lungs, rises in the air; as of the caterpillar, and bee-nymph, which
+feed on vegetable leaves or farina, and at length bursting from their
+self-formed graves, become beautiful winged inhabitants of the skies,
+journeying from flower to flower, and nourished by the ambrosial food of
+honey.
+
+There is still another class of animals, which are termed vermes by
+Linnæus, which are without feet, or brain, and are hermaphrodites, as
+worms, leeches, snails, shell-fish, coralline insects, and sponges; which
+possess the simplest structure of all animals, and appear totally different
+from those already described. The simplicity of their structure, however,
+can afford no argument against their having been produced from a living
+filament as above contended.
+
+Last of all the various tribes of vegetables are to be enumerated amongst
+the inferior orders of animals. Of these the anthers and stigmas have
+already been shewn to possess some organs of sense, to be nourished by
+honey, and to have the power of generation like insects, and have thence
+been announced amongst the animal kingdom in Sect. XIII. and to these must
+be added the buds and bulbs which constitute the viviparous offspring of
+vegetation. The former I suppose to be beholden to a single living filament
+for their seminal or amatorial procreation; and the latter to the same
+cause for their lateral or branching generation, which they possess in
+common with the polypus, tænia, and volvox; and the simplicity of which is
+an argument in favour of the similarity of its cause.
+
+Linnæus supposes, in the Introduction to his Natural Orders, that very few
+vegetables were at first created, and that their numbers were increased by
+their intermarriages, and adds, suadent hæc Creatoris leges a simplicibus
+ad composita. Many other changes seem to have arisen in them by their
+perpetual contest for light and air above ground, and for food or moisture
+beneath the soil. As noted in Botanic Garden, Part II. Note on Cuscuta.
+Other changes of vegetables from climate, or other causes, are remarked in
+the Note on Curcuma in the same work. From these one might be led to
+imagine, that each plant at first consisted of a single bulb or flower to
+each root, as the gentianella and daisy; and that in the contest for air
+and light new buds grew on the old decaying flower stem, shooting down
+their elongated roots to the ground, and that in process of ages tall trees
+were thus formed, and an individual bulb became a swarm of vegetables.
+Other plants, which in this contest for light and air were too slender to
+rise by their own strength, learned by degrees to adhere to their
+neighbours, either by putting forth roots like the ivy, or by tendrils like
+the vine, or by spiral contortions like the honeysuckle; or by growing upon
+them like the misleto, and taking nourishment from their barks; or by only
+lodging or adhering on them, and deriving nourishment from the air, as
+tillandsia.
+
+Shall we then say that the vegetable living filament was originally
+different from that of each tribe of animals above described? And that the
+productive living filament of each of those tribes was different originally
+from the other? Or, as the earth and ocean were probably peopled with
+vegetable productions long before the existence of animals; and many
+families of these animals long before other families of them, shall we
+conjecture that one and the same kind of living filaments is and has been
+the cause of all organic life?
+
+This idea of the gradual formation and improvement of the animal world
+accords with the observations of some modern philosophers, who have
+supposed that the continent of America has been raised out of the ocean at
+a later period of time than the other three quarters of the globe, which
+they deduce from the greater comparative heights of its mountains, and the
+consequent greater coldness of its respective climates, and from the less
+size and strength of its animals, as the tygers and allegators compared
+with those of Asia or Africa. And lastly, from the less progress in the
+improvements of the mind of its inhabitants in respect to voluntary
+exertions.
+
+This idea of the gradual formation and improvement of the animal world
+seems not to have been unknown to the ancient philosophers. Plato having
+probably observed the reciprocal generation of inferior animals, as snails
+and worms, was of opinion, that mankind with all other animals were
+originally hermaphrodites during the infancy of the world, and were in
+process of time separated into male and female. The breasts and teats of
+all male quadrupeds, to which no use can be now assigned, adds perhaps some
+shadow of probability to this opinion. Linnæus excepts the horse from the
+male quadrupeds, who have teats; which might have shewn the earlier origin
+of his exigence; but Mr. J. Hunter asserts, that he has discovered the
+vestiges of them on his sheath, and has at the same time enriched natural
+history with a very curious fact concerning the male pigeon; at the time of
+hatching the eggs both the male and female pigeon undergo a great change in
+their crops; which thicken and become corrugated, and secrete a kind of
+milky fluid, which coagulates, and with which alone they for a few days
+feed their young, and afterwards feed them with this coagulated fluid mixed
+with other food. How this resembles the breasts of female quadrupeds after
+the production of their young! and how extraordinary, that the male should
+at this time give milk as well as the female! See Botanic Garden, Part II.
+Note on Curcuma.
+
+The late Mr. David Hume, in his posthumous works, places the powers of
+generation much above those of our boasted reason; and adds, that reason
+can only make a machine, as a clock or a ship, but the power of generation
+makes the maker of the machine; and probably from having observed, that the
+greatest part of the earth has been formed out of organic recrements; as
+the immense beds of limestone, chalk, marble, from the shells of fish; and
+the extensive provinces of clay, sandstone, ironstone, coals, from
+decomposed vegetables; all which have been first produced by generation, or
+by the secretions of organic life; he concludes that the world itself might
+have been generated, rather than created; that is, it might have been
+gradually produced from very small beginnings, increasing by the activity
+of its inherent principles, rather than by a sudden evolution of the whole
+by the Almighty fire.--What a magnificent idea of the infinite power of THE
+GREAT ARCHITECT! THE CAUSE OF CAUSES! PARENT OF PARENTS! ENS ENTIUM!
+
+For if we may compare infinities, it would seem to require a greater
+infinity of power to cause the causes of effects, than to cause the effects
+themselves. This idea is analogous to the improving excellence observable
+in every part of the creation; such as in the progressive increase of the
+solid or habitable parts of the earth from water; and in the progressive
+increase of the wisdom and happiness of its inhabitants; and is consonant
+to the idea of our present situation being a state of probation, which by
+our exertions we may improve, and are consequently responsible for our
+actions.
+
+V. 1. The efficient cause of the various colours of the eggs of birds, and
+of the air and feathers of animals, is a subject so curious, that I shall
+beg to introduce it in this place. The colours of many animals seem adapted
+to their purposes of concealing themselves either to avoid danger, or to
+spring upon their prey. Thus the snake and wild cat, and leopard, are so
+coloured as to resemble dark leaves and their lighter interstices; birds
+resemble the colour of the brown ground, or the green hedges, which they
+frequent; and moths and butterflies are coloured like the flowers which
+they rob of their honey. Many instances are mentioned of this kind in
+Botanic Garden, p. 2. Note on Rubia.
+
+These colours have, however, in some instances another use, as the black
+diverging area from the eyes of the swan; which, as his eyes are placed
+less prominent than those of other birds, for the convenience of putting
+down his head under water, prevents the rays of light from being reflected
+into his eye, and thus dazzling his sight, both in air and beneath the
+water; which must have happened, if that surface had been white like the
+rest of his feathers.
+
+There is a still more wonderful thing concerning these colours adapted to
+the purpose of concealment; which is, that the eggs of birds are so
+coloured as to resemble the colour of the adjacent objects and their
+interfaces. The eggs of hedge-birds are greenish with dark spots; those of
+crows and magpies, which are seen from beneath through wicker nests, are
+white with dark spots; and those of larks and partridges are russet or
+brown, like their nests or situations.
+
+A thing still more astonishing is, that many animals in countries covered
+with snow become white in winter, and are said to change their colour again
+in the warmer months, as bears, hares, and partridges. Our domesticated
+animals lose their natural colours, and break into great variety, as
+horses, dogs, pigeons. The final cause of these colours is easily
+understood, as they serve some purposes of the animal, but the efficient
+cause would seem almost beyond conjecture.
+
+First, the choroid coat of the eye, on which the semitransparent retina is
+expanded, is of different colour in different animals; in those which feed
+on grass it is green; from hence there would appear some connexion between
+the colour of the choroid coat and of that constantly painted on the retina
+by the green grass. Now, when the ground becomes covered with snow, it
+would seem, that that action of the retina, which is called whiteness,
+being constantly excited in the eye, may be gradually imitated by the
+extremities of the nerves of touch, or rete mucosum of the skin. And if it
+be supposed, that the action of the retina in producing the perception of
+any colour consists in so disposing its own fibres or surface, as to
+reflect those coloured rays only, and transmit the others like
+soap-bubbles; then that part of the retina, which gives us the perception
+of snow, must at that time be white; and that which gives us the perception
+of grass, must be green.
+
+Then if by the laws of imitation, as explained in Section XII. 3. 3. and
+XXXIX. 6. the extremities of the nerves of touch in the rete mucosum be
+induced into similar action, the skin or feathers, or hair, may in like
+manner so dispose their extreme fibres, as to reflect white; for it is
+evident, that all these parts were originally obedient to irritative
+motions during their growth, and probably continue to be so; that those
+irritative motions are not liable in a healthy state to be succeeded by
+sensation; which however is no uncommon thing in their diseased state, or
+in their infant state, as in plica polonica, and in very young
+pen-feathers, which are still full of blood.
+
+It was shewn in Section XV. on the Production of Ideas, that the moving
+organ of sense in some circumstances resembled the object which produced
+that motion. Hence it may be conceived, that the rete mucosum, which is the
+extremity of the nerves of touch, may by imitating the motions of the
+retina become coloured. And thus, like the fable of the camelion, all
+animals may possess a tendency to be coloured somewhat like the colours
+they most frequently inspect, and finally, that colours may be thus given
+to the egg-shell by the imagination of the female parent; which shell is
+previously a mucous membrane, indued with irritability, without which it
+could not circulate its fluids, and increase in its bulk. Nor is this more
+wonderful than that a single idea of imagination mould in an instant colour
+the whole surface of the body of a bright scarlet, as in the blush of
+shame, though by a very different process. In this intricate subject
+nothing but loose analogical conjectures can be had, which may however lead
+to future discoveries; but certain it is that both the change of the colour
+of animals to white in the winters of snowy countries, and the spots on
+birds eggs, must have some efficient cause; since the uniformity of their
+production shews it cannot arise from a fortuitous concurrence of
+circumstances; and how is this efficient cause to be detected, or
+explained, but from its analogy to other animal facts?
+
+2. The nutriment supplied by the female parent in viviparous animals to
+their young progeny may be divided into three kinds, corresponding with the
+age of the new creature. 1. The nutriment contained in the ovum as
+previously prepared for the embryon in the ovary. 2. The liquor amnii
+prepared for the fetus in the uterus, and in which it swims; and lastly,
+the milk prepared in the pectoral glands for the new born-child. There is
+reason to conclude that variety of changes may be produced in the new
+animal from all these sources of nutriment, but particularly from the first
+of them..
+
+The organs of digestion and of sanguification in adults, and afterwards
+those of secretion, prepare or separate the particles proper for
+nourishment from other combinations of matter, or recombine them into new
+kinds of matter, proper to excite into action the filaments, which absorb
+or attract them by animal appetency. In this process we must attend not
+only to the action of the living filament which receives a nutritive
+particle to its bosom, but also to the kind of particle, in respect to
+form, or size, or colour, or hardness, which is thus previously prepared
+for it by digestion, sanguification, and secretion. Now as the first
+filament of entity cannot be furnished with the preparative organs above
+mentioned, the nutritive particles, which are at first to be received by
+it, are prepared by the mother; and deposited in the ovum ready for its
+reception. These nutritive particles must be supposed to differ in some
+respects, when thus prepared by different animals. They may differ in size,
+solidity, colour, and form; and yet may be sufficiently congenial to the
+living filament, to which they are applied, as to excite its activity by
+their stimulus, and its animal appetency to receive them, and to combine
+them with itself into organization.
+
+By this first nutriment thus prepared for the embryon is not meant the
+liquor amnii, which is produced afterwards, nor the larger exterior parts
+of the white of the egg; but the fluid prepared, I suppose, in the ovary of
+viviparous animals, and that which immediately surrounds the cicatricula of
+an impregnated egg, and is visible to the eye in a boiled one.
+
+Now these ultimate particles of animal matter prepared by the glands of the
+mother may be supposed to resemble the similar ultimate particles, which
+were prepared for her own nourishment; that is, to the ultimate particles
+of which her own organization consists. And that hence when these become
+combined with a new embryon, which in its early state is not furnished with
+stomach, or glands, to alter them; that new embryon will bear some
+resemblance to the mother.
+
+This seems to be the origin of the compound forms of mules, which evidently
+partake of both parents, but principally of the male parent. In this
+production of chimeras the antients seem to have indulged their fancies,
+whence the sphinxes, griffins, dragons, centaurs, and minotaurs, which are
+vanished from modern credulity.
+
+It would seem, that in these unnatural conjunctions, when the nutriment
+deposited by the female was so ill adapted to stimulate the living filament
+derived from the male into action, and to be received; or embraced by it,
+and combined with it into organization, as not to produce the organs
+necessary to life, as the brain, or heart, or stomach, that no mule was
+produced. Where all the parts necessary to life in these compound animals
+were formed sufficiently perfect, except the parts of generation, those
+animals were produced which are now called mules.
+
+The formation of the organs of sexual generation, in contradistinction to
+that by lateral buds, in vegetables, and in some animals, as the polypus,
+the tænia, and the volvox, seems the chef d'oeuvre, the master-piece of
+nature; as appears from many flying insects, as in moths and butterflies,
+who seem to undergo a general change of their forms solely for the purpose
+of sexual reproduction, and in all other animals this organ is not complete
+till the maturity of the creature. Whence it happens that, in the
+copulation of animals of different species, the parts necessary to life are
+frequently completely formed; but those for the purpose of generation are
+defective, as requiring a nicer organization; or more exact coincidence of
+the particles of nutriment to the irritabilities or appetencies of the
+original living filament. Whereas those mules, where all the parts could be
+perfectly formed, may have been produced in early periods of time, and may
+have added to the numbers of our various species of animals, as before
+observed.
+
+As this production of mules is a constant effect from the conjunction of
+different species of animals, those between the horse and the female ass
+always resembling the horse more than the ass; and those, on the contrary,
+between the male ass and the mare, always resembling the ass more than the
+mare; it cannot be ascribed to the imagination of the male animal which
+cannot be supposed to operate so uniformly; but to the form of the first
+nutritive particles, and to their peculiar stimulus exciting the living
+filament to select and combine them with itself. There is a similar
+uniformity of effect in respect to the colour of the progeny produced
+between a white man, and a black woman, which, if I am well informed, is
+always of the mulatto kind, or a mixture of the two; which may perhaps be
+imputed to the peculiar form of the particles of nutriment supplied to the
+embryon by the mother at the early period of its existence, and their
+peculiar stimulus; as this effect, like that of the mule progeny above
+treated of, is uniform and consistent, and cannot therefore be ascribed to
+the imagination of either of the parents.
+
+Dr. Thunberg observes, in his Journey to the Cape of Good Hope, that there
+are some families, which have descended from blacks in the female line for
+three generations. The first generation proceeding from an European, who
+married a tawny slave, remains tawny, but approaches to a white complexion;
+but the children of the third generation, mixed with Europeans, become
+quite white, and are often remarkably beautiful. V. i. p. 112.
+
+When the embryon has produced a placenta, and furnished itself with vessels
+for selection of nutritious particles, and for oxygenation of them, no
+great change in its form or colour is likely to be produced by the
+particles of sustenance it now takes from the fluid, in which it is
+immersed; because it has now acquired organs to alter or new combine them.
+Hence it continues to grow, whether this fluid, in which it swims, be
+formed by the uterus or by any other cavity of the body, as in
+extra-uterine gestation; and which would seem to be produced by the
+stimulus of the fetus on the sides of the cavity, where it is found, as
+mentioned before. And thirdly, there is still less reason to expect any
+unnatural change to happen to the child after its birth from the difference
+of the milk it now takes; because it has acquired a stomach, and lungs, and
+glands, of sufficient power to decompose and recombine the milk; and thus
+to prepare from it the various kinds of nutritious particles, which the
+appetencies of the various fibrils or nerves may require.
+
+From all this reasoning I would conclude, that though the imagination of
+the female may be supposed to affect the embryon by producing a difference
+in its early nutriment; yet that no such power can affect it after it has
+obtained a placenta, and other organs; which may select or change the food,
+which is presented to it either in the liquor amnii, or in the milk. Now as
+the eggs in pullets, like the seeds in vegetables, are produced gradually,
+long before they are impregnated, it does not appear how any sudden effect
+of imagination of the mother at the time of impregnation can produce any
+considerable change in the nutriment already thus laid up for the expected
+or desired embryon. And that hence any changes of the embryon, except those
+uniform ones in the production of mules and mulattoes, more probably depend
+on the imagination of the male parent. At the same time it seems manifest,
+that those monstrous births, which consist in some deficiencies only, or
+some redundancies of parts, originate from the deficiency or redundance of
+the first nutriment prepared in the ovary, or in the part of the egg
+immediately surrounding the cicatricula, as described above; and which
+continues some time to excite the first living filament into action, after
+the simple animal is completed; or ceases to excite it, before the complete
+form is accomplished. The former of these circumstances is evinced by the
+eggs with double yolks, which frequently happen to our domesticated
+poultry, and which, I believe, are so formed before impregnation, but which
+would be well worth attending to, both before and after impregnation; as it
+is probable, something valuable on this subject might be learnt from them.
+The latter circumstance, or that of deficiency of original nutriment, may
+be deduced from reverse analogy.
+
+There are, however, other kinds of monstrous births, which neither depend
+on deficiency of parts, or supernumerary ones; nor are owing to the
+conjunction of animals of different species; but which appear to be new
+conformations, or new dispositions of parts in respect to each other, and
+which, like the variation of colours and forms of our domesticated animals,
+and probably the sexual parts of all animals, may depend on the imagination
+of the male parent, which we now come to consider.
+
+VI. 1. The nice actions of the extremities of our various glands are
+exhibited in their various productions, which are believed to be made by
+the gland, and not previously to exist as such in the blood.
+
+Thus the glands, which constitute the liver, make bile; those of the
+stomach make gastric acid; those beneath the jaw, saliva; those of the
+ears, ear-wax; and the like. Every kind of gland must possess a peculiar
+irritability, and probably a sensibility, at the early state of its
+existence; and must be furnished with a nerve of sense, or of motion, to
+perceive, and to select, and to combine the particles, which compose the
+fluid it secretes. And this nerve of sense which perceives the different
+articles which compose the blood, must at least be conceived to be as fine
+and subtile an organ, as the optic or auditory nerve, which perceive light
+or sound. See Sect. XIV. 9.
+
+But in nothing is this nice action of the extremities of the blood-vessels
+so wonderful, as in the production of contagious matter. A small drop of
+variolous contagion diffused in the blood, or perhaps only by being
+inserted beneath the cuticle, after a time, (as about a quarter of a
+lunation,) excites the extreme vessels of the skin into certain motions,
+which produce a similar contagious material, filling with it a thousand
+pustules. So that by irritation, or by sensation in consequence of
+irritation, or by association of motions, a material is formed by the
+extremities of certain cutaneous vessels, exactly similar to the
+stimulating material, which caused the irritation, or consequent sensation,
+or association.
+
+Many glands of the body have their motions, and in consequence their
+secreted fluids, affected by pleasurable or painful ideas, since they are
+in many instances influenced by sensitive associations, as well as by the
+irritations of the particles of the passing blood. Thus the idea of meat,
+excited in the minds of hungry dogs, by their sense of vision, or of smell,
+increases the discharge of saliva, both in quantity and viscidity; as is
+seen in its hanging down in threads from their mouths, as they stand round
+a dinner-table. The sensations of pleasure, or of pain, of peculiar kinds,
+excite in the same manner a great discharge of tears; which appear also to
+be more saline at the time of their secretion, from their inflaming the
+eyes and eye-lids. The paleness from fear, and the blush of shame, and of
+joy, are other instances of the effects of painful, or pleasurable
+sensations, on the extremities of the arterial system.
+
+It is probable, that the pleasurable sensation excited in the stomach by
+food, as well as its irritation, contributes to excite into action the
+gastric glands, and to produce a greater secretion of their fluids. The
+same probably occurs in the secretion of bile; that is, that the
+pleasurable sensation excited in the stomach, affects this secretion by
+sensitive association, as well as by irritative association.
+
+And lastly it would seem, that all the glands in the body have their
+secreted fluids affected, in quantity and quality, by the pleasurable or
+painful sensations, which produce or accompany those secretions. And that
+the pleasurable sensations arising from these secretions may constitute the
+unnamed pleasure of exigence, which is contrary to what is meant by tedium
+vitæ, or ennui; and by which we sometimes feel ourselves happy, without
+being able to ascribe it to any mental cause, as after an agreeable meal,
+or in the beginning of intoxication.
+
+Now it would appear, that no secretion or excretion of fluid is attended
+with so much agreeable sensation, as that of the semen; and it would thence
+follow, that the glands, which perform this secretion, are more likely to
+be much affected by their catenations with pleasurable sensations. This
+circumstance is certain, that much more of this fluid is produced in a
+given time, when the object of its exclusion is agreeable to the mind.
+
+2. A forceable argument, which shews the necessity of pleasurable sensation
+to copulation, is, that the act cannot be performed without it; it is
+easily interrupted by the pain of fear or bashfulness; and no efforts of
+volition or of irritation can effect this process, except such as induce
+pleasurable ideas or sensations. See Sect. XXXIII. 1. 1.
+
+A curious analogical circumstance attending hermaphrodite insects, as
+snails and worms, still further illustrates this theory; if the snail or
+worm could have impregnated itself, there might have been a saving of a
+large male apparatus; but as this is not so ordered by nature, but each
+snail and worm reciprocally receives and gives impregnation, it appears,
+that a pleasurable excitation seems also to have been required.
+
+This wonderful circumstance of many insects being hermaphrodites, and at
+the same time not having power to impregnate themselves, is attended to by
+Dr. Lister, in his Exercitationes Anatom. de Limacibus, p. 145; who,
+amongst many other final causes, which he adduces to account for it, adds,
+ut tam tristibus et frigidis animalibus majori cum voluptate perficiatur
+venus.
+
+There is, however, another final cause, to which this circumstance may be
+imputed: it was observed above, that vegetable buds and bulbs, which are
+produced without a mother, are always exact resemblances of their parent;
+as appears in grafting fruit-trees, and in the flower-buds of the dioiceous
+plants, which are always of the same sex on the same tree; hence those
+hermaphrodite insects, if they could have produced young without a mother,
+would not have been, capable of that change or improvement, which is seen
+in all other animals, and in those vegetables, which are procreated by the
+male embryon received and nourished by the female. And it is hence
+probable, that if vegetables could only have been produced by buds and
+bulbs, and not by sexual generation, that there would not at this time have
+existed one thousandth part of their present number of species; which have
+probably been originally mule-productions; nor could any kind of
+improvement or change have happened to them, except by the difference of
+soil or climate.
+
+3. I conclude, that the imagination of the male at the time of copulation,
+or at the time of the secretion of the semen, may so affect this secretion
+by irritative or sensitive association, as described in No. 5. 1. of this
+section, as to cause the production of similarity of form and of features,
+with the distinction of sex; as the motions of the chissel of the turner
+imitate or correspond with those of the ideas of the artist. It is not here
+to be understood, that the first living fibre, which is to form an animal,
+is produced with any similarity of form to the future animal; but with
+propensities, or appetences, which shall produce by accretion of parts the
+similarity of form, feature, or sex, corresponding to the imagination of
+the father.
+
+Our ideas are movements of the nerves of sense, as of the optic nerve in
+recollecting visible ideas, suppose of a triangular piece of ivory. The
+fine moving fibres of the retina act in a manner to which I give the name
+of white; and this action is confined to a defined part of it; to which
+figure I give the name of triangle. And it is a preceding pleasurable
+sensation existing in my mind, which occasions me to produce this
+particular motion of the retina, when no triangle is present. Now it is
+probable, that the acting fibres of the ultimate terminations of the
+secreting apertures of the vessels of the testes, are as fine as those of
+the retina; and that they are liable to be thrown into that peculiar
+action, which marks the sex of the secreted embryon, by sympathy with the
+pleasurable motions of the nerves of vision or of touch; that is, with
+certain ideas of imagination. From hence it would appear, that the world
+has long been mistaken in ascribing great power to the imagination of the
+female, whereas from this account of it, the real power of imagination, in
+the act of generation, belongs solely to the male. See Sect. XII. 3. 3.
+
+It may be objected to this theory, that a man may be supposed to have in
+his mind, the idea of the form and features of the female, rather than his
+own, and therefore there should be a greater number of female births. On
+the contrary, the general idea of our own form occurs to every one almost
+perpetually, and is termed consciousness of our existence, and thus may
+effect, that the number of males surpasses that of females. See Sect. XV.
+3. 4. and XVIII. 13. And what further confirms this idea is, that the male
+children most frequently resemble the father in form, or feature, as well
+as in sex; and the female most frequently resemble the mother, in feature,
+and form, as well as in sex.
+
+It may again be objected, if a female child sometimes resembles the father,
+and a male child the mother, the ideas of the father, at the time of
+procreation, must suddenly change from himself to the mother, at the very
+instant, when the embryon is secreted or formed. This difficulty ceases
+when we consider, that it is as easy to form an idea of feminine features
+with male organs of reproduction, or of male features with female ones, as
+the contrary; as we conceive the idea of a sphinx or mermaid as easily and
+as distinctly as of a woman. Add to this, that at the time of procreation
+the idea of the male organs, and of the female features, are often both
+excited at the same time, by contact, or by vision.
+
+I ask, in my turn, is the sex of the embryon produced by accident?
+Certainly whatever is produced has a cause; but when this cause is too
+minute for our comprehension, the effect is said in common language to
+happen by chance, as in throwing a certain number on dice. Now what cause
+can occasionally produce the male or female character of the embryon, but
+the peculiar actions of those glands, which form the embryon? And what can
+influence or govern these actions of the gland, but its associations or
+catenations with other sensitive motions? Nor is this more extraordinary,
+than that the catenations of irritative motions with the apparent
+vibrations of objects at sea should produce sickness of the stomach; or
+that a nauseous story should occasion vomiting.
+
+4. An argument, which evinces the effect of imagination on the first
+rudiment of the embryon, may be deduced from the production of some
+peculiar monsters. Such, for instance, as those which have two heads joined
+to one body, and those which have two bodies joined to one head; of which
+frequent examples occur amongst our domesticated quadrupeds, and poultry.
+It is absurd to suppose, that such forms could exist in primordial germs,
+as explained in No. IV. 4. of this section. Nor is it possible, that such
+deformities could be produced by the growth of two embryons, or living
+filaments; which should afterwards adhere together; as the head and tail
+part of different polypi are said to do (Blumenbach on Generation, Cadel,
+London); since in that case one embryon, or living filament, must have
+begun to form one part first, and the other another part first. But such
+monstrous conformations become less difficult to comprehend, when they are
+considered as an effect of the imagination, as before explained, on the
+living filament at the time of its secretion; and that such duplicature of
+limbs were produced by accretion of new parts, in consequence of
+propensities, or animal appetencies thus acquired from the male parent.
+
+For instance, I can conceive, if a turkey-cock should behold a rabbit, or a
+frog, at the time of procreation, that it might happen, that a forcible or
+even a pleasurable idea of the form of a quadruped might so occupy his
+imagination, as to cause a tendency in the nascent filament to resemble
+such a form, by the apposition of a duplicature of limbs. Experiments on
+the production of mules and monsters would be worthy the attention of a
+Spallanzani, and might throw much light upon this subject, which at present
+must be explained by conjectural analogies.
+
+The wonderful effect of imagination, both in the male and female parent, is
+shewn in the production of a kind of milk in the crops both of the male and
+female pigeons after the birth of their young, as observed by Mr. Hunter,
+and mentioned before. To this should be added, that there are some
+instances of men having had milk secreted in their breasts, and who have
+given suck to children, as recorded by Mr. Buffon. This effect of
+imagination, of both the male and female parent, seems to have been
+attended to in very early times; Jacob is said not only to have placed rods
+of trees, in part stripped of their bark, so as to appear spotted, but also
+to have placed spotted lambs before the flocks, at the time of their
+copulation. Genesis, chap. xxx. verse 40.
+
+5. In respect to the imagination of the mother, it is difficult to
+comprehend, how this can produce any alteration in the fetus, except by
+affecting the nutriment laid up for its first reception, as described in
+No. V. 2. of this section, or by affecting the nourishment or oxygenation
+with which she supplies it afterwards. Perpetual anxiety may probably
+affect the secretion of the liquor amnii into the uterus, as it enfeebles
+the whole system; and sudden fear is a frequent cause of miscarriage; for
+fear, contrary to joy, decreases for a time the action of the extremities
+of the arterial system; hence sudden paleness succeeds, and a shrinking or
+contraction of the vessels of the skin, and other membranes. By this
+circumstance, I imagine, the terminations of the placental vessels are
+detached from their adhesions, or insertions, into the membrane of the
+uterus; and the death of the child succeeds, and consequent miscarriage.
+
+Of this I recollect a remarkable instance, which could be ascribed to no
+other cause, and which I shall therefore relate in few words. A healthy
+young woman, about twenty years of age, had been about five months
+pregnant, and going down into her cellar to draw some beer, was frighted by
+a servant boy starting up from behind the barrel, where he had concealed
+himself with design to alarm the maid-servant, for whom he mistook his
+mistress. She came with difficulty up stairs, began to flood immediately,
+and miscarried in a few hours. She has since borne several children, nor
+ever had any tendency to miscarry of any of them.
+
+6. In respect to the power of the imagination of the male over the form,
+colour, and sex of the progeny, the following instances have fallen under
+my observation, and may perhaps be found not very unfrequent, if they were
+more attended to. I am acquainted with a gentleman, who has one child with
+dark hair and eyes, though his lady and himself have light hair and eyes;
+and their other four children are like their parents. On observing this
+dissimilarity of one child to the others he assured me, that he believed it
+was his own imagination, that produced the difference; and related to me
+the following story. He said, that when his lady lay in of her third child,
+he became attached to a daughter of one of his inferior tenants, and
+offered her a bribe for her favours in vain; and afterwards a greater
+bribe, and was equally unsuccessful; that the form of this girl dwelt much
+in his mind for some weeks, and that the next child, which was the
+dark-ey'd young lady above mentioned, was exceedingly like, in both
+features and colour, to the young woman who refused his addresses.
+
+To this instance I must add, that I have known two families, in which, on
+account of an intailed estate in expectation, a male heir was most eagerly
+desired by the father; and on the contrary, girls were produced to the
+seventh in one, and to the ninth in another; and then they had each of them
+a son. I conclude, that the great desire of a male heir by the father
+produced rather a disagreeable than an agreeable sensation; and that his
+ideas dwelt more on the fear of generating a female, than on the
+pleasurable sensations or ideas of his own male form or organs at the time
+of copulation, or of the secretion of the semen; and that hence the idea of
+the female character was more present to his mind than that of the male
+one; till at length in despair of generating a male these ideas ceased, and
+those of the male character presided at the genial hour.
+
+7. Hence I conclude, that the act of generation cannot exist without being
+accompanied with ideas, and that a man must have at that time either a
+general idea of his own male form, or of the form of his male organs; or an
+idea of the female form, or of her organs; and that this marks the sex, and
+the peculiar resemblances of the child to either parent. From whence it
+would appear, that the phalli, which were hung round the necks of the Roman
+ladies, or worn in their hair, might have effect in producing a greater
+proportion of male children; and that the calipædia, or art of begetting
+beautiful children, and of procreating either males or females, may be
+taught by affecting the imagination of the male-parent; that is, by the
+fine extremities of the seminal glands, imitating the actions of the organs
+of sense either of sight or touch. But the manner of accomplishing this
+cannot be unfolded with sufficient delicacy for the public eye; but may be
+worth the attention of those, who are seriously interested in the
+procreation of a male or female child.
+
+_Recapitulation._
+
+VII. 1. A certain quantity of nutritive particles are produced by the
+female parent before impregnation, which require no further digestion,
+secretion, or oxygenation. Such are seen in the unimpregnated eggs of
+birds, and in the unimpregnated seed-vessels of vegetables.
+
+2. A living filament is produced by the male, which being inserted amidst
+these first nutritive particles, is stimulated into action by them; and in
+consequence of this action, some of the nutritive particles are embraced,
+and added to the original living filament; in the same manner as common
+nutrition is performed in the adult animal.
+
+3. Then this new organization, or additional part, becomes stimulated by
+the nutritive particles in its vicinity, and sensation is now superadded to
+irritation; and other particles are in consequence embraced, and added to
+the living filament; as is seen in the new granulations of flesh in ulcers.
+
+By the power of association, or by irritation, the parts already produced
+continue their motions, and new ones are added by sensation, as above
+mentioned; and lastly by volition, which last sensorial power is proved to
+exist in the fetus in its maturer age, because it has evidently periods of
+activity and of sleeping; which last is another word for a temporary
+suspension of volition.
+
+The original living filament may be conceived to possess a power of
+repulsing the particles applied to certain parts of it, as well as of
+embracing others, which stimulate other parts of it; as these powers exist
+in different parts of the mature animal; thus the mouth of every gland
+embraces the particles or fluid, which suits its appetency; and its
+excretory duct repulses those particles, which are disagreeable to it.
+
+4. Thus the outline or miniature of the new animal is produced gradually,
+but in no great length of time; because the original nutritive particles
+require no previous preparation by digestion, secretion, and oxygenation:
+but require simply the selection and apposition, which is performed by the
+living filament. Mr. Blumenbach says, that he possesses a human fetus of
+only five weeks old, which is the size of a common bee, and has all the
+features of the face, every finger, and every toe, complete; and in which
+the organs of generation are distinctly seen. P. 76. In another fetus,
+whose head was not larger than a pea, the whole of the basis of the skull
+with all its depressions, apertures, and processes, were marked in the most
+sharp and distinct manner, though without any ossification. Ib.
+
+5. In some cases by the nutriment originally deposited by the mother the
+filament acquires parts not exactly similar to those of the father, as in
+the production of mules and mulattoes. In other cases, the deficiency of
+this original nutriment causes deficiencies of the extreme parts of the
+fetus, which are last formed, as the fingers, toes, lips. In other cases, a
+duplicature of limbs are caused by the superabundance of this original
+nutritive fluid, as in the double yolks of eggs, and the chickens from them
+with four legs and four wings. But the production of other monsters, as
+those with two heads, or with parts placed in wrong situations, seems to
+arise from the imagination of the father being in some manner imitated by
+the extreme vessels of the seminal glands; as the colours of the spots on
+eggs, and the change of the colour of the hair and feathers of animals by
+domestication, may be caused in the same manner by the imagination of the
+mother.
+
+6. The living filament is a part of the father, and has therefore certain
+propensities, or appetencies, which belong to him; which may have been
+gradually acquired during a million of generations, even from the infancy
+of the habitable earth; and which now possesses such properties, as would
+render, by the apposition of nutritious particles, the new fetus exactly
+similar to the father; as occurs in the buds and bulbs of vegetables, and
+in the polypus, and tænia or tape-worm. But as the first nutriment is
+supplied by the mother, and therefore resembles such nutritive particles,
+as have been used for her own nutriment or growth, the progeny takes in
+part of the likeness of the mother.
+
+Other similarity of the excitability, or of the form of the male parent,
+such as the broad or narrow shoulders, or such as constitute certain
+hereditary diseases, as scrophula, epilepsy, insanity, have their origin
+produced in one or perhaps two generations; as in the progeny of those who
+drink much vinous spirits; and those hereditary propensities cease again,
+as I have observed, if one or two sober generations succeed; otherwise the
+family becomes extinct.
+
+This living filament from the father is also liable to have its
+propensities, or appetencies, altered at the time of its production by the
+imagination of the male parent; the extremities of the seminal glands
+imitating the motions of the organs of sense; and thus the sex of the
+embryon is produced; which may be thus made a male or a female by affecting
+the imagination of the father at the time of impregnation. See Sect. XXXIX.
+6. 3. and 7.
+
+7. After the fetus is thus completely formed together with its umbilical
+vessels and placenta, it is now supplied with a different kind of food, as
+appears by the difference of consistency of the different parts of the
+white of the egg, and of the liquor amnii, for it has now acquired organs
+for digestion or secretion, and for oxygenation, though they are as yet
+feeble; which can in some degree change, as well as select, the nutritive
+particles, which are now presented to it. But may yet be affected by the
+deficiency of the quantity of nutrition supplied by the mother, or by the
+degree of oxygenation supplied to its placenta by the maternal blood.
+
+The augmentation of the complete fetus by additional particles of nutriment
+is not accomplished by distention only, but by apposition to every part
+both external and internal; each of which acquires by animal appetencies
+the new addition of the particles which it wants. And hence the enlarged
+parts are kept similar to their prototypes, and may be said to be extended;
+but their extension must be conceived only as a necessary consequence of
+the enlargement of all their parts by apposition of new particles.
+
+Hence the new apposition of parts is not produced by capillary attraction,
+because the whole is extended; whereas capillary attraction would rather
+tend to bring the sides of flexible tubes together, and not to distend
+them. Nor is it produced by chemical affinities, for then a solution of
+continuity would succeed, as when sugar is dissolved in water; but it is
+produced by an animal process, which is the consequence of irritation, or
+sensation; and which may be termed animal appetency.
+
+This is further evinced from experiments, which have been instituted to
+shew, that a living muscle of an animal body requires greater force to
+break it, than a similar muscle of a dead body. Which evinces, that besides
+the attraction of cohesion, which all matter possesses, and besides the
+chemical attractions of affinities, which hold many bodies together, there
+is an animal adhesion, which adds vigour to these common laws of the
+inanimate world.
+
+8. At the nativity of the child it deposits the placenta or gills, and by
+expanding its lungs acquires more plentiful oxygenation from the currents
+of air, which it must now continue perpetually to respire to the end of its
+life; as it now quits the liquid element, in which it was produced, and
+like the tadpole, when it changes into a frog, becomes an aerial animal.
+
+9. As the habitable parts of the earth have been, and continue to be,
+perpetually increasing by the production of sea-shells and corallines, and
+by the recrements of other animals, and vegetables; so from the beginning
+of the existence of this terraqueous globe, the animals, which inhabit it,
+have constantly improved, and are still in a state of progressive
+improvement.
+
+This idea of the gradual generation of all things seems to have been as
+familiar to the ancient philosophers as to the modern ones; and to have
+given rise to the beautiful hieroglyphic figure of the [Greek: proton ôon],
+or first great egg, produced by NIGHT, that is, whose origin is involved in
+obscurity, and animated by [Greek: eros], that is, by DIVINE LOVE; from
+whence proceeded all things which exist.
+
+_Conclusion._
+
+VIII. 1. Cause and effect may be considered as the progression, or
+successive motions, of the parts of the great system of Nature. The state
+of things at this moment is the effect of the state of things, which
+existed in the preceding moment; and the cause of the state of things,
+which shall exist in the next moment.
+
+These causes and effects may be more easily comprehended, if motion be
+considered as a change of the figure of a group of bodies, as proposed in
+Sect. XIV. 2. 2. inasmuch as our ideas of visible or tangible objects are
+more distinct, than our abstracted ideas of their motions. Now the change
+of the configuration of the system of nature at this moment must be an
+effect of the preceding configuration, for a change of configuration cannot
+exist without a previous configuration; and the proximate cause of every
+effect must immediately precede that effect. For example, a moving ivory
+ball could not proceed onwards, unless it had previously began to proceed;
+or unless an impulse had been previously given it; which previous motion or
+impulse constitutes a part of the last situation of things.
+
+As the effects produced in this moment of time become causes in the next,
+we may consider the progressive motions of objects as a chain of causes
+only; whose first link proceeded from the great Creator, and which have
+existed from the beginning of the created universe, and are perpetually
+proceeding.
+
+2. These causes may be conveniently divided into two kinds, efficient and
+inert causes, according with the two kinds of entity supposed to exist in
+the natural world, which may be termed matter and spirit, as proposed in
+Sect. I. and further treated of in Sect. XIV. The efficient causes of
+motion, or new configuration, consist either of the principle of general
+gravitation, which actuates the sun and planets; or of the principle of
+particular gravitation, as in electricity, magnetism, heat; or of the
+principle of chemical affinity, as in combustion, fermentation,
+combination; or of the principle of organic life, as in the contraction of
+vegetable and animal fibres. The inert causes of motion, or new
+configuration, consist of the parts of matter, which are introduced within
+the spheres of activity of the principles above described. Thus, when an
+apple falls on the ground, the principle of gravitation is the efficient
+cause, and the matter of the apple the inert cause. If a bar of iron be
+approximated to a magnet, it may be termed the inert cause of the motion,
+which brings these two bodies into contact; while the magnetic principle
+may be termed the efficient cause. In the same manner the fibres, which
+constitute the retina, may be called the inert cause of the motions of that
+organ in vision, while the sensorial power may be termed the efficient
+cause.
+
+3. Another more common distribution of the perpetual chain of causes and
+effects, which constitute the motions, or changing configurations, of the
+natural world, is into active and passive. Thus, if a ball in motion
+impinges against another ball at rest, and communicates its motion to it,
+the former ball is said to act, and the latter to be acted upon. In this
+sense of the words a magnet is said to attract iron; and the prick of a
+spur to stimulate a horse into exertion; so that in this view of the works
+of nature all things may be said either simply to exist, or to exist as
+causes, or to exist as effects; that is, to exist either in an active or
+passive state.
+
+This distribution of objects, and their motions, or changes of position,
+has been found so convenient for the purposes of common life, that on this
+foundation rests the whole construction or theory of language. The names of
+the things themselves are termed by grammarians Nouns, and their modes of
+existence are termed Verbs. The nouns are divided into substantives, which
+denote the principal things spoken of; and into adjectives, which denote
+some circumstances, or less kinds of things, belonging to the former. The
+verbs are divided into three kinds, such as denote the existence of things
+simply, as, to be; or their existence in an active state, as, to eat; or
+their existence in a passive state, as, to be eaten. Whence it appears,
+that all languages consist only of nouns and verbs, with their
+abbreviations for the greater expedition of communicating our thoughts; as
+explained in the ingenious work of Mr. Horne Tooke, who has unfolded by a
+single flash of light the whole theory of language, which had so long lain
+buried beneath the learned lumber of the schools. Diversions of Purley.
+Johnson. London.
+
+4. A third division of causes has been into proximate and remote; these
+have been much spoken of by the writers on medical subjects, but without
+sufficient precision. If to proximate and remote causes we add proximate
+and remote effects, we shall include four links of the perpetual chain of
+causation; which will be more convenient for the discussion of many
+philosophical subjects.
+
+Thus if a particle of chyle be applied to the mouth of a lacteal vessel, it
+may be termed the remote cause of the motions of the fibres, which compose
+the mouth of that lacteal vessel; the sensorial power is the proximate
+cause; the contraction of the fibres of the mouth of the vessel is the
+proximate effect; and their embracing the particle of chyle is the remote
+effect; and these four links of causation constitute absorption.
+
+Thus when we attend to the rising sun, first the yellow rays of light
+stimulate the sensorial power residing in the extremities of the optic
+nerve, this is the remote cause. 2. The sensorial power is excited into a
+state of activity, this is the proximate cause. 3. The fibrous extremities
+of the optic nerve are contracted, this is the proximate effect. 4. A
+pleasurable or painful sensation is produced in consequence of the
+contraction of these fibres of the optic nerve, this is the remote effect;
+and these four links of the chain of causation constitute the sensitive
+idea, or what is commonly termed the sensation of the rising sun.
+
+5. Other causes have been announced by medical writers under the names of
+causa procatarctica, and causa proegumina, and causa sine quâ non. All
+which are links more or less distant of the chain of remote causes.
+
+To these must be added the final cause, so called by many authors, which
+means the motive, for the accomplishment of which the preceding chain of
+causes was put into action. The idea of a final cause, therefore, includes
+that of a rational mind, which employs means to effect its purposes; thus
+the desire of preserving himself from the pain of cold, which he has
+frequently experienced, induces the savage to construct his hut; the fixing
+stakes into the ground for walls, branches of trees for rafters, and turf
+for a cover, are a series of successive voluntary exertions; which are so
+many means to produce a certain effect. This effect of preserving himself
+from cold, is termed the final cause; the construction of the hut is the
+remote effect; the action of the muscular fibres of the man, is the
+proximate effect; the volition, or activity of desire to preserve himself
+from cold, is the proximate cause; and the pain of cold, which excited that
+desire, is the remote cause.
+
+6. This perpetual chain of causes and effects, whose first link is rivetted
+to the throne of GOD, divides itself into innumerable diverging branches,
+which, like the nerves arising from the brain, permeate the most minute and
+most remote extremities of the system, diffusing motion and sensation to
+the whole. As every cause is superior in power to the effect, which it has
+produced, so our idea of the power of the Almighty Creator becomes more
+elevated and sublime, as we trace the operations of nature from cause to
+cause, climbing up the links of these chains of being, till we ascend to
+the Great Source of all things.
+
+Hence the modern discoveries in chemistry and in geology, by having traced
+the causes of the combinations of bodies to remoter origins, as well as
+those in astronomy, which dignify the present age, contribute to enlarge
+and amplify our ideas of the power of the Great First Cause. And had those
+ancient philosophers, who contended that the world was formed from atoms,
+ascribed their combinations to certain immutable properties received from
+the hand of the Creator, such as general gravitation, chemical affinity, or
+animal appetency, instead of ascribing them to a blind chance; the doctrine
+of atoms, as constituting or composing the material world by the variety of
+their combinations, so far from leading the mind to atheism, would
+strengthen the demonstration of the existence of a Deity, as the first
+cause of all things; because the analogy resulting from our perpetual
+experience of cause and effect would have thus been exemplified through
+universal nature.
+
+_The heavens declare the glory of _GOD_, and the firmament sheweth his
+handywork! One day telleth another, and one night certifieth another; they
+have neither speech nor language, yet their voice is gone forth into all
+lands, and their words into the ends of the world. Manifold are thy works,
+_O LORD!_ in wisdom hast thou made them all._ Psal. xix. civ.
+
+       *       *       *       *       *
+
+SECT. XL.
+
+    On the OCULAR SPECTRA of Light and Colours, by Dr. R. W. Darwin, of
+    Shrewsbury. Reprinted, by Permission, from the Philosophical
+    Transactions, Vol. LXXVI. p. 313.
+
+    _Spectra of four kinds._ 1. _Activity of the retina in vision._ 2.
+    _Spectra from defect of sensibility._ 3. _Spectra from excess of
+    sensibility_. 4. _Of direct ocular spectra._ 5. _Greater stimulus
+    excites the retina into spasmodic action._ 6. _Of reverse ocular
+    spectra._ 7. _Greater stimulus excites the retina into various
+    successive spasmodic actions._ 8. _Into fixed spasmodic action._ 9.
+    _Into temporary paralysis._ 10. _Miscellaneous remarks;_ 1. _Direct and
+    reverse spectra at the same time. A spectral halo. Rule to predetermine
+    the colours of spectra._ 2. _Variation of spectra from extraneous
+    light._ 3. _Variation of spectra in number, figure, and remission._ 4.
+    _Circulation of the blood in the eye is visible._ 5. _A new way of
+    magnifying objects. Conclusion._
+
+When any one has long and attentively looked at a bright object, as at the
+setting sun, on closing his eyes, or removing them, an image, which
+resembles in form the object he was attending to, continues some time to be
+visible; this appearance in the eye we shall call the ocular spectrum of
+that object.
+
+These ocular spectra are of four kinds: 1st, Such as are owing to a less
+sensibility of a defined part of the retina; or _spectra from defect of
+sensibility._ 2d, Such as are owing to a greater sensibility of a defined
+part of the retina; or _spectra from excess of sensibility_. 3d, Such as
+resemble their object in its colour as well as form; which may be termed
+_direct ocular spectra_. 4th, Such as are of a colour contrary to that of
+their object; which may be termed _reverse ocular spectra_.
+
+The laws of light have been most successfully explained by the great
+Newton, and the perception of visible objects has been ably investigated by
+the ingenious Dr. Berkeley and M. Malebranche; but these minute phenomena
+of vision have yet been thought reducible to no theory, though many
+philosophers have employed a considerable degree of attention upon them:
+among these are Dr. Jurin, at the end of Dr. Smith's Optics; M. Æpinus, in
+the Nov. Com. Petropol. V. 10.; M. Beguelin, in the Berlin Memoires, V. II.
+1771; M. d'Arcy, in the Histoire de l'Acad. des Scienc. 1765; M. de la
+Hire; and, lastly, the celebrated M. de Buffon, in the Memoires de l'Acad.
+des Scien. who has termed them accidental colours, as if subjected to no
+established laws, Ac. Par. 1743. M. p. 215.
+
+I must here apprize the reader, that it is very difficult for different
+people to give the same names to various shades of colours; whence, in the
+following pages, something must be allowed, if on repeating the experiments
+the colours here mentioned should not accurately correspond with his own
+names of them.
+
+I. _Activity of the Retina in Vision._
+
+From the subsequent experiments it appears, that the retina is in an active
+not in a passive state during the existence of these ocular spectra; and it
+is thence to be concluded, that all vision is owing to the activity of this
+organ.
+
+1. Place a piece of red silk, about an inch in diameter, as in plate 1, at
+Sect. III. 1., on a sheet of white paper, in a strong light; look steadily
+upon it from about the distance of half a yard for a minute; then closing
+your eyelids cover them with your hands, and a green spectrum will be seen
+in your eyes, resembling in form the piece of red silk: after some time,
+this spectrum will disappear and shortly reappear; and this alternately
+three or four times, if the experiment is well made, till at length it
+vanishes entirely.
+
+2. Place on a sheet of white paper a circular piece of blue silk, about
+four inches in diameter, in the sunshine; cover the center of this with a
+circular piece of yellow silk, about three inches in diameter; and the
+center of the yellow silk with a circle of pink silk, about two inches in
+diameter; and the center of the pink silk with a circle of green silk,
+about one inch in diameter; and the centre of this with a circle of indigo,
+about half an inch in diameter; make a small speck with ink in the very
+center of the whole, as in plate 3, at Sect. III. 3. 6.; look steadily for
+a minute on this central spot, and then closing your eyes, and applying
+your hand at about an inch distance before them, so as to prevent too much
+or too little light from passing through the eyelids, you will see the most
+beautiful circles of colours that imagination can conceive, which are most
+resembled by the colours occasioned by pouring a drop or two of oil on a
+still lake in a bright day; but these circular irises of colours are not
+only different from the colours of the silks above mentioned, but are at
+the same time perpetually changing as long as they exist.
+
+3. When any one in the dark presses either corner of his eye with his
+finger, and turns his eye away from his finger, he will see a circle of
+colours like those in a peacock's tail: and a sudden flash of light is
+excited in the eye by a stroke on it. (Newton's Opt. Q. 16.)
+
+4. When any one turns round rapidly on one foot, till he becomes dizzy, and
+falls upon the ground, the spectra of the ambient objects continue to
+present themselves in rotation, or appear to librate, and he seems to
+behold them for some time still in motion.
+
+From all these experiments it appears, that the spectra in the eye are not
+owing to the mechanical impulse of light impressed on the retina, nor to
+its chemical combination with that organ, nor to the absorption and
+emission of light, as is observed in many bodies; for in all these cases
+the spectra must either remain uniformly, or gradually diminish; and
+neither their alternate pretence and evanescence as in the first
+experiment, nor the perpetual changes of their colours as in the second,
+nor the flash of light or colours in the pressed eye as in the third, nor
+the rotation or libration of the spectra as in the fourth, could exist.
+
+It is not absurd to conceive, that the retina may be stimulated into
+motion, as well as the red and white muscles which form our limbs and
+vessels; since it consists of fibres, like those, intermixed with its
+medullary substance. To evince this structure, the retina of an ox's eye
+was suspended in a glass of warm water, and forcibly torn in a few places;
+the edges of these parts appeared jagged and hairy, and did not contract,
+and become smooth like simple mucus, when it is distended till it breaks;
+which shews that it consists of fibres; and that its fibrous construction
+became still more distinct to the sight, by adding some caustic alkali to
+the water, as the adhering mucus was first eroded, and the hair-like fibres
+remained floating in the vessel. Nor does the degree of transparency of the
+retina invalidate the evidence of its fibrous structure, since Leeuwenhoek
+has shewn that the crystalline humour itself consists of fibres. (Arcana
+Naturæ, V. 1. p. 70.)
+
+Hence it appears, that as the muscles have larger fibres intermixed with a
+smaller quantity of nervous medulla, the organ of vision has a greater
+quantity of nervous medulla intermixed with smaller fibres; and it is
+probable that the locomotive muscles, as well as the vascular ones, of
+microscopic animals have much greater tenuity than these of the retina.
+
+And besides the similar laws, which will be shewn in this paper to govern
+alike the actions of the retina and of the muscles, there are many other
+analogies which exist between them. They are both originally excited into
+action by irritations, both are nearly in the same quantity of time, are
+alike strengthened or fatigued by exertion, are alike painful if excited
+into action when they are in an inflamed state, are alike liable to
+paralysis, and to the torpor of old age.
+
+II. OF SPECTRA FROM DEFECT OF SENSIBILITY.
+
+    _The retina is not so easily excited into action by less irritation
+    after having been lately subjected to greater._
+
+1. When any one passes from the bright daylight into a darkened room, the
+irises of his eyes expand themselves to their utmost extent in a few
+seconds of time; but it is very long before the optic nerve, after having
+been stimulated by the greater light of the day, becomes sensible of the
+less degree of it in the room; and, if the room is not too obscure, the
+irises will again contract themselves in some degree, as the sensibility of
+the retina returns.
+
+2. Place about half an inch square of white paper on a black hat, and
+looking steadily on the center of it for a minute, remove your eyes to a
+sheet of white paper; and after a second or two a dark square will be seen
+on the white paper, which will continue some time. A similar dark square
+will be seen in the closed eye, if light be admitted through the eyelids.
+
+So after looking at any luminous object of a small size, as at the sun, for
+a short time, so as not much to fatigue the eyes, this part of the retina
+becomes less sensible to smaller quantities of light; hence, when the eyes
+are turned on other less luminous parts of the sky, a dark spot is seen
+resembling the shape of the sun, or other luminous object which we last
+beheld. This is the source of one kind of the dark-coloured _muscæ
+volitantes_. If this dark spot lies above the center of the eye, we turn
+our eyes that way, expecting to bring it into the center of the eye, that
+we may view it more distinctly; and in this case the dark spectrum seems to
+move upwards. If the dark spectrum is found beneath the centre of the eye,
+we pursue it from the same motive, and it seems to move downwards. This has
+given rise to various conjectures of something floating in the aqueous
+humours of the eyes; but whoever, in attending to these spots, keeps his
+eyes unmoved by looking steadily at the corner of a cloud, at the same time
+that he observes the dark spectra, will be thoroughly convinced, that they
+have no motion but what is given to them by the movement of our eyes in
+pursuit of them. Sometimes the form of the spectrum, when it has been
+received from a circular luminous body, will become oblong; and sometimes
+it will be divided into two circular spectra, which is not owing to our
+changing the angle made by the two optic axises, according to the distance
+of the clouds or other bodies to which the spectrum is supposed to be
+contiguous, but to other causes mentioned in No. X. 3. of this section. The
+apparent size of it will also be variable according to its supposed
+distance.
+
+As these spectra are more easily observable when our eyes are a little
+weakened by fatigue, it has frequently happened, that people of delicate
+constitutions have been much alarmed at them, fearing a beginning decay of
+their sight, and have thence fallen into the hands of ignorant oculists;
+but I believe they never are a prelude to any other disease of the eye, and
+that it is from habit alone, and our want of attention to them, that we do
+not see them on all objects every hour of our lives. But as the nerves of
+very weak people lose their sensibility, in the same manner as their
+muscles lose their activity, by a small time of exertion, it frequently
+happens, that sick people in the extreme debility of fevers are perpetually
+employed in picking something from the bed-clothes, occasioned by their
+mistaking the appearance of these _muscæ volitantes_ in their eyes.
+Benvenuto Celini, an Italian artist, a man of strong abilities, relates,
+that having passed the whole night on a distant mountain with some
+companions and a conjurer, and performed many ceremonies to raise the
+devil, on their return in the morning to Rome, and looking up when the sun
+began to rise, they saw numerous devils run on the tops of the houses, as
+they passed along; so much were the spectra of their weakened eyes
+magnified by fear, and made subservient to the purposes of fraud or
+superstition. (Life of Ben. Celini.)
+
+3. Place a square inch of white paper on a large piece of straw-coloured
+silk; look steadily some time on the white paper, and then move the centre
+of your eyes on the silk, and a spectrum of the form of the paper will
+appear on the silk, of a deeper yellow than the other part of it: for the
+central part of the retina, having been some time exposed to the stimulus
+of a greater quantity of white light, is become less sensible to a smaller
+quantity of it, and therefore sees only the yellow rays in that part of the
+straw-coloured silk.
+
+Facts similar to these are observable in other parts of our system: thus,
+if one hand be made warm, and the other exposed to the cold, and then both
+of them immersed in subtepid water, the water is perceived warm to one
+hand, and cold to the other; and we are not able to hear weak sounds for
+some time after we have been exposed to loud ones; and we feel a chilliness
+on coming into an atmosphere of temperate warmth, after having been some
+time confined in a very warm room: and hence the stomach, and other organs
+of digestion, of those who have been habituated to the greater stimulus of
+spirituous liquor, are not excited into their due action by the less
+stimulus of common food alone; of which the immediate consequence is
+indigestion and hypochondriacism.
+
+III. OF SPECTRA FROM EXCESS OF SENSIBILITY.
+
+    _The retina is more easily excited into action by greater irritation
+    after having been lately subjected to less._
+
+1. If the eyes are closed, and covered perfectly with a hat, for a minute
+or two, in a bright day; on removing the hat a red or crimson light is seen
+through the eyelids. In this experiment the retina, after being some time
+kept in the dark, becomes so sensible to a small quantity of light, as to
+perceive distinctly the greater quantity of red rays than of others which
+pass through the eyelids. A similar coloured light is seen to pass through
+the edges of the fingers, when the open hand is opposed to the flame of a
+candle.
+
+2. If you look for some minutes steadily on a window in the beginning of
+the evening twilight, or in a dark day, and then move your eyes a little,
+so that those parts of the retina, on which the dark frame-work of the
+window was delineated, may now fall on the glass part of it, many luminous
+lines, representing the frame-work, will appear to lie across the glass
+panes: for those parts of the retina, which were before least stimulated by
+the dark frame-work, are now more sensible to light than the other parts of
+the retina which were exposed to the more luminous parts of the window,
+
+3. Make with ink on white paper a very black spot, about half an inch in
+diameter, with a tail about an inch in length, so as to represent a
+tadpole, as in plate 2, at Sect. III. 3. 3.; look steadily for a minute on
+this spot, and, on moving the eye a little, the figure of the tadpole will
+be seen on the white part of the paper, which figure of the tadpole will
+appear whiter or more luminous than the other parts of the white paper; for
+the part of the retina on which the tadpole was delineated, is now more
+sensible to light, than the other parts of it, which were exposed to the
+white paper. This experiment is mentioned by Dr. Irwin, but is not by him
+ascribed to the true cause, namely, the greater sensibility of that part of
+the retina which has been exposed to the black spot, than of the other
+parts which had received the white field of paper, which is put beyond a
+doubt by the next experiment.
+
+4. On closing the eyes after viewing the black spot on the white paper, as
+in the foregoing experiment, a red spot is seen of the form of the black
+spot: for that part of the retina, on which the black spot was delineated,
+being now more sensible to light than the other parts of it, which were
+exposed to the white paper, is capable of perceiving the red rays which
+penetrate the eyelids. If this experiment be made by the light of a tallow
+candle, the spot will be yellow instead of red; for tallow candles abound
+much with yellow light, which passes in greater quantity and force through
+the eyelids than blue tight; hence the difficulty of distinguishing blue
+and green by this kind of candle light. The colour of the spectrum may
+possibly vary in the daylight, according to the different colour of the
+meridian or the morning or evening light.
+
+M. Beguelin, in the Berlin Memoires, V. II. 1771, observes, that, when he
+held a book so that the sun shone upon his half-closed eyelids, the black
+letters, which he had long inspected, became red, which must have been thus
+occasioned. Those parts of the retina which had received for some time the
+black letters, were so much more sensible than those parts which had been
+opposed to the white paper, that to the former the red light, which passed
+through the eyelids, was perceptible. There is a similar story told, I
+think, in de Voltaire's Historical Works, of a Duke of Tuscany, who was
+playing at dice with the general of a foreign army, and, believing he saw
+bloody spots upon the dice, portended dreadful events, and retired in
+confusion. The observer, after looking for a minute on the black spots of a
+die, and carelessly closing his eyes, on a bright day; would see the image
+of a die with red spots upon it, as above explained.
+
+5. On emerging from a dark cavern, where we have long continued, the light
+of a bright day becomes intolerable to the eye for a considerable time,
+owing to the excess of sensibility existing in the eye, after having been
+long exposed to little or no stimulus. This occasions us immediately to
+contract the iris to its smallest aperture, which becomes again gradually
+dilated, as the retina becomes accustomed to the greater stimulus of the
+daylight.
+
+The twinkling of a bright star, or of a distant candle in the night, is
+perhaps owing to the same cause. While we continue to look upon these
+luminous objects, their central parts gradually appear paler, owing to the
+decreasing sensibility of the part of the retina exposed to their light;
+whilst, at the same time, by the unsteadiness of the eye, the edges of them
+are perpetually falling on parts of the retina that were just before
+exposed to the darkness of the night, and therefore tenfold more sensible
+to light than the part on which the star or candle had been for some time
+delineated. This pains the eye in a similar manner as when we come suddenly
+from a dark room into bright daylight, and gives the appearance of bright
+scintillations. Hence the stars twinkle most when the night is darkest, and
+do not twinkle through telescopes, as observed by Musschenbroeck; and it
+will afterwards be seen why this twinkling is sometimes of different
+colours when the object is very bright, as Mr. Melvill observed in looking
+at Sirius. For the opinions of others on this subject, see Dr. Priestley's
+valuable History of Light and Colours, p. 494.
+
+Many facts observable in the animal system are similar to these; as the hot
+glow occasioned by the usual warmth of the air, or our clothes, on coming
+out of a cold bath; the pain of the fingers on approaching the fire after
+having handled snow; and the inflamed heels from walking in snow. Hence
+those who have been exposed to much cold have died on being brought to a
+fire, or their limbs have become so much inflamed as to mortify. Hence much
+food or wine given suddenly to those who have almost perished by hunger has
+destroyed them; for all the organs of the famished body are now become so
+much more irritable to the stimulus of food and wine, which they have long
+been deprived of, that inflammation is excited, which terminates in
+gangrene or fever.
+
+IV. OF DIRECT OCULAR SPECTRA.
+
+    _A quantity of stimulus somewhat greater than natural excites the
+    retina into spasmodic action, which ceases in a few seconds._
+
+A certain duration and energy of the stimulus of light and colours excites
+the perfect action of the retina in vision; for very quick motions are
+imperceptible to us, as well as very slow ones, as the whirling of a top,
+or the shadow on a sun-dial. So perfect darkness does not affect the eye at
+all; and excess of light produces pain, not vision.
+
+1. When a fire-coal is whirled round in the dark, a lucid circle remains a
+considerable time in the eye; and that with so much vivacity of light, that
+it is mistaken for a continuance of the irritation of the object. In the
+same manner, when a fiery meteor shoots across the night, it appears to
+leave a long lucid train behind it, part of which, and perhaps sometimes
+the whole, is owing to the continuance of the action of the retina after
+having been thus vividly excited. This is beautifully illustrated by the
+following experiment: fix a paper sail, three or four inches in diameter,
+and made like that of a smoke jack, on a tube of pasteboard; on looking
+through the tube at a distant prospect, some disjointed parts of it will be
+seen through the narrow intervals between the sails; but as the fly begins
+to revolve, these intervals appear larger; and when it revolves quicker,
+the whole prospect is seen quite as distinct as if nothing intervened,
+though less luminous.
+
+[Illustration: Fig. 3.]
+
+2. Look through a dark tube, about half a yard long, at the area of a
+yellow circle of half an inch diameter, lying upon a blue area of double
+that diameter, for half a minute; and on closing your eyes the colours of
+the spectrum will appear similar to the two areas, as in fig. 3.; but if
+the eye is kept too long upon them, the colours of the spectrum will be the
+reverse of those upon the paper, that is, the internal circle will become
+blue, and the external area yellow; hence some attention is required in
+making this experiment.
+
+3. Place the bright flame of a spermaceti candle before a black object in
+the night; look steadily at it for a short time, till it is observed to
+become somewhat paler; and on closing the eyes, and covering them
+carefully, but not so as to compress them, the image of the blazing candle
+will continue distinctly to be visible.
+
+4. Look steadily, for a short time, at a window in a dark day, as in Exp.
+2. Sect. III. and then closing your eyes, and covering them with your
+hands, an exact delineation of the window remains for some time visible in
+the eye. This experiment requires a little practice to make it succeed
+well; since, if the eyes are fatigued by looking too long on the window, or
+the day be too bright, the luminous parts of the window will appear dark in
+the spectrum, and the dark parts of the frame-work will appear luminous, as
+in Exp. 2. Sect. III. And it is even difficult for many, who first try this
+experiment, to perceive the spectrum at all; for any hurry of mind, or even
+too great attention to the spectrum itself, will disappoint them, till they
+have had a little experience in attending to such small sensations.
+
+The spectra described in this section, termed direct ocular spectra, are
+produced without much fatigue of the eye; the irritation of the luminous
+object being soon withdrawn, or its quantity of light being not so great as
+to produce any degree of uneasiness in the organ of vision; which
+distinguishes them from the next class of ocular spectra, which are the
+consequence of fatigue. These direct spectra are best observed in such
+circumstances that no light, but what comes from the object, can fall upon
+the eye; as in looking through a tube, of half a yard long, and an inch
+wide, at a yellow paper on the side of a room, the direct spectrum was
+easily produced on closing the eye without taking it from the tube; but if
+the lateral light is admitted through the eyelids, or by throwing the
+spectrum on white paper, it becomes a reverse spectrum, as will be
+explained below.
+
+The other senses also retain for a time the impressions that have been made
+upon them, or the actions they have been excited into. So if a hard body is
+pressed upon the palm of the hand, as is practised in tricks of
+legerdemain, it is not easy to distinguish for a few seconds whether it
+remains or is removed; and tastes continue long to exist vividly in the
+mouth, as the smoke of tobacco, or the taste of gentian, after the sapid
+material is withdrawn.
+
+    V. _A quantity of stimulus somewhat greater than the last mentioned
+    excites the retina into spasmodic action, which ceases and recurs
+    alternately._
+
+1. On looking for a time on the setting sun, so as not greatly to fatigue
+the sight, a yellow spectrum is seen when the eyes are closed and covered,
+which continues for a time, and then disappears and recurs repeatedly
+before it entirely vanishes. This yellow spectrum of the sun when the
+eyelids are opened becomes blue; and if it is made to fall on the green
+grass, or on other coloured objects, it varies its own colour by an
+intermixture of theirs, as will be explained in another place.
+
+2. Place a lighted spermaceti candle in the night about one foot from your
+eye, and look steadily on the centre of the flame, till your eye becomes
+much more fatigued than in Sect. IV. Exp. 3.; and on closing your eyes a
+reddish spectrum will be perceived, which will cease and return
+alternately.
+
+The action of vomiting in like manner ceases, and is renewed by intervals,
+although the emetic drug is thrown up with the first effort: so after-pains
+continue some time after parturition; and the alternate pulsations of the
+heart of a viper are renewed for some time after it is cleared from its
+blood.
+
+VI. OF REVERSE OCULAR SPECTRA.
+
+    _The retina, after having been excited into action by a stimulus
+    somewhat greater them the last mentioned falls into opposite spasmodic
+    action._
+
+The actions of every part of animal bodies may be advantageously compared
+with each other. This strict analogy contributes much to the investigation
+of truth; while those looser analogies, which compare the phenomena of
+animal life with those of chemistry or mechanics, only serve to mislead our
+inquiries.
+
+When any of our larger muscles have been in long or in violent action, and
+their antagonists have been at the same time extended, as soon as the
+action of the former ceases, the limb is stretched the contrary way for our
+ease, and a pandiculation or yawning takes place.
+
+By the following observations it appears, that a similar circumstance
+obtains in the organ of vision; after it has been fatigued by one kind of
+action, it spontaneously falls into the opposite kind.
+
+1. Place a piece of coloured silk, about an inch in diameter, on a sheet of
+white paper, about half a yard from your eyes; look steadily upon it for a
+minute; then remove your eyes upon another part of the white paper, and a
+spectrum will be seen of the form of the silk thus inspected, but of a
+colour opposite to it. A spectrum nearly similar will appear if the eyes
+are closed, and the eyelids shaded by approaching the hand near them, so as
+to permit some, but to prevent too much light falling on them.
+
+  Red silk produced a green spectrum.
+  Green produced a red one.
+  Orange produced blue.
+  Blue produced orange.
+  Yellow produced violet.
+  Violet produced yellow.
+
+That in these experiments the colours of the spectra are the reverse of the
+colours which occasioned them, may be seen by examining the third figure in
+Sir Isaac Newton's Optics, L. II. p. 1, where those thin laminæ of air,
+which reflected yellow, transmitted violet; those which reflected red,
+transmitted a blue green; and so of the rest, agreeing with the experiments
+above related.
+
+2. These reverse spectra are similar to a colour, formed by a combination
+of all the primary colours except that with which the eye has been fatigued
+in making the experiment: thus the reverse spectrum of red must be such a
+green as would be produced by a combination of all the other prismatic
+colours. To evince this fact the following satisfactory experiment was
+made. The prismatic colours were laid on a circular pasteboard wheel, about
+four inches in diameter, in the proportions described in Dr. Priestley's
+History of Light and Colours, pl. 12. fig. 83. except that the red
+compartment was entirely left out, and the others proportionably extended
+so as to complete the circle. Then, as the orange is a mixture of red and
+yellow, and as the violet is a mixture of red and indigo, it became
+necessary to put yellow on the wheel instead of orange, and indigo instead
+of violet, that the experiment might more exactly quadrate with the theory
+it was designed to establish or confute; because in gaining a green
+spectrum from a red object, the eye is supposed to have become insensible
+to red light. This wheel, by means of an axis, was made to whirl like a
+top; and on its being put in motion, a green colour was produced,
+corresponding with great exactness to the reverse spectrum of red.
+
+3. In contemplating any one or these reverse spectra in the closed and
+covered eye, it disappears and re-appears several times successively, till
+at length it entirely vanishes, like the direct spectra in Sect. V.; but
+with this additional circumstance, that when the spectrum becomes faint or
+evanescent, it is instantly revived by removing the hand from before the
+eyelids, so as to admit more light: because then not only the fatigued part
+of the retina is inclined spontaneously to fall into motions of a contrary
+direction, but being still sensible to all other rays of light, except that
+with which it was lately fatigued, is by these rays at the same time
+stimulated into those motions which form the reverse spectrum.
+
+From these experiments there is reason to conclude, that the fatigued part
+of the retina throws itself into a contrary mode of action, like oscitation
+or pandiculation, as soon as the stimulus which has fatigued it is
+withdrawn; and that it still remains sensible, that is, liable to be
+excited into action by any other colours at the same time, except the
+colour with which it has been fatigued.
+
+    VII. _The retina after having been excited into action by a stimulus
+    somewhat greater than the last mentioned falls into various successive
+    spasmodic actions._
+
+1. On looking at the meridian sun as long as the eyes can well bear its
+brightness, the disk first becomes pale, with a luminous crescent, which
+seems to librate from one edge of it to the other, owing to the
+unsteadiness of the eye; then the whole phasis of the sun becomes blue,
+surrounded with a white halo; and on closing the eyes, and covering them
+with the hands, a yellow spectrum is seen, which in a little time changes
+into a blue one.
+
+M. de la Hire observed, after looking at the bright sun, that the
+impression in his eye first assumed a yellow appearance, and then green,
+and then blue; and wishes to ascribe these appearances to some affection of
+the nerves. (Porterfield on the Eye, Vol. I. p. 313.)
+
+2. After looking steadily on about an inch square of pink silk, placed on
+white paper, in a bright sunshine, at the distance of a foot from my eyes,
+and closing and covering my eyelids, the spectrum of the silk was at first
+a dark green, and the spectrum of the white paper became of a pink. The
+spectra then both disappeared; and then the internal spectrum was blue; and
+then, after a second disappearance, became yellow, and lastly pink, whilst
+the spectrum of the field varied into red and green.
+
+These successions of different coloured spectra were not exactly the same
+in the different experiments, though observed, as near as could be, with
+the same quantity of light, and other similar circumstances; owing, I
+suppose, to trying too many experiments at a time; so that the eye was not
+quite free from the spectra of the colours which were previously attended
+to.
+
+The alternate exertions of the retina in the preceding section resembled
+the oscitation or pandiculation of the muscles, as they were performed in
+directions contrary to each other, and were the consequence of fatigue
+rather than of pain. And in this they differ from the successive dissimilar
+exertions of the retina, mentioned in this section, which resemble in
+miniature the more violent agitations of the limbs in convulsive diseases,
+as epilepsy, chorea S. Viti, and opisthotonos; all which diseases are
+perhaps, at first, the consequence of pain, and have their periods
+afterwards established by habit.
+
+    VIII. _The retina, after having been excited into action by a stimulus
+    somewhat greater than the last mentioned falls into a fixed spasmodic
+    action, which continues for some days._
+
+1. After having looked long at the meridian sun, in making some of the
+preceding experiments, till the disks faded into a pale blue, I frequently
+observed a bright blue spectrum of the sun on other objects all the next
+and the succeeding day, which constantly occurred when I attended to it,
+and frequently when I did not previously attend to it. When I closed and
+covered my eyes, this appeared of a dull yellow; and at other times mixed
+with the colours of other objects on which it was thrown. It may be
+imagined, that this part of the retina was become insensible to white
+light, and thence a bluish spectrum became visible on all luminous objects;
+but as a yellowish spectrum was also seen in the closed and covered eye,
+there can remain no doubt of this being the spectrum of the sun. A similar
+appearance was observed by M. Æpinus, which he acknowledges he could give
+no account of. (Nov. Com. Petrop. V. 10. p. 2. and 6.)
+
+The locked jaw, and some cataleptic spasms, are resembled by this
+phenomenon; and from hence we may learn the danger to the eye by inspecting
+very luminous objects too long a time.
+
+IX. _A quantity of stimulus greater than the preceding induces a temporary
+paralysis of the organ of vision._
+
+1. Place a circular piece of bright red silk, about half an inch in
+diameter, on the middle of a sheet of white paper; lay them on the floor in
+a bright sunshine, and fixing your eyes steadily on the center of the red
+circle, for three or four minutes, at the distance of four or six feet from
+the object, the red silk will gradually become paler, and finally cease to
+appear red at all.
+
+2. Similar to these are many other animal facts; as purges, opiates, and
+even poisons, and contagious matter, cease to stimulate our system, after
+we have been habituated to their use. So some people sleep undisturbed by a
+clock, or even by a forge hammer in their neighbourhood: and not only
+continued irritations, but violent exertions of any kind, are succeeded by
+temporary paralysis. The arm drops down after violent action, and continues
+for a time useless; and it is probable, that those who have perished
+suddenly in swimming, or in scating on the ice, have owed their deaths to
+the paralysis, or extreme fatigue, which succeeds every violent and
+continued exertion.
+
+X. MISCELLANEOUS REMARKS.
+
+There were some circumstances occurred in making these experiments, which
+were liable to alter the results of them, and which I shall here mention
+for the assistance of others, who may wish to repeat them.
+
+1. _Of direct and inverse spectra existing at the same time_; _of
+reciprocal direct spectra_; _of a combination of direct and inverse
+spectra_; _of a spectral halo_; _rules to pre-determine the colours of
+spectra_.
+
+a. When an area, about six inches square, of bright pink Indian paper, had
+been viewed on an area, about a foot square, of white writing paper, the
+internal spectrum in the closed eye was green, being the reverse spectrum
+of the pink paper; and the external spectrum was pink, being the direct
+spectrum of the pink paper. The same circumstance happened when the
+internal area was white, and external one pink; that is, the internal
+spectrum was pink, and the external one green. All the same appearances
+occurred when the pink paper was laid on a black hat.
+
+b. When six inches square of deep violet polished paper was viewed on a
+foot square of white writing paper, the internal spectrum was yellow, being
+the reverse spectrum of the violet paper, and the external one was violet,
+being the direct spectrum of the violet paper.
+
+c. When six inches square of pink paper was viewed on a foot square of blue
+paper, the internal spectrum was blue, and the external spectrum was pink;
+that is, the internal one was the direct spectrum of the external object,
+and the external one was the direct spectrum of the internal object,
+instead of their being each the reverse spectrum of the objects they
+belonged to.
+
+d. When six inches square of blue paper were viewed on a foot square of
+yellow paper, the interior spectrum became a brilliant yellow, and the
+exterior one a brilliant blue. The vivacity of the spectra was owing to
+their being excited both by the stimulus of the interior and exterior
+objects; so that the interior yellow spectrum was both the reverse spectrum
+of the blue paper, and the direct one of the yellow paper; and the exterior
+blue spectrum was both the reverse spectrum of the yellow paper, and the
+direct one of the blue paper.
+
+e. When the internal area was only a square half-inch of red paper, laid on
+a square foot of dark violet paper, the internal spectrum was green, with a
+reddish-blue halo. When the red internal paper was two inches square, the
+internal spectrum was a deeper green, and the external one redder. When the
+internal paper was six inches square, the spectrum of it became blue, and
+the spectrum of the external paper was red.
+
+f. When a square half-inch of blue paper was laid on a six-inch square of
+yellow paper, the spectrum of the central paper in the closed eye was
+yellow, incircled with a blue halo. On looking long on the meridian sun,
+the disk fades into a pale blue surrounded with a whitish halo.
+
+These circumstances, though they very much perplexed the experiments till
+they were investigated, admit of a satisfactory explanation; for while the
+rays from the bright internal object in exp. a. fall with their full force
+on the center of the retina, and, by fatiguing that part of it, induce the
+reverse spectrum, many scattered rays, from the same internal pink paper,
+fall on the more external parts of the retina, but not in such quantity as
+to occasion much fatigue, and hence induce the direct spectrum of the pink
+colour in those parts of the eye. The same reverse and direct spectra occur
+from the violet paper in exp. b.: and in exp. c. the scattered rays from
+the central pink paper produce a direct spectrum of this colour on the
+external parts of the eye, while the scattered rays from the external blue
+paper produce a direct spectrum of that colour on the central part of the
+eye, instead of these parts of the retina falling reciprocally into their
+reverse spectra. In exp. d. the colours being the reverse of each other,
+the scattered rays from the exterior object falling on the central parts of
+the eye, and there exciting their direct spectrum, at the same time that
+the retina was excited into a reverse spectrum by the central object, and
+this direct and reverse spectrum being of similar colour, the superior
+brilliancy of this spectrum was produced. In exp. e. the effect of various
+quantities of stimulus on the retina, from the different respective sizes
+of the internal and external areas, induced a spectrum of the internal area
+in the center of the eye, combined of the reverse spectrum of that internal
+area and the direct one of the external area, in various shades of colour,
+from a pale green to a deep blue, with similar changes in the spectrum of
+the external area. For the same reasons, when an internal bright object was
+small, as in exp. f. instead of the whole of the spectrum of the external
+object being reverse to the colour of the internal object, only a kind of
+halo, or radiation of colour, similar to that of the internal object, was
+spread a little way on the external spectrum. For this internal blue area
+being so small, the scattered rays from it extended but a little way on the
+image of the external area of yellow paper, and could therefore produce
+only a blue halo round the yellow spectrum in the center.
+
+If any one should suspect that the scattered rays from the exterior
+coloured object do not intermix with the rays from the interior coloured
+object, and thus affect the central part of the eye, let him look through
+an opake tube, about two feet in length, and an inch in diameter, at a
+coloured wall of a room with one eye, and with the other eye naked; and he
+will find, that by shutting out the lateral light, the area of the wall
+seen through a tube appears as if illuminated by the sunshine, compared
+with the other parts of it; from whence arises the advantage of looking
+through a dark tube at distant paintings.
+
+Hence we may safely deduce the following rules to determine before-hand the
+colours of all spectra. 1. The direct spectrum without any lateral light is
+an evanescent representation of its object in the unfatigued eye. 2. With
+some lateral light it becomes of a colour combined of the direct spectrum
+of the central object, and of the circumjacent objects, in proportion to
+their respective quantity and brilliancy. 3. The reverse spectrum without
+lateral light is a representation in the fatigued eye of the form of its
+objects, with such a colour as would be produced by all the primary
+colours, except that of the object. 4. With lateral light the colour is
+compounded of the reverse spectrum of the central object, and the direct
+spectrum of the circumjacent objects, in proportion to their respective
+quantity and brilliancy.
+
+2. _Variation and vivacity of the spectra occasioned by extraneous light._
+
+The reverse spectrum, as has been before explained, is similar to a colour,
+formed by a combination of all the primary colours, except that with which
+the eye has been fatigued in making the experiment: so the reverse spectrum
+of red is such a green as would be produced by a combination of all the
+other prismatic colours. Now it must be observed, that this reverse
+spectrum of red is therefore the direct spectrum of a combination of all
+the other prismatic colours, except the red; whence, on removing the eye
+from a piece of red silk to a sheet of white paper, the green spectrum,
+which is perceived, may either be called the reverse spectrum of the red
+silk, or the direct spectrum of all the rays from the white paper, except
+the red; for in truth it is both. Hence we see the reason why it is not
+easy to gain a direct spectrum of any coloured object in the day-time,
+where there is much lateral light, except of very bright objects, as of the
+setting sun, or by looking through an opake tube; because the lateral
+external light falling also on the central part of the retina, contributes
+to induce the reverse spectrum, which is at the same time the direct
+spectrum of that lateral light, deducting only the colour of the central
+object which we have been viewing. And for the same reason, it is difficult
+to gain the reverse spectrum, where there is no lateral light to contribute
+to its formation. Thus, in looking through an opake tube on a yellow wall,
+and closing my eye, without admitting any lateral light, the spectra were
+all at first yellow; but at length changed into blue. And on looking in the
+same manner on red paper, I did at length get a green spectrum; but they
+were all at first red ones: and the same after looking at a candle in the
+night.
+
+The reverse spectrum was formed with greater facility when the eye was
+thrown from the object on a sheet of white paper, or when light was
+admitted through the closed eyelids; because not only the fatigued part of
+the retina was inclined spontaneously to fall into motions of a contrary
+direction; but being still sensible to all other rays of light except that
+with which it was lately fatigued, was by these rays stimulated at the same
+time into those motions which form the reverse spectrum. Hence, when, the
+reverse spectrum of any colour became faint, it was wonderfully revived by
+admitting more light through the eyelids, by removing the hand from before
+them: and hence, on covering the closed eyelids, the spectrum would often
+cease for a time, till the retina became sensible to the stimulus of the
+smaller quantity of light, and then it recurred. Nor was the spectrum only
+changed in vivacity, or in degree, by this admission of light through the
+eyelids; but it frequently happened, after having viewed bright objects,
+that the spectrum in the closed and covered eye was changed into a third
+spectrum, when light was admitted through the eyelids: which third spectrum
+was composed of such colours as could pass through the eyelids, except
+those of the object. Thus, when an area of half an inch diameter of pink
+paper was viewed on a sheet of white paper in the sunshine, the spectrum
+with closed and covered eyes was green; but on removing the hands from
+before the closed eyelids, the spectrum became yellow, and returned
+instantly again to green, as often as the hands were applied to cover the
+eyelids, or removed from them: for the retina being now insensible to red
+light, the yellow rays passing through the eyelids in greater quantity than
+the other colours, induced a yellow spectrum; whereas if the spectrum was
+thrown on white paper, with the eyes open, it became only a lighter green.
+
+Though a certain quantity of light facilitates the formation of the reverse
+spectrum, a greater quantity prevents its formation, as the more powerful
+stimulus excites even the fatigued parts of the eye into action; otherwise
+we should see the spectrum of the last viewed object as often as we turn
+our eyes. Hence the reverse spectra are best seen by gradually approaching
+the hand near the closed eyelids to a certain distance only, which must be
+varied with the brightness of the day, or the energy of the spectrum. Add
+to this, that all dark spectra, as black, blue, or green, if light be
+admitted through the eyelids, after they have been some time covered, give
+reddish spectra, for the reasons given in Sect. III. Exp. 1.
+
+From these circumstances of the extraneous light coinciding with the
+spontaneous efforts of the fatigued retina to produce a reverse spectrum,
+as was observed before, it is not easy to gain a direct spectrum, except of
+objects brighter than the ambient light; such as a candle in the night, the
+setting sun, or viewing a bright object through an opake tube; and then the
+reverse spectrum is instantaneously produced by the admission of some
+external light; and is as instantly converted again to the direct spectrum
+by the exclusion of it. Thus, on looking at the setting sun, on closing the
+eyes, and covering them, a yellow spectrum is seen, which is the direct
+spectrum of the setting sun; but on opening the eyes on the sky, the yellow
+spectrum is immediately changed into a blue one, which is the reverse
+spectrum of the yellow sun, or the direct spectrum of the blue sky, or a
+combination of both. And this is again transformed into a yellow one on
+closing the eyes, and so reciprocally, as quick as the motions of the
+opening and closing eyelids. Hence, when Mr. Melvill observed the
+scintillations of the star Sirius to be sometimes coloured, these were
+probably the direct spectrum of the blue sky on the parts of the retina
+fatigued by the white light of the star. (Essays Physical and Literary, p.
+81. V. 2.)
+
+When a direct spectrum is thrown on colours darker than itself, it mixes
+with them; as the yellow spectrum of the setting sun, thrown on the green
+grass, becomes a greener yellow. But when a direct spectrum is thrown on
+colours brighter than itself, it becomes instantly changed into the reverse
+spectrum, which mixes with those brighter colours. So the yellow spectrum
+of the setting sun thrown on the luminous sky becomes blue, and changes
+with the colour or brightness of the clouds on which it appears. But the
+reverse spectrum mixes with every kind of colour on which it is thrown,
+whether brighter than itself or not; thus the reverse spectrum, obtained by
+viewing a piece of yellow silk, when thrown on white paper, was a lucid
+blue green; when thrown on black Turkey leather, becomes a deep violet. And
+the spectrum of blue silk, thrown on white paper, was a light yellow; on
+black silk was an obscure orange; and, the blue spectrum, obtained from
+orange-coloured silk, thrown on yellow, became a green.
+
+In these cases the retina is thrown into activity or sensation by the
+stimulus of external colours, at the same time that it continues the
+activity or sensation which forms the spectra; in the same manner as the
+prismatic colours, painted on a whirling top, are seen to mix together.
+When these colours of external objects are brighter than the direct
+spectrum which is thrown upon them, they change it into the reverse
+spectrum, like the admission of external light on a direct spectrum, as
+explained above. When they are darker than the direct spectrum, they mix
+with it, their weaker stimulus being inefficient to induce the reverse
+spectrum.
+
+3. _Variation of spectra in respect to number, and figure, and remission._
+
+[Illustration: Fig. 4.]
+
+When we look long and attentively at any object, the eye cannot always be
+kept entirely motionless; hence, on inspecting a circular area of red silk
+placed on white paper, a lucid crescent or edge is seen to librate on one
+side or other of the red circle: for the exterior parts of the retina
+sometimes falling on the edge of the central silk, and sometimes on the
+white paper, are less fatigued with red light than the central part of the
+retina, which is constantly, exposed to it; and therefore, when they fall
+on the edge of the red silk, they perceive it more vividly. Afterwards,
+when the eye becomes fatigued, a green spectrum in the form of a crescent
+is seen to librate on one side or other of the central circle, as by the
+unsteadiness of the eye a part of the fatigued retina falls on the white
+paper; and as by the increasing fatigue of the eye the central part of the
+silk appears paler, the edge on which the unfatigued part of the retina
+occasionally falls will appear of a deeper red than the original silk,
+because it is compared with the pale internal part of it. M. de Buffon in
+making this experiment observed, that the red edge of the silk was not only
+deeper coloured than the original silk; but, on his retreating a little
+from it, it became oblong, and at length divided into two, which must have
+been owing to his observing it either before or behind the point of
+intersection of the two optic axises. Thus, if a pen is held up before a
+distant candle, when we look intensely at the pen two candles are seen
+behind it; when we look intensely at the candle two pens are seen. If the
+sight be unsteady at the time of beholding the sun, even though one eye
+only be used, many images of the sun will appear, or luminous lines, when
+the eye is closed. And as some parts of these will be more vivid than
+others, and some parts of them will be produced nearer the center of the
+eye than others, these will disappear sooner than the others; and hence the
+number and shape of these spectra of the sun will continually vary, as long
+as they exist. The cause of some being more vivid than others, is the
+unsteadiness of the eye of the beholder, so that some parts of the retina
+have been longer exposed to the sunbeams. That some parts of a complicated
+spectrum fade and return before other parts of it, the following experiment
+evinces. Draw three concentric circles; the external one an inch and a half
+in diameter, the middle one an inch, and the internal one half an inch;
+colour the external and internal areas blue, and the remaining one yellow,
+as in Fig. 4.; after having looked about a minute on the center of these
+circles, in a bright light, the spectrum of the external area appears first
+in the closed eye, then the middle area, and lastly the central one; and
+then the central one disappears, and the others in inverted order. If
+concentric circles of more colours are added, it produces the beautiful
+ever changing spectrum in Sect. I. Exp. 2.
+
+From hence it would seem, that the center of the eye produces quicker
+remissions of spectra, owing perhaps to its greater sensibility; that is,
+to its more energetic exertions. These remissions of spectra bear some
+analogy to the tremors of the hands, and palpitations of the heart, of weak
+people: and perhaps a criterion of the strength of any muscle or nerve may
+be taken from the time it can be continued in exertion.
+
+4. _Variation of spectra in respect to brilliancy; the visibility of the
+circulation of the blood in the eye._
+
+1. The meridian or evening light makes a difference in the colours of some
+spectra; for as the sun descends, the red rays, which are less refrangible
+by the convex atmosphere, abound in great quantity. Whence the spectrum of
+the light parts of a window at this time, or early in the morning, is red;
+and becomes blue either a little later or earlier; and white in the
+meridian day; and is also variable from the colour of the clouds or sky
+which are opposed to the window.
+
+2. All these experiments are liable to be confounded, if they are made too
+soon after each other, as the remaining spectrum will mix with the new
+ones. This is a very troublesome circumstance to painters, who are obliged
+to look long upon the same colour; and in particular to those whose eyes,
+from natural debility, cannot long, continue the same kind of exertion. For
+the same reason, in making these experiments, the result becomes much
+varied if the eyes, after viewing any object, are removed on other objects
+for but an instant of time, before we close them to view the spectrum; for
+the light from the object, of which we had only a transient view, in the
+very time of closing our eyes acts as a stimulus on the fatigued retina;
+and for a time prevents the defined spectrum from appearing, or mixes its
+own spectrum with it. Whence, after the eyelids are closed, either a dark
+field, or some unexpected colours, are beheld for a few seconds, before the
+desired spectrum becomes distinctly visible.
+
+3. The length of time taken up in viewing an object, of which we are to
+observe the spectrum, makes a great difference in the appearance of the
+spectrum, not only in its vivacity, but in its colour; as the direct
+spectrum of the central object, or of the circumjacent ones, and also the
+reverse spectra of both, with their various combinations, as well as the
+time of their duration in the eye, and of their remissions or alternations,
+depend upon the degree of fatigue the retina is subjected to. The Chevalier
+d'Arcy constructed a machine by which a coal of fire was whirled round in
+the dark, and found, that when a luminous body made a revolution in eight
+thirds of time, it presented to the eye a complete circle of fire; from
+whence he concludes, that the impression continues on the organ about the
+seventh part of a second. (Mem. de l'Acad. des Sc. 1765.) This, however, is
+only to be considered as the shortest time of the duration of these direct
+spectra; since in the fatigued eye both the direct and reverse spectra,
+with their intermissions, appear to take up many seconds of time, and seem
+very variable in proportion to the circumstances of fatigue or energy.
+
+4. It sometimes happens, if the eyeballs have been rubbed hard with the
+fingers, that lucid sparks are seen in quick motion amidst the spectrum we
+are attending to. This is similar to the flashes of fire from a stroke on
+the eye in fighting, and is resembled by the warmth and glow, which appears
+upon the skin after friction, and is probably owing to an acceleration of
+the arterial blood into the vessels emptied by the previous pressure. By
+being accustomed to observe such small sensations in the eye, it is easy to
+see the circulation of the blood in this organ. I have attended to this
+frequently, when I have observed my eyes more than commonly sensible to
+other spectra. The circulation may be seen either in both eyes at a time,
+or only in one of them; for as a certain quantity of light is necessary to
+produce this curious phenomenon, if one hand be brought nearer the closed
+eyelids than the other, the circulation in that eye will for a time
+disappear. For the easier viewing the circulation, it is sometimes
+necessary to rub the eyes with a certain degree of force after they are
+closed, and to hold the breath rather longer than is agreeable, which, by
+accumulating more blood in the eye, facilitates the experiment; but in
+general it may be seen distinctly after having examined other spectra with
+your back to the light, till the eyes become weary; then having covered
+your closed eyelids for half a minute, till the spectrum is faded away
+which you were examining, turn your face to the light, and removing your
+hands from the eyelids, by and by again shade them a little, and the
+circulation becomes curiously distinct. The streams of blood are however
+generally seen to unite, which shews it to be the venous circulation,
+owing, I suppose, to the greater opacity of the colour of the blood in
+these vessels; for this venous circulation is also much more easily seen by
+the microscope in the tail of a tadpole.
+
+5. _Variation of spectra in respect to distinctness and size; with a new
+way of magnifying objects._
+
+1. It was before observed, that when the two colours viewed together were
+opposite to each other, as yellow and blue, red and green, &c. according to
+the table of reflections and transmissions of light in Sir Isaac Newton's
+Optics, B. II. Fig. 3. the spectra of those colours were of all others the
+most brilliant, and best defined; because they were combined of the reverse
+spectrum of one colour, and of the direct spectrum of the other. Hence, in
+books printed with small types, or in the minute graduation of
+thermometers, or of clock-faces, which are to be seen at a distance, if the
+letters or figures are coloured with orange, and the ground with indigo; or
+the letters with red, and the ground with green; or any other lucid colour
+is used for the letters, the spectrum of which is similar to the colour of
+the ground; such letters will be seen much more distinctly, and with less
+confusion, than in black or white: for as the spectrum of the letter is the
+same colour with the ground on which they are seen, the unsteadiness of the
+eye in long attending to them will not produce coloured lines by the edges
+of the letters, which is the principal cause of their confusion. The beauty
+of colours lying in vicinity to each other, whose spectra are thus
+reciprocally similar to each colour, is owing to this greater ease that the
+eye experiences in beholding them distinctly; and it is probable, in the
+organ of hearing, a similar circumstance may constitute the pleasure of
+melody. Sir Isaac Newton observes, that gold and indigo were agreeable when
+viewed together; and thinks there may be some analogy between the
+sensations of light and sound. (Optics, Qu. 14.)
+
+In viewing the spectra of bright objects, as of an area of red silk of half
+an inch diameter on white paper, it is easy to magnify it to tenfold its
+size: for if, when the spectrum is formed, you still keep your eye fixed on
+the silk area, and remove it a few inches further from you, a green circle
+is seen round the red silk: for the angle now subtended by the silk is less
+than it was when the spectrum was formed, but that of the spectrum
+continues the same, and our imagination places them at the same distance.
+Thus when you view a spectrum on a sheet of white paper, if you approach
+the paper to the eye, you may diminish it to a point; and if the paper is
+made to recede from the eye, the spectrum will appear magnified in
+proportion to the distance.
+
+[Illustration: Fig. 5.]
+
+I was surprised, and agreeably amused, with the following experiment. I
+covered a paper about four inches square with yellow, and with a pen filled
+with a blue colour wrote upon the middle of it the word BANKS in capitals,
+as in Fig. 5, and sitting with my back to the sun, fixed my eyes for a
+minute exactly on the center of the letter N in the middle of the word;
+after closing my eyes, and shading them somewhat with my hand, the word was
+distinctly seen in the spectrum in yellow letters on a blue field; and
+then, on opening my eyes on a yellowish wall at twenty feet distance, the
+magnified name of BANKS appeared written on the wall in golden characters.
+
+_Conclusion._
+
+It was observed by the learned M. Sauvage (Nosol. Method. Cl. VIII. Ord.
+i.) that the pulsations of the optic artery might be perceived by looking
+attentively on a white wall well illuminated. A kind of net-work, darker
+than the other parts of the wall, appears and vanishes alternately with
+every pulsation. This change of the colour of the wall he well ascribes to
+the compression of the retina by the diastole of the artery. The various
+colours produced in the eye by the pressure of the finger, or by a stroke
+on it, as mentioned by Sir Isaac Newton, seem likewise to originate from
+the unequal pressure on various parts of the retina. Now as Sir Isaac
+Newton has shewn, that all the different colours are reflected or
+transmitted by the laminæ of soap bubbles, or of air, according to their
+different thickness or thinness, is it not probable, that the effect of the
+activity of the retina may be to alter its thickness or thinness, so as
+better to adapt it to reflect or transmit the colours which stimulate it
+into action? May not muscular fibres exist in the retina for this purpose,
+which may be less minute than the locomotive muscles of microscopic
+animals? May not these muscular actions of the retina constitute the
+sensation of light and colours; and the voluntary repetitions of them, when
+the object is withdrawn, constitute our memory of them? And lastly, may not
+the laws of the sensations of light, here investigated, be applicable to
+all our other senses, and much contribute to elucidate many phenomena of
+animal bodies both in their healthy and diseased state; and thus render
+this investigation well worthy the attention of the physician, the
+metaphysician, and the natural philosopher?
+
+November 1, 1785.
+
+       *       *       *       *       *
+
+  Dum, Liber! astra petis volitans trepidantibus alis,
+    Irruis immemori, parvula gutta, mari.
+  Me quoque, me currente rotâ revolubilis ætas
+    Volverit in tenebras,--i, Liber, ipse sequor.
+
+       *       *       *       *       *
+
+INDEX TO THE SECTIONS OF PART FIRST.
+
+
+                  A.
+
+  Abortion from fear, xxxix. 6. 5.
+  Absorbent vessels, xxiii. 3. xxix. 1.
+  ---- regurgitate their fluids, xxix. 2.
+  ---- their valves, xxix. 2.
+  ---- communicate with vena portarum, xxvii. 2.
+  Absorption of solids, xxxiii. 3. 1. xxxvii.
+  ---- of fluids in anasarca, xxxv. 1. 3.
+  Accumulation of sensorial power, iv. 2. xii. 5. 2.
+  Activity of system too great, cure of, xii. 6.
+  ---- too small, cure of, xii. 7.
+  Age, old, xii. 3. 1. xxxvii. 4.
+  Ague-fit, xii. 7. 1. xxxii. 3. 4. xxxii. 9.
+  ---- how cured by bark, xii. 3. 4.
+  ---- periods, how occasioned, xii. 2. 3. xxxii. 3. 4.
+  Ague cakes, xxxii. 7. xxxii. 9.
+  Air, sense of fresh, xiv. 8.
+  ---- injures ulcers, xxviii. 2.
+  ---- injected into veins, xxxii. 5.
+  Alcohol deleterious, xxx. 3.
+  Alliterations, why agreeable, xxii. 2.
+  Aloes in lessened doses, xii. 3. 1.
+  American natives indolent, xxxi. 2.
+  ---- narrow shouldered, xxxi. 1.
+  Analogy intuitive, xvii. 3. 7.
+  Animals less liable to madness, xxxiii. 1.
+  ---- less liable to contagion, xxxiii. 1.
+  ---- how to teach, xxii. 3. 2.
+  ---- their similarity to each other, xxxix. 4. 8.
+  ---- their changes after nativity, xxxix. 4. 8.
+  ---- their changes before nativity, xxxix. 4. 8.
+  ---- less liable to contagious diseases, why, xxxiii. 1. 5.
+  ---- less liable to delirium and insanity, why, xxxiii. 1. 5.
+  ---- easier to preserve than to reproduce, xxxvii.
+  ---- food, distaste of, xxviii. 1.
+  ---- appetency, xxxix. 4. 7.
+  Antipathy, x. 2. 2.
+  Aphthæ, xxviii.
+  Apoplexy, xxxiv. 1. 7.
+  ---- not from deficient irritation, xxxii. 2. 1.
+  Appetites, xi. 2. 2. xiv. 8.
+  Architecture, xxii. 2. xvi. 10.
+  Arts, fine, xxii. 2.
+  Asparagus, its smell in urine, xxix.
+  Association defined, ii. 2. 11. iv. 7. v. 2.
+  ---- associate motions, x.
+  ---- stronger than irritative ones, xxiv. 2. 8.
+  ---- formed before nativity, xi. 3.
+  ---- with irritative ones, xxiv. 2. 8.
+  ---- with retrograde ones, xxv. 7. xxv. 10. xxv. 15.
+  ---- diseases from, xxxv.
+  Asthma, xviii. 15.
+  Attention, language of, xvi. 8. 6.
+  Atrophy, xxviii.
+  Aversion, origin of, xi. 2. 3.
+
+                  B.
+
+  Balance ourselves by vision, xx. 1.
+  Bandage increases absorption, xxxiii. 3. 2.
+  Barrenness, xxxvi. 2. 3.
+  Battement of sounds, xx. 7.
+  Bath, cold.  See Cold Bath.
+  Beauty, sense of, xvi. 6. xxii. 2.
+  Bile-ducts, xxx.
+  ---- stones, xxx. 1. 3.
+  ---- regurgitates into the blood, xxiv. 2. 7.
+  ---- vomiting of, xxx. 1. 3.
+  Birds of passage, xvi. 12.
+  ---- nests of, xvi. 13.
+  ---- colour of their eggs, xxxix. 5.
+  Biting in pain, xxxiv. 1. 3.
+  ---- of mad animals, xxxiv. 1. 3.
+  Black spots on dice appear red, xl. 3.
+  Bladder, communication of with the intestines, xxix. 3.
+  ---- of fish, xxiv. 1. 4.
+  Blood, transfusion of in nervous fevers, xxxii. 4.
+  ---- deficiency of, xxxii. 2. and 4.
+  ---- from the vena portarum into the intestines, xxvii. 2.
+  ---- its momentum, xxxii. 5. 2.
+  ---- momentum increased by venesection, xxxii. 5. 4.
+  ---- drawn in nervous pains, xxxii. 5. 4.
+  ---- its oxygenation, xxxviii.
+  Breasts of men, xiv. 8.
+  Breathing, how learnt, xvi. 4.
+  Brutes differ from men, xi. 2. 3. xvi. 17.
+  Brutes. See Animals.
+  Buxton bath, why it feels warm, xii. 2. 1. xxxii. 3. 3.
+
+                  C.
+
+  Capillary vessels are glands, xxvi. 1.
+  Catalepsy, xxxiv. 1. 5.
+  Catarrh from cold skin, xxxv. 1. 3. xxxv. 2. 3.
+  ---- from thin caps in sleep, xviii. 15.
+  Catenation of motions defined, ii. 2. 11. iv. 7.
+  ---- cause of them, xvii. 1. 3.
+  ---- described, xvii.
+  ---- continue some time after their production, xvii. 1. 3.
+  ---- voluntary ones dissevered in sleep, xvii. 1. 12. xvii. 3. 7.
+  Cathartics, external, their operation, xxix. 7. 6.
+  Causation, animal, defined, ii. 2. 11. iv. 7.
+  Cause of causes, xxxix. 4. 8.
+  Causes inert and efficient, xxxix. 8. 2.
+  ---- active and passive, xxxix. 8. 3.
+  ---- proximate and remote, xxxix. 8. 4.
+  Chick in the egg, oxygenation of, xxxviii. 2.
+  Child riding on a stick, xxxiv. 2. 6.
+  Chilness after meals, xxi. 3. xxxv. 1. 1.
+  Cholera, case of, xxv. 13.
+  Circulation in the eye visible, xl. 10. 4.
+  Cold in the head, xii. 6. 5.
+  ---- perceived by the teeth, xxxii. 3. 1. xiv. 6.
+  ---- air, uses of in fevers, xxxii. 3. 3.
+  ---- feet, produces coryza, xxxv. 2. 3. xxxv. 1. 3.
+  ---- bath, why it strengthens, xxxii. 3. 2.
+  ---- short and cold breathing in it, xxxii. 3. 2.
+  ---- produces a fever-fit, xxxii. 3. 2.
+  ---- fit of fever the consequence of hot fit, xxxii. 9. 3.
+  ---- bathing in pulmonary hæmorrhage, xxvii. 1.
+  ---- fits of fever, xxxii. 4. xxxii. 9. xvii. 3. 3.
+  Colours of animals, efficient cause of, xxxix. 5. 1.
+  ---- of eggs from female imagination, xxxix. 5. 1.
+  ---- of the choroid coat of the eye, xxxix. 5. 1.
+  ---- of birds nests, xvi. 13.
+  Comparing ideas, xv. 3.
+  Consciousness, xv. 3. 4.
+  ---- in dreams, xviii. 13.
+  Consent of parts. See Sympathy.
+  Consumption, its temperament, xxxi. 1. and 2.
+  ---- of dark-eyed patients, xxvii. 2.
+  ---- of light-eyed patients, xxviii. 2.
+  ---- is contagious, xxxiii. 2. 7.
+  Contagion, xii. 3. 6. xix. 9. xxxiii. 2. 6. and 8. xxii. 3. 3.
+  ---- does not enter the blood, xxxiii. 2. 10. xxii. 3. 3.
+  Contraction and attraction, iv. 1.
+  ---- of fibres produces sensation, iv. 5. xii. 1. 6.
+  ---- continues some time, xii. 1. 5.
+  ---- alternates with relaxation, xii. 1. 3.
+  Convulsion, xvii. 1. 8. xxxiv. 1. 1. and 4. iii. 5. 8.
+  ---- of particular muscles, xvii. 1. 8.
+  ---- periods of, xxxvi. 3. 9.
+  Coryza. See Catarrh.
+  Cough, nervous, periods of, xxxvi. 3. 9.
+  Cramp, xviii. 15. xxxiv. 1. 7.
+  Critical days from lunations, xxxvi. 4.
+
+                  D.
+
+  Darkish room, why we see well in it, xii. 2. 1.
+  Debility sensorial and stimulatory, xii. 2. 1.
+  ---- direct and indirect of Dr. Brown, xii. 2. 1. xxxii. 3. 2.
+  ---- See Weakness.
+  ---- from drinking spirits, cure of, xii. 7. 8.
+  ---- in fevers, cure of, xii. 7. 8.
+  Deliberation, what, xxxiv. 1.
+  Delirium, two kinds of, xxxiii. 1. 4. xxxiv. 2. 2.
+  ---- cases of, iii. 5. 8.
+  ---- prevented by dreams, xviii. 2.
+  Desire, origin of, xi. 2. 3.
+  Diabetes explained, xxix. 4.
+  ---- with bloody urine, xxvii. 2.
+  ---- in the night, xviii. 15.
+  Diarrhoea, xxix. 4.
+  Digestion, xxxiii. 1. xxxvii.
+  ---- strengthened by emetics, xxxv. 1. 3.
+  ---- strengthened by regular hours, why, xxxvi. 2. 1.
+  Digitalis, use of in dropsy, xxix. 5. 2.
+  Distention acts as a stimulus, xxxii. 4.
+  ---- See Extension.
+  Distinguishing, xv. 3.
+  Diurnal circle of actions, xxv. 4.
+  Doubting, xv. 3.
+  Dreams, viii. 1. 2. xiv. 2. 5.
+  ---- their inconsistency, xviii. 17.
+  ---- no surprise in them, xviii. 17.
+  ---- much novelty of combination, xviii. 9.
+  Dropsies explained, xxix. 5. 1.
+  Dropsy cured by insanity, xxxiv. 2. 7.
+  ---- cure of, xxix. 5. 2.
+  Drunkards weak till next day, xvii. 1. 7.
+  ---- stammer, and stagger, and weep, xii. 4. 1. xxi. 4.
+  ---- see objects double, why, xxi. 7.
+  ---- become delirious, sleepy, stupid, xxi. 5.
+  Drunkenness. See Intoxication, xxi.
+  ---- diminished by attention, xxi. 8.
+  Dyspnoea in cold bath, xxxii. 3. 2.
+
+                  E.
+
+  Ear, a good one, xvi. 10.
+  ---- noise in, xx. 7.
+  Eggs of frogs, fish, fowl, xxxix. 2.
+  ---- of birds, why spotted, xxxix. 5.
+  ---- with double yolk, xxxix. 4. 4.
+  Electricity, xii. 1. xiv. 9.
+  ---- jaundice cured by it, xxx. 1. 2.
+  Embryon produced by the male, xxxix. 2.
+  ---- consists of a living fibre, xxxix. 4.
+  ---- absorbs nutriment, receives oxygen, xxxix. 1.
+  ---- its actions and sensations, xvi. 2.
+  Emetic. See Vomiting.
+  Emotions, xi. 2. 2.
+  Ennui, or tædium vitæ, xxxiv. 2. 3. xxxiii. 1. 1. xxxix. 6.
+  Epileptic fits explained, xxxiv. 1. 4. xxvii. 2.
+  ---- in sleep, why, xviii. 14. & 15.
+  Equinoxial lunations, xxxii. 6.
+  Excitability perpetually varies, xii. 1. 7.
+  ---- synonymous to quantity of sensorial power, xii. 1. 7.
+  Exercise, its use, xxxii. 5. 3.
+  Exertion of sensorial power defined, xii. 2. 1.
+  Existence in space, xiv. 2. 5.
+  Extension, sense of, xiv. 7.
+  Eyes become black in some epilepsies, xxvii. 2.
+
+                  F.
+
+  Face, flushing of after dinner, xxxv. 1. 1.
+  ---- why first affected in small-pox, xxxv. 1. 1.
+  ---- red from inflamed liver, xxxv. 2. 2.
+  Fainting fits, xii. 7. 1. xiv. 7.
+  Fear, language of, xvi. 8. 1.
+  ---- a cause of fever, xxxii. 8.
+  ---- cause of, xvii. 3. 7.
+  Fetus.  See Embryon, xvi. 2. xxxix. 1.
+  Fevers, irritative, xxxii. 1.
+  ---- intermittent, xxxii. 1. xxxii. 3.
+  ---- sensitive, xxxiii. 1.
+  ---- not an effort of nature for relief, xxxii. 10.
+  ---- paroxysms of, xii. 7. 1. xii. 2. 3. xii. 3. 5.
+  ---- why some intermit and not others, xxxvi. 1.
+  ---- cold fits of, xxxii. 4. xxxii. 9. xvii. 3. 3.
+  ---- periods of, xxxvi. 3.
+  ---- have solar or lunar periods, xxxii. 6.
+  ---- source of the symptoms of, xxxii. 1.
+  ---- prostration of strength in, xii. 4. 1. xxxii. 3. 2.
+  ---- cure of, xii. 6. 1.
+  ---- how cured by the bark, xii. 3. 4.
+  ---- cured by increased volition, xii. 2. 4. xxxiv. 2. 8.
+  ---- best quantity of stimulus in, xii. 7. 8.
+  Fibres. See Muscles.
+  Fibres, their mobility, xii. 1. 7. xii. 1. 1.
+  ---- contractions of, vi. xii. 1. 1.
+  ---- four classes of their motions, vi.
+  ---- their motions distinguished from sensorial ones, v. 3.
+  Figure, xiv. 2. 2. iii. 1.
+  Fish, their knowledge, xvi. 14.
+  Foxglove, its use in dropsies, xxix. 5. 2.
+  ---- overdose of, xxv. 17.
+  Free-will, xv. 3. 7.
+
+                  G.
+
+  Gall-stone, xxv. 17.
+  ---- See Bile-stones.
+  Generation, xxxiii. 1. xxxix.
+  Gills of fish, xxxviii. 2.
+  Glands, xxiii. 2.
+  ---- conglobate glands, xxiii. 3.
+  ---- have their peculiar stimulus, xi. 1.
+  ---- their senses, xiv. 9. xxxix. 6.
+  ---- invert their motions, xxv. 7.
+  ---- increase their motions, xxv. 7.
+  Golden rule for exhibiting wine, xii. 7. 8.
+  ---- for leaving off wine, xii. 7. 8.
+  Gout from inflamed liver, xxxv. 2. 2. xviii. 16. xxiv. 2. 8.
+  ---- in the stomach, xxiv. 2. 8. xxv. 17.
+  ---- why it returns after evacuations, xxxii. 4.
+  ---- owing to vinous spirit only, xxi. 10.
+  ---- periods of, xxxvi. 3. 6.
+  Grinning in pain, xxxiv. 1. 3.
+  Gyration on one foot, xx. 5. and 6.
+
+                  H.
+
+  Habit defined, ii. 2. 11. iv. 7.
+  Hæmorrhages, periods of, xxxvi. 3. 11.
+  ---- from paralysis of veins, xxvii. 1. and 2.
+  Hair and nails, xxxix. 3. 2.
+  ---- colour of, xxxix. 5. 1.
+  Harmony, xxii. 2.
+  Head-achs, xxxv. 2. 1.
+  Hearing, xiv. 4.
+  Heat, sense of, xiv. 6. xxxii. 3. 1.
+  ---- produced by the glands, xxxii. 3.
+  ---- external and internal, xxxii. 3. 1.
+  ---- atmosphere of heat, xxxii. 3. 1.
+  ---- increases during sleep, xviii. 15.
+  Hemicrania, xxxv. 2. 1.
+  ---- from decaying teeth, xxxv. 2. 1.
+  Hepatitis, cause of, xxxv. 2. 3.
+  Hereditary diseases, xxxix. 7. 6.
+  Hermaphrodite insects, xxxix. 5.
+  Herpes, xxviii. 2.
+  ---- from inflamed kidney, xxxv. 2. 2.
+  Hilarity from diurnal fever, xxxvi. 3. 1.
+  Hunger, sense of, xiv. 8.
+  Hydrophobia, xxii. 3. 3.
+  Hypochondriacism, xxxiii. 1. 1. xxxiv. 2. 3.
+
+                  I.
+
+  Ideas defined, ii. 2. 7.
+  ---- are motions of the organs of sense, iii. 4. xviii. 5. xviii. 10.
+      xviii. 6.
+  ---- analogous to muscular motions, iii. 5.
+  ---- continue some time, xx. 6.
+  ---- new ones cannot be invented, iii. 6. 1.
+  ---- abstracted ones, iii. 6. 4.
+  ---- inconsistent trains of, xviii. 17.
+  ---- perish with the organ of sense, iii. 4. 4.
+  ---- painful from inflammation of the organ, iii. 5. 5.
+  ---- irritative ones, vii. 1. 4. vii. 3. 2. xv. 2. xx. 7.
+  ---- of resemblance, contiguity, causation, viii. 3. 2. x. 3. 3.
+  ---- resemble the figure and other properties of bodies, xiv. 2. 2.
+  ---- received in tribes, xv. 1.
+  ---- of the same sense easier combined, xv. 1. 1.
+  ---- of reflection, xv. 1. 6. ii. 2. 12.
+  Ideal presence, xv. 1. 7.
+  Identity, xv. 3. 5. xviii. 13.
+  Iliac passion, xxv. 15.
+  Imagination, viii. 1. 2. xv. 1. 7. xv. 2. 2.
+  ---- of the male forms the sex, xxxix. 6.
+  Imitation, origin of, xii. 3. 3. xxxix. 5. xxii. 3. xvi. 7.
+  Immaterial beings, xiv. 1. xiv. 2. 4.
+  Impediment of speech, xvii. 1. 10. xvii. 2. 10.
+  Infection. See Contagion.
+  Inflammation, xii. 2. 3. xxxiii. 2. 2.
+  ---- great vascular exertion in, xii. 2. 1.
+  ---- not from pains from defect of stimulus, xxxiii. 2. 3.
+  ---- of parts previously insensible, xii. 3. 7.
+  ---- often distant from its cause, xxiv. 2. 8.
+  ---- observes solar days, xxxii. 6.
+  ---- of the eye, xxxiii. 3. 1.
+  ---- of the bowels prevented by their continued action in sleep, xviii.
+      2.
+  Inoculation with blood, xxxiii. 2. 10.
+  Insane people, their great strength, xii. 2. 1.
+  Insanity (see Madness) pleasurable one, xxxiv. 2. 6.
+  Insects, their knowledge, xvi. 15. and 16.
+  ---- in the heads of calves, xxxix. 1.
+  ---- class of, xxxix. 4. 8.
+  Instinctive actions defined, xvi. 1.
+  Intestines, xxv. 3.
+  Intoxication relieves pain, why, xxi. 3.
+  ---- from food after fatigue, xxi. 2.
+  ---- diseases from it, xxi. 10.
+  ---- See Drunkenness.
+  Intuitive analogy, xvii. 3. 7.
+  Invention, xv. 3. 3.
+  Irritability increases during sleep, xviii. 15.
+  Itching, xiv. 9.
+
+                  J.
+
+  Jaundice from paralysis of the liver, xxx. 1. 2.
+  ---- cured by electricity, xxx. 1. 2.
+  Jaw-locked, xxxiv. 1. 5.
+  Judgment, xv. 3.
+
+                  K.
+
+  Knowledge of various animals, xvi. 11.
+
+                  L.
+
+  Lachrymal sack, xvi. 8. xxiv. 2. 2. and 7.
+  Lacteals, paralysis of, xxviii.
+  ---- See Absorbents.
+  Lady playing on the harpsichord, xvii. 2.
+  ---- distressed for her dying bird, xvii. 2. 10.
+  Language, natural, its origin, xvi. 7. & 8.
+  ---- of various passions described, xvi. 8.
+  ---- artificial, of various animals, xvi. 9.
+  ---- theory of, xxxix. 8. 3.
+  Lapping of puppies, xvi. 4.
+  Laughter explained, xxxiv. 1. 4.
+  ---- from tickling, xvii. 3. 5. xxxiv. 1. 4.
+  ---- from frivolous ideas, xxxiv. 1. 4. xviii. 12.
+  Life, long, art of producing, xxxvii.
+  Light has no momentum, iii. 3. 1.
+  Liquor amnii, xvi. 2. xxxviii. 2.
+  ---- is nutritious, xxxviii. 3.
+  ---- frozen, xxxviii. 3.
+  Liver, paralysis of, xxx. 1. 4.
+  ---- large of geese, xxx. 1. 6.
+  Love, sentimental, its origin, xvi. 6.
+  ---- animal, xiv. 8. xvi. 5.
+  Lunar periods affect diseases, xxxii. 6.
+  Lust, xiv. 8. xvi. 5.
+  Lymphatics, paralysis of, xxviii.
+  ---- See Absorbents.
+
+                  M.
+
+  Mad-dog, bite of, xxii. 3. 3.
+  Madness, xxxiv. 2. 1. xii. 2. 1.
+  Magnetism, xii. 1. 1.
+  Magnifying objects, new way of, xl. 10. 5.
+  Male animals have teats, xxxix. 4. 8.
+  ---- pigeons give milk, xxxix. 4. 8.
+  Man distinguished from brutes, xi. 2. 3. xvi. 17.
+  Material world, xiv. 1. xiv. 2. 5. xviii. 7.
+  Matter, penetrability of, xiv. 2. 3.
+  ---- purulent, xxxiii. 2. 4.
+  Measles, xxxiii. 2. 9.
+  Membranes, xxvi. 2.
+  Memory defined, ii. 2. 10. xv. 1. 7. xv. 3.
+  Menstruation by lunar periods, xxxii. 6.
+  Miscarriage from fear, xxxix. 6. 5.
+  Mobility of fibres, xii. 1. 7.
+  Momentum of the blood, xxxii. 5. 2.
+  ---- sometimes increased by venesection, xxxii. 5. 4.
+  Monsters, xxxix. 4. 4. and 5. 2.
+  ---- without heads, xxxviii. 3.
+  Moon and sun, their influence, xxxii. 6.
+  Mortification, xxxiii. 3. 3.
+  Motion is either cause or effect, i. xiv. 2. 2.
+  ---- primary and secondary, i.
+  ---- animal, i. iii. 1.
+  ---- propensity to, xxii. 1.
+  ---- animal, continue some time after their production, xvii. 1. 3.
+  ---- defined, a variation of figure, iii. 1. xiv. 2. 2. xxxix. 8.
+  Mucus, experiments on, xxvi. 1.
+  ---- secretion of, xxvi. 2.
+  Mules, xxxix. 4. 5. and 6. xxxix. 5. 2.
+  Mule plants, xxxix. 2.
+  Muscæ volitantes, xl. 2.
+  Muscles constitute an organ of sense, xiv. 7. ii. 2. 4.
+  ---- stimulated by extension, xi. 1. xiv. 7.
+  ---- contract by spirit of animation, xii. 1. 1. and 3.
+  Music, xvi. 10. xxii. 2.
+  Musical time, why agreeable, xii. 3. 3.
+
+                  N.
+
+  Nausea, xxv. 6.
+  Nerves and brain, ii. 2. 3.
+  ---- extremities of form the whole system, xxxvii. 3.
+  ---- are not changed with age, xxxvii. 4.
+  Nervous pains defined, xxxiv. 1. 1.
+  Number defined, xiv. 2. 2.
+  Nutriment for the embryon, xxxix. 5. 2.
+  Nutrition owing to stimulus, xxxvii. 3.
+  ---- by animal selection, xxxvii. 3.
+  ---- when the fibres are elongated, xxxvii. 3.
+  ---- like inflammation, xxxvii. 3.
+
+                  O.
+
+  Objects long viewed become faint, iii. 3. 2.
+  Ocular spectra, xl.
+  Oil externally in diabætes, xxix. 4.
+  Old age from inirritability, xxxvii.
+  Opium is stimulant, xxxii. 2. 2.
+  ---- promotes absorption after evacuation, xxxiii. 3. 1.
+  ---- in increasing doses, xii. 3. 1.
+  Organs of sense, ii. 2. 5. and 6.
+  Organs when destroyed cease to produce ideas, iii. 4. 4.
+  Organic particles of Buffon, xxxvii. 3. xxxix. 3. 3.
+  Organ-pipes, xx. 7.
+  Oxygenation of the blood, xxxviii.
+
+                  P.
+
+  Pain from excess and defect of motion, iv. 5. xii. 5. 3. xxxiv. 1. xxxv.
+      2. 1.
+  ---- not felt during exertion, xxxiv. 1. 2.
+  ---- from greater contraction of fibres, xii. 1. 6.
+  ---- from accumulation of sensorial power, xii. 5. 3.
+  ---- from light, pressure, heat, caustics, xiv. 9.
+  ---- in epilepsy, xxxv. 2. 1.
+  ---- distant from its cause, xxiv. 2. 8.
+  ---- from stone in the bladder, xxxv. 2. 1.
+  ---- of head and back from defect, xxxii. 3.
+  ---- from a gall-stone, xxxv. 2. 1. xxv. 17.
+  ---- of the stomach in gout, xxv. 17.
+  ---- of shoulder in hepatitis, xxxv. 2. 4.
+  ---- produces volition, iv. 6.
+  Paleness in cold fit, xxxii. 3. 2.
+  Palsies explained, xxxiv. 1. 7.
+  Paralytic limbs stretch from irritation, vii. 1. 3.
+  ---- patients move their sound limb much, xii. 5. 1.
+  Paralysis from great exertion, xii. 4. 6.
+  ---- from less exertion, xii. 5. 6.
+  ---- of the lacteals, xxviii.
+  ---- of the liver, xxx. 1. 4.
+  ---- of the right arm, why, xxxiv. 1. 7.
+  ---- of the veins, xxvii. 2.
+  Particles of matter will not approach, xii. 1. 1.
+  Passions, xi. 2. 2.
+  ---- connate, xvi. 1.
+  Pecking of chickens, xvi. 4.
+  Perception defined, ii. 2. 8. xv. 3. 1.
+  Periods of agues, how formed, xxxii. 3. 4.
+  ---- of diseases, xxxvi.
+  ---- of natural actions and of diseased actions, xxxvi.
+  Perspiration in fever-fits, xxxii. 9. See Sweat.
+  Petechiæ, xxvii. 2.
+  Pigeons secrete milk in their stomachs, xxxix. 4. 8.
+  Piles, xxvii. 2.
+  Placenta a pulmonary organ, xxxviii. 2.
+  Pleasure of life, xxxiii. 1. xxxix. 5.
+  ---- from greater fibrous contractions, xii. 1. 6.
+  ---- what kind causes laughter, xxxiv. 1. 4.
+  ---- what kind causes sleep, xxxiv. 1. 4.
+  Pleurisy, periods of, xxxvi. 3. 7.
+  ---- cause of, xxxv. 2. 3.
+  Prometheus, story of, xxx. 3.
+  Prostration of strength in fevers, xii. 4. 1.
+  Pupils of the eyes large, xxxi. 1.
+  Pulse quick in fevers with debility, xii. 1. 4. xii. 5. 4. xxxii. 2. 1.
+  ---- in fevers with strength, xxxii. 2.
+  ---- from defect of blood, xxxii. 2. 3. xii. 1. 4.
+  ---- weak from emetics, xxv. 17.
+
+                  Q.
+
+  Quack advertisements injurious. Preface.
+  Quadrupeds have no sanguiferous lochia, xxxviii. 2.
+  ---- have nothing similar to the yolk of egg, xxxix. 1.
+
+                  R.
+
+  Rhaphania, periods of, xxxvi. 3. 9.
+  Reason, ix. 1. 2. xv. 3.
+  Reasoning, xv. 3.
+  Recollection, ii. 2. 10. ix. 1. 2. xv. 2. 3.
+  Relaxation and bracing, xxxii. 3. 2.
+  Repetition, why agreeable, xii. 3. 3. xxii. 2.
+  Respiration affected by attention, xxxvi. 2. 1.
+  Restlessness in fevers, xxxiv. 1. 2.
+  Retrograde motions, xii. 5. 5. xxv. 6. xxix. 11.
+  ---- of the stomach, xxv. 6.
+  ---- of the skin, xxv. 9.
+  ---- of fluids, how distinguished, xxix. 8.
+  ---- how caused, xxix. 11. 5.
+  ---- vegetable motions, xxix. 9.
+  Retina is fibrous, iii. 2. xl. 1.
+  ---- is active in vision, iii. 3. xl. 1.
+  ---- excited into spasmodic motions, xl. 7.
+  ---- is sensible during sleep, xviii. 5. xix. 8.
+  Reverie, xix. 1. xxxiv. 3.
+  ---- case of a sleep-walker, xix. 2.
+  ---- is an epileptic disease, xix. 9.
+  Rhymes in poetry, why agreeable, xxii. 2.
+  Rheumatism, three kinds of, xxvi. 3.
+  Rocking young children, xxi. 3.
+  Ruminating animals, xxv. 1.
+
+                  S.
+
+  Saliva produced by mercury, xxiv. 1.
+  ---- by food, xxiv. 1. 1.
+  ---- by ideas, xxiv. 1. 2. and 5.
+  ---- by disordered volition, xxiv. 1. 7.
+  Schirrous tumours revive, xii. 2. 2.
+  Screaming in pain, xxxiv. 1. 3.
+  Scrophula, its temperament, xxxi. 1.
+  ---- xxviii. 2. xxxix. 4. 5.
+  Scurvy of the lungs, xxvii. 2.
+  Sea-sickness, xx. 4.
+  ---- stopped by attention, xx. 5.
+  Secretion, xxxiii. 1. xxxvii.
+  ---- increased during sleep, xviii. 16.
+  Seeds require oxygenation, xxxviii. 2.
+  Sensation defined, ii. 2. 9. v. 2. xxxix. 8. 4.
+  ---- diseases of, xxxiii.
+  ---- from fibrous contractions, iv. 5. xii. 1. 6.
+  ---- in an amputated limb, iii. 6. 3.
+  ---- affects the whole sensorium, xi. 2.
+  ---- produces volition, iv. 6.
+  Sensibility increases during sleep, xviii. 15.
+  Sensitive motions, viii. xxxiii. 2. xxxiv. 1.
+  ---- fevers of two kinds, xxxiii. 1. 2.
+  ---- ideas, xv. 2. 2.
+  Sensorium defined, ii. 2. 1.
+  Senses correct one another, xviii. 7.
+  ---- distinguished from appetites, xxxiv. 1. 1.
+  Sensorial power. See Spirit of Animation.
+  ---- great expence of in the vital motions, xxxii. 3. 2.
+  ---- two kinds of excited in sensitive fevers, xxxiii. 1. 3.
+  ---- powers defined, v. 1.
+  ---- motions distinguished from fibrous motions, v. 3.
+  ---- not much, accumulated in sleep, xviii. 2.
+  ---- powers, accumulation of, xii. 5. 1.
+  ---- exhaustion of, xii. 4. 1.
+  ---- wasted below natural in hot fits, xxxii. 9. 3.
+  ---- less exertion of produces pain, xii. 5. 3.
+  ---- less quantity of it, xii. 5. 4.
+  Sensual motions distinguished from muscular, ii. 2. 7.
+  Sex owing to the imagination of the father, xxxix. 7. 6. xxxix. 6. 3.
+      xxxix. 6. 7. xxxix. 5.
+  Shingles from inflamed kidney, xxxv. 2. 2.
+  Shoulders broad, xxxi. 1. xxxix. 7. 6.
+  Shuddering from cold, xxxiv. 1. 1. and 2.
+  Sight, its accuracy in men, xvi. 6.
+  Skin, skurf on it, xxvi. 1.
+  Sleep suspends volition, xviii. 1.
+  ---- defined, xviii. 21.
+  ---- remote causes, xviii. 20.
+  ---- sensation continues in it, xviii. 2.
+  ---- from food, xxi. 1.
+  ---- from rocking, uniform sounds, xxi. 1.
+  ---- from wine and opium, xxi. 3.
+  ---- why it invigorates, xii. 5. 1.
+  ---- pulse slower and fuller, xxxii. 2. 2.
+  ---- interrupted, xxvii. 2.
+  ---- from breathing less oxygene, xviii. 20.
+  ---- from being whirled on a millstone, xviii. 20.
+  ---- from application of cold, xviii. 20.
+  ---- induced by regular hours, xxxvi. 2. 2.
+  Sleeping animals, xii. 2. 2.
+  Sleep-walkers. See Reverie, xix. 1.
+  Small-pox, xxxiii. 2. 6. xxxix. 6. 1.
+  ---- eruption first on the face, why, xxxv. 1. 1. xxxiii. 2. 10.
+  ---- the blood will not infect, xxxiii. 2. 10.
+  ---- obeys lunations, xxxvi. 4.
+  Smell, xiv. 5. xvi. 5.
+  Smiling, origin of, xvi. 8. 4.
+  Solidity, xiv. 2. 1.
+  Somnambulation. See Reverie, xix. 1.
+  Space, xiv. 2. 2.
+  Spasm, doctrine of, xxxii. 10.
+  Spectra, ocular, xl.
+  ---- mistaken for spectres, xl. 2.
+  ---- vary from long inspection, iii. 3. 5.
+  Spirit of animation. See Sensorial Power.
+  ---- of animation causes fibrous contraction, iv. 2. ii. 2. 1. xiv. 2. 4.
+  ---- possesses solidity, figure, and other properties of matter, xiv. 2.
+      4.
+  Spirits and angels, xiv. 2. 4.
+  Stammering explained, xvii. 1. 10. xvii. 2. 10.
+  Stimulus defined, ii. 2. 13. iv. 4. xii. 2. 1.
+  ---- of various kinds, xi. 1.
+  ---- with lessened effect, xii. 3. 1.
+  ---- with greater effect, xii. 3. 3.
+  ---- ceases to produce sensation, xii. 3. 6.
+  Stomach and intestines, xxv.
+  ---- inverted by great stimulus, xxv. 6.
+  ---- its actions decreased in vomiting, xxxv. 1. 3.
+  ---- a blow on it occasions death, xxv. 17.
+  Stools black, xxvii. 2.
+  Strangury, xxxv. 2. 1.
+  Sucking before nativity, xvi. 4.
+  Suckling children, sense of, xiv. 8.
+  Suggestion defined, ii. 2. 10. xv. 2. 4.
+  Sun and moon, their influence, xxxii. 6.
+  Surprise, xvii. 3. 7. xviii. 17.
+  Suspicion attends madness, xxxiv. 2. 4.
+  Swallowing, act of, xxv. 1. xvi. 4.
+  Sweat, cold, xxv. 9. xxix. 6.
+  ---- in hot fit of fever, xxxii. 9.
+  ---- in a morning, why, xviii. 15.
+  Sweaty hands cured by lime, xxix. 4. 9.
+  Swinging and rocking, why agreeable, xxi. 3.
+  Sympathy, xxxv. 1.
+  Syncope, xii. 7. 1. xxxiv. 1. 6.
+
+                  T.
+
+  Tædium vitæ. See Ennui.
+  Tape-worm, xxxix. 2. 3.
+  Taste, sense of, xiv. 5.
+  Tears, secretion of, xxiv.
+  ---- from grief, xvi. 8. 2.
+  ---- from tender pleasure, xvi. 8. 3.
+  ---- from stimulus of nasal duct, xvi. 8. xxiv. 2. 4.
+  ---- by volition, xxiv. 2. 6.
+  Teeth decaying cause headachs, xxxv. 2. 1.
+  Temperaments, xxxi.
+  Theory of medicine, wanted. Preface.
+  Thirst, sense of, xiv. 8.
+  ---- why in dropsies, xxix. 5.
+  Tickle themselves, children cannot, xvii. 3. 5.
+  Tickling, xiv. 9.
+  Time, xiv. 2. 2. xviii. 12.
+  ---- lapse of, xv. 3. 6.
+  ---- poetic and musical, why agreeable, xxii. 2.
+  ---- dramatic, xviii. 12.
+  Tooth-edge, xvi. 10. iii. 4. 3. xxii. 3. 3.
+  Touch, sense of, xiv. 2. 1.
+  ---- liable to vertigo, xxi. 9.
+  ---- of various animals, xvi. 6.
+  Trains of motions inverted, xii. 5. 5.
+  Transfusion of blood in nervous fever, xxxii. 4.
+  Translations of matter, xxix. 7.
+  Typhus, best quantity of stimulus in, xii. 7. 8.
+  ---- periods of observe lunar days, xxxii. 6.
+
+                  U.
+
+  Ulcers, art of healing, xxxiii. 3. 2.
+  ---- of the lungs, why difficult to heal, xxviii. 2.
+  Uniformity in the fine arts, why agreeable, xxii. 2.
+  Urine pale in intoxication, xxi. 6.
+  ---- paucity of in anasarca, why, xxix. 5.
+  ---- its passage from intestines to bladder, xxix. 3.
+  ---- copious during sleep, xviii. 15.
+
+                  V.
+
+  Variation, perpetual, of irritability, xii. 2. 1.
+  Vegetable buds are inferior animals, xiii. 1.
+  ---- exactly resemble their parents, xxxix.
+  ---- possess sensation and volition, xiii. 2.
+  ---- have associate and retrograde motions, xiii. 4. xxix. 9.
+  ---- their anthers and stigmas are alive, xiii. 5.
+  ---- have organs of sense and ideas, xiii. 5.
+  ---- contend for light and air, xxxix. 4. 8.
+  ---- duplicature of their flowers, xxxix. 4. 4.
+  Veins are absorbents, xxvii. 1.
+  ---- paralysis of, xxvii. 1.
+  Venereal orgasm of brutes, xxxii. 6.
+  Venesection in nervous pains, xxxii. 5. 4.
+  Verbs of three kinds, xv. 3. 4.
+  Verses, their measure, xxii. 2.
+  Vertigo, xx.
+  ---- defined, xx. 11.
+  ---- in looking from a tower, xx. 1.
+  ---- in a ship at sea, xx. 4.
+  ---- of all the senses, xxi. 9.
+  ---- by intoxication, xxxv. 1. 2.
+  Vibratory motions perceived after sailing, xx. 5. xx. 10.
+  Vinegar makes the lips pale, xxvii. 1.
+  Vis medicatrix of nature, xxxix. 4. 7.
+  Vision, sense of, xiv. 3.
+  Volition defined, v. 2. xxxiv. 1.
+  ---- affects the whole sensorium, xi. 2.
+  ---- diseases of, xxxiv.
+  Voluntarity, xi. 2. 4.
+  Voluntary motions, ix. xxxiv. 1.
+  Voluntary ideas, xv. 2. 3.
+  ---- criterion of, xi. 2. 3. xxxiv. 1.
+  Vomiting from vertigo, xx. 8.
+  ---- from drunkenness, xx. 8. xxi. 6.
+  ---- by intervals, xxv. 8.
+  ---- by voluntary efforts, xxv. 6.
+  ---- of two kinds, xxxv. 1. 3.
+  ---- in cold fit of fever, xxxii. 9. 1.
+  ---- stopped by quicksilver, xxv. 16.
+  ---- weakens the pulse, xxv. 17.
+
+                  W.
+
+  Waking, how, xviii. 14.
+  Walking, how learnt, xvi. 3.
+  Warmth in sleep, why, xviii. 15.
+  Weakness defined, xii. 1. 3. xii. 2. 1. xxxii. 3. 2.
+  ---- cure of, xii. 7. 8.
+  ---- See Debility.
+  Wit producing laughter, xxxiv. 1. 4.
+  World generated, xxxix. 4. 8.
+
+       *       *       *       *       *
+
+END OF THE FIRST VOLUME.
+
+
+
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