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+The Project Gutenberg EBook of A Practical Physiology, by Albert F. Blaisdell
+
+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: A Practical Physiology
+
+Author: Albert F. Blaisdell
+
+Release Date: December 14, 2003 [EBook #10453]
+[Most recently updated: May 4, 2020]
+
+Language: English
+
+Character set encoding: UTF-8
+
+*** START OF THIS PROJECT GUTENBERG EBOOK A PRACTICAL PHYSIOLOGY ***
+
+
+
+
+Produced by Distributed Proofreaders
+
+
+
+
+
+
+
+
+[Transcriber’s Note: Figures 162-167 have
+been renumbered. In the original, Figure 162 was labeled as 161; 163 as 162;
+etc.]
+
+
+
+
+[Illustration]
+
+
+A Practical Physiology
+
+
+
+A Text-Book for Higher Schools
+
+
+
+By Albert F. Blaisdell, M.D.
+
+
+
+Author of “Child’s Book of Health,” “How to Keep Well,”
+
+“Our Bodies and How We Live,” Etc., Etc.
+
+
+
+
+Preface.
+
+
+
+The author has aimed to prepare a text-book on human physiology for use in
+higher schools. The design of the book is to furnish a practical manual of
+the more important facts and principles of physiology and hygiene, which
+will be adapted to the needs of students in high schools, normal schools,
+and academies.
+
+
+Teachers know, and students soon learn to recognize the fact, that it is
+impossible to obtain a clear understanding of the functions of the various
+parts of the body without first mastering a few elementary facts about
+their structure. The course adopted, therefore, in this book, is to devote
+a certain amount of space to the anatomy of the several organs before
+describing their functions.
+
+
+A mere knowledge of the facts which can be gained in secondary schools,
+concerning the anatomy and physiology of the human body, is of little real
+value or interest in itself. Such facts are important and of practical
+worth to young students only so far as to enable them to understand the
+relation of these facts to the great laws of health and to apply them to
+daily living. Hence, it has been the earnest effort of the author in this
+book, as in his other physiologies for schools, to lay special emphasis
+upon such points as bear upon personal health.
+
+
+Physiology cannot be learned as it should be by mere book study. The
+result will be meagre in comparison with the capabilities of the subject.
+The study of the text should always be supplemented by a series of
+practical experiments. Actual observations and actual experiments are as
+necessary to illuminate the text and to illustrate important principles in
+physiology as they are in botany, chemistry, or physics. Hence, as
+supplementary to the text proper, and throughout the several chapters, a
+series of carefully arranged and practical experiments has been added. For
+the most part, they are simple and can be performed with inexpensive and
+easily obtained apparatus. They are so arranged that some may be omitted
+and others added as circumstances may allow.
+
+
+If it becomes necessary to shorten the course in physiology, the various
+sections printed in smaller type may be omitted or used for home study.
+
+
+The laws of most of the states now require in our public schools the study
+of the effects of alcoholic drinks, tobacco, and other narcotics upon the
+bodily life. This book will be found to comply fully with all such laws.
+
+
+The author has aimed to embody in simple and concise language the latest
+and most trustworthy information which can be obtained from the standard
+authorities on modern physiology, in regard to the several topics.
+
+
+In the preparation of this text-book the author has had the editorial help
+of his esteemed friend, Dr. J. E. Sanborn, of Melrose, Mass., and is also
+indebted to the courtesy of Thomas E. Major, of Boston, for assistance in
+revising the proofs.
+
+Albert F. Blaisdell.
+
+Boston, August, 1897.
+
+
+
+
+CONTENTS.
+
+Chapter I Introduction
+Chapter II The Bones
+Chapter III The Muscles
+Chapter IV Physical Exercise
+Chapter V Food and Drink
+Chapter VI Digestion
+Chapter VII The Blood and Its Circulation
+Chapter VIII Respiration
+Chapter IX The Skin and the Kidneys
+Chapter X The Nervous System
+Chapter XI The Special Sense
+Chapter XII The Throat and the Voice
+Chapter XIII Accidents and Emergencies
+Chapter XIV In Sickness and in Health
+        Care of the Sick-Room; Poisons and their Antidotes; Bacteria;
+        Disinfectants; Management of Contagious Diseases.
+Chapter XV Experimental Work in Physiology
+        Practical Experiments; Use of the Microscope; Additional
+        Experiments;
+Surface Anatomy and Landmarks.
+Glossary
+Index
+
+
+
+
+
+Chapter I.
+Introduction.
+
+
+1. The Study of Physiology. We are now to take up a new study, and in a
+field quite different from any we have thus far entered. Of all our
+other studies,—mathematics, physics, history, language,—not one comes
+home to us with such peculiar interest as does physiology, because this
+is the study of ourselves.
+
+Every thoughtful young person must have asked himself a hundred
+questions about the problems of human life: how it can be that the few
+articles of our daily food—milk, bread, meats, and similar things—build
+up our complex bodies, and by what strange magic they are transformed
+into hair, skin, teeth, bones, muscles, and blood.
+
+How is it that we can lift these curtains of our eyes and behold all
+the wonders of the world around us, then drop the lids, and though at
+noonday, are instantly in total darkness? How does the minute structure
+of the ear report to us with equal accuracy the thunder of the tempest,
+and the hum of the passing bee? Why is breathing so essential to our
+life, and why cannot we stop breathing when we try? Where within us,
+and how, burns the mysterious fire whose subtle heat warms us from the
+first breath of infancy till the last hour of life?
+
+These and scores of similar questions it is the province of this deeply
+interesting study of physiology to answer.
+
+2. What Physiology should Teach us. The study of physiology is not only
+interesting, but it is also extremely useful. Every reasonable person
+should not only wish to acquire the knowledge how best to protect and
+preserve his body, but should feel a certain profound respect for an
+organism so wonderful and so perfect as his physical frame. For our
+bodies are indeed not ourselves, but the frames that contain us,—the
+ships in which we, the real selves, are borne over the sea of life. He
+must be indeed a poor navigator who is not zealous to adorn and
+strengthen his ship, that it may escape the rocks of disease and
+premature decay, and that the voyage of his life may be long, pleasant,
+and successful.
+
+But above these thoughts there rises another,—that in studying
+physiology we are tracing the myriad lines of marvelous ingenuity and
+forethought, as they appear at every glimpse of the work of the Divine
+Builder. However closely we study our bodily structure, we are, at our
+best, but imperfect observers of the handiwork of Him who made us as we
+are.
+
+3. Distinctive Characters of Living Bodies. Even a very meagre
+knowledge of the structure and action of our bodies is enough to reveal
+the following distinctive characters: our bodies are continually
+breathing, that is, they take in oxygen from the surrounding air; they
+take in certain substances known as food, similar to those composing
+the body, which are capable through a process called oxidation, or
+through other chemical changes, of setting free a certain amount of
+energy.
+
+Again, our bodies are continually making heat and giving it out to
+surrounding objects, the production and the loss of heat being so
+adjusted that the whole body is warm, that is, of a temperature higher
+than that of surrounding objects. Our bodies, also, move themselves,
+either one part on another, or the whole body from place to place. The
+motive power is not from the outside world, but the energy of their
+movements exists in the bodies themselves, influenced by changes in
+their surroundings. Finally, our bodies are continually getting rid of
+so-called waste matters, which may be considered products of the
+oxidation of the material used as food, or of the substances which make
+up the organism.
+
+4. The Main Problems of Physiology briefly Stated. We shall learn in a
+subsequent chapter that the living body is continually losing energy,
+but by means of food is continually restoring its substance and
+replenishing its stock of energy. A great deal of energy thus stored up
+is utilized as mechanical work, the result of physical movements. We
+shall learn later on that much of the energy which at last leaves the
+body as heat, exists for a time within the organism in other forms than
+heat, though eventually transformed into heat. Even a slight change in
+the surroundings of the living body may rapidly, profoundly, and in
+special ways affect not only the amount, but the kind of energy set
+free. Thus the mere touch of a hair may lead to such a discharge of
+energy, that a body previously at rest may be suddenly thrown into
+violent convulsions. This is especially true in the case of tetanus, or
+lockjaw.
+
+The main problem we have to solve in the succeeding pages is to
+ascertain how it is that our bodies can renew their substance and
+replenish the energy which they are continually losing, and can,
+according to the nature of their surroundings, vary not only the
+amount, but the kind of energy which they set free.
+
+5. Technical Terms Defined. All living organisms are studied usually
+from two points of view: first, as to their form and structure; second,
+as to the processes which go on within them. The science which treats
+of all living organisms is called biology. It has naturally two
+divisions,—morphology, which treats of the form and structure of living
+beings, and physiology, which investigates their functions, or the
+special work done in their vital processes.
+
+The word anatomy, however, is usually employed instead of morphology.
+It is derived from two Greek words, and means the science of
+dissection. Human anatomy then deals with the form and structure of the
+human body, and describes how the different parts and organs are
+arranged, as revealed by observation, by dissection, and by the
+microscope.
+
+Histology is that part of anatomy which treats of the minute structure
+of any part of the body, as shown by the microscope.
+
+Human physiology describes the various processes that go on in the
+human body in health. It treats of the work done by the various parts
+of the body, and of the results of the harmonious action of the several
+organs. Broadly speaking, physiology is the science which treats of
+functions. By the word function is meant the special work which an
+organ has to do. An organ is a part of the body which does a special
+work. Thus the eye is the organ of sight, the stomach of digestion, and
+the lungs of breathing.
+
+It is plain that we cannot understand the physiology of our bodies
+without a knowledge of their anatomy. An engineer could not understand
+the working of his engine unless well acquainted with all its parts,
+and the manner in which they were fitted together. So, if we are to
+understand the principles of elementary physiology, we must master the
+main anatomical facts concerning the organs of the body before
+considering their special functions.
+
+As a branch of study in our schools, physiology aims to make clear
+certain laws which are necessary to health, so that by a proper
+knowledge of them, and their practical application, we may hope to
+spend happier and more useful, because healthier, lives. In brief, the
+study of hygiene, or the science of health, in the school curriculum,
+is usually associated with that of physiology.[1]
+
+6. Chemical Elements in the Body. All of the various complex substances
+found in nature can be reduced by chemical analysis to about 70
+elements, which cannot be further divided. By various combinations of
+these 70 elements all the substances known to exist in the world of
+nature are built up. When the inanimate body, like any other substance,
+is submitted to chemical analysis, it is found that the bone, muscle,
+teeth, blood, etc., may be reduced to a few chemical elements.
+
+In fact, the human body is built up with 13 of the 70 elements, namely:
+oxygen, hydrogen, nitrogen, chlorine, fluorine, carbon, phosphorus,
+sulphur, calcium, potassium, sodium, magnesium, and iron. Besides
+these, a few of the other elements, as silicon, have been found; but
+they exist in extremely minute quantities.
+
+The following table gives the proportion in which these various
+elements are present:
+
+Oxygen     62.430     per cent
+Carbon     21.150       ”     ”
+Hydrogen     9.865       ”     ”
+Nitrogen     3.100       ”     ”
+Calcium     1.900       ”     ”
+Phosphorus     0.946       ”     ”
+Potassium     0.230       ”     ”
+Sulphur     0.162       ”     ”
+Chlorine     0.081       ”     ”
+Sodium     0.081       ”     ”
+Magnesium     0.027       ”     ”
+Iron     0.014       ”     ”
+Fluorine     0.014       ”     ”
+———     
+100.000     
+
+As will be seen from this table, oxygen, hydrogen, and nitrogen, which
+are gases in their uncombined form, make up ¾ of the weight of the
+whole human body. Carbon, which exists in an impure state in charcoal,
+forms more than ⅕ of the weight of the body. Thus carbon and the three
+gases named, make up about 96 per cent of the total weight of the body.
+
+7. Chemical Compounds in the Body. We must keep in mind that, with
+slight exceptions, none of these 13 elements exist in their elementary
+form in the animal economy. They are combined in various proportions,
+the results differing widely from the elements of which they consist.
+Oxygen and hydrogen unite to form water, and water forms more than ⅔ of
+the weight of the whole body. In all the fluids of the body, water acts
+as a solvent, and by this means alone the circulation of nutrient
+material is possible. All the various processes of secretion and
+nutrition depend on the presence of water for their activities.
+
+8. Inorganic Salts. A large number of the elements of the body unite
+one with another by chemical affinity and form inorganic salts. Thus
+sodium and chlorine unite and form chloride of sodium, or common salt.
+This is found in all the tissues and fluids, and is one of the most
+important inorganic salts the body contains. It is absolutely necessary
+for continued existence. By a combination of phosphorus with sodium,
+potassium, calcium, and magnesium, the various phosphates are formed.
+
+The phosphates of lime and soda are the most abundant of the salts of
+the body. They form more than half the material of the bones, are found
+in the teeth and in other solids and in the fluids of the body. The
+special place of iron is in the coloring matter of the blood. Its
+various salts are traced in the ash of bones, in muscles, and in many
+other tissues and fluids. These compounds, forming salts or mineral
+matters that exist in the body, are estimated to amount to about 6 per
+cent of the entire weight.
+
+9. Organic Compounds. Besides the inorganic materials, there exists in
+the human body a series of compound substances formed of the union of
+the elements just described, but which require the agency of living
+structures. They are built up from the elements by plants, and are
+called organic. Human beings and the lower animals take the organized
+materials they require, and build them up in their own bodies into
+still more highly organized forms.
+
+The organic compounds found in the body are usually divided into three
+great classes:
+
+
+Proteids, or albuminous substances.
+
+Carbohydrates (starches, sugars, and gums).
+
+Fats.
+
+The extent to which these three great classes of organic materials of
+the body exist in the animal and vegetable kingdoms, and are utilized
+for the food of man, will be discussed in the chapter on food (Chapter
+V.). The Proteids, because they contain the element nitrogen and the
+others do not, are frequently called nitrogenous, and the other two are
+known as non-nitrogenous substances. The proteids, the type of which is
+egg albumen, or the white of egg, are found in muscle and nerve, in
+glands, in blood, and in nearly all the fluids of the body. A human
+body is estimated to yield on an average about 18 per cent of
+albuminous substances. In the succeeding chapters we shall have
+occasion to refer to various and allied forms of proteids as they exist
+in muscle (myosin), coagulated blood (fibrin), and bones (gelatin).
+
+The Carbohydrates are formed of carbon, hydrogen, and oxygen, the last
+two in the proportion to form water. Thus we have animal starch, or
+glycogen, stored up in the liver. Sugar, as grape sugar, is also found
+in the liver. The body of an average man contains about 10 per cent of
+Fats. These are formed of carbon, hydrogen, and oxygen, in which the
+latter two are not in the proportion to form water. The fat of the body
+consists of a mixture which is liquid at the ordinary temperature.
+
+Now it must not for one moment be supposed that the various chemical
+elements, as the proteids, the salts, the fats, etc., exist in the body
+in a condition to be easily separated one from another. Thus a piece of
+muscle contains all the various organic compounds just mentioned, but
+they are combined, and in different cases the amount will vary. Again,
+fat may exist in the muscles even though it is not visible to the naked
+eye, and a microscope is required to show the minute fat cells.
+
+10. Protoplasm. The ultimate elements of which the body is composed
+consist of “masses of living matter,” microscopic in size, of a
+material commonly called protoplasm.[2] In its simplest form protoplasm
+appears to be a homogeneous, structureless material, somewhat
+resembling the raw white of an egg. It is a mixture of several chemical
+substances and differs in appearance and composition in different parts
+of the body.
+
+Protoplasm has the power of appropriating nutrient material, of
+dividing and subdividing, so as to form new masses like itself. When
+not built into a tissue, it has the power of changing its shape and of
+moving from place to place, by means of the delicate processes which it
+puts forth. Now, while there are found in the lowest realm of animal
+life, organisms like the amœba of stagnant pools, consisting of nothing
+more than minute masses of protoplasm, there are others like them which
+possess a small central body called a nucleus. This is known as
+nucleated protoplasm.
+
+Illustration: Fig. 1.—Diagram of a Cell.
+
+A, nucleus;
+B, nucleolus;
+C, protoplasm. (Highly magnified)
+
+
+11. Cells. When we carry back the analysis of an organized body as far
+as we can, we find every part of it made up of masses of nucleated
+protoplasm of various sizes and shapes. In all essential features these
+masses conform to the type of protoplasmic matter just described. Such
+bodies are called cells. In many cells the nucleus is finely granular
+or reticulated in appearance, and on the threads of the meshwork may be
+one or more enlargements, called nucleoli. In some cases the protoplasm
+at the circumference is so modified as to give the appearance of a
+limiting membrane called the cell wall. In brief, then, a cell is a
+mass of nucleated protoplasm; the nucleus may have a nucleolus, and the
+cell may be limited by a cell wall. Every tissue of the human body is
+formed through the agency of protoplasmic cells, although in most cases
+the changes they undergo are so great that little evidence remains of
+their existence.
+
+There are some organisms lower down in the scale, whose whole activity
+is confined within the narrow limits of a single cell. Thus, the amœba
+begins its life as a cell split off from its parent. This divides in
+its turn, and each half is a complete amœba. When we come a little
+higher than the amœba, we find organisms which consist of several
+cells, and a specialization of function begins to appear. As we ascend
+in the animal scale, specialization of structure and of function is
+found continually advancing, and the various kinds of cells are grouped
+together into colonies or organs.
+
+12. Cells and the Human Organism. If the body be studied in its
+development, it is found to originate from a single mass of nucleated
+protoplasm, a single cell with a nucleus and nucleolus. From this
+original cell, by growth and development, the body, with all its
+various tissues, is built up. Many fully formed organs, like the liver,
+consist chiefly of cells. Again, the cells are modified to form fibers,
+such as tendon, muscle, and nerve. Later on, we shall see the white
+blood corpuscles exhibit all the characters of the amœba (Fig. 2). Even
+such dense structures as bone, cartilage, and the teeth are formed from
+cells.
+
+Illustration: Fig. 2.—Amœboid Movement of a Human White Blood
+Corpuscle. (Showing various phases of movement.)
+
+
+In short, cells may be regarded as the histological units of animal
+structures; by the combination, association, and modification of these
+the body is built up. Of the real nature of the changes going on within
+the living protoplasm, the process of building up lifeless material
+into living structures, and the process of breaking down by which waste
+is produced, we know absolutely nothing. Could we learn that, perhaps
+we should know the secret of life.
+
+13. Kinds of Cells. Cells vary greatly in size, some of the smallest
+being only 1/3500 an inch or less in diameter. They also vary greatly
+in form, as may be seen in Figs. 3 and 5. The typical cell is usually
+_globular_ in form, other shapes being the result of pressure or of
+similar modifying influences. The globular, as well as the large, flat
+cells, are well shown in a drop of saliva. Then there are the
+_columnar_ cells, found in various parts of the intestines, in which
+they are closely arranged side by side. These cells sometimes have on
+the free surface delicate prolongations called cilia. Under the
+microscope they resemble a wave, as when the wind blows over a field of
+grain (Fig. 5). There are besides cells known as _spindle, stellate,
+squamous_ or pavement, and various other names suggested by their
+shapes. Cells are also described as to their contents. Thus _fat_ and
+_pigment_ cells are alluded to in succeeding sections. Again, they may
+be described as to their functions or location or the tissue in which
+they are found, as _epithelial_ cells, _blood_ cells (corpuscles, Figs.
+2 and 66), _nerve_ cells (Fig. 4), and _connective-tissue_ cells.
+
+14. Vital Properties of Cells. Each cell has a life of its own. It
+manifests its vital properties in that it is born, grows, multiplies,
+decays, and at last dies.[3] During its life it assimilates food,
+works, rests, and is capable of spontaneous motion and frequently of
+locomotion. The cell can secrete and excrete substance, and, in brief,
+presents nearly all the phenomena of a human being.
+
+Cells are produced only from cells by a process of self-division,
+consisting of a cleavage of the whole cell into parts, each of which
+becomes a separate and independent organism. Cells rapidly increase in
+size up to a certain definite point which they maintain during adult
+life. A most interesting quality of cell life is motion, a beautiful
+form of which is found in ciliated epithelium. Cells may move actively
+and passively. In the blood the cells are swept along by the current,
+but the white corpuscles, seem able to make their way actively through
+the tissues, as if guided by some sort of instinct.
+
+Illustration: Fig. 3.—Various Forms of Cells.
+
+
+A,  columnar cells found lining various parts of the intestines (called
+_columnar epithelium_);
+  B, cells of a fusiform or spindle shape found in the loose tissue
+  under the skin and in other parts (called _connective-tissue cells_);
+  C, cell having many processes or projections—such are found in
+  connective tissue, D, primitive cells composed of protoplasm with
+  nucleus, and having no cell wall. All are represented about 400 times
+  their real size.
+
+
+Some cells live a brief life of 12 to 24 hours, as is probably the case
+with many of the cells lining the alimentary canal; others may live for
+years, as do the cells of cartilage and bone. In fact each cell goes
+through the same cycle of changes as the whole organism, though
+doubtless in a much shorter time. The work of cells is of the most
+varied kind, and embraces the formation of every tissue and
+product,—solid, liquid, or gaseous. Thus we shall learn that the cells
+of the liver form bile, those of the salivary glands and of the glands
+of the stomach and pancreas form juices which aid in the digestion of
+food.
+
+15. The Process of Life. All living structures are subject to constant
+decay. Life is a condition of incessant changes, dependent upon two
+opposite processes, repair and decay. Thus our bodies are not composed
+of exactly the same particles from day to day, or even from one moment
+to another, although to all appearance we remain the same individuals.
+The change is so gradual, and the renewal of that which is lost may be
+so exact, that no difference can be noticed except at long intervals of
+time.[4] (See under “Bacteria,” Chapter XIV.)
+
+The entire series of chemical changes that take place in the living
+body, beginning with assimilation and ending with excretion, is
+included in one word, metabolism. The process of building up living
+material, or the change by which complex substances (including the
+living matter itself) are built up from simpler materials, is called
+anabolism. The breaking down of material into simple products, or the
+changes in which complex materials (including the living substance) are
+broken down into comparatively simple products, is known as katabolism.
+This reduction of complex substances to simple, results in the
+production of animal force and energy. Thus a complex substance, like a
+piece of beef-steak, is built up of a large number of molecules which
+required the expenditure of force or energy to store up. Now when this
+material is reduced by the process of digestion to simpler bodies with
+fewer molecules, such as carbon dioxid, urea, and water, the force
+stored up in the meat as potential energy becomes manifest and is used
+as active life-force known as _kinetic energy_.
+
+16. Epithelium. Cells are associated and combined in many ways to form
+a simple tissue. Such a simple tissue is called an epithelium or
+surface-limiting tissue, and the cells are known as epithelial cells.
+These are united by a very small amount of a cement substance which
+belongs to the proteid class of material. The epithelial cells, from
+their shape, are known as squamous, columnar, glandular, or ciliated.
+Again, the cells may be arranged in only a single layer, or they may be
+several layers deep. In the former case the epithelium is said to be
+simple; in the latter, stratified. No blood-vessels pass into these
+tissues; the cells derive their nourishment by the imbibition of the
+plasma of the blood exuded into the subjacent tissue.
+
+Illustration: Fig. 4.—Nerve Cells from the Gray Matter of the
+Cerebellum. (Magnified 260 diameters.)
+
+
+17. Varieties of Epithelium. The squamous or pavement epithelium
+consists of very thin, flattened scales, usually with a small nucleus
+in the center. When the nucleus has disappeared, they become mere horny
+plates, easily detached. Such cells will be described as forming the
+outer layer of the skin, the lining of the mouth and the lower part of
+the nostrils.
+
+The columnar epithelium consists of pear-shaped or elongated cells,
+frequently as a single layer of cells on the surface of a mucous
+membrane, as on the lining of the stomach and intestines, and the free
+surface of the windpipe and large air-tubes.
+
+The glandular or spheroidal epithelium is composed of round cells or
+such as become angular by mutual pressure. This kind forms the lining
+of glands such as the liver, pancreas, and the glands of the skin.
+
+The ciliated epithelium is marked by the presence of very fine
+hair-like processes called cilia, which develop from the free end of
+the cell and exhibit a rapid whip-like movement as long as the cell is
+alive. This motion is always in the same direction, and serves to carry
+away mucus and even foreign particles in contact with the membrane on
+which the cells are placed. This epithelium is especially common in the
+air passages, where it serves to keep a free passage for the entrance
+and exit of air. In other canals a similar office is filled by this
+kind of epithelium.
+
+18. Functions of Epithelial Tissues. The epithelial structures may be
+divided, as to their functions, into two main divisions. One is chiefly
+protective in character. Thus the layers of epithelium which form the
+superficial layer of the skin have little beyond such an office to
+discharge. The same is to a certain extent true of the epithelial cells
+covering the mucous membrane of the mouth, and those lining the air
+passages and air cells of the lungs.
+
+Illustration: Fig. 5.—Various Kinds of Epithelial Cells
+
+
+A,  columnar cells of intestine;
+  B, polyhedral cells of the conjunctiva;
+  C, ciliated conical cells of the trachea;
+  D, ciliated cell of frog’s mouth;
+  E, inverted conical cell of trachea;
+  F, squamous cell of the cavity of mouth, seen from its broad surface;
+  G, squamous cell, seen edgeways.
+
+
+The second great division of the epithelial tissues consists of those
+whose cells are formed of highly active protoplasm, and are busily
+engaged in some sort of secretion. Such are the cells of glands,—the
+cells of the salivary glands, which secrete the saliva, of the gastric
+glands, which secrete the gastric juice, of the intestinal glands, and
+the cells of the liver and sweat glands.
+
+19. Connective Tissue. This is the material, made up of fibers and
+cells, which serves to unite and bind together the different organs and
+tissues. It forms a sort of flexible framework of the body, and so
+pervades every portion that if all the other tissues were removed, we
+should still have a complete representation of the bodily shape in
+every part. In general, the connective tissues proper act as packing,
+binding, and supporting structures. This name includes certain tissues
+which to all outward appearance vary greatly, but which are properly
+grouped together for the following reasons: first, they all act as
+supporting structures; second, under certain conditions one may be
+substituted for another; third, in some places they merge into each
+other.
+
+All these tissues consist of a ground-substance, or matrix, cells, and
+fibers. The ground-substance is in small amount in connective tissues
+proper, and is obscured by a mass of fibers. It is best seen in hyaline
+cartilage, where it has a glossy appearance. In bone it is infiltrated
+with salts which give bone its hardness, and make it seem so unlike
+other tissues. The cells are called connective-tissue corpuscles,
+cartilage cells, and bone corpuscles, according to the tissues in which
+they occur. The fibers are the white fibrous and the yellow elastic
+tissues.
+
+The following varieties are usually described:
+
+Connective Tissues Proper:
+White Fibrous Tissue.
+Yellow Elastic Tissue.
+Areolar or Cellular Tissue.
+Adipose or Fatty Tissue.
+Adenoid or Retiform Tissue.
+
+Cartilage (Gristle):
+Hyaline.
+White Fibro-cartilage.
+Yellow Fibro-cartilage.
+
+Bone and Dentine of Teeth.
+
+
+20. White Fibrous Tissue. This tissue consists of bundles of very
+delicate fibrils bound together by a small amount of cement substance.
+Between the fibrils protoplasmic masses (connective-tissue corpuscles)
+are found. These fibers may be found so interwoven as to form a sheet,
+as in the periosteum of the bone, the fasciæ around muscles, and the
+capsules of organs; or they may be aggregated into bundles and form
+rope-like bands, as in the ligaments of joints and the tendons of
+muscles. On boiling, this tissue yields gelatine. In general, where
+white fibrous tissue abounds, structures are held together, and there
+is flexibility, but little or no distensibility.
+
+Illustration: Fig. 6.—White Fibrous Tissue. (Highly magnified.)
+
+
+21. Yellow Elastic Tissue. The fibers of yellow elastic tissue are much
+stronger and coarser than those of the white. They are yellowish, tend
+to curl up at the ends, and are highly elastic. It is these fibers
+which give elasticity to the skin and to the coats of the arteries. The
+typical form of this tissue occurs in the ligaments which bind the
+vertebræ together (Fig. 26), in the true vocal cords, and in certain
+ligaments of the larynx. In the skin and fasciæ, the yellow elastic is
+found mixed with white fibrous and areolar tissues. It does not yield
+gelatine on boiling, and the cells are, if any, few.
+
+Illustration: Fig. 7.—Yellow Elastic Tissue. (Highly magnified.)
+
+
+22. Areolar or Cellular Tissue. This consists of bundles of delicate
+fibers interlacing and crossing one another, forming irregular spaces
+or meshes. These little spaces, in health, are filled with fluid that
+has oozed out of the blood-vessels. The areolar tissue forms a
+protective covering for the tissues of delicate and important organs.
+
+23. Adipose or Fatty Tissue. In almost every part of the body the
+ordinary areolar tissue contains a variable quantity of adipose or
+fatty tissue. Examined by the microscope, the fat cells consist of a
+number of minute sacs of exceedingly delicate, structureless membrane
+filled with oil. This is liquid in life, but becomes solidified after
+death. This tissue is plentiful beneath the skin, in the abdominal
+cavity, on the surface of the heart, around the kidneys, in the marrow
+of bones, and elsewhere. Fat serves as a soft packing material. Being a
+poor conductor, it retains the heat, and furnishes a store rich in
+carbon and hydrogen for use in the body.
+
+24. Adenoid or Retiform Tissue. This is a variety of connective tissue
+found in the tonsils, spleen, lymphatic glands, and allied structures.
+It consists of a very fine network of cells of various sizes. The
+tissue combining them is known as adenoid or gland-like tissue.
+
+Illustration: Fig. 8.—Fibro-Cartilage Fibers. (Showing network
+surrounded cartilage cells.)
+
+
+25. Cartilage. Cartilage, or gristle, is a tough but highly elastic
+substance. Under the microscope cartilage is seen to consist of a
+matrix, or base, in which nucleated cells abound, either singly or in
+groups. It has sometimes a fine ground-glass appearance, when the
+cartilage is spoken of as hyaline. In other cases the matrix is almost
+replaced by white fibrous tissue. This is called white fibro-cartilage,
+and is found where great strength and a certain amount of rigidity are
+required.
+
+Again, there is between the cells a meshwork of yellow elastic fibers,
+and this is called yellow fibro-cartilage (Fig. 8). The hyaline
+cartilage forms the early state of most of the bones, and is also a
+permanent coating for the articular ends of long bones. The white
+fibro-cartilage is found in the disks between the bodies of the
+vertebræ, in the interior of the knee joint, in the wrist and other
+joints, filling the cavities of the bones, in socket joints, and in the
+grooves for tendons. The yellow fibro-cartilage forms the expanded part
+of the ear, the epiglottis, and other parts of the larynx.
+
+26. General Plan of the Body. To get a clearer idea of the general plan
+on which the body is constructed, let us imagine its division into
+perfectly equal parts, one the right and the other the left, by a great
+knife severing it through the median, or middle line in front, backward
+through the spinal column, as a butcher divides an ox or a sheep into
+halves for the market. In a section of the body thus planned the skull
+and the spine together are shown to have formed a tube, containing the
+brain and spinal cord. The other parts of the body form a second tube
+(ventral) in front of the spinal or dorsal tube. The upper part of the
+second tube begins with the mouth and is formed by the ribs and
+breastbone. Below the chest in the abdomen, the walls of this tube
+would be made up of the soft parts.
+
+Illustration: Fig. 9.—Diagrammatic Longitudinal Section of the Trunk
+and Head. (Showing the dorsal and the ventral tubes.)
+
+  A,  the cranial cavity;
+  B, the cavity of the nose;
+  C, the mouth;
+  D, the alimentary canal represented as a simple straight tube;
+  E, the sympathetic nervous system;
+  F, heart;
+  G, diaphragm;
+  H, stomach;
+  K, end of spinal portion of cerebro-spinal nervous system.
+
+We may say, then, that the body consists of two tubes or cavities,
+separated by a bony wall, the dorsal or nervous tube, so called because
+it contains the central parts of the nervous system; and the visceral
+or ventral tube, as it contains the viscera, or general organs of the
+body, as the alimentary canal, the heart, the lungs, the sympathetic
+nervous system, and other organs.
+
+The more detailed study of the body may now be begun by a description
+of the skeleton or framework which supports the soft parts.
+
+Experiments.
+
+For general directions and explanations and also detailed suggestions
+for performing experiments, see Chapter XV.
+
+Experiment 1. _To examine squamous epithelium._ With an ivory
+paper-knife scrape the back of the tongue or the inside of the lips or
+cheek; place the substance thus obtained upon a glass slide; cover it
+with a thin cover-glass, and if necessary add a drop of water. Examine
+with the microscope, and the irregularly formed epithelial cells will
+be seen.
+
+Experiment 2. _To examine ciliated epithelium._ Open a frog’s mouth,
+and with the back of a knife blade gently scrape a little of the
+membrane from the roof of the mouth. Transfer to a glass slide, add a
+drop of salt solution, and place over it a cover-glass with a hair
+underneath to prevent pressure upon the cells. Examine with a
+microscope under a high power. The cilia move very rapidly when quite
+fresh, and are therefore not easily seen.
+
+For additional experiments which pertain to the microscopic examination
+of the elementary tissues and to other points in practical histology,
+see Chapter XV.
+
+Note. Inasmuch as most of the experimental work of this chapter depends
+upon the use of the microscope and also necessarily assumes a knowledge
+of facts which are discussed later, it would be well to postpone
+experiments in histology until they can be more satisfactorily handled
+in connection with kindred topics as they are met with in the
+succeeding chapters.]
+
+
+
+
+Chapter II.
+The Bones.
+
+
+27. The Skeleton. Most animals have some kind of framework to support
+and protect the soft and fleshy parts of their bodies. This framework
+consists chiefly of a large number of bones, and is called the
+skeleton. It is like the keel and ribs of a vessel or the frame of a
+house, the foundation upon which the bodies are securely built.
+
+There are in the adult human body 200 distinct bones, of many sizes and
+shapes. This number does not, however, include several small bones
+found in the tendons of muscles and in the ear. The teeth are not
+usually reckoned as separate bones, being a part of the structure of
+the skin.
+
+The number of distinct bones varies at different periods of life. It is
+greater in childhood than in adults, for many bones which are then
+separate, to allow growth, afterwards become gradually united. In early
+adult life, for instance, the skull contains 22 naturally separate
+bones, but in infancy the number is much greater, and in old age far
+less.
+
+The bones of the body thus arranged give firmness, strength, and
+protection to the soft tissues and vital organs, and also form levers
+for the muscles to act upon.
+
+28. Chemical Composition of Bone. The bones, thus forming the framework
+of the body, are hard, tough, and elastic. They are twice as strong as
+oak; one cubic inch of compact bone will support a weight of 5000
+pounds. Bone is composed of earthy or mineral matter (chiefly in the
+form of lime salts), and of animal matter (principally gelatine), in
+the proportion of two-thirds of the former to one-third of the latter.
+
+Illustration: Fig. 10.—The Skeleton.
+
+
+The proportion of earthy to animal matter varies with age. In infancy
+the bones are composed almost wholly of animal matter. Hence, an
+infant’s bones are rarely broken, but its legs may soon become
+misshapen if walking is allowed too early. In childhood, the bones
+still contain a larger percentage of animal matter than in more
+advanced life, and are therefore more liable to bend than to break;
+while in old age, they contain a greater percentage of mineral matter,
+and are brittle and easily broken.
+
+Experiment 3. _To show the mineral matter in bone_. Weigh a large soup
+bone; put it on a hot, clear fire until it is at a red heat. At first
+it becomes black from the carbon of its organic matter, but at last it
+turns white. Let it cool and weigh again. The animal matter has been
+burnt out, leaving the mineral or earthy part, a white, brittle
+substance of exactly the same shape, but weighing only about two-thirds
+as much as the bone originally weighed.
+
+Experiment 4. _To show the animal matter in bone_. Add a teaspoonful of
+muriatic acid to a pint of water, and place the mixture in a shallow
+earthen dish. Scrape and clean a chicken’s leg bone, part of a sheep’s
+rib, or any other small, thin bone. Soak the bone in the acid mixture
+for a few days. The earthy or mineral matter is slowly dissolved, and
+the bone, although retaining its original form, loses its rigidity, and
+becomes pliable, and so soft as to be readily cut. If the experiment be
+carefully performed, a long, thin bone may even be tied into a knot.
+
+Illustration: Fig. 11.—The fibula tied into a knot, after the hard
+mineral matter has been dissolved by acid.
+
+
+29. Physical Properties of Bone. If we take a leg bone of a sheep, or a
+large end of beef shin bone, and saw it lengthwise in halves, we see
+two distinct structures. There is a hard and compact tissue, like
+ivory, forming the outside shell, and a spongy tissue inside having the
+appearance of a beautiful lattice work. Hence this is called cancellous
+tissue, and the gradual transition from one to the other is apparent.
+
+It will also be seen that the shaft is a hollow cylinder, formed of
+compact tissue, enclosing a cavity called the medullary canal, which is
+filled with a pulpy, yellow fat called _marrow_. The marrow is richly
+supplied with blood-vessels, which enter the cavity through small
+openings in the compact tissue. In fact, all over the surface of bone
+are minute canals leading into the substance. One of these, especially
+constant and large in many bones, is called the _nutrient foramen_, and
+transmits an artery to nourish the bone.
+
+At the ends of a long bone, where it expands, there is no medullary
+canal, and the bony tissue is spongy, with only a thin layer of dense
+bone around it. In flat bones we find two layers or plates of compact
+tissue at the surface, and a spongy tissue between. Short and irregular
+bones have no medullary canal, only a thin shell of dense bone filled
+with cancellous tissue.
+
+Illustration: Fig. 12.—The Right femur sawed in two, lengthwise.
+(Showing arrangement of compact and cancellous tissue.)
+
+
+Experiment 5. Obtain a part of a beef shin bone, or a portion of a
+sheep’s or calf’s leg, including if convenient the knee joint. Have the
+bone sawed in two, lengthwise, keeping the marrow in place. Boil,
+scrape, and carefully clean one half. Note the compact and spongy
+parts, shaft, etc.
+
+Experiment 6. Trim off the flesh from the second half. Note the pinkish
+white appearance of the bone, the marrow, and the tiny specks of blood,
+etc. Knead a small piece of the marrow in the palm; note the oily
+appearance. Convert some marrow into a liquid by heating. Contrast this
+fresh bone with an old dry one, as found in the fields. Fresh bones
+should be kept in a cool place, carefully wrapped in a damp cloth,
+while waiting for class use.
+
+A fresh or living bone is covered with a delicate, tough, fibrous
+membrane, called the periosteum. It adheres very closely to the bone,
+and covers every part except at the joints and where it is protected
+with cartilage. The periosteum is richly supplied with blood-vessels,
+and plays a chief part in the growth, formation, and repair of bone. If
+a portion of the periosteum be detached by injury or disease, there is
+risk that a layer of the subjacent bone will lose its vitality and be
+cast off.[5]
+
+30. Microscopic Structure of Bone. If a very thin slice of bone be cut
+from the compact tissue and examined under a microscope, numerous
+minute openings are seen. Around these are arranged rings of bone, with
+little black bodies in them, from which radiate fine, dark lines. These
+openings are sections of canals called _Haversian canals_, after
+Havers, an English physician, who first discovered them. The black
+bodies are minute cavities called _lacunæ_, while the fine lines are
+very minute canals, _canaliculi_, which connect the lacunæ and the
+Haversian canals. These Haversian canals are supplied with tiny
+blood-vessels, while the lacunæ contain bone cells. Very fine branches
+from these cells pass into the canaliculi. The Haversian canals run
+lengthwise of the bone; hence if the bone be divided longitudinally
+these canals will be opened along their length (Fig. 13).
+
+Thus bones are not dry, lifeless substances, but are the very type of
+activity and change. In life they are richly supplied with blood from
+the nutrient artery and from the periosteum, by an endless network of
+nourishing canals throughout their whole structure. Bone has,
+therefore, like all other living structures, a _self-formative_ power,
+and draws from the blood the materials for its own nutrition.
+
+Illustration: Fig. 13.
+
+  A,  longitudinal section of bone, by which the Haversian canals are
+      seen branching and communicating with one another;
+  B, cross section of a very thin slice of bone, magnified about 300
+  diameters—little openings (Haversian canals) are seen, and around
+  them are ranged rings of bones with little black bodies (lacunæ),
+  from which branch out fine dark lines (canaliculi);
+  C, a bone cell, highly magnified, lying in lacuna.
+
+The Bones of the Head.
+
+31. The Head, or Skull. The bones of the skeleton, the bony framework
+of our bodies, may be divided into those of the head, the trunk, and
+the limbs.
+
+The bones of the head are described in two parts,—those of the cranium,
+or brain-case, and those of the face. Taken together, they form the
+skull. The head is usually said to contain 22 bones, of which 8 belong
+to the cranium and 14 to the face. In early childhood, the bones of the
+head are separate to allow the brain to expand; but as we grow older
+they gradually unite, the better to protect the delicate brain tissue.
+
+32. The Cranium. The cranium is a dome-like structure, made up in the
+adult of 8 distinct bones firmly locked together. These bones are:
+
+  One Frontal,
+  Two Parietal,
+  Two Temporal
+  One Occipital,
+  One Sphenoid,
+  One Ethmoid.
+
+The frontal bone forms the forehead and front of the head. It is united
+with the two parietal bones behind, and extends over the forehead to
+make the roofs of the sockets of the eyes. It is this bone which, in
+many races of man, gives a dignity of person and a beauty of form seen
+in no other animal.
+
+The parietal bones form the sides and roof of the skull. They are
+bounded anteriorly by the frontal bone, posteriorly by the occipital,
+and laterally by the temporal and sphenoid bones. The two bones make a
+beautiful arch to aid in the protection of the brain.
+
+The temporal bones, forming the temples on either side, are attached to
+the sphenoid bone in front, the parietals above, and the occipital
+behind. In each temporal bone is the cavity containing the organs of
+hearing. These bones are so called because the hair usually first turns
+gray over them.
+
+The occipital bone forms the lower part of the base of the skull, as
+well as the back of the head. It is a broad, curved bone, and rests on
+the topmost vertebra (atlas) of the backbone; its lower part is pierced
+by a large oval opening called the _foramen magnum_, through which the
+spinal cord passes from the brain (Fig. 15).
+
+The sphenoid bone is in front of the occipital, forming a part of the
+base of the skull. It is wedged between the bones of the face and those
+of the cranium, and locks together fourteen different bones. It bears a
+remarkable resemblance to a bat with extended wings, and forms a series
+of girders to the arches of the cranium.
+
+The ethmoid bone is situated between the bones of the cranium and those
+of the face, just at the root of the nose. It forms a part of the floor
+of the cranium. It is a delicate, spongy bone, and is so called because
+it is perforated with numerous holes like a sieve, through which the
+nerves of smell pass from the brain to the nose.
+
+Illustration: Fig. 14.—The Skull
+
+33. The Face. The bones of the face serve, to a marked extent, in
+giving form and expression to the human countenance. Upon these bones
+depend, in a measure, the build of the forehead, the shape of the chin,
+the size of the eyes, the prominence of the cheeks, the contour of the
+nose, and other marks which are reflected in the beauty or ugliness of
+the face.
+
+The face is made up of fourteen bones which, with the exception of the
+lower jaw, are, like those of the cranium, closely interlocked with
+each other. By this union these bones help form a number of cavities
+which contain most important and vital organs. The two deep, cup-like
+sockets, called the orbits, contain the organs of sight. In the
+cavities of the nose is located the sense of smell, while the buccal
+cavity, or mouth, is the site of the sense of taste, and plays besides
+an important part in the first act of digestion and in the function of
+speech.
+
+The bones of the face are:
+
+  Two Superior Maxillary,
+  Two Malar,
+  Two Nasal,
+  Two Lachrymal,
+  Two Palate,
+  Two Turbinated,
+  One Vomer,
+  One Lower Maxillary.
+
+34. Bones of the Face. The superior maxillary or upper jawbones form a
+part of the roof of the mouth and the entire floor of the orbits. In
+them is fixed the upper set of teeth.
+
+The malar or cheek bones are joined to the upper jawbones, and help
+form the sockets of the eyes. They send an arch backwards to join the
+temporal bones. These bones are remarkably thick and strong, and are
+specially adapted to resist the injury to which this part of the face
+is exposed.
+
+The nasal or nose bones are two very small bones between the eye
+sockets, which form the bridge of the nose. Very near these bones are
+the two small lachrymal bones. These are placed in the inner angles of
+the orbit, and in them are grooves in which lie the ducts through which
+the tears flow from the eyes to the nose.
+
+The palate bones are behind those of the upper jaw and with them form
+the bony part of the roof of the mouth. The inferior turbinated are
+spongy, scroll-like bones, which curve about within the nasal cavities
+so as to increase the surface of the air passages of the nose.
+
+The vomer serves as a thin and delicate partition between the two
+cavities of the nose. It is so named from its resemblance to a
+ploughshare.
+
+Illustration: Fig. 15.—The Base of the Skull.
+
+  A,  palate process of upper jawbone;
+  B, zygoma, forming zygomatic arch;
+  C, condyle for forming articulation with atlas;
+  D, foramen magnum;
+  E, occipital bone.
+
+The longest bone in the face is the inferior maxillary, or lower jaw.
+It has a horseshoe shape, and supports the lower set of teeth. It is
+the only movable bone of the head, having a vertical and lateral motion
+by means of a hinge joint with a part of the temporal bone.
+
+35. Sutures of the Skull. Before leaving the head we must notice the
+peculiar and admirable manner in which the edges of the bones of the
+outer shell of the skull are joined together. These edges of the bones
+resemble the teeth of a saw. In adult life these tooth-like edges fit
+into each other and grow together, suggesting the dovetailed joints
+used by the cabinet-maker. When united these serrated edges look almost
+as if sewed together; hence their name, sutures. This manner of union
+gives unity and strength to the skull.
+
+In infants, the corners of the parietal bones do not yet meet, and the
+throbbing of the brain may be seen and felt under these “soft spots,”
+or _fontanelles_, as they are called. Hence a slight blow to a babe’s
+head may cause serious injury to the brain (Fig. 14).
+
+The Bones of the Trunk.
+
+36. The Trunk. The trunk is that central part of the body which
+supports the head and the upper pair of limbs. It divides itself into
+an upper cavity, the thorax, or chest; and a lower cavity, the abdomen.
+These two cavities are separated by a movable, muscular partition
+called the diaphragm, or midriff (Figs. 9 and 49).
+
+The bones of the trunk are variously related to each other, and some of
+them become united during adult life into bony masses which at earlier
+periods are quite distinct. For example, the sacrum is in early life
+made up of five distinct bones which later unite into one.
+
+The upper cavity, or chest, is a bony enclosure formed by the
+breastbone, the ribs, and the spine. It contains the heart and the
+lungs (Fig. 86).
+
+The lower cavity, or abdomen, holds the stomach, liver, intestines,
+spleen, kidneys, and some other organs (Fig. 59).
+
+The bones of the trunk may be subdivided into those of the spine, the
+ribs, and the hips.
+
+The trunk includes 54 bones usually thus arranged:
+
+Spinal Column, 26 bones:
+
+7 Cervical Vertebræ.
+    12 Dorsal Vertebræ.
+     5 Lumbar Vertebræ.
+     1 Sacrum.
+     1 Coccyx.
+
+Ribs, 24 bones:
+
+14 True Ribs.
+     6 False Ribs.
+     4 Floating Ribs.
+
+Sternum.
+  IV. Two Hip Bones.
+   V. Hyoid Bone.
+
+37. The Spinal Column. The spinal column, or backbone, is a marvelous
+piece of mechanism, combining offices which nothing short of perfection
+in adaptation and arrangement could enable it to perform. It is the
+central structure to which all the other parts of the skeleton are
+adapted. It consists of numerous separate bones, called vertebræ. The
+seven upper ones belong to the neck, and are called cervical vertebræ.
+The next twelve are the dorsal vertebræ; these belong to the back and
+support the ribs. The remaining five belong to the loins, and are
+called lumbar vertebræ. On looking at the diagram of the backbone (Fig.
+9) it will be seen that the vertebræ increase in size and strength
+downward, because of the greater burden they have to bear, thus clearly
+indicating that an erect position is the one natural to man.
+
+Illustration: Fig. 16.—The Spinal Column.
+
+This column supports the head, encloses and protects the spinal cord,
+and forms the basis for the attachment of many muscles, especially
+those which maintain the body in an erect position. Each vertebra has
+an opening through its center, and the separate bones so rest, one upon
+another, that these openings form a continuous canal from the head to
+the lower part of the spine. The great nerve, known as the spinal cord,
+extends from the cranium through the entire length of this canal. All
+along the spinal column, and between each two adjoining bones, are
+openings on each side, through which nerves pass out to be distributed
+to various parts of the body.
+
+Between the vertebræ are pads or cushions of cartilage. These act as
+“buffers,” and serve to give the spine strength and elasticity and to
+prevent friction of one bone on another. Each vertebra consists of a
+body, the solid central portion, and a number of projections called
+processes. Those which spring from the posterior of each arch are the
+spinous processes. In the dorsal region they are plainly seen and felt
+in thin persons.
+
+The bones of the spinal column are arranged in three slight and
+graceful curves. These curves not only give beauty and strength to the
+bony framework of the body, but also assist in the formation of
+cavities for important internal organs. This arrangement of elastic
+pads between the vertebræ supplies the spine with so many elastic
+springs, which serve to break the effect of shock to the brain and the
+spinal cord from any sudden jar or injury.
+
+The spinal column rests on a strong three-sided bone called the sacrum,
+or sacred-bone, which is wedged in between the hip bones and forms the
+keystone of the pelvis. Joined to the lower end of the sacrum is the
+coccyx, or cuckoo-bone, a tapering series of little bones.
+
+Experiment 7. Run the tips of the fingers briskly down the backbone,
+and the spines of the vertebræ will be tipped with red so that they can
+be readily counted. Have the model lean forward with the arms folded
+across the chest; this will make the spines of the vertebræ more
+prominent.
+
+Experiment 8. _To illustrate the movement of torsion in the spine, or
+its rotation round its own axis_. Sit upright, with the back and
+shoulders well applied against the back of a chair. Note that the head
+and neck can be turned as far as 60° or 70°. Now bend forwards, so as
+to let the dorsal and lumbar vertebræ come into play, and the head can
+be turned 30° more.
+
+Experiment 9. _To show how the spinal vertebræ make a firm but flexible
+column._ Take 24 hard rubber overcoat buttons, or the same number of
+two-cent pieces, and pile them on top of each other. A thin layer of
+soft putty may be put between the coins to represent the pads of
+cartilage between the vertebræ. The most striking features of the
+spinal column may be illustrated by this simple apparatus.
+
+38. How the Head and Spine are Joined together. The head rests upon the
+spinal column in a manner worthy of special notice. This consists in
+the peculiar structure of the first two cervical vertebræ, known as the
+axis and atlas. The atlas is named after the fabled giant who supported
+the earth on his shoulders. This vertebra consists of a ring of bone,
+having two cup-like sockets into which fit two bony projections arising
+on either side of the great opening (_foramen magnum_) in the occipital
+bone. The hinge joint thus formed allows the head to nod forward, while
+ligaments prevent it from moving too far.
+
+On the upper surface of the axis, the second vertebra, is a peg or
+process, called the _odontoid process_ from its resemblance to a tooth.
+This peg forms a pivot upon which the head with the atlas turns. It is
+held in its place against the front inner surface of the atlas by a
+band of strong ligaments, which also prevents it from pressing on the
+delicate spinal cord. Thus, when we turn the head to the right or left,
+the skull and the atlas move together, both rotating on the odontoid
+process of the axis.
+
+39. The Ribs and Sternum. The barrel-shaped framework of the chest is
+in part composed of long, slender, curved bones called ribs. There are
+twelve ribs on each side, which enclose and strengthen the chest; they
+somewhat resemble the hoops of a barrel. They are connected in pairs
+with the dorsal vertebræ behind.
+
+The first seven pairs, counting from the neck, are called the _true_
+ribs, and are joined by their own special cartilages directly to the
+breastbone. The five lower pairs, called the _false_ ribs, are not
+directly joined to the breastbone, but are connected, with the
+exception of the last two, with each other and with the last true ribs
+by cartilages. These elastic cartilages enable the chest to bear great
+blows with impunity. A blow on the sternum is distributed over fourteen
+elastic arches. The lowest two pairs of false ribs, are not joined even
+by cartilages, but are quite free in front, and for this reason are
+called _floating_ ribs.
+
+The ribs are not horizontal, but slope downwards from the backbone, so
+that when raised or depressed by the strong intercostal muscles, the
+size of the chest is alternately increased or diminished. This movement
+of the ribs is of the utmost importance in breathing (Fig. 91).
+
+The sternum, or breastbone, is a long, flat, narrow bone forming the
+middle front wall of the chest. It is connected with the ribs and with
+the collar bones. In shape it somewhat resembles an ancient dagger.
+
+40. The Hip Bones. Four immovable bones are joined together so as to
+form at the lower extremity of the trunk a basin-like cavity called the
+pelvis. These four bones are the sacrum and the coccyx, which have been
+described, and the two hip bones.
+
+Illustration: Fig. 17.—Thorax. (Anterior view.)
+
+The hip bones are large, irregularly shaped bones, very firm and
+strong, and are sometimes called the haunch bones or _ossa innominata_
+(nameless bones). They are united to the sacrum behind and joined to
+each other in front. On the outer side of each hip bone is a deep cup,
+or socket, called the _acetabulum_, resembling an ancient vinegar cup,
+into which fits the rounded head of the thigh bone. The bones of the
+pelvis are supported like a bridge on the legs as pillars, and they in
+turn contain the internal organs in the lower part of the trunk.
+
+41. The Hyoid Bone. Under the lower jaw is a little horseshoe shaped
+bone called the hyoid bone, because it is shaped like the Greek letter
+upsilon (Υ). The root of the tongue is fastened to its bend, and the
+larynx is hung from it as from a hook. When the neck is in its natural
+position this bone can be plainly felt on a level with the lower jaw
+and about one inch and a half behind it. It serves to keep open the top
+of the larynx and for the attachment of the muscles, which move the
+tongue. (See Fig. 46.) The hyoid bone, like the knee-pan, is not
+connected with any other bone.
+
+The Bones of the Upper Limbs.
+
+42. The Upper Limbs. Each of the upper limbs consist of the upper arm,
+the forearm, and the hand. These bones are classified as follows:
+
+Upper Arm: Scapula, or shoulder-blade,
+      Clavicle, or collar bone,
+      Humerus, or arm bone,
+
+    Forearm: Ulna,
+      Radius,
+
+    Hand: 8 Carpal or wrist bones,
+      5 Metacarpal bones,
+     14 Phalanges, or finger bones,
+
+making 32 bones in all.
+
+43. The Upper Arm. The two bones of the shoulder, the scapula and the
+clavicle, serve in man to attach the arm to the trunk. The scapula, or
+shoulder-blade, is a flat, triangular bone, placed point downwards, and
+lying on the upper and back part of the chest, over the ribs. It
+consists of a broad, flat portion and a prominent ridge or _spine_. At
+its outer angle it has a shallow cup known as the _glenoid cavity_.
+Into this socket fits the rounded head of the humerus. The
+shoulder-blade is attached to the trunk chiefly by muscles, and is
+capable of extensive motion.
+
+The clavicle, or collar bone, is a slender bone with a double curve
+like an italic _f_, and extends from the outer angle of the
+shoulder-blade to the top of the breastbone. It thus serves like the
+keystone of an arch to hold the shoulder-blade firmly in its place, but
+its chief use is to keep the shoulders wide apart, that the arm may
+enjoy a freer range of motion. This bone is often broken by falls upon
+the shoulder or arm.
+
+The humerus is the strongest bone of the upper extremity. As already
+mentioned, its rounded head fits into the socket of the shoulder-blade,
+forming a ball-and-socket joint, which permits great freedom of motion.
+The shoulder joint resembles what mechanics call a universal joint, for
+there is no part of the body which cannot be touched by the hand.
+
+Illustration: Fig. 18.—Left Scapula, or Shoulder-Blade.
+
+When the shoulder is dislocated the head of the humerus has been forced
+out of its socket. The lower end of the bone is grooved to help form a
+hinge joint at the elbow with the bones of the forearm (Fig. 27).
+
+44. The Forearm. The forearm contains two long bones, the ulna and the
+radius. The ulna, so called because it forms the elbow, is the longer
+and larger bone of the forearm, and is on the same side as the little
+finger. It is connected with the humerus by a hinge joint at the elbow.
+It is prevented from moving too far back by a hook-like projection
+called the _olecranon process_, which makes the sharp point of the
+elbow.
+
+The radius is the shorter of the two bones of the forearm, and is on
+the same side as the thumb. Its slender, upper end articulates with the
+ulna and humerus; its lower end is enlarged and gives attachment in
+part to the bones of the wrist. This bone radiates or turns on the
+ulna, carrying the hand with it.
+
+Experiment 10. Rest the forearm on a table, with the palm up (an
+attitude called supination). The radius is on the outer side and
+parallel with the ulna If now, without moving the elbow, we turn the
+hand (pronation), as if to pick up something from the table, the radius
+may be seen and felt crossing over the ulna, while the latter has not
+moved.
+
+Illustration: Fig. 19.—Left Clavicle, or Collar Bone. (Anterior
+surface.)
+
+45. The Hand. The hand is the executive or essential part of the upper
+limb. Without it the arm would be almost useless. It consists of 27
+separate bones, and is divided into three parts, the wrist, the palm,
+and the fingers.
+
+Illustration: Fig. 20.—Left Humerus.    Fig. 21.—Left Radius and Ulna.
+
+The carpus, or wrist, includes 8 short bones, arranged in two rows of
+four each, so as to form a broad support for the hand. These bones are
+closely packed, and tightly bound with ligaments which admit of ample
+flexibility. Thus the wrist is much less liable to be broken than if it
+were to consist of a single bone, while the elasticity from having the
+eight bones movable on each other, neutralizes, to a great extent, a
+shock caused by falling on the hands. Although each of the wrist bones
+has a very limited mobility in relation to its neighbors, their
+combination gives the hand that freedom of action upon the wrist, which
+is manifest in countless examples of the most accurate and delicate
+manipulation.
+
+The metacarpal bones are the five long bones of the back of the hand.
+They are attached to the wrist and to the finger bones, and may be
+easily felt by pressing the fingers of one hand over the back of the
+other. The metacarpal bones of the fingers have little freedom of
+movement, while the thumb, unlike the others, is freely movable. We are
+thus enabled to bring the thumb in opposition to each of the fingers, a
+matter of the highest importance in manipulation. For this reason the
+loss of the thumb disables the hand far more than the loss of either of
+the fingers. This very significant opposition of the thumb to the
+fingers, furnishing the complete grasp by the hand, is characteristic
+of the human race, and is wanting in the hand of the ape, chimpanzee,
+and ourang-outang.
+
+The phalanges, or finger bones, are the fourteen small bones arranged
+in three rows to form the fingers. Each finger has three bones; each
+thumb, two.
+
+The large number of bones in the hand not only affords every variety of
+movement, but offers great resistance to blows or shocks. These bones
+are united by strong but flexible ligaments. The hand is thus given
+strength and flexibility, and enabled to accomplish the countless
+movements so necessary to our well-being.
+
+In brief, the hand is a marvel of precise and adapted mechanism,
+capable not only of performing every variety of work and of expressing
+many emotions of the mind, but of executing its orders with
+inconceivable rapidity.
+
+The Bones of the Lower Limbs.
+
+46. The Lower Limbs. The general structure and number of the bones of
+the lower limbs bear a striking similarity to those of the upper limbs.
+Thus the leg, like the arm, is arranged in three parts, the thigh, the
+lower leg, and the foot. The thigh bone corresponds to the humerus; the
+tibia and fibula to the ulna and radius; the ankle to the wrist; and
+the metatarsus and the phalanges of the foot, to the metacarpus and the
+phalanges of the hand.
+
+The bones of the lower limbs may be thus arranged:
+
+  Thigh: Femur, or thigh bone,
+
+  Lower Leg: Patella, or knee cap,
+    Tibia, or shin bone,
+    Fibula, or splint bone,
+
+  Foot: 7 Tarsal or ankle bones,
+    5 Metatarsal or instep bones,
+   14 Phalanges, or toes bones,
+
+making 30 bones in all.
+
+Illustration: Fig. 22.—Right Femur, or Thigh Bone.
+
+
+47. The Thigh. The longest and strongest of all the bones is the femur,
+or thigh bone. Its upper end has a rounded head which fits into the
+_acetabulum_, or the deep cup-like cavity of the hip bone, forming a
+perfect ball-and-socket joint. When covered with cartilage, the ball
+fits so accurately into its socket that it may be retained by
+atmospheric pressure alone (sec. 50).
+
+The shaft of the femur is strong, and is ridged and roughened in places
+for the attachment of the muscles. Its lower end is broad and
+irregularly shaped, having two prominences called _condyles_, separated
+by a groove, the whole fitted for forming a hinge joint with the bones
+of the lower leg and the knee-cap.
+
+48. The Lower Leg. The lower leg, like the forearm, consists of two
+bones. The tibia, or shin bone, is the long three-sided bone forming
+the front of the leg. The sharp edge of the bone is easily felt just
+under the skin. It articulates with the lower end of the thigh bone,
+forming with it a hinge joint.
+
+The fibula, the companion bone of the tibia, is the long, slender bone
+on the outer side of the leg. It is firmly fixed to the tibia at each
+end, and is commonly spoken of as the small bone of the leg. Its lower
+end forms the outer projection of the ankle. In front of the knee
+joint, embedded in a thick, strong tendon, is an irregularly
+disk-shaped bone, the patella, or knee-cap. It increases the leverage
+of important muscles, and protects the front of the knee joint, which
+is, from its position, much exposed to injury.
+
+Illustration: Fig. 23.—Patella, or Knee-Cap.
+
+49. The Foot. The bones of the foot, 26 in number, consist of the
+tarsal bones, the metatarsal, and the phalanges. The tarsal bones are
+the seven small, irregular bones which make up the ankle. These bones,
+like those of the wrist, are compactly arranged, and are held firmly in
+place by ligaments which allow a considerable amount of motion.
+
+One of the ankle bones, the _os calcis_, projects prominently
+backwards, forming the heel. An extensive surface is thus afforded for
+the attachment of the strong tendon of the calf of the leg, called the
+tendon of Achilles. The large bone above the heel bone, the
+_astragalus_, articulates with the tibia, forming a hinge joint, and
+receives the weight of the body.
+
+The metatarsal bones, corresponding to the metacarpals of the hand, are
+five in number, and form the lower instep.
+
+The phalanges are the fourteen bones of the toes,—three in each except
+the great toe, which, like the thumb, has two. They resemble in number
+and plan the corresponding bones in the hand. The bones of the foot
+form a double arch,—an arch from before backwards, and an arch from
+side to side. The former is supported behind by the os calcis, and in
+front by the ends of the metatarsal bones. The weight of the body falls
+perpendicularly on the astragalus, which is the key-bone or crown of
+the arch. The bones of the foot are kept in place by powerful
+ligaments, combining great strength with elasticity.
+
+Illustration: Fig. 24.—Right Tibia and Fibula (Anterior surface.)
+
+Illustration: Fig. 25.—Bones of Right Foot. (Dorsal surface.)
+
+The Joints.
+
+50. Formation of Joints. The various bones of the skeleton are
+connected together at different parts of their surfaces by joints, or
+articulations. Many different kinds of joints have been described, but
+the same general plan obtains for nearly all. They vary according to
+the kind and the amount of motion.
+
+The principal structures which unite in the formation of a joint are:
+bone, cartilage, synovial membrane, and ligaments. Bones make the chief
+element of all the joints, and their adjoining surfaces are shaped to
+meet the special demands of each joint (Fig. 27). The joint-end of
+bones is coated with a thin layer of tough, elastic cartilage. This is
+also used at the edge of joint-cavities, forming a ring to deepen them.
+The rounded heads of bones which move in them are thus more securely
+held in their sockets.
+
+Besides these structures, the muscles also help to maintain the
+joint-surfaces in proper relation. Another essential to the action of
+the joints is the pressure of the outside air. This may be sufficient
+to keep the articular surfaces in contact even after all the muscles
+are removed. Thus the hip joint is so completely surrounded by
+ligaments as to be air-tight; and the union is very strong. But if the
+ligaments be pierced and air allowed to enter the joint, the union at
+once becomes much less close, and the head of the thigh bone falls away
+as far as the ligaments will allow it.
+
+51. Synovial Membrane. A very delicate connective tissue, called the
+synovial membrane, lines the capsules of the joints, and covers the
+ligaments connected with them. It secretes the _synovia_, or joint oil,
+a thick and glairy fluid, like the white of a raw egg, which thoroughly
+lubricates the inner surfaces of the joints. Thus the friction and heat
+developed by movement are reduced, and every part of a joint is enabled
+to act smoothly.
+
+52. Ligaments. The bones are fastened together, held in place, and
+their movements controlled, to a certain extent, by bands of various
+forms, called ligaments. These are composed mainly of bundles of white
+fibrous tissue placed parallel to, or closely interlaced with, one
+another, and present a shining, silvery aspect. They extend from one of
+the articulating bones to another, strongly supporting the joint, which
+they sometimes completely envelope with a kind of cap (Fig. 28). This
+prevents the bones from being easily dislocated. It is difficult, for
+instance, to separate the two bones in a shoulder or leg of mutton,
+they are so firmly held together by tough ligaments.
+
+While ligaments are pliable and flexible, permitting free movement,
+they are also wonderfully strong and inextensible. A bone may be
+broken, or its end torn off, before its ligaments can be ruptured. The
+wrist end of the radius, for instance, is often torn off by force
+exerted on its ligaments without their rupture.
+
+The ligaments are so numerous and various and are in some parts so
+interwoven with each other, that space does not allow even mention of
+those that are important. At the knee joint, for instance, there are no
+less than fifteen distinct ligaments.
+
+53. Imperfect Joints. It is only perfect joints that are fully equipped
+with the structures just mentioned. Some joints lack one or more, and
+are therefore called imperfect joints. Such joints allow little or no
+motion and have no smooth cartilages at their edges. Thus, the bones of
+the skull are dovetailed by joints called sutures, which are immovable.
+The union between the vertebræ affords a good example of imperfect
+joints which are partially movable.
+
+Illustration: Fig. 26.—Elastic Tissue from the Ligaments about Joints.
+(Highly magnified.)
+
+54. Perfect Joints. There are various forms of perfect joints,
+according to the nature and amount of movement permitted. They an
+divided into hinge joints, ball-and-socket joints and pivot joints.
+
+The hinge joints allow forward and backward movements like a hinge.
+These joints are the most numerous in the body, as the elbow, the
+ankle, and the knee joints.
+
+In the ball-and-socket joints—a beautiful contrivance—the rounded head
+of one bone fits into a socket in the other, as the hip joint and
+shoulder joint. These joints permit free motion in almost every
+direction.
+
+In the pivot joint a kind of peg in one bone fits into a notch in
+another. The best example of this is the joint between the first and
+second vertebræ (see sec. 38). The radius moves around on the ulna by
+means of a pivot joint. The radius, as well as the bones of the wrist
+and hand, turns around, thus enabling us to turn the palm of the hand
+upwards and downwards. In many joints the extent of motion amounts to
+only a slight gliding between the ends of the bones.
+
+55. Uses of the Bones. The bones serve many important and useful
+purposes. The skeleton, a general framework, affords protection,
+support, and leverage to the bodily tissues. Thus, the bones of the
+skull and of the chest protect the brain, the lungs, and the heart; the
+bones of the legs support the weight of the body; and the long bones of
+the limbs are levers to which muscles are attached.
+
+Owing to the various duties they have to perform, the bones are
+constructed in many different shapes. Some are broad and flat; others,
+long and cylindrical; and a large number very irregular in form. Each
+bone is not only different from all the others, but is also curiously
+adapted to its particular place and use.
+
+Illustration: Fig. 27.—Showing how the Ends of the Bones are shaped to
+form the Elbow Joint. (The cut ends of a few ligaments are seen.)
+
+Nothing could be more admirable than the mechanism by which each one of
+the bones is enabled to fulfill the manifold purposes for which it was
+designed. We have seen how the bones of the cranium are united by
+sutures in a manner the better to allow the delicate brain to grow, and
+to afford it protection from violence. The arched arrangement of the
+bones of the foot has several mechanical advantages, the most important
+being that it gives firmness and elasticity to the foot, which thus
+serves as a support for the weight of the body, and as the chief
+instrument of locomotion.
+
+The complicated organ of hearing is protected by a winding series of
+minute apartments, in the rock-like portion of the temporal bone. The
+socket for the eye has a jutting ridge of bone all around it, to guard
+the organ of vision against injury. Grooves and canals, formed in hard
+bone, lodge and protect minute nerves and tiny blood-vessels. The
+surfaces of bones are often provided with grooves, sharp edges, and
+rough projections, for the origin and insertion of muscles.
+
+Illustration: Fig. 28.—External Ligaments of the Knee.
+
+56. The Bones in Infancy and Childhood. The bones of the infant,
+consisting almost wholly of cartilage, are not stiff and hard as in
+after life, but flexible and elastic. As the child grows, the bones
+become more solid and firmer from a gradually increased deposit of lime
+salts. In time they become capable of supporting the body and
+sustaining the action of the muscles. The reason is that well-developed
+bones would be of no use to a child that had not muscular strength to
+support its body. Again, the numerous falls and tumbles that the child
+sustains before it is able to walk, would result in broken bones almost
+every day of its life. As it is, young children meet with a great
+variety of falls without serious injury.
+
+But this condition of things has its dangers. The fact that a child’s
+bones bend easily, also renders them liable to permanent change of
+shape. Thus, children often become bow-legged when allowed to walk too
+early. Moderate exercise, however, even in infancy, promotes the health
+of the bones as well as of the other tissues. Hence a child may be kept
+too long in its cradle, or wheeled about too much in a carriage, when
+the full use of its limbs would furnish proper exercise and enable it
+to walk earlier.
+
+57. Positions at School. Great care must be exercised by teachers that
+children do not form the habit of taking injurious positions at school.
+The desks should not be too low, causing a forward stoop; or too high,
+throwing one shoulder up and giving a twist to the spine. If the seats
+are too low there will result an undue strain on the shoulder and the
+backbone; if too high, the feet have no proper support, the thighs may
+be bent by the weight of the feet and legs, and there is a prolonged
+strain on the hips and back. Curvature of the spine and round shoulders
+often result from long-continued positions at school in seats and at
+desks which are not adapted to the physical build of the occupant.
+
+Illustration: Fig. 29.—Section of the Knee Joint. (Showing its internal
+structure)
+
+A,  tendon of the semi-membranosus muscle cut across;
+  B, F, tendon of same muscle;
+  C, internal condyle of femur;
+  D, posterior crucial ligament;
+  E, internal interarticular fibro cartilage;
+  G, bursa under knee-cap;
+  H, ligament of knee-cap;
+  K, fatty mass under knee-cap;
+  L, anterior crucial ligament cut across;
+  P, patella, or knee-cap
+
+A few simple rules should guide teachers and school officials in
+providing proper furniture for pupils. Seats should be regulated
+according to the size and age of the pupils, and frequent changes of
+seats should be made. At least three sizes of desks should be used in
+every schoolroom, and more in ungraded schools. The feet of each pupil
+should rest firmly on the floor, and the edge of the desk should be
+about one inch higher than the level of the elbows. A line dropped from
+the edge of the desk should strike the front edge of the seat. Sliding
+down into the seat, bending too much over the desk while writing and
+studying, sitting on one foot or resting on the small of the back, are
+all ungraceful and unhealthful positions, and are often taken by pupils
+old enough to know better. This topic is well worth the vigilance of
+every thoughtful teacher, especially of one in the lower grades.
+
+58. The Bones in After Life. Popular impression attributes a less share
+of life, or a lower grade of vitality, to the bones than to any other
+part of the body. But really they have their own circulation and
+nutrition, and even nervous relations. Thus, bones are the seat of
+active vital processes, not only during childhood, but also in adult
+life, and in fact throughout life, except perhaps in extreme old age.
+The final knitting together of the ends of some of the bones with their
+shafts does not occur until somewhat late in life. For example, the
+upper end of the tibia and its shaft do not unite until the
+twenty-first year. The separate bones of the sacrum do not fully knit
+into one solid bone until the twenty-fifth year. Hence, the risk of
+subjecting the bones of young persons to undue violence from
+injudicious physical exercise as in rowing, baseball, football, and
+bicycle-riding.
+
+The bones during life are constantly going through the process of
+absorption and reconstruction. They are easily modified in their
+growth. Thus the continued pressure of some morbid deposit, as a tumor
+or cancer, or an enlargement of an artery, may cause the absorption or
+distortion of bones as readily as of one of the softer tissues. The
+distortion resulting from tight lacing is a familiar illustration of
+the facility with which the bones may be modified by prolonged
+pressure.
+
+Some savage races, not content with the natural shape of the head, take
+special methods to mould it by continued artificial pressure, so that
+it may conform in its distortion to the fashion of their tribe or race.
+This custom is one of the most ancient and widespread with which we are
+acquainted. In some cases the skull is flattened, as seen in certain
+Indian tribes on our Pacific coast, while with other tribes on the same
+coast it is compressed into a sort of conical appearance. In such cases
+the brain is compelled, of course, to accommodate itself to the change
+in the shape of the head; and this is done, it is said, without any
+serious result.
+
+59. Sprains and Dislocations. A twist or strain of the ligaments and
+soft parts about a joint is known as a sprain, and may result from a
+great variety of accidents. When a person falls, the foot is frequently
+caught under him, and the twist comes upon the ligaments and tissues of
+the ankle. The ligaments cannot stretch, and so have to endure the
+wrench upon the joint. The result is a sprained ankle. Next to the
+ankle, a sprain of the wrist is most common. A person tries, by
+throwing out his hand, to save himself from a fall, and the weight of
+the body brings the strain upon the firmly fixed wrist. As a result of
+a sprain, the ligaments may be wrenched or torn, and even a piece of an
+adjacent bone may be torn off; the soft parts about the injured joint
+are bruised, and the neighboring muscles put to a severe stretch. A
+sprain may be a slight affair, needing only a brief rest, or it may be
+severe and painful enough to call for the most skillful treatment by a
+surgeon. Lack of proper care in severe sprains often results in
+permanent lameness.
+
+A fall or a blow may bring such a sudden wrench or twist upon the
+ligaments as to force a bone out of place. This displacement is known
+as a dislocation. A child may trip or fall during play and put his
+elbow out of joint. A fall from horseback, a carriage, or a bicycle may
+result in a dislocation of the shoulder joint. In playing baseball a
+swift ball often knocks a finger out of joint. A dislocation must be
+reduced at once. Any delay or carelessness may make a serious and
+painful affair of it, as the torn and bruised parts rapidly swell and
+become extremely sensitive.
+
+60. Broken Bones. The bones, especially those of the upper limbs, are
+often fractured or broken. The _simple_ fracture is the most common
+form, the bone being broken in a single place with no opening through
+the skin. When properly adjusted, the bone heals rapidly. Sometimes
+bones are crushed into a number of fragments; this is a _comminuted_
+fracture. When, besides the break, there is an opening through the soft
+parts and surface of the body, we have a _compound_ fracture. This is a
+serious injury, and calls for the best surgical treatment.
+
+A bone may be bent, or only partly broken, or split. This is called “a
+green-stick fracture,” from its resemblance to a half-broken green
+stick. This fracture is more common in the bones of children.
+
+Fractures may be caused by direct violence, as when a bone is broken at
+a certain point by some powerful force, as a blow from a baseball bat
+or a fall from a horse. Again, a bone may be broken by indirect
+violence, as when a person being about to fall, throws out his hand to
+save himself. The force of the fall on the hand often breaks the wrist,
+by which is meant the fracture of the lower end of the radius, often
+known as the “silver-fork fracture.” This accident is common in winter
+from a fall or slip on the ice.
+
+Sometimes bones are broken at a distance from the point of injury, as
+in a fracture of the ribs by violent compression of the chest; or
+fracture may occur from the vibration of a blow, as when a fall or blow
+upon the top of the head produces fracture of the bones at the base of
+the brain.[6]
+
+61. Treatment for Broken Bones. When a bone is broken a surgeon is
+needed to set it, that is, to bring the broken parts into their natural
+position, and retain them by proper appliances. Nature throws out
+between and around the broken ends of bones a supply of repair material
+known as plastic lymph, which is changed to fibrous tissue, then to
+cartilage, and finally to bone. This material serves as a sort of
+cement to hold the fractured parts together. The excess of this at the
+point of union can be felt under the skin for some time after the bone
+is healed.
+
+With old people a broken bone is often a serious matter, and may
+cripple them for life or prove fatal. A trifling fall, for instance,
+may cause a broken hip (popularly so called, though really a fracture
+of the neck of the femur), from the shock of which, and the subsequent
+pain and exhaustion, an aged person may die in a few weeks. In young
+people, however, the parts of a broken bone will knit together in three
+or four weeks after the fracture is reduced; while in adults, six or
+even more may be required for firm union. After a broken bone is strong
+enough to be used, it is fragile for some time; and great care must be
+taken, especially with children, that the injured parts may not be
+broken again before perfect union takes place.[7]
+
+62. The Effect of Alcohol upon the Bones. While the growth of the bones
+occurs, of course, mainly during the earlier years of life, yet they do
+not attain their full maturity until about the twenty-fifth year; and
+it is stated that in persons devoted to intellectual pursuits, the
+skull grows even after that age. It is plainly necessary that during
+this period of bone growth the nutrition of the body should be of the
+best, that the bones may be built up from pure blood, and supplied with
+all the materials for a large and durable framework. Else the body will
+be feeble and stunted, and so through life fall short of its purpose.
+
+If this bony foundation be then laid wrong, the defect can never be
+remedied. This condition is seen in young persons who have been
+underfed and overworked. But the use of alcoholic liquors produces a
+similar effect, hindering bone cell-growth and preventing full
+development.[8] The appetite is diminished, nutrition perverted and
+impaired, the stature stunted, and both bodily and mental powers are
+enfeebled.
+
+63. Effect of Tobacco upon the Bones. Another narcotic, the destructive
+influence of which is wide and serious, is tobacco. Its pernicious
+influence, like that of alcohol, is peculiarly hurtful to the young, as
+the cell development during the years of growth is easily disturbed by
+noxious agents. The bone growth is by cells, and a powerful narcotic
+like tobacco retards cell-growth, and thus hinders the building up of
+the bodily frame. The formation of healthy bone demands good,
+nutritious blood, but if instead of this, the material furnished for
+the production of blood is poor in quality or loaded with poisonous
+narcotics, the body thus defrauded of its proper building material
+becomes undergrown and enfeebled.
+
+Two unfavorable facts accompany this serious drawback: one is, that
+owing to the insidious nature of the smoky poison[9] (cigarettes are
+its worst form) the cause may often be unsuspected, and so go on,
+unchecked; and the other, that the progress of growth once interrupted,
+the gap can never be fully made up. Nature does her best to repair
+damages and to restore defects, but never goes backwards to remedy
+neglects.
+
+Additional Experiments.
+
+Experiment 11. Take a portion of the decalcified bone obtained from
+Experiment 4, and wash it thoroughly in water: in this it is insoluble.
+Place it in a solution of carbonate of soda and wash it again. Boil it
+in water, and from it gelatine will be obtained.
+
+Experiment 12. Dissolve in hydrochloric acid a small piece of the
+powdered bone-ash obtained from Experiment 3. Bubbles of carbon dioxid
+are given off, indicating the presence of a carbonate. Dilute the
+solution; add an excess of ammonia, and we find a white precipitate of
+the phosphate of lime and of magnesia.
+
+Experiment 13. Filter the solution in the preceding experiment, and to
+the filtrate add oxalate of ammonia. The result is a white precipitate
+of the oxalate of lime, showing there is lime present, but not as a
+phosphate.
+
+Experiment 14. To the solution of mineral matters obtained from
+Experiment 3, add acetate of soda until free acetic acid is present,
+recognized by the smell (like dilute vinegar); then add oxalate of
+ammonia. The result will be a copious white precipitate of lime salts.
+
+Experiment 15. _To show how the cancellous structure of bone is able to
+support a great deal of weight_. Have the market-man saw out a cubic
+inch from the cancellous tissue of a fresh beef bone and place it on a
+table with its principal layers upright. Balance a heavy book upon it,
+and then gradually place upon it various articles and note how many
+pounds it will support before giving way.
+
+Experiment 16. Repeat the last experiment, using a cube of the
+decalcified bone obtained from Experiment 4.
+
+Note. As the succeeding chapters are studied, additional experiments on
+bones and their relation to other parts of the body, will readily
+suggest themselves to the ingenious instructor or the thoughtful
+student. Such experiments may be utilized for review or other
+exercises.
+
+Review Analysis: The Skeleton (206 bones).
+
+                    /                 / 1 Frontal,
+                   /                 /  2 Parietal,
+                  /     I. Cranium  |   2 Temporal,
+                 /       (8 bones)  |   1 Occipital,
+                /                    \  1 Sphenoid,
+               |                      \ 1 Ethmoid.
+               |
+               |                       / 2 Superior Maxillary,
+   The Head    |                      /  2 Malar,
+  (28 bones).  |                     /   2 Nasal,
+               |       II. Face     |    2 Lachrymal Bones,
+               |      (14 bones)    |    2 Palate Bones,
+               |                     \   2 Turbinated,
+               |                      \  1 Vomer,
+               \                       \ 1 Lower Maxillary.
+                \
+                 \                   / Hammer,
+                  \   III. The Ear  |  Anvil,
+                   \   (6 bones)     \ Stirrup.
+
+                  /                         /  7 Cervical Vertebræ.
+                 /                         /  12 Dorsal Vertebræ,
+                /       I. Spinal Column  |    5 Lumbar Vertebræ,
+               |           (26 bones)      \     Sacrum,
+               |                            \    Coccyx.
+   The Trunk   |
+  (54 bones).  |                       /  7 True Ribs,
+               |       II. The Ribs   |   3 False Ribs,
+               |        (24 bones)     \  2 Floating Ribs.
+               |
+                \     III. Sternum.
+                 \     IV. Two Hip Bones.
+                  \     V. Hyoid Bone.
+
+
+
+                     /                    /   Scapula,
+                    /      I. Upper Arm  |    Clavicle,
+                   |                      \   Humerus.
+                   |
+  The Upper Limbs  |      II. Forearm    /    Ulna,
+    (64 bones).    |                     \    Radius.
+                   |
+                   |                     /  8 Carpal Bones,
+                    \    III. Hand      |   5 Metacarpal Bones,
+                     \                   \ 14 Phalanges.
+
+                     /     I. Thigh           Femur.
+                    /
+                   |                      /   Patella,
+  The Lower Limbs  |      II. Lower Leg  |    Tibia,
+    (60 bones).    |                      \   Fibula.
+                   |
+                   |                     /  7 Tarsal Bones,
+                    \    III. Foot      |   5 Metatarsal Bones,
+                     \                   \ 14 Phalanges.
+
+
+
+Chapter III.
+The Muscles.
+
+
+64. Motion in Animals. All motion of our bodies is produced by means of
+muscles. Not only the limbs are moved by them, but even the movements
+of the stomach and of the heart are controlled by muscles. Every part
+of the body which is capable of motion has its own special set of
+muscles.
+
+Even when the higher animals are at rest it is possible to observe some
+kind of motion in them. Trees and stones never move unless acted upon
+by external force, while the infant and the tiniest insect can execute
+a great variety of movements. Even in the deepest sleep the beating of
+the heart and the motion of the chest never cease. In fact, the power
+to execute spontaneous movement is the most characteristic property of
+living animals.
+
+65. Kinds of Muscles. Most of the bodily movements, such as affect the
+limbs and the body as a whole, are performed by muscles under our
+control. These muscles make up the red flesh or lean parts, which,
+together with the fat, clothe the bony framework, and give to it
+general form and proportion. We call these muscular tissues voluntary
+muscles, because they usually act under the control of the will.
+
+The internal organs, as those of digestion, secretion, circulation, and
+respiration, perform their functions by means of muscular activity of
+another kind, that is, by that of muscles not under our control. This
+work goes on quite independently of the will, and during sleep. We call
+the instruments of this activity involuntary muscles. The voluntary
+muscles, from peculiarities revealed by the microscope, are also known
+as striped or striated muscles. The involuntary from their smooth,
+regular appearance under the microscope are called the unstriped or
+non-striated muscles.
+
+The two kinds of muscles, then, are the red, voluntary, striated
+muscles, and the smooth, involuntary, non-striated muscles.
+
+66. Structure of Voluntary Muscles. The main substance which clothes
+the bony framework of the body, and which forms about two-fifths of its
+weight, is the voluntary muscular tissue. These muscles do not cover
+and surround the bones in continuous sheets, but consist of separate
+bundles of flesh, varying in size and length, many of which are capable
+of independent movement.
+
+Each muscle has its own set of blood-vessels, lymphatics, and nerves.
+It is the blood that gives the red color to the flesh. Blood-vessels
+and nerves on their way to other parts of the body, do not pass through
+the muscles, but between them. Each muscle is enveloped in its own
+sheath of connective tissue, known as the fascia. Muscles are not
+usually connected directly with bones, but by means of white,
+glistening cords called tendons.
+
+Illustration: Fig. 30.—Striated (voluntary) Muscular Fibers.
+
+A,  fiber serparating into disks;
+  B, fibrillæ (highly magnified);
+  C, cross section of a disk
+
+If a small piece of muscle be examined under a microscope it is found
+to be made up of bundles of fibers. Each fiber is enclosed within a
+delicate, transparent sheath, known as the sarcolemma. If one of these
+fibers be further examined under a microscope, it will be seen to
+consist of a great number of still more minute fibers called fibrillæ.
+These fibers are also seen marked cross-wise with dark stripes, and can
+be separated at each stripe into disks. These cross markings account
+for the name _striped_ or _striated_ muscle.
+
+The fibrillæ, then, are bound together in a bundle to form a fiber,
+which is enveloped in its own sheath, the sarcolemma. These fibers, in
+turn, are further bound together to form larger bundles called
+fasciculi, and these, too, are enclosed in a sheath of connective
+tissue. The muscle itself is made up of a number of these fasciculi
+bound together by a denser layer of connective tissue.
+
+Experiment 17. _To show the gross structure of muscle._ Take a small
+portion of a large muscle, as a strip of lean corned beef. Have it
+boiled until its fibers can be easily separated. Pick the bundles and
+fasciculi apart until the fibers are so fine as to be almost invisible
+to the naked eye. Continue the experiment with the help of a hand
+magnifying glass or a microscope.
+
+67. The Involuntary Muscles. These muscles consist of ribbon-shaped
+bands which surround hollow fleshy tubes or cavities. We might compare
+them to India rubber rings on rolls of paper. As they are never
+attached to bony levers, they have no need of tendons.
+
+Illustration: Fig. 31.—A, Muscular Fiber, showing Stripes, and Nuclei,
+b and c. (Highly magnified.)
+
+The microscope shows these muscles to consist not of fibers, but of
+long spindle-shaped cells, united to form sheets or bands. They have no
+sarcolemma, stripes, or cross markings like those of the voluntary
+muscles. Hence their name of _non-striated_, or _unstriped_, and
+_smooth_ muscles.
+
+The involuntary muscles respond to irritation much less rapidly than do
+the voluntary. The wave of contraction passes over them more slowly and
+more irregularly, one part contracting while another is relaxing. This
+may readily be seen in the muscular action of the intestines, called
+vermicular motion. It is the irregular and excessive contraction of the
+muscular walls of the bowels that produces the cramp-like pains of
+colic.
+
+The smooth muscles are found in the tissues of the heart, lungs,
+blood-vessels, stomach, and intestines. In the stomach their
+contraction produces the motion by which the food is churned about; in
+the arteries and veins they help supply the force by which the blood is
+driven along, and in the intestines that by which the partly digested
+food is mainly kept in motion.
+
+Thus all the great vital functions are carried on, regardless of the
+will of the individual, or of any outward circumstances. If it required
+an effort of the will to control the action of the internal organs we
+could not think of anything else. It would take all our time to attend
+to living. Hence the care of such delicate and important machinery has
+wisely been put beyond our control.
+
+Thus, too, these muscles act instinctively without training; but the
+voluntary need long and careful education. A babe can use the muscles
+of swallowing on the first day of its life as well as it ever can. But
+as it grows up, long and patient education of its voluntary muscles is
+needed to achieve walking, writing, use of musical instruments, and
+many other acts of daily life.
+
+Illustration: Fig. 32.—A Spindle Cell of Involuntary Muscle. (Highly
+magnified.)
+
+Experiment 18. _To show the general appearance of the muscles._ Obtain
+the lower part of a sheep’s or calf’s leg, with the most of the lean
+meat and the hoof left on. One or more of the muscles with their
+bundles of fibers, fascia, and tendons; are readily made out with a
+little careful dissection. The dissection should be made a few days
+before it is wanted and the parts allowed to harden somewhat in dilute
+alcohol.
+
+68. Properties of Muscular Tissue. The peculiar property of living
+muscular tissue is irritability, or the capacity of responding to a
+stimulus. When a muscle is irritated it responds by contracting. By
+this act the muscle does not diminish its bulk to any extent; it simply
+changes its form. The ends of the muscle are drawn nearer each other
+and the middle is thicker.
+
+Muscles do not shorten themselves all at once, but the contraction
+passes quickly over them in the form of a wave. They are usually
+stimulated by nervous action. The delicate nerve fibrils which end in
+the fibers communicate with the brain, the center of the will power.
+Hence, when the brain commands, a nervous impulse, sent along the nerve
+fibers, becomes the exciting stimulus which acts upon the muscles and
+makes them shorter, harder, and more rigid.[10]
+
+Muscles, however, will respond to other than this usual stimulus. Thus
+an electrical current may have a similar effect. Heat, also, may
+produce muscular contraction. Mechanical means, such as a sharp blow or
+pinching, may irritate a muscle and cause it to contract.
+
+We must remember that this property of contraction is inherent and
+belongs to the muscle itself. This power of contraction is often
+independent of the brain. Thus, on pricking the heart of a fish an hour
+after removal from its body, obvious contraction will occur. In this
+case it is not the nerve force from the brain that supplies the energy
+for contraction. The power of contraction is inherent in the muscle
+substance, and the stimulus by irritating the nerve ganglia of the
+heart simply affords the opportunity for its exercise.
+
+Contraction is not, however, the natural state of a muscle. In time it
+is tired, and begins to relax. Even the heart, the hardest-working
+muscle, has short periods of rest between its beats. Muscles are highly
+elastic as well as contractile. By this property muscle yields to a
+stretching force, and returns to its original length if the stretching
+has not been excessive.
+
+Illustration: Fig. 33.—Principal Muscles of the Body. (Anterior view.)
+
+69. The Object of Contraction. The object of contraction is obvious.
+Like rubber bands, if one end of a muscle be fixed and the other
+attached to some object which is free to move, the contraction of the
+muscle will bring the movable body nearer to the fixed point. A weight
+fastened to the free end of a muscle may be lifted when the muscle
+contracts. Thus by their contraction muscles are able to do their work.
+They even contract more vigorously when resistance is opposed to them
+than when it is not. With increased weight there is an increased amount
+of work to be done. The greater resistance calls forth a greater action
+of the muscle. This is true up to a certain point, but when the limit
+has been passed, the muscle quickly fails to respond.
+Again, muscles work best with a certain degree of rapidity provided the
+irritations do not follow each other too rapidly. If, however, the
+contractions are too rapid, the muscles become exhausted and fatigue
+results. When the feeling of fatigue passes away with rest, the muscle
+recovers its power. While we are resting, the blood is pouring in fresh
+supplies of building material.
+
+Experiment 19. _To show how muscles relax and contract_. Lay your left
+forearm on a table; grasp with the right hand the mass of flesh on the
+front of the upper arm. Now gradually raise the forearm, keeping the
+elbow on the table. Note that the muscle thickens as the hand rises.
+This illustrates the contraction of the biceps, and is popularly called
+“trying your muscle” Reverse the act. Keep the elbow in position, bring
+the forearm slowly to the table, and the biceps appears to become
+softer and smaller,—it relaxes.
+
+Experiment 20. Repeat the same experiment with other muscles. With the
+right hand grasp firmly the extended left forearm. Extend and flex the
+fingers vigorously. Note the effect on the muscles and tendons of the
+forearm. Grasp with the right hand the calf of the extended right leg,
+and vigorously flex the leg, bringing it near to the body. Note the
+contractions and relaxations of the muscles.
+
+70. Arrangement of Muscles. Muscles are not connected directly with
+bones. The mass of flesh tapers off towards the ends, where the fibers
+pass into white, glistening cords known as tendons. The place at which
+a muscle is attached to a bone, generally by means of a tendon, is
+called its origin; the end connected with the movable bone is its
+insertion.
+
+There are about 400 muscles in the human body, all necessary for its
+various movements. They vary greatly in shape and size, according to
+their position and use. Some are from one to two feet long, others only
+a fraction of an inch. Some are long and spindle-shaped, others thin
+and broad, while still others form rings. Thus some of the muscles of
+the arm and thigh are long and tapering, while the abdominal muscles
+are thin and broad because they help form walls for cavities. Again,
+the muscular fibers which surround and by their contraction close
+certain orifices, as those of the eyelids and lips, often radiate like
+the spokes of a wheel.
+
+Muscles are named according to their shape, position, division of
+origin or insertion, and their function. Thus we have the _recti_
+(straight), and the _deltoid_ (Δ, delta), the _brachial_ (arm),
+_pectoral_ (breast), and the _intercostals_ (between the ribs), so
+named from their position. Again, we have the _biceps_ (two-headed),
+_triceps_ (three-headed), and many others with similar names, so called
+from the points of origin and insertion. We find other groups named
+after their special use. The muscles which bend the limbs are called
+_flexors_ while those which straighten them are known as _extensors_.
+
+After a bone has been moved by the contraction of a muscle, it is
+brought back to its position by the contraction of another muscle on
+the opposite side, the former muscle meanwhile being relaxed. Muscles
+thus acting in opposition to each other are called antagonistic. Thus
+the biceps serves as one of the antagonists to the triceps, and the
+various flexors and extensors of the limbs are antagonistic to one
+another.
+
+71. The Tendons. The muscles which move the bones by their contraction
+taper for the most part, as before mentioned, into tendons. These are
+commonly very strong cords, like belts or straps, made up of white,
+fibrous tissue.
+
+Tendons are most numerous about the larger joints, where they permit
+free action and yet occupy but little space. Large and prominent
+muscles in these places would be clumsy and inconvenient. If we bend
+the arm or leg forcibly, and grasp the inside of the elbow or knee
+joint, we can feel the tendons beneath the skin. The numerous tendons
+in the palm or on the back of the hand contribute to its marvelous
+dexterity and flexibility. The thickest and strongest tendon in the
+body is the tendon of Achilles, which connects the great muscles in the
+calf of the leg with the heel bone (sec. 49).
+
+When muscles contract forcibly, they pull upon the tendons which
+transmit the movement to the bones to which they are attached. Tendons
+may be compared to ropes or cords which, when pulled, are made to act
+upon distant objects to which one end is fastened. Sometimes the tendon
+runs down the middle of a muscle, and the fibers run obliquely into it,
+the tendon resembling the quill in a feather. Again, tendons are spread
+out in a flat layer on the surface of muscles, in which case they are
+called aponeuroses. Sometimes a tendon is found in the middle of a
+muscle as well as at each end of it.
+
+Illustration: Fig. 34.—The Biceps Muscle dissected to show its Tendons.
+
+72. Synovial Sheaths and Sacs. The rapid movement of the tendons over
+bony surfaces and prominences would soon produce an undue amount of
+heat and friction unless some means existed to make the motion as easy
+as possible. This is supplied by sheaths which form a double lining
+around the tendons. The opposed surfaces are lined with synovial
+membrane,[11] the secretion from which oils the sheaths in which the
+tendons move.
+
+Little closed sacs, called synovial sacs or bursæ, similarly lined and
+containing fluid, are also found in special places between two surfaces
+where much motion is required. There are two of these bursæ near the
+patella, one superficial, just under the skin; the other deep beneath
+the bone (Fig. 29). Without these, the constant motion of the knee-pan
+and its tendons in walking would produce undue friction and heat and
+consequent inflammation. Similar, though smaller, sacs are found over
+the point of the elbow, over the knuckles, the ankle bones, and various
+other prominent points. These sacs answer a very important purpose, and
+are liable to various forms of inflammation.
+
+Experiment 21. Examine carefully the tendons in the parts dissected in
+Experiment 18. Pull on the muscles and the tendons, and note how they
+act to move the parts. This may be also admirably shown on the leg of a
+fowl or turkey from a kitchen or obtained at the market.
+    Obtain the hoof of a calf or sheep with one end of the tendon of
+    Achilles still attached. Dissect it and test its strength.
+
+73. Mechanism of Movement. The active agents of bodily movements, as we
+have seen, are the muscles, which by their contraction cause the bones
+to move one on the other. All these movements, both of motion and of
+locomotion, occur according to certain fixed laws of mechanics. The
+bones, to which a great proportion of the muscles in the body are
+attached, act as distinct levers. The muscles supply the power for
+moving the bones, and the joints act as fulcrums or points of support.
+The weight of the limb, the weight to be lifted, or the force to
+overcome, is the resistance.
+
+74. Levers in the Body. In mechanics three classes of levers are
+described, according to the relative position of the power, the
+fulcrum, and the resistance. All the movements of the bones can be
+referred to one or another of these three classes.
+
+Levers of the first class are those in which the fulcrum is between the
+power and the weight. The crowbar, when used to lift a weight at one
+end by the application of power at the other, with a block as a
+fulcrum, is a familiar example of this class. There are several
+examples of this in the human body. The head supported on the atlas is
+one. The joint between the atlas and the skull is the fulcrum, the
+weight of the head is the resistance. The power is behind, where the
+muscles from the neck are attached to the back of the skull. The object
+of this arrangement is to keep the head steady and balanced on the
+spinal column, and to move it backward and forward.
+
+Illustration: Fig. 35.—Showing how the Bones of the Arm serve as
+Levers.
+
+  P, power;
+  W, weight;
+  F, fulcrum.
+
+Levers of the second class are those in which the weight is between the
+fulcrum and the power. A familiar example is the crowbar when used for
+lifting a weight while one end rests on the ground. This class of
+levers is not common in the body. Standing on tiptoe is, however, an
+example. Here the toes in contact with the ground are the fulcrum, the
+power is the action of the muscles of the calf, and between these is
+the weight of the body transmitted down the bones of the leg to the
+foot.
+
+Levers of the third class are those in which the power is applied at a
+point between the fulcrum and weight. A familiar example is where a
+workman raises a ladder against a wall. This class of levers is common
+in the body. In bending the forearm on the arm, familiarly known as
+“trying your muscle,” the power is supplied by the biceps muscle
+attached to the radius, the fulcrum is the elbow joint at one end of
+the lever, and the resistance is the weight of the forearm at the other
+end.
+
+Experiment 22. _To illustrate how the muscles use the bones as levers._
+First, practice with a ruler, blackboard pointer, or any other
+convenient object, illustrating the different kinds of levers until the
+principles are familiar. Next, illustrate these principles on the
+person, by making use of convenient muscles. Thus, lift a book on the
+toes, by the fingers, on the back of the hand, by the mouth, and in
+other ways.
+    These experiments, showing how the bones serve as levers, may be
+    multiplied and varied as circumstances may require.
+
+75. The Erect Position. The erect position is peculiar to man. No other
+animal naturally assumes it or is able to keep it long. It is the
+result of a somewhat complex arrangement of muscles which balance each
+other, some pulling backwards and some forwards. Although the whole
+skeleton is formed with reference to the erect position, yet this
+attitude is slowly learned in infancy.
+
+In the erect position the center of gravity lies in the joint between
+the sacrum and the last lumbar vertebra. A line dropped from this point
+would fall between the feet, just in front of the ankle joints. We
+rarely stand with the feet close together, because that basis of
+support is too small for a firm position. Hence, in all efforts
+requiring vigorous muscular movements the feet are kept more or less
+apart to enlarge the basis of support.
+
+Now, on account of the large number and flexibility of the joints, the
+body could not be kept in an upright position without the cooperation
+of certain groups of muscles. The muscles of the calf of the leg,
+acting on the thigh bone, above the knee, keep the body from falling
+forward, while another set in front of the thigh helps hold the leg
+straight. These thigh muscles also tend to pull the trunk forward, but
+in turn are balanced by the powerful muscles of the lower back, which
+help keep the body straight and braced.
+
+The head is kept balanced on the neck partly by the central position of
+the joint between the atlas and axis, and partly by means of strong
+muscles. Thus, the combined action of these and other muscles serves to
+balance the body and keep it erect. A blow on the head, or a sudden
+shock to the nervous system, causes the body to fall in a heap, because
+the brain has for the time lost its power over the muscles, and they
+cease to contract.
+
+Illustration: Fig. 36.—Diagram showing the Action of the Chief Muscles
+which keep the Body Erect. (The arrows indicate the direction in which
+these muscles act, the feet serving as a fixed basis.) [After Huxley.]
+
+_Muscles which tend to keep the body from falling forward._
+
+A,  muscles of the calf;
+  B, of the back of the thigh;
+  C, of the spinal column.
+
+_Muscles which tend to keep the body from falling backward._
+  D, muscles of the front of the leg;
+  E, of the front of the thigh;
+  F, of the front of the abdomen;
+  G, of the front of the neck.
+
+76. Important Muscles. There are scores of tiny muscles about the head,
+face, and eyes, which, by their alternate contractions and relaxations,
+impart to the countenance those expressions which reflect the feelings
+and passions of the individual. Two important muscles, the temporal,
+near the temples, and the masseter, or chewing muscle, are the chief
+agents in moving the lower jaw. They are very large in the lion, tiger,
+and other flesh-eating animals. On the inner side of each cheek is the
+buccinator, or trumpeter’s muscle, which is largely developed in those
+who play on wind instruments. Easily seen and felt under the skin in
+thin persons, on turning the head to one side, is the
+sterno-cleido-mastoid muscle, which passes obliquely down on each side
+of the neck to the collar bone—prominent in sculpture and painting.
+
+The chest is supplied with numerous muscles which move the ribs up and
+down in the act of breathing. A great, fan-shaped muscle, called the
+pectoralis major, lies on the chest. It extends from the chest to the
+arm and helps draw the arm inward and forward. The arm is raised from
+the side by a large triangular muscle on the shoulder, the deltoid, so
+called from its resemblance to the Greek letter delta, Δ. The biceps,
+or two-headed muscle, forms a large part of the fleshy mass in front of
+the arm. Its use is to bend the forearm on the arm, an act familiarly
+known as “trying your muscle.” Its direct antagonist is the
+three-headed muscle called the triceps. It forms the fleshy mass on the
+back of the arm, its use being to draw the flexed forearm into a right
+line.
+
+On the back and outside of the forearm are the extensors, which
+straighten the wrist, the hand, and the fingers. On the front and
+inside of the forearm are the flexors, which bend the hand, the wrist,
+and the fingers. If these muscles are worked vigorously, their tendons
+can be readily seen and felt under the skin. At the back of the
+shoulder a large, spread-out muscle passes upward from the back to the
+humerus. From its wide expanse on the back it is known as the
+latissimus dorsi (broadest of the back). When in action it draws the
+arm downward and backward, or, if one hangs by the hands, it helps to
+raise the body. It is familiarly known as the “climbing muscle.”
+
+Illustration: Fig. 37.—A Few of the Important Muscles of the Back.
+
+Passing to the lower extremity, the thigh muscles are the largest and
+the most powerful in the body. In front a great, four-headed muscle,
+quadriceps extensor, unites into a single tendon in which the knee-cap
+is set, and serves to straighten the knee, or when rising from a
+sitting posture helps elevate the body. On the back of the thigh are
+several large muscles which bend the knee, and whose tendons, known as
+the “hamstrings,” are readily felt just behind the knee. On the back of
+the leg the most important muscles, forming what is known as the calf,
+are the gastrocnemius and the soleus. The first forms the largest part
+of the calf. The soleus, so named from resembling a sole-fish, is a
+muscle of broad, flattened shape, lying beneath the gastrocnemius. The
+tendons of these two muscles unite to form the tendon of Achilles, as
+that hero is said to have been invulnerable except at this point. The
+muscles of the calf have great power, and are constantly called into
+use in walking, cycling, dancing, and leaping.
+
+77. The Effect of Alcoholic Drinks upon the Muscles. It is found that a
+man can do more work without alcohol than with it. After taking it
+there may be a momentary increase of activity, but this lasts only ten
+or fifteen minutes at the most. It is followed by a rapid reduction of
+power that more than outweighs the momentary gain, while the quality of
+the work is decidedly impaired from the time the alcohol is taken.
+
+Even in the case of hard work that must be speedily done, alcohol does
+not help, but hinders its execution. The tired man who does not
+understand the effects of alcohol often supposes that it increases his
+strength, when in fact it only deadens his sense of fatigue by
+paralyzing his nerves. When put to the test he is surprised at his
+self-deception.
+
+Full intoxication produces, by its peculiar depression of the brain and
+nervous system, an artificial and temporary paralysis of the muscles,
+as is obvious in the pitifully helpless condition of a man fully
+intoxicated. But even partial approach to intoxication involves its
+proportionate impairment of nervous integrity, and therefore just so
+much diminution of muscular force. All athletes recognize this fact, as
+while training for a contest, rigid abstinence is the rule, both from
+liquors and tobacco. This muscular weakness is shown also in the
+unsteady hand, the trembling limbs of the inebriate, his thick speech,
+wandering eye, and lolling head.
+
+78. Destructive Effect of Alcoholic Liquors upon Muscular Tissue.
+Alcoholic liquors retard the natural chemical changes so essential to
+good health, by which is meant the oxidation of the nutritious elements
+of food. Careful demonstration has proved also that the amount of
+carbon dioxide escaping from the lungs of intoxicated persons is from
+thirty to fifty per cent less than normal. This shut-in carbon stifles
+the nervous energy, and cuts off the power that controls muscular
+force. This lost force is in close ratio to the retained carbon: so
+much perverted chemical change, so much loss of muscular power. Not
+only the strength but the fine delicacy of muscular action is lost, the
+power of nice control of the hand and fingers, as in neat penmanship,
+or the use of musical instruments.
+
+To this perverted chemical action is also due the fatty degeneration so
+common in inebriates, affecting the muscles, the heart, and the liver.
+These organs are encroached upon by globules of fat (a hydrocarbon),
+which, while very good in their proper place and quantity, become a
+source of disorder and even of death when they abnormally invade vital
+structures. Other poisons, as phosphorus, produce this fatty decay more
+rapidly; but alcohol causes it in a much more general way.
+
+This is proved by the microscope, which plainly shows the condition
+mentioned, and the difference between the healthy tissues and those
+thus diseased.
+
+Illustration: Fig. 38.—Principal Muscles on the Left Side of Neck.
+
+A,  buccinator;
+  B, masseter;
+  C, depressor anguli oris;
+  D, anterior portion of the digastric;
+  E, mylo-hyoid;
+  F, tendon of the digastric;
+  G, sterno-hyoid;
+  H, sterno-thyroid;
+  K, omo-hyoid;
+  L, sternal origin of sterno-cleido-mastoid muscle;
+  M, superior fibers of deltoid;
+  N, posterior scalenus;
+  O, clavicular origin of sterno-cleido-mastoid;
+  P, sterno-cleido-mastoid;
+  R, trapezius;
+  S, anterior constrictor;
+  T, splenius capitis;
+  V, stylo-hyoid;
+  W, posterior portion of the digastric;
+  X, fasciculi of ear muscles;
+  Z, occipital.
+
+[Note. It was proposed during the Civil War to give each soldier in a
+certain army one gill of whiskey a day, because of great hardship and
+exposure. The eminent surgeon, Dr. Frank H. Hamilton of New York, thus
+expressed his views of the question: “It is earnestly desired that no
+such experiment will ever be repeated in the armies of the United
+States. In our own mind, the conviction is established, by the
+experience and observation of a life, that the regular routine
+employment of alcoholic stimulants by man in health is never, under any
+circumstances, useful. We make no exceptions in favor of cold or heat
+or rain.”
+    “It seems to me to follow from these Arctic experiences that the
+    regular use of spirits, even in moderation, under conditions of
+    great physical hardship, continued and exhausting labor, or
+    exposure to severe cold cannot be too strongly deprecated.”
+    A. W. Greely, retired Brigadier General, U.S.A., and formerly
+    leader of the Greely Expedition.]
+
+79. Effect of Tobacco on the Muscles. That other prominent narcotic,
+tobacco, impairs the energy of the muscles somewhat as alcohol does, by
+its paralyzing effect upon the nervous system. As all muscular action
+depends on the integrity of the nervous system, whatever lays its
+deadening hand upon that, saps the vigor and growth of the entire
+frame, dwarfs the body, and retards mental development. This applies
+especially to the young, in the growing age between twelve or fourteen
+and twenty, the very time when the healthy body is being well knit and
+compacted.
+
+Hence many public schools, as well as our national naval and military
+academies, rigidly prohibit the use of tobacco by their pupils. So also
+young men in athletic training are strictly forbidden to use it.[12]
+This loss of muscular vigor is shown by the unsteady condition of the
+muscles, the trembling hand, and the inability to do with precision and
+accuracy any fine work, as in drawing or nice penmanship.
+
+Additional Experiments.
+
+Experiment 23. _ To examine the minute structure of voluntary muscular
+fiber._ Tease, with two needles set in small handles, a bit of raw,
+lean meat, on a slip of glass, in a little water. Continue until the
+pieces are almost invisible to the naked eye.
+
+Experiment 24. Place a clean, dry cover-glass of about the width of the
+slip, over the water containing the torn fragments. Absorb the excess
+of moisture at the edge of the cover, by pressing a bit of
+blotting-paper against it for a moment. Place it on the stage of a
+microscope and examine with highest obtainable power, by light
+reflected upward from the mirror beneath the stage. Note the apparent
+size of the finest fibers; the striation of the fibers, or their
+markings, consisting of alternate dim and bright cross bands. Note the
+arrangement of the fibers in bundles, each thread running parallel with
+its neighbor.
+
+Experiment 25. _To examine the minute structure of involuntary muscular
+fiber, a tendon, or a ligament._ Obtain a very small portion of the
+muscular coat of a cow’s or a pig’s stomach. Put it to soak in a
+solution of one dram of bichromate of potash in a pint of water. Take
+out a morsel on the slip of glass, and tease as directed for the
+voluntary muscle. Examine with a high power of the microscope and note:
+(1) the isolated cells, long and spindle-shaped, that they are much
+flattened; (2) the arrangement of the cells, or fibers, in sheets, or
+layers, from the torn ends of which they project like palisades.
+
+Experiment 26. Tease out a small portion of the tendon or ligament in
+water, and examine with a glass of high power. Note the large fibers in
+the ligament, which branch and interlace.
+
+Experiment 27. With the head slightly bent forwards, grasp between the
+fingers of the right hand the edge of the left sterno-cleido-mastoid,
+just above the collar bone. Raise the head and turn it from left to
+right, and the action of this important muscle is readily seen and
+felt. In some persons it stands out in bold relief.
+
+Experiment 28. The tendons which bound the space (popliteal) behind the
+knee can be distinctly felt when the muscles which bend the knee are in
+action. On the outer side note the tendons of the biceps of the leg,
+running down to the head of the fibula. On the inside we feel three
+tendons of important muscles on the back of the thigh which flex the
+leg upon the thigh.
+
+Experiment 29. _To show the ligamentous action of the muscles._
+Standing with the back fixed against a wall to steady the pelvis, the
+knee can be flexed so as to almost touch the abdomen. Take the same
+position and keep the knee rigid. When the heel has been but slightly
+raised a sharp pain in the back of the thigh follows any effort to
+carry it higher. Flexion of the leg to a right angle, increases the
+distance from the lines of insertion on the pelvic bones to the
+tuberosities of the tibia by two or three inches—an amount of
+stretching these muscle cannot undergo. Hence the knee must be flexed
+in flexion of the hip.
+
+Experiment 30. A similar experiment may be tried at the wrist. Flex the
+wrist with the fingers extended, and again with the fingers in the
+fist. The first movement can be carried to 90°, the second only to 30°,
+or in some persons up to 60°. Making a fist had already stretched the
+extensor muscles of the arm, and they can be stretched but little
+farther. Hence, needless pain will be avoided by working a stiff wrist
+with the parts loose, or the fingers extended, and not with a clenched
+fist.
+
+Review Analysis: Important Muscles
+Location.     Name.     Chief Function.
+Head and Neck.     Occipito-frontalis.     moves scalp and raises eye brow.
+Orbicularis palpebrarum.     shuts the eyes.
+Levator palpebrarum.     opens the eyes.
+Temporal.     raise the lower jaw.
+Masseter.     ”    ”    ”    ”
+Sterno-cleido-mastoid.     depresses head upon neck and neck upon chest.
+Platysma myoides.     depresses lower jaw and lower lip.
+Trunk.     Pectoralis major.     draws arm across front of chest.
+Pectoralis minor.     depresses point of shoulder,
+Latissimus dorsi.     draws arm downwards and backwards.
+Serratus magnus.     assists in raising ribs.
+Trapezius. Rhomboideus.     backward movements of head and shoulder,
+Intercostals.     raise and depress the ribs.
+External oblique.     various forward movements of trunk
+Internal oblique.
+Rectus abdominis.     compresses abdominal viscera and acts upon pelvis.
+Upper Limbs.     Deltoid.     carries arm outwards and upwards.
+Biceps.     flexes elbow and raises arm.
+Triceps.     extends the forearm.
+Brachialis anticus.     flexor of elbow.
+Supinator longus.     flexes the forearm.
+Flexor carpi radialis.     flexors of wrist.
+Flexor carpi ulnaris.     ”    ”    ”    ”
+Lower Limbs.     Gluteus maximus.     adducts the thigh.
+Adductors of thigh.     draw the leg inwards.
+Sartorius.     crosses the legs.
+Rectus femoris.     flexes the thigh.
+Vastus externus.     extensor of leg.
+Vastus internus.     extensor of leg upon thigh.
+Biceps femoris.     flexes leg upon thigh.
+Gracilis.     flexes the leg and adducts thigh.
+Tibialis anticus.     draws up inner border of foot.
+Peroneus longus.     raises outer edge of foot,
+Gastrocnemius.     keep the body erect, and
+Soleus.     aid in walking and running.
+
+
+
+
+Chapter IV.
+Physical Exercise.
+
+
+80. Importance of Bodily Exercise. Nothing is so essential to success
+in life as sound physical health. It enables us to work with energy and
+comfort, and better to endure unusual physical and mental strains.
+While others suffer the penalties of feebleness, a lower standard of
+functional activities, and premature decay, the fortunate possessor of
+a sound mind in a sound body is better prepared, with proper
+application, to endure the hardships and win the triumphs of life[13].
+
+This element of physical capacity is as necessary to a useful and
+energetic life, as are mental endowment and intellectual acquirement.
+Instinct impels us to seek health and pleasure in muscular exercise. A
+healthy and vigorous child is never still except during sleep. The
+restless limbs and muscles of school children pent up for several
+hours, feel the need of movement, as a hungry man craves food. This
+natural desire for exercise, although too often overlooked, is really
+one of the necessities of life. One must be in ill health or of an
+imperfect nature, when he ceases to feel this impulse. Indeed, motion
+within proper bounds is essential to the full development and perfect
+maintenance of the bodily health. Unlike other machines, the human body
+becomes within reasonable limits, stronger and more capable the more it
+is used.
+
+As our tenure of life at best is short, it is our duty to strive to
+live as free as possible from bodily ills. It is, therefore, of
+paramount importance to rightly exercise every part of the body, and
+this without undue effort or injurious strain.
+
+Strictly speaking, physical exercise refers to the functional activity
+of each and every tissue, and properly includes the regulation of the
+functions and movements of the entire body. The word exercise, however,
+is used usually in a narrower sense as applied to those movements that
+are effected by the contraction of the voluntary muscles.
+
+Brief reference will be made in this chapter only to such natural and
+systematic physical training as should enter into the life of every
+healthy person.
+
+81. Muscular Activity. The body, as we have learned, is built up of
+certain elementary tissues which are combined to make bones, muscles,
+nerves, and other structures. The tissues, in turn, are made up of
+countless minute cells, each of which has its birth, lives its brief
+moment to do its work in the animal economy, is separated from the
+tissue of which it was a part, and is in due time eliminated by the
+organs of excretion,—the lungs, the skin, or the kidneys. Thus there is
+a continuous process of growth, of decay, and removal, among the
+individual cells of each tissue.
+
+Note. The Incessant Changes in Muscular Tissue. “In every tiny block of
+muscle there is a part which is really alive, there are parts which are
+becoming alive, there are parts which have been alive, and are now
+dying or dead; there is an upward rush from the lifeless to the living,
+a downward rush from the living to the dead. This is always going on,
+whether the muscle be quiet and at rest, or whether it be active and
+moving,—some of the capital of living material is being spent, changed
+into dead waste; some of the new food is always being raised into
+living capital. But when the muscle is called upon to do work, when it
+is put into movement, the expenditure is quickened, there is a run upon
+the living capital, the greater, the more urgent the call for
+action.”—Professor Michael Foster.
+
+These ceaseless processes are greatly modified by the activity of the
+bodily functions. Every movement of a muscle, for instance, involves
+change in its component cells. And since the loss of every atom of the
+body is in direct relation to its activity, a second process is
+necessary to repair this constant waste; else the body would rapidly
+diminish in size and strength, and life itself would soon end. This
+process of repair is accomplished, as we shall learn in Chapters VI.
+and VII., by the organs of nutrition, which convert the food into
+blood.
+
+Illustration: Fig. 39.—Showing how the Muscles of the Back may be
+developed by a Moderate Amount of Dumb-Bell Exercise at Home. (From a
+photograph.)
+
+82. Effect of Exercise upon the Muscles. Systematic exercise influences
+the growth and structure of the muscles of the body in a manner
+somewhat remarkable. Muscular exercise makes muscular tissue; from the
+lack of it, muscles become soft and wasted. Muscles properly exercised
+not only increase in size, both as a whole and in their individual
+structure, but are better enabled to get rid of material which tends to
+hamper their movements. Thus muscular exercise helps to remove any
+needless accumulation of fat, as well as useless waste matters, which
+may exist in the tissues. As fat forms no permanent structural part of
+the organism, its removal is, within limits, effected with no
+inconvenience.
+
+Muscular strength provides the joints with more powerful ligaments and
+better developed bony parts. After long confinement to the bed from
+disease, the joints have wasted ligaments, thin cartilages, and the
+bones are of smaller proportions. Duly exercised muscles influence the
+size of the bones upon which they act. Thus the bones of a
+well-developed man are stronger, firmer, and larger than those of a
+feeble person.
+
+He who has been physically well trained, has both a more complete and a
+more intelligent use of his muscles. He has acquired the art of causing
+his muscles to act in concert. Movements once difficult are now carried
+on with ease. The power of coördination is increased, so that a desired
+end is attained with the least amount of physical force and nervous
+energy. In learning to row, play baseball, ride the bicycle, or in any
+other exercises, the beginner makes his movements in a stiff and
+awkward manner. He will use and waste more muscular force in playing
+one game of ball, or in riding a mile on his wheel, than an expert
+would in doing ten times the work. He has not yet learned to balance
+one set of muscles against their antagonists.
+
+Illustration: Fig. 40.—The Standard Special Chest Weight.
+
+A convenient machine by means of which all the muscles of the body may
+be easily and pleasantly exercised with sufficient variations in the
+movements to relieve it of monotony.
+
+A space 6 ft wide, 6 ft deep, and 7 ft high nearly in front of the
+machine is required for exercise.]
+
+In time, however, acts which were first done only with effort and by a
+conscious will, become automatic. The will ceases to concern itself. By
+what is called reflex action, memory is developed in the spinal cord
+and the muscular centers (sec. 273). There is thus a great saving of
+actual brain work, and one important cause of fatigue is removed.
+
+83. Effect of Exercise on Important Organs. The importance of regular
+exercise is best understood by noting its effects upon the principal
+organs of the body. As the action of the heart is increased both in
+force and frequency during exercise, the flow of blood throughout the
+body is augmented. This results from the force of the muscular
+contractions which play their part in pressing the blood in the veins
+onward towards the heart. Exercise also induces a more vigorous
+respiration, and under increased breathing efforts the lung capacity is
+increased and the size of the chest is enlarged. The amount of air
+inspired and expired in a given time is much larger than if the body
+were at rest. The blood is thus supplied with a much larger amount of
+oxygen from the air inhaled, and gives off to the air a corresponding
+excess of carbon dioxid and water.
+
+Again, exercise stimulates and strengthens the organs of digestion. The
+appetite is improved, as is especially noted after exercise in the open
+air. The digestion is more complete, absorption becomes more rapid, the
+peristaltic movements of the bowels are promoted, and the circulation
+through the liver is more vigorous. More food is taken to supply the
+force necessary for the maintenance of the mechanical movements. Ample
+exercise also checks the tendency towards a torpid circulation in the
+larger digestive organs, as the stomach and the liver, so common with
+those who eat heartily, but lead sedentary lives. In short, exercise
+may be regarded as a great regulator of nutrition.
+
+Exercise increases the flow of blood through the small vessels of the
+skin, and thus increases the radiation of heat from the surface. If the
+exercise be vigorous and the weather hot, a profuse sweat ensues, the
+rapid evaporation of which cools the body. The skin is thus a most
+important regulator of the bodily temperature, and prevents any rise
+above the normal which would otherwise result from vigorous exercise.
+(See secs. 226 and 241).
+
+84. Effect of Exercise upon the Personal Appearance. Judicious and
+systematic exercise, if moderately employed, soon gives a more upright
+and symmetrical figure, and an easier and more graceful carriage.
+Rounded shoulders become square, the awkward gait disappears, and there
+is seen a graceful poise to the head and a bearing of the body which
+mark those whose muscles have been well trained. A perfectly formed
+skeleton and well-developed muscles give the graceful contour and
+perfect outline to the human body. The lean, soft limbs of those who
+have never had any physical education, often look as if they belonged
+to persons recovering from sickness. The effects of sound physical
+exercise are well exhibited in the aspect of the neck, shoulders, and
+chest of one who has been well trained. This is noticeable in gymnasts
+and others who practice upon the horizontal bar, with chest weights,
+dumb-bells, and other apparatus which develop more especially the
+muscles of the upper half of the trunk.
+
+Illustration: Fig. 41.—Young Woman practicing at Home with the “Whitely
+Exerciser.” (From a photograph)
+
+
+Exercise improves the condition of the tissues generally. They become
+more elastic, and in all respects sounder. The skin becomes firm,
+clear, and wholesome. Hence, every part of the surface of the body
+rapidly takes on a change in contour, and soon assumes that appearance
+of vigor and soundness which marks those of firm physical condition.
+The delicate, ruddy aspect of the complexion, the swing about the body
+and the bearing of the head and shoulders, of young women whose
+physical training has been efficient, are in marked contrast with those
+characteristics in persons whose education in this respect has been
+neglected.
+
+85. Effect of Unsuitable or Excessive Exercise. But exercise, like
+everything else which contributes to our welfare, may be carried to
+excess. The words excessive and unsuitable, when applied to muscular
+exertion, are relative terms, and apply to the individual rather than
+to amount of work done. Thus what may be excessive for one person,
+might be suitable and beneficial to another. Then the condition of the
+individual, rather than the character of the muscular work, is always a
+most important factor.
+
+Breathlessness is, perhaps, the most common effect of undue exertion.
+Let a middle-aged person, who is out of practice, run a certain
+distance, and he is soon troubled with his breathing. The respirations
+become irregular, and there is a sense of oppression in his chest. He
+pants, and his strength gives out. His chest, and not his legs, has
+failed him. He is said to be “out of breath.” He might have practiced
+dumb-bells or rowed for some time without inconvenience.
+
+The heart is often overstrained, and at times has been ruptured during
+violent exertion, as in lifting an immense weight. The various forms of
+heart-disease are common with those whose occupations involve severe
+muscular effort, as professional athletes and oarsmen. Hæmorrhages of
+various kinds, especially from the lungs, or rupture of blood-vessels
+in the brain, are not uncommon results of over-exertion.
+
+Excessive repetition of muscular movements may lead to permanent
+contractions of the parts involved. Thus sailors, mechanics, and others
+frequently develop a rigidity of the tendons of the hand which prevents
+the full extension of the fingers. So stenographers, telegraphers and
+writers occasionally suffer from permanent contractions of certain
+muscles of the arm, known as writer’s cramp, due to their excessive
+use. But the accidents which now and then may result from severe
+physical exertion, should discourage no one from securing the benefits
+which accrue from moderate and reasonable exercise.
+
+86. Muscular Fatigue. We all know how tiresome it is to hold the arm
+outstretched horizontally even for a few moments. A single muscle, the
+deltoid, in this case does most of the work. Even in a vigorous man,
+this muscle can act no longer than four to six minutes before the arm
+drops helpless. We may prolong the period by a strong effort of the
+will, but a time soon comes when by no possible effort are we able to
+hold out the arm. The muscle is said to be fatigued. It has by no means
+lost its contractile power, for if we apply a strong electric stimulus
+to it, the fatigue seems to disappear. Thus we see the functional power
+of a muscle has a definite limit, and in fatigue that limit is reached.
+
+Illustration: Fig. 42.—A Well-Equipped Gymnasium. (From a photograph.)
+
+
+The strength of the muscle, its physical condition, the work it has
+done, and the mental condition of the individual, all modify the state
+of fatigue. In those difficult acts which involve a special effort of
+the will, the matter of nerve exhaustion is largely concerned. Thus,
+the incessant movements in St. Vitus’ dance result in comparatively
+little fatigue, because there is no association of the brain with the
+muscular action. If a strong man should attempt to perform voluntarily
+the same movements, he would soon have to rest. None of the movements
+which are performed independently of the will, as the heart-beats and
+breathing movements, ever involve the sensation of fatigue. As a result
+of fatigue the normal irritability of muscular tissue becomes weakened,
+and its force of contraction is lessened. There is, also, often noticed
+in fatigue a peculiar tremor of the muscles, rendering their movements
+uncertain. The stiffness of the muscles which comes on during severe
+exercise, or the day after, are familiar results of fatigue.
+
+This sense of fatigue should put us on guard against danger. It is a
+kind of regulator which serves in the ordinary actions of life to warn
+us not to exceed the limits of useful exercise. Fatigue summons us to
+rest long before all the force of the motor organs has been expended,
+just as the sensation of hunger warns us that we need food, long before
+the body has become weak from the lack of nourishment.
+
+We should never forget that it is highly essential to maintain an
+unused reserve of power, just as a cautious merchant always keeps at
+the bank an unexpended balance of money. If he overspends his money he
+is bankrupt, and the person who overspends his strength is for the time
+physically bankrupt. In each case the process of recovery is slow and
+painful.
+
+87. Rest for the Muscles. Rest is necessary for the tissues, that they
+may repair the losses sustained by work; that is, a period of rest must
+alternate with a period of activity. Even the heart, beating
+ceaselessly, has its periods of absolute rest to alternate with those
+of work. A steam-engine is always slowly, but surely, losing its
+fitness for work. At last it stops from the need of repair. Unlike the
+engine, the body is constantly renewing itself and undergoing continual
+repair. Were it not for this power to repair and renew its various
+tissues, the body would soon be worn out.
+
+This repair is really a renovation of the structure. Rest and work are
+relative terms, directly opposed to each other. Work quickens the pulse
+and the respiration, while rest slows both. During sleep the voluntary
+muscles are relaxed, and those of organic life work with less energy.
+The pulse and the respiration are less frequent, and the temperature
+lower than when awake. Hence sleep, “tired Nature’s sweet restorer,”
+may be regarded as a complete rest.
+
+The periods of rest should vary with the kind of exercise. Thus
+exercise which produces breathlessness requires frequent but short
+rests. The trained runner, finding his respiration embarrassed, stops a
+moment to regain his breath. Exercises of endurance cause fatigue less
+quickly than those of speed, but require longer rest. Thus a man not
+used to long distances may walk a number of hours without stopping, but
+while fatigue is slow to result, it is also slow to disappear. Hence a
+lengthy period of rest is necessary before he is able to renew his
+journey.
+
+88. Amount of Physical Exercise Required. The amount of physical
+exercise that can be safely performed by each person, is a most
+important and practical question. No rule can be laid down, for what
+one person bears well, may prove very injurious to another. To a
+certain extent, each must be guided by his own judgment. If, after
+taking exercise, we feel fatigued and irritable, are subject to
+headache and sleeplessness, or find it difficult to apply the mind to
+its work, it is plain that we have been taxing our strength unduly, and
+the warnings should be heeded.
+
+Age is an important factor in the problem, as a young man may do with
+ease and safety, what might be injurious to an older person. In youth,
+when the body is making its most active development, the judicious use
+of games, sports, and gymnastics is most beneficial. In advanced life,
+both the power and the inclination for exercise fail, but even then
+effort should be made to take a certain reasonable amount of exercise.
+
+Abundant evidence shows that physical development is most active from
+thirteen to seventeen years of age; this manifests itself clearly by
+increase in weight. Hence this period of life is of great consequence.
+If at this age a boy or girl is subjected to undue physical strain, the
+development may suffer, the growth be retarded, and the foundation laid
+for future ill health.
+
+Illustration: Fig. 43.—Student exercising in the School Gymnasium on
+the Rowing Machine. (From a photograph.)
+
+
+The proper amount of exercise must vary greatly with circumstances. It
+may be laid down as a fairly safe rule, that a person of average height
+and weight, engaged in study or in any indoor or sedentary occupation,
+should take an amount of exercise equivalent to walking five or six
+miles a day. Growing children, as a rule, take more exercise than this,
+while most men working indoors take far less, and many women take less
+exercise than men. Exercise may be varied in many ways, the more the
+better; but for the most part it should always be taken in the open
+air.
+
+89. Time for Exercise. It is not prudent to do hard work or take severe
+exercise, just before or just after a full meal. The best time is one
+or two hours after a meal. Vigorous exercise while the stomach is
+busily digesting food, may prove injurious, and is apt to result sooner
+or later in dyspepsia. On the other hand, severe exercise should not be
+taken on an empty stomach. Those who do much work or study before
+breakfast, should first take a light lunch, just enough to prevent any
+faint feeling. With this precaution, there is no better time for
+moderate exercise than the early morning.
+
+In the case of children, physical exercises should not be undertaken
+when they are overtired or hungry. Neither is it judicious for adults
+to take vigorous exercise in the evening, after a long and arduous
+day’s work.
+
+90. Walking, Running, and Jumping. Walking is generally regarded as the
+simplest and most convenient mode of taking exercise. Man is
+essentially a walking animal. When taken with a special object in view,
+it is the best and most pleasant of all physical activities. It is
+suited for individuals of all ages and occupations, and for residents
+of every climate. The child, the athlete, and the aged are all able to
+indulge in this simple and effective means of keeping the body in
+health.
+
+In walking, the muscles of the entire body are brought into action, and
+the movements of breathing and the circulation of the blood are
+increased. The body should be erect, the chest thrown out, the head and
+shoulders held back, and the stride long and elastic. It is an
+excellent custom to add to the usefulness of this fine exercise, by
+deep, voluntary inhalations of pure air.
+
+Running is an excellent exercise for children and young people, but
+should be sparingly indulged in after the age of thirty-five. If it be
+accompanied with a feeling of faintness, breathlessness, and
+palpitation of the heart, the exercise is too severe, and its
+continuance may do serious harm. Running as an exercise is beneficial
+to those who have kept themselves in practice and in sound condition.
+It brings into play nearly every muscle of the body, and thus serves to
+develop the power of endurance, as well as strength and capacity for
+rapid movement.
+
+Jumping may well be left to boys and young men under twenty, but
+skipping with a rope, allied to jumping, is an admirable and beneficial
+form of exercise. It brings into action many muscles without putting
+undue strain upon any particular group.
+
+91. Skating, Swimming, and Rowing. Skating is a delightful and
+invigorating exercise. It calls into play a great variety of muscles,
+and is admirably adapted for almost all ages. It strengthens the ankles
+and helps give an easy and graceful carriage to the body. Skating is
+especially valuable, as it can be enjoyed when other out-door exercises
+are not convenient.
+
+Every child above ten years of age should be taught to swim. The art,
+once mastered, is never forgotten. It calls into use a wide combination
+of muscles. This accomplishment, so easily learned, should be a part of
+our education, as well as baseball or bicycling, as it may chance to
+any one to save his own life or that of a companion.
+
+In many respects rowing is one of the most perfect exercises at our
+command. It expands the chest, strengthens the body, and gives tone to
+the muscles of the abdomen. It is very suitable for girls and women, as
+no other exercise is so well adapted to remedy the muscular defects so
+marked in their sex. Even elderly persons can row day after day without
+difficulty. The degree of muscular effort required, can be regulated so
+that those with weak hearts and weak lungs can adjust themselves to the
+exercise.
+
+92. Bicycling as an Exercise. The bicycle as a means of taking exercise
+has come into popular use with remarkable rapidity. Sharp competition
+bids fair to make the wheel more popular and less expensive than ever.
+Its phenomenal use by persons of all ages and in all stations of life,
+is proof of the enthusiasm with which this athletic exercise is
+employed by women as well as by men.
+
+Mechanical skill has removed most of the risks to health and person
+which once existed. A good machine, used by its owner with judgment, is
+the most convenient, the safest, and the least expensive means of
+traveling for pleasure or exercise. It is doing more than any other
+form of exercise to improve the bodily condition of thousands whose
+occupations confine them all day to sedentary work. Dependent upon no
+one but himself, the cyclist has his means of exercise always at hand.
+No preparation is necessary to take a spin of ten miles or so on the
+road, during a summer evening or before breakfast.
+
+Bicycling brings into active use the muscles of the legs as well as
+those of the trunk and arms. It seems to benefit those who suffer from
+dyspepsia, constipation, and functional disorders of the liver.
+
+A special caution must be used against overdoing in cycling, for the
+temptation by rivalry, making a record, by social competition on the
+road, is stronger in this form of exercise than in any other,
+especially for young folks. Many cases have occurred of permanent
+injury, and even loss of life, from collapse simply by excessive
+exertion and exhaustion.
+
+93. Outdoor Games and Physical Education. While outdoor games are not
+necessary to maintain health, yet we can scarcely overestimate the part
+that the great games of baseball, football, tennis, golf, and croquet,
+play in the physical development of young people. When played in
+moderation and under suitable conditions, they are most useful and
+beneficial exercises. They are played in the open air, and demand a
+great variety of vigorous muscular movement, with a considerable amount
+of skill and adroitness of action. These games not only involve
+healthful exercise, but develop all those manly and wholesome qualities
+so essential to success in life.
+
+A vigorous body is well-nigh essential to success, but equally
+important are readiness of action, sound judgment, good temper,
+personal courage, a sense of fair play, and above all, a spirit of
+honor. Outdoor games, when played in a reasonable and honorable manner,
+are most efficient and practical means to develop these qualities in
+young people.
+
+94. The School and Physical Education. The advantages to be derived,
+during the school period, from the proper care and development of the
+body, should be understood and appreciated by school officials,
+teachers, and parents. The school period is the best time to shape the
+lives of pupils, not mentally or morally alone, but physically as well.
+This is the time, by the use of a few daily exercises at school, to
+draw back the rounding shoulders, to form the habit of sitting and
+standing erect, to build up strong and comely arms and chests, and
+otherwise to train pupils to those methods which will serve to ripen
+them into vigorous and well-knit men and women.
+
+Teachers can by a little effort gain the knowledge requisite properly
+to instruct their pupils in a few systematic exercises. Gratifying
+results will follow just as the teacher and pupils evince interest and
+judgment in the work. It is found by experience that pupils are not
+only quick to learn, but look forward eagerly to the physical exercises
+as an interesting change from the routine of school life.
+
+There should be a stated time for these school exercises, as for any
+other duty. There can be practiced in the schoolroom a great variety of
+interesting and useful exercises, which call for little or no expense
+for apparatus. Such exercises should no more interfere with the
+children’s usual games than any other study does. Under no
+circumstances should the play hours be curtailed.
+
+95. Physical Exercises in School. Physical exercises of some sort,
+then, should be provided for pupils in our schools, especially in large
+towns and cities, where there is little opportunity for outdoor games,
+and they should form a part of the regular course of study. The object
+should be the promotion of sound health rather than the development of
+muscle, or performing feats of agility or strength. Exercises with
+dumb-bells and wands, or even without any apparatus, practiced a few
+times a day, for five minutes at a time, do a great deal of good. They
+relax the tension of body and mind, and introduce an element of
+pleasure into the routine of school life. They increase the breathing
+power and quicken the action of the heart.
+
+Illustration: Fig. 44.—Physical Exercises as carried on in Schools.
+(From photographs.)
+
+
+Note. “In early boyhood and youth nothing can replace the active sports
+so much enjoyed at this period; and while no needless restrictions
+should be placed upon them, consideration should be paid to the amount,
+and especially to the character, of the games pursued by delicate
+youth. For these it would be better to develop the weakened parts by
+means of systematic physical exercises and by lighter sports.”—Dr. John
+M. Keating on “Physical Development” in Pepper’s _Cyclopædia of the
+Diseases of Children_.
+
+
+If vigorously and systematically carried out, these exercises
+invigorate all the tissues and organs of the body, and stimulate them
+to renewed activity. They serve to offset the lack of proper
+ventilation, faulty positions at the desks, and the prolonged inaction
+of the muscles. To secure the greatest benefit from physical training
+in school, it is important that the pupils be interested in these
+exercises, and consider them a recreation, and not a task[14].
+
+96. Practical Points about Physical Exercise. The main object in
+undertaking systematic and graduated physical exercises is not to learn
+to do mere feats of strength and skill, but the better to fit the
+individual for the duties and the work of life. Exercises should be
+considered with reference to their availability from the learner’s
+standpoint. The most beneficial exercises ordinarily are the gentle
+ones, in which no strain is put upon the heart and the respiration. The
+special aim is to secure the equal use of all the muscles, not the
+development of a few. The performance of feats of strength should never
+come within the scope of any educational scheme. Exercises which call
+for sustained effort, violent exertion, or sudden strain are best
+avoided by those who have had no preparation or training.
+
+Regular exercise, not sudden and occasional prolonged exertion, is
+necessary for health. The man or woman who works in an office or store
+all the week, and on Sunday or a holiday indulges in a long spin on the
+bicycle, often receives more harm than good from the exertion. Exercise
+should be taken, so far as is convenient, in the open air, or in a
+large and well-ventilated room.[15]
+
+After the more violent exercises, as baseball, football, a long ride on
+the bicycle, or even after a prolonged walk, a warm bath should be
+taken at the first convenient opportunity. Care should be taken to rub
+down thoroughly, and to change a part or all of the clothing. Exercise
+is comparatively valueless until the idea of taking it for health is
+quite forgotten in the interest and pleasure excited by the occasion.
+No exercise should be carried to such a degree as to cause fatigue or
+exhaustion. Keep warmly clad after exercise, avoid chills, and always
+stop exercising as soon as fatigue is felt.
+
+Wear clothing which allows free play to all the muscles of the body.
+The clothing should be light, loose, and made of wool. Care should be
+taken not to take cold by standing about in clothes which are damp with
+perspiration. In brisk walking and climbing hills keep the mouth shut,
+especially in cold weather, and breathe through the nose, regulating
+the pace so that it can be done without discomfort.
+
+97. Effect of Alcoholic Liquors and Tobacco upon Physical Culture. As a
+result of the unusual attention given to physical culture in the last
+few years, hundreds of special instructors are now employed in training
+young people in the theory and practice of physical exercise. These
+expert teachers, to do their work with thoroughness and discipline,
+recognize the necessity of looking after the daily living of their
+students. The time of rising and retiring, the hours of sleep, the
+dress, the care of the diet, and many other details of personal health
+become an important part of the training.
+
+Recognizing the fact that alcoholic drink and tobacco are so disastrous
+to efficiency in any system of physical training, these instructors
+rigidly forbid the use of these drugs under all circumstances. While
+this principle is perhaps more rigorously enforced in training for
+athletic contests, it applies equally to those who have in view only
+the maintenance of health.
+
+Books on Physical Education. There are many excellent books on physical
+education, which are easily obtained for reading or for reference.
+Among these one of the most useful and suggestive is Blackie’s
+well-known book, “How to Get Strong and how to Stay so.” This little
+book is full of kindly advice and practical suggestions to those who
+may wish to begin to practice health exercises at home with inexpensive
+apparatus. For more advanced work, Lagrange’s “Physiology of Bodily
+Exercise” and the Introduction to Maclaren’s “Physical Education” may
+be consulted. A notable article on “Physical Training” by Joseph H.
+Sears, an Ex-Captain of the Harvard Football Team, may be found in
+Roosevelt’s “In Sickness and in Health.”
+    Price lists and catalogues of all kinds of gymnastic apparatus are
+    easily obtained on application to firms handling such goods.
+
+
+Various Systems of Physical Exercises. The recent revival of popular
+interest in physical education has done much to call the attention of
+the public to the usefulness and importance of a more thorough and
+systematic use of physical exercises, both at home and in the schools.
+It is not within the scope of this book to describe the various systems
+of gymnastic and calisthenic exercises now in common use in this
+country. For the most part they have been modified and rearranged from
+other sources, notably from the two great systems, _i.e._, Swedish and
+German.
+    For a most comprehensive work on the Swedish system, the teacher is
+    referred to the “Swedish System of Educational Gymnastics,” with
+    264 illustrations, by Baron Nils Posse. There is also a small
+    manual for teachers, called “Handbook of School Gymnastics of the
+    Swedish Systems,” by the same author.
+
+
+
+
+Chapter V.
+Food and Drink.
+
+
+98. Why we need Food. The body is often compared to a steam-engine in
+good working order. An engine uses up fuel and water to obtain from
+them the energy necessary to do its work. So, we consume within our
+bodies certain nutritious substances to obtain from them the energy
+necessary for our activities. Just as the energy for the working of the
+engine is obtained from steam by the combustion of fuel, so the energy
+possessed by our bodies results from the combustion or oxidation within
+us of the food we eat. Unless this energy is provided for the body it
+will have but little power of doing work, and like an engine without
+steam, must soon become motionless.
+
+99. Waste and Repair. A steam-engine from the first stroke of its
+piston-rod begins to wear out, and before long needs repair. All work
+involves waste. The engine, unless kept in thorough repair, would soon
+stop. So with our bodies. In their living cells chemical changes are
+constantly going on; energy, on the whole, is running down; complex
+substances are being broken up into simpler combinations. So long as
+life lasts, food must be brought to the tissues, and waste products
+carried away from them. It is impossible to move a single muscle, or
+even to think for one moment, without some minute part of the muscular
+or brain tissue becoming of no further use in the body. The
+transformation of dead matter into living tissue is the ever-present
+miracle which life presents even in its lowest forms.
+
+In childhood the waste is small, and the amount of food taken is more
+than sufficient to repair the loss. Some of the extra food is used in
+building up the body, especially the muscles. As we shall learn in
+Chapter VIII., food is also required to maintain the bodily heat. Food,
+then, is necessary for the production of energy, for the repair of the
+body, for the building up of the tissues, and for the maintenance of
+bodily heat.
+
+100. Nature of the Waste Material. An ordinarily healthy person passes
+daily, on an average, by the kidneys about 50 ounces of waste material,
+of which 96 per cent is water, and from the intestines, on an average,
+5½ ounces, a large proportion of which is water. By the skin, in the
+shape of sweat and insensible perspiration, there is cast out about 23
+ounces, of which 99 per cent is water; and by the lungs about 34
+ounces, 10 of which are water and the remainder carbon dioxid.
+
+Now if we omit an estimate of the undigestible remains of the food, we
+find that the main bulk of what daily leaves the body consists of
+water, carbon dioxid, and certain solid matters contained in solution
+in the renal secretion and the sweat. The chief of these solid matters
+is urea, a complex product made up of four elements,—carbon, hydrogen,
+oxygen, and nitrogen. Water contains only two elements, hydrogen and
+oxygen; and carbon dioxid also has only two, carbon and oxygen. Hence,
+what we daily cast out of our bodies consists essentially of these four
+elements in the form mainly of water, carbon dioxid, and urea.
+
+These waste products represent the oxidation that has taken place in
+the tissues in producing the energy necessary for the bodily
+activities, just as the smoke, ashes, clinkers, and steam represent the
+consumption of fuel and water in the engine. Plainly, therefore, if we
+could restore to the body a supply of these four elements equivalent to
+that cast out, we could make up for the waste. The object of food,
+then, is to restore to the body an amount of the four elements equal to
+that consumed. In other words, and briefly: The purpose of food is to
+supply the waste of the tissues and to maintain the normal composition
+of the blood.
+
+101. Classification of Foods. Foods may be conveniently divided into
+four great classes, to which the name food-stuffs or alimentary
+principles has been given. They correspond to the chief “proximate
+principles” of which the body consists. To one or the other of these
+classes all available foods belong[16]. The classification of
+food-stuffs usually given is as follows:
+
+     Proteids, or Nitrogenous Foods.
+    Starches and Sugars, or Carbohydrates.
+   Fats and Oils.
+    Inorganic or Mineral Foods,—Water, Salt.
+
+102. Proteids; or Nitrogenous Foods. The proteids, frequently spoken of
+as the nitrogenous foods, are rich in one or more of the following
+organic substances: albumen, casein, fibrin, gelatine, myosin, gluten,
+and legumin.
+
+The type of this class of foods is albumen, well known as the white of
+an egg. The serum of the blood is very rich in albumen, as is lean
+meat. The curd of milk consists mainly of casein. Fibrin exists largely
+in blood and flesh foods. Gelatine is obtained from the animal parts of
+bones and connective tissue by prolonged boiling. One of the chief
+constituents of muscular fiber is myosin. Gluten exists largely in the
+cereals wheat, barley, oats, and rye. The proteid principle of peas and
+beans is legumin, a substance resembling casein.
+
+As the name implies, the proteids, or nitrogenous foods, contain
+nitrogen; carbohydrates and fats, on the contrary, do not contain
+nitrogen. The principal proteid food-stuffs are milk, eggs, flesh foods
+of all kinds, fish, and the cereals among vegetable foods. Peas and
+beans are rich in proteids. The essential use of the proteids to the
+tissues is to supply the material from which the new proteid tissue is
+made or the old proteid tissue is repaired. They are also valuable as
+sources of energy to the body. Now, as the proteid part of its molecule
+is the most important constituent of living matter, it is evident that
+proteid food is an absolute necessity. If our diet contained no
+proteids, the tissues of the body would gradually waste away, and death
+from starvation would result. All the food-stuffs are necessary in one
+way or another to the preservation of perfect health, but proteids,
+together with a certain proportion of water and inorganic salts, are
+absolutely necessary for the bare maintenance of animal life—that is,
+for the formation and preservation of living protoplasm.
+
+103. Starches and Sugars. The starches, sugars, and gums, also known as
+carbohydrates, enter largely into the composition of foods of vegetable
+origin. They contain no nitrogen, but the three elements, carbon,
+hydrogen, and oxygen, the last two in the same proportion as in water.
+The starches are widely distributed throughout the vegetable kingdom.
+They are abundant in potatoes and the cereals, and in arrowroot, rice,
+sago, and tapioca. Starch probably stands first in importance among the
+various vegetable foods.
+
+The sugars are also widely distributed substances, and include the
+cane, grape, malt, maple, and milk sugars. Here also belong the gums
+and cellulose found in fruit, cereals, and all vegetables which form
+the basis of the plant cells and fibers. Honey, molasses, and manna are
+included in this class.
+
+The physiological value of the starches and sugars lies in the fact
+that they are oxidized in the body, and a certain amount of energy is
+thereby liberated. The energy of muscular work and of the heat of the
+body comes largely from the oxidation, or destruction, of this class of
+foods. Now, inasmuch as we are continually giving off energy from the
+body, chiefly in the form of muscular work and heat, it is evident that
+material for the production of this energy must be taken in the food.
+The carbohydrates constitute the bulk of our ordinary food.
+
+104. Fats and Oils. These include not only the ordinary fats of meat,
+but many animal and vegetable oils. They are alike in chemical
+composition, consisting of carbon and hydrogen, with a little oxygen
+and no nitrogen. The principal kinds of fat used as food are the fat of
+meat, butter, suet, and lard; but in many parts of the world various
+vegetable oils are largely used, as the olive, palm, cotton seed,
+cocoanut, and almond.
+
+The use of the fats in the body is essentially the same as that of the
+starches and sugars. Weight for weight they are more valuable than the
+carbohydrates as sources of energy, but the latter are more easily
+digested, and more easily oxidized in the body. An important use of
+fatty foods is for the maintenance of the bodily heat. The inhabitants
+of Arctic regions are thus enabled, by large use of the fat and oil
+from the animals they devour, to endure safely the severe cold. Then
+there is reason to believe that fat helps the digestion of other foods,
+for it is found that the body is better nourished when the fats are
+used as food. When more fat is consumed than is required to keep up the
+bodily heat and to yield working power, the excess is stored up in
+various parts of the body, making a sort of reserve fuel, which may be
+drawn upon at any future time.
+
+105. Saline or Mineral Foods. All food contains, besides the substances
+having potential energy, as described, certain saline matters. Water
+and salts are not usually considered foods, but the results of
+scientific research, as well as the experience of life, show that these
+substances are absolutely necessary to the body. The principal mineral
+foods are salt, lime, iron, magnesia, phosphorus, potash, and water.
+Except common salt and water, these substances are usually taken only
+in combination with other foods.
+
+These saline matters are essential to health, and when not present in
+due proportion nutrition is disturbed. If a dog be fed on food freed
+from all salines, but otherwise containing proper nutrients, he soon
+suffers from weakness, after a time amounting to paralysis, and often
+dies in convulsions.
+
+About 200 grains of common salt are required daily by an adult, but a
+large proportion of this is in our food. Phosphate of lime is obtained
+from milk and meats, and carbonate of lime from the hard water we
+drink. Both are required for the bones and teeth. The salts of potash,
+which assist in purifying the blood, are obtained from vegetables and
+fruits. An iron salt is found in most foods, and sulphur in the yolk of
+eggs.
+
+106. Water. Water is of use chiefly as a solvent, and while not
+strictly a food, is necessary to life. It enters into the construction
+of every tissue and is constantly being removed from the body by every
+channel of waste[17].
+
+As a solvent water aids digestion, and as it forms about 80 per cent of
+the blood, it serves as a carrier of nutrient material to all the
+tissues of the body.
+
+Important Articles of Diet.
+
+107. Milk. The value of milk as a food cannot be overestimated. It
+affords nourishment in a very simple, convenient, and perfect form. It
+is the sole food provided for the young of all animals which nourish
+their young. It is an ideal food containing, in excellent proportions,
+all the four elements necessary for growth and health in earlier youth.
+
+Composition of Food Materials. Careful analyses have been made of the
+different articles of food, mostly of the raw, or uncooked foods. As
+might be expected, the analyses on record differ more or less in the
+percentages assigned to the various constituents, but the following
+table will give a fair idea of the fundamental nutritive value of the
+more common foods:
+
+In 100 parts     Water     Proteid     Fat     Carbohydrate     Ash
+Digestible     Cellulose     
+Meat     76.7     20.8     1.5     0.3     —     1.3
+Eggs     73.7     12.6     12.1     —     —     1.1
+Cheese     36-60     25-33     7-30     3-7     —     3.4
+Cow’s Milk     87.7     3.4     3.2     4.8     —     0.7
+Wheat Flour     13.3     10.2     0.9     74.8     0.3     0.5
+Wheat Bread     35.6     7.1     0.2     55.5     0.3     1.1
+Rye Flour     13.7     11.5     2.1     69.7     1.6     1.4
+Rye bread     42.3     6.1     0.4     49.2     0.5     1.5
+Rice     13.1     7.0     0.9     77.4     0.6     1.0
+Corn     13.1     9.9     4.6     68.4     2.5     1.5
+Macaroni     10.1     9.0     0.3     79.0     0.3     0.5
+Peas and Beans     12-15     23-26     1½-2     49-54     4.7     2-3
+Potatoes     75.5     2.0     0.2     20.6     0.7     1.0
+Carrots     87.1     1.0     0.2     9.3     1.4     0.9
+Cabbage     90     2.3     0.5     4-6     1-2     1.3
+Fruit     84     0.5     —     10     4     0.5
+
+Cheese is the nitrogenous part of milk, which has been coagulated by
+the use of rennet. The curd is then carefully dried, salted, and
+pressed. Cheese is sometimes difficult of digestion, as on account of
+its solid form it is not easily acted upon by the digestive fluids.
+
+108. Meats. The flesh of animals is one of our main sources of food.
+Containing a large amount of proteid, it is admirably adapted for
+building up and repairing the tissues of the body. The proportion of
+water is also high, varying from 50 to 75 per cent. The most common
+meats used in this country are beef, mutton, veal, pork, poultry, and
+game.
+
+Beef contains less fat and is more nutritious than either mutton or
+pork. Mutton has a fine flavor and is easily digested. Veal and lamb,
+though more tender, are less easily digested. Pork contains much fat,
+and its fiber is hard, so that it is the most difficult to digest of
+all the meats. Poultry and game have usually a small proportion of fat,
+but are rich in phosphates and are valued for their flavor.
+
+109. Eggs. Consisting of about two-thirds water and the rest albumen
+and fat, eggs are often spoken of as typical natural food. The white of
+an egg is chiefly albumen, with traces of fat and salt; the yolk is
+largely fat and salts. The yellow color is due partly to sulphur. It is
+this which blackens a silver spoon. Eggs furnish a convenient and
+concentrated food, and if properly cooked are readily digested.
+
+110. Fish. Fish forms an important and a most nutritious article of
+diet, as it contains almost as much nourishment as butcher’s meat. The
+fish-eating races and classes are remarkably strong and healthy. Fish
+is less stimulating than meat, and is thus valuable as a food for
+invalids and dyspeptics. To be at its best, fish should be eaten in its
+season. As a rule shell-fish, except oysters, are not very digestible.
+Some persons are unable to eat certain kinds of fish, especially
+shell-fish, without eruptions on the skin and other symptoms of mild
+poisoning.
+
+111. Vegetable Foods. This is a large and important group of foods, and
+embraces a remarkable number of different kinds of diet. Vegetable
+foods include the cereals, garden vegetables, the fruits, and other
+less important articles. These foods supply a certain quantity of
+albumen and fat, but their chief use is to furnish starches, sugars,
+acids, and salts. The vegetable foods indirectly supply the body with a
+large amount of water, which they absorb in cooking.
+
+112. Proteid Vegetable Foods. The most important proteid vegetable
+foods are those derived from the grains of cereals and certain
+leguminous seeds, as peas and beans. The grains when ground make the
+various flours or meals. They contain a large quantity of starch, a
+proteid substance peculiar to them called gluten, and mineral salts,
+especially phosphate of lime. Peas and beans contain a smaller
+proportion of starch, but more proteid matter, called legumin, or
+vegetable casein. Of the cereal foods, wheat is that most generally
+useful. Wheat, and corn and oatmeal form most important articles of
+diet. Wheat flour has starch, sugar, and gluten—nearly everything to
+support life except fat.
+
+Oatmeal is rich in proteids. In some countries, as Scotland, it forms
+an important article of diet, in the form of porridge or oatmeal cakes.
+
+Corn meal is not only rich in nitrogen, but the proportion of fat is
+also large; hence it is a most important and nutritious article of
+food. Rice, on the other hand, contains less proteids than any other
+cereal grain, and is the least nutritious. Where used as a staple
+article of food, as in India, it is commonly mixed with milk, cheese,
+or other nutritious substances. Peas and beans, distinguished from all
+other vegetables by their large amount of proteids—excel in this
+respect even beef, mutton, and fish. They take the place of meats with
+those who believe in a vegetable diet.
+
+113. Non-proteid Vegetable Foods. The common potato is the best type of
+non-proteid vegetable food. When properly cooked it is easily digested
+and makes an excellent food. It contains about 75 per cent of water,
+about 20 per cent of carbohydrates, chiefly starch, 2 per cent of
+proteids, and a little fat and saline matters. But being deficient in
+flesh-forming materials, it is unfit for an exclusive food, but is best
+used with milk, meat, and other foods richer in proteid substances.
+Sweet potatoes, of late years extensively used as food, are rich in
+starch and sugar. Arrowroot, sago, tapioca, and similar foods are
+nutritious, and easily digested, and with milk furnish excellent
+articles of diet, especially for invalids and children.
+
+Explanation of the Graphic Chart. The graphic chart, on the next page,
+presents in a succinct and easily understood form the composition of
+food materials as they are bought in the market, including the edible
+and non-edible portions. It has been condensed from Dr. W. O. Atwater’s
+valuable monograph on “Foods and Diet.” This work is known as the
+Yearbook of the U.S. Department of Agriculture for 1894.
+
+KEY: 1, percentage of nutrients; 2, fuel value of 1 pound in calories.
+The unit of heat, called a _calorie_, or gramme-degree, is the amount
+of heat which is necessary to raise one gramme (15.43 grains) of water
+one degree centigrade (1.8° Fahr.). A, round beef; B, sirloin beef; C,
+rib beef; D, leg of mutton; E, spare rib of pork; F, salt pork; G,
+smoked ham; H, fresh codfish; I, oysters; J, milk; K, butter; L,
+cheese; M, eggs; N, wheat bread; O, corn meal; P, oatmeal; Q, dried
+beans; R, rice; S, potatoes; T, sugar.
+
+This table, among other things, shows that the flesh of fish contains
+more water than that of warm-blooded animals. It may also be seen that
+animal foods contain the most water; and vegetable foods, except
+potatoes, the most nutrients. Proteids and fats exist only in small
+proportions in most vegetables, except beans and oatmeal. Vegetable
+foods are rich in carbohydrates while meats contain none. The fatter
+the meat the less the amount of water. Thus very lean meat may be
+almost four-fifths water, and fat pork almost one-tenth water.
+
+COMPOSITION OF FOOD MATERIALS
+Nutritive ingredients, refuse, and fuel value.
+
+Illustration: Fig. 45.—Graphic Chart of the Composition of Food
+Materials.
+
+
+114. Non-proteid Animal Foods. Butter is one of the most digestible of
+animal fats, agreeable and delicate in flavor, and is on this account
+much used as a wholesome food. Various substitutes have recently come
+into use. These are all made from animal fat, chiefly that of beef, and
+are known as butterine, oleomargarine, and by other trade names. These
+preparations, if properly made, are wholesome, and may be useful
+substitutes for butter, from which they differ but little in
+composition.
+
+115. Garden Vegetables. Various green, fresh, and succulent vegetables
+form an essential part of our diet. They are of importance not so much
+on account of their nutritious elements, which are usually small, as
+for the salts they supply, especially the salts of potash. It is a
+well-known fact that the continued use of a diet from which fresh
+vegetables are excluded leads to a disease known as scurvy. They are
+also used for the agreeable flavor possessed by many, and the pleasant
+variety and relish they give to the food. The undigested residue left
+by all green vegetables affords a useful stimulus to intestinal
+contraction, and tends to promote the regular action of the bowels.
+
+116. Fruits. A great variety of fruits, both fresh and dry, is used as
+food, or as luxuries. They are of little nutritive value, containing,
+as they do, much water and only a small amount of proteid, but are of
+use chiefly for the sugar, vegetable acids, and salts they contain.
+
+In moderate quantity, fruits are a useful addition to our regular diet.
+They are cooling and refreshing, of agreeable flavor, and tend to
+prevent constipation. Their flavor and juiciness serve to stimulate a
+weak appetite and to give variety to an otherwise heavy diet. If eaten
+in excess, especially in an unripe or an overripe state, fruits may
+occasion a disturbance of the stomach and bowels, often of a severe
+form.
+
+117. Condiments. The refinements of cookery as well as the craving of
+the appetite, demand many articles which cannot be classed strictly as
+foods. They are called condiments, and as such may be used in
+moderation. They give flavor and relish to food, excite appetite and
+promote digestion. Condiments increase the pleasure of eating, and by
+their stimulating properties promote secretions of the digestive fluids
+and excite the muscular contractions of the alimentary canal.
+
+The well-known condiments are salt, vinegar, pepper, ginger, nutmeg,
+cloves, and various substances containing ethereal oils and aromatics.
+Their excessive use is calculated to excite irritation and disorder of
+the digestive organs.
+
+118. Salt The most important and extensively used of the condiments is
+common salt. It exists in all ordinary articles of diet, but in
+quantities not sufficient to meet the wants of the bodily tissues.
+Hence it is added to many articles of food. It improves their flavor,
+promotes certain digestive secretions, and meets the nutritive demands
+of the body. The use of salt seems based upon an instinctive demand of
+the system for something necessary for the full performance of its
+functions. Food without salt, however nutritious in other respects, is
+taken with reluctance and digested with difficulty.
+
+Salt has always played an important and picturesque part in the history
+of dietetics. Reference to its worth and necessity abounds in sacred
+and profane history. In ancient times, salt was the first thing placed
+on the table and the last removed. The place at the long table, above
+or below the salt, indicated rank. It was everywhere the emblem of
+hospitality. In parts of Africa it is so scarce that it is worth its
+weight in gold, and is actually used as money. Torture was inflicted
+upon prisoners of state in olden times by limiting the food to water
+and bread, without salt. So intense may this craving for salt become,
+that men have often risked their liberty and even their lives to obtain
+it.
+
+119. Water. The most important natural beverage is pure water; in fact
+it is the only one required. Man has, however, from the earliest times
+preferred and daily used a variety of artificial drinks, among which
+are tea, coffee, and cocoa.
+
+All beverages except certain strong alcoholic liquors, consist almost
+entirely of water. It is a large element of solid foods, and our bodies
+are made up to a great extent of water. Everything taken into the
+circulating fluids of the body, or eliminated from them, is done
+through the agency of water. As a solvent it is indispensable in all
+the activities of the body.
+
+It has been estimated that an average-sized adult loses by means of the
+lungs, skin, and kidneys about eighty ounces of water every twenty-four
+hours. To restore this loss about four pints must be taken daily. About
+one pint of this is obtained from the food we eat, the remaining three
+pints being taken as drink. One of the best ways of supplying water to
+the body is by drinking it in its pure state, when its solvent
+properties can be completely utilized. The amount of water consumed
+depends largely upon the amount of work performed by the body, and upon
+the temperature.
+
+Being one of the essential elements of the body, it is highly important
+that water should be free from harmful impurities. If it contain the
+germs of disease, sickness may follow its use. Without doubt the most
+important factor in the spread of disease is, with the exception of
+impure air, impure water. The chief agent in the spread of typhoid
+fever is impure water. So with cholera, the evidence is overwhelming
+that filthy water is an all-powerful agent in the spread of this
+terrible disease.
+
+120. Tea, Coffee, and Cocoa. The active principle of tea is called
+theine; that of coffee, caffeine, and of cocoa, theobromine. They also
+contain an aromatic, volatile oil, to which they owe their distinctive
+flavor. Tea and coffee also contain an astringent called tannin, which
+gives the peculiar bitter taste to the infusions when steeped too long.
+In cocoa, the fat known as cocoa butter amounts to fifty per cent.
+
+121. Tea. It has been estimated that one-half of the human race now use
+tea, either habitually or occasionally. Its use is a prolific source of
+indigestion, palpitation of the heart, persistent wakefulness, and of
+other disorders. When used at all it should be only in moderation.
+Persons who cannot use it without feeling its hurtful effects, should
+leave it alone. It should not be taken on an empty stomach, nor sipped
+after every mouthful of food.
+
+122. Coffee. Coffee often disturbs the rhythm of the heart and causes
+palpitation. Taken at night, coffee often causes wakefulness. This
+effect is so well known that it is often employed to prevent sleep.
+Immoderate use of strong coffee may produce other toxic effects, such
+as muscular tremors, nervous anxiety, sick-headache, palpitation, and
+various uncomfortable feelings in the cardiac region. Some persons
+cannot drink even a small amount of tea or coffee without these
+unpleasant effects. These favorite beverages are unsuitable for young
+people.
+
+123. Cocoa. The beverage known as cocoa comes from the seeds of the
+cocoa-tree, which are roasted like the coffee berries to develop the
+aroma. Chocolate is manufactured cocoa,—sugar and flavors being added
+to the prepared seeds. Chocolate is a convenient and palatable form of
+highly nutritious food. For those with whom tea and coffee disagree, it
+may be an agreeable beverage. The large quantity of fat which it
+contains, however, often causes it to be somewhat indigestible.
+
+124. Alcoholic Beverages. There is a class of liquids which are
+certainly not properly food or drink, but being so commonly used as
+beverages, they seem to require special notice in this chapter. In view
+of the great variety of alcoholic beverages, the prevalence of their
+use, and the very remarkable deleterious effects they produce upon the
+bodily organism, they imperatively demand our most careful attention,
+both from a physiological and an hygienic point of view.
+
+125. Nature of Alcohol. The ceaseless action of minute forms of plant
+life, in bringing about the decomposition of the elaborated products of
+organized plant or animal structures, will be described in more detail
+(secs. 394-398).
+
+All such work of vegetable organisms, whether going on in the moulding
+cheese, in the souring of milk, in putrefying meat, in rotting fruit,
+or in decomposing fruit juice, is essentially one of fermentation,
+caused by these minute forms of plant life. There are many kinds of
+fermentation, each with its own special form of minute plant life or
+micro-organism.
+
+In this section we are more especially concerned about that
+fermentation which results from the decomposition of sweet fruit,
+plant, or other vegetable, juices which are composed largely of water
+containing sugar and flavoring matters.
+
+This special form of fermentation is known as alcoholic or vinous
+fermentation, and the micro-organisms that cause it are familiarly
+termed alcoholic ferments. The botanist classes them as
+_Saccharomycetes_, of which there are several varieties. Germs of
+_Saccharomycetes_ are found on the surfaces and stems of fruit as it is
+ripening. While the fruit remains whole these germs have no power to
+invade the juice, and even when the skins are broken the conditions are
+less favorable for their work than for that of the moulds,[18] which
+are the cause of the rotting of fruit.
+
+But when fruit is crushed and its juice pressed out, the
+_Saccharomycetes_ are carried into it where they cannot get the oxygen
+they need from the air. They are then able to obtain oxygen by taking
+it from the sugar of the juice. By so doing they cause a breaking up of
+the sugar and a rearrangement of its elements. Two new substances are
+formed in this decomposition of sugar, viz., carbon dioxid, which
+arises from the liquid in tiny bubbles, and alcohol, a poison which
+remains in the fermenting fluid.
+
+Now we must remember that fermentation entirely changes the nature of
+the substance fermented. For all forms of decomposition this one law
+holds good. Before alcoholic fermentation, the fruit juice was
+wholesome and beneficial; after fermentation, it becomes, by the action
+of the minute germs, a poisonous liquid known as alcohol, and which
+forms an essential part of all intoxicating beverages.
+
+Taking advantage of this great law of fermentation which dominates the
+realm of nature, man has devised means to manufacture various alcoholic
+beverages from a great variety of plant structures, as ripe grapes,
+pears, apples, and other fruits, cane juices, corn, the malt of barley,
+rye, wheat, and other cereals.
+
+The process differs according to the substance used and the manner in
+which it is treated, but the ultimate outcome is always the same, viz.,
+the manufacture of a beverage containing a greater or less proportion
+of alcoholic poison. By the process of _distillation_, new and stronger
+liquor is made. Beverages thus distilled are known as ardent spirits.
+Brandy is distilled from wine, rum from fermented molasses, and
+commercial alcohol mostly from whiskey.
+
+The poisonous element in all forms of intoxicating drinks, and the one
+so fraught with danger to the bodily tissues, is the alcohol they
+contain. The proportion of the alcoholic ingredient varies, being about
+50 per cent in brandy, whiskey, and rum, about 20 to 15 per cent in
+wines, down to 5 per cent, or less, in the various beers and cider; but
+whether the proportion of alcohol be more or less, the same element of
+danger is always present.
+
+126. Effects of Alcoholic Beverages upon the Human System. One of the
+most common alcoholic beverages is wine, made from the juice of grapes.
+As the juice flows from the crushed fruit the ferments are washed from
+the skins and stems into the vat. Here they bud and multiply rapidly,
+producing alcohol. In a few hours the juice that was sweet and
+wholesome while in the grape is changed to a poisonous liquid, capable
+of injuring whoever drinks it. One of the gravest dangers of
+wine-drinking is the power which the alcohol in it has to create a
+thirst which demands more alcohol. The spread of alcoholism in
+wine-making countries is an illustration of this fact.
+
+Another alcoholic beverage, common in apple-growing districts, is
+cider. Until the microscope revealed the ferment germ on the “bloom” of
+the apple-skin, very little was known of the changes produced in cider
+during the mysterious process of “working.” Now, when we see the
+bubbles of gas in the glass of cider we know what has produced them,
+and we know too that a poison which we do not see is there also in
+corresponding amounts. We have learned, too, to trace the wrecked hopes
+of many a farmer’s family to the alcohol in the cider which he provided
+so freely, supposing it harmless.
+
+Beer and other malt liquors are made from grain. By sprouting the
+grain, which changes its starch to sugar, and then dissolving out the
+sugar with water, a sweet liquid is obtained which is fermented with
+yeast, one kind of alcoholic ferment. Some kinds of beer contain only a
+small percentage of alcohol, but these are usually drunk in
+proportionately large amounts. The life insurance company finds the
+beer drinker a precarious risk; the surgeon finds him an unpromising
+subject; the criminal court finds him conspicuous in its proceedings.
+The united testimony from all these sources is that beer is
+demoralizing, mentally, morally, and physically.
+
+127. Cooking. The process through which nearly all food used by
+civilized man has to pass before it is eaten is known as cooking. Very
+few articles indeed are consumed in their natural state, the exceptions
+being eggs, milk, oysters, fruit and a few vegetables. Man is the only
+animal that cooks his food. Although there are savage races that have
+no knowledge of cooking, civilized man invariably cooks most of his
+food. It seems to be true that as nations advance in civilization they
+make a proportionate advance in the art of cooking.
+
+Cooking answers most important purposes in connection with our food,
+especially from its influence upon health. It enables food to be more
+readily chewed, and more easily digested. Thus, a piece of meat when
+raw is tough and tenacious, but if cooked the fibers lose much of their
+toughness, while the connective tissues are changed into a soft and
+jelly-like mass. Besides, the meat is much more readily masticated and
+acted upon by the digestive fluids. So cooking makes vegetables and
+grains softer, loosens their structure, and enables the digestive
+juices readily to penetrate their substance.
+
+Cooking also improves or develops flavors in food, especially in animal
+foods, and thus makes them attractive and pleasant to the palate. The
+appearance of uncooked meat, for example, is repulsive to our taste,
+but by the process of cooking, agreeable flavors are developed which
+stimulate the appetite and the flow of digestive fluids.
+
+Another important use of cooking is that it kills any minute parasites
+or germs in the raw food. The safeguard of cooking thus effectually
+removes some important causes of disease. The warmth that cooking
+imparts to food is a matter of no slight importance; for warm food is
+more readily digested, and therefore nourishes the body more quickly.
+
+The art of cooking plays a very important part in the matter of health,
+and thus of comfort and happiness. Badly cooked and ill-assorted foods
+are often the cause of serious disorders. Mere cooking is not enough,
+but good cooking is essential.
+
+Experiments.
+
+Experiments with the Proteids.
+
+Experiment 31. As a type of the group of proteids we take the white of
+egg, egg-white or egg-albumen. Break an egg carefully, so as not to mix
+the white with the yolk. Drop about half a teaspoonful of the raw white
+of egg into half a pint of distilled water. Beat the mixture vigorously
+with a glass rod until it froths freely. Filter through several folds
+of muslin until a fairly clear solution is obtained.
+
+Experiment 32. To a small quantity of this solution in a test tube add
+strong nitric acid, and boil. Note the formation of a white
+precipitate, which turns yellow. After cooling, add ammonia, and note
+that the precipitate becomes orange.
+
+Experiment 33. Add to the solution of egg-albumen, excess of strong
+solution of caustic soda (or potash), and then a drop or two of very
+dilute solution (one per cent) of copper sulphate. A violet color is
+obtained which deepens on boiling.
+
+Experiment 34. Boil a small portion of the albumen solution in a test
+tube, adding drop by drop dilute acetic acid (two per cent) until a
+flaky coagulum of insoluble albumen separates.
+
+Experiments with Starch.
+
+Experiment 35. Wash a potato and peel it. Grate it on a nutmeg grater
+into a tall cylindrical glass full of water. Allow the suspended
+particles to subside, and after a time note the deposit. The lowest
+layer consists of a white powder, or starch, and above it lie coarser
+fragments of cellulose and other matters.
+
+Experiment 36. Examine under the microscope a bit of the above white
+deposit. Note that each starch granule shows an eccentric hilum with
+concentric markings. Add a few drops of very dilute solution of iodine.
+Each granule becomes blue, while the markings become more distinct.
+
+Experiment 37. Examine a few of the many varieties of other kinds of
+starch granules, as in rice, arrowroot, etc. Press some dry starch
+powder between the thumb and forefinger, and note the peculiar
+crepitation.
+
+Experiment 38. Rub a few bits of starch in a little cold water. Put a
+little of the mixture in a large test tube, and then fill with boiling
+water. Boil until an imperfect opalescent solution is obtained.
+
+Experiment 39. Add powdered dry starch to cold water. It is insoluble.
+Filter and test the filtrate with iodine. It gives no blue color.
+
+Experiment 40. Boil a little starch with water; if there is enough
+starch it sets on cooling and a paste results.
+
+Experiment 41. Moisten some flour with water until it forms a tough,
+tenacious dough; tie it in a piece of cotton cloth, and knead it in a
+vessel containing water until all the starch is separated. There
+remains on the cloth a grayish white, sticky, elastic “gluten,” made up
+of albumen, some of the ash, and fats. Draw out some of the gluten into
+threads, and observe its tenacious character.
+
+Experiment 42. Shake up a little flour with ether in a test tube, with
+a tight-fitting cork. Allow the mixture to stand for an hour, shaking
+it from time to time. Filter off the ether, and place some of it on a
+perfectly clean watch glass. Allow the ether to evaporate, when a
+greasy stain will be left, thus showing the presence of fats in the
+flour.
+
+Experiment 43. Secure a specimen of the various kinds of flour, and
+meal, peas, beans, rice, tapioca, potato, etc. Boil a small quantity of
+each in a test tube for some minutes. Put a bit of each thus cooked on
+a white plate, and pour on it two or three drops of the tincture of
+iodine. Note the various changes of color,—blue, greenish, orange, or
+yellowish.
+
+Experiments with Milk.
+
+Experiment 44. Use fresh cow’s milk. Examine the naked-eye character of
+the milk. Test its reaction with litmus paper. It is usually neutral or
+slightly alkaline.
+
+Experiment 45. Examine with the microscope a drop of milk, noting
+numerous small, highly refractive oil globules floating in a fluid.
+
+Experiment 46. Dilute one ounce of milk with ten times its volume of
+water. Add cautiously dilute acetic acid until there is a copious,
+granular-looking precipitate of the chief proteid of milk (caseinogen),
+formerly regarded as a derived albumen. This action is hastened by
+heating.
+
+Experiment 47. Saturate milk with Epsom salts, or common salt. The
+proteid and fat separate, rise to the surface, and leave a clear fluid
+beneath.
+
+Experiment 48. Place some milk in a basin; heat it to about 100° F.,
+and add a few drops of acetic acid. The mass curdles and separates into
+a solid curd (proteid and fat) and a clear fluid (the whey), which
+contains the lactose.
+
+Experiment 49. Take one or two teaspoonfuls of fresh milk in a test
+tube; heat it, and add a small quantity of extract of rennet. Note that
+the whole mass curdles in a few minutes, so that the tube can be
+inverted without the curd falling out. Soon the curd shrinks, and
+squeezes out a clear, slightly yellowish fluid, the whey.
+
+Experiment 50. Boil the milk as before, and allow it to cool; then add
+rennet. No coagulation will probably take place. It is more difficult
+to coagulate boiled milk with rennet than unboiled milk.
+
+Experiment 51. Test fresh milk with red litmus paper; it should turn
+the paper pale blue, showing that it is slightly alkaline. Place aside
+for a day or two, and then test with blue litmus paper; it will be
+found to be acid. This is due to the fact that lactose undergoes the
+lactic acid fermentation. The lactose is converted into lactic acid by
+means of a special ferment.
+
+Experiment 52. Evaporate a small quantity of milk to dryness in an open
+dish. After the dry residue is obtained, continue to apply heat;
+observe that it chars and gives off pungent gases. Raise the
+temperature until it is red hot; allow the dish then to cool; a fine
+white ash will be left behind. This represents the _inorganic matter_
+of the milk.
+
+Experiments with the Sugars.
+
+Experiment 53. Cane sugar is familiar as cooking and table sugar. The
+little white grains found with raisins are grape sugar, or glucose.
+Milk sugar is readily obtained of the druggist. Prepare a solution of
+the various sugars by dissolving a small quantity of each in water.
+Heat each solution with sulphuric acid, and it is seen to darken or
+char slowly.
+
+Experiment 54. Place some Fehling solution (which can be readily
+obtained at the drug store as a solution, or tablets may be bought
+which answer the same purpose) in a test tube, and boil. If no yellow
+discoloration takes place, it is in good condition. Add a few drops of
+the grape sugar solution and boil, when the mixture suddenly turns to
+an opaque yellow or red color.
+
+Experiment 55. Repeat same experiment with milk sugar.
+
+
+
+
+Chapter VI.
+Digestion.
+
+
+128. The Purpose of Digestion. As we have learned, our bodies are
+subject to continual waste, due both to the wear and tear of their
+substance, and to the consumption of material for the production of
+their heat and energy. The waste occurs in no one part alone, but in
+all the tissues.
+
+Now, the blood comes into direct contact with every one of these
+tissues. The ultimate cells which form the tissues are constantly being
+bathed by the myriads of minute blood-vessels which bring to the cells
+the raw material needed for their continued renewal. These cells are
+able to select from the nutritive fluid whatever they require to repair
+their waste, and to provide for their renewed activity. At the same
+time, the blood, as it bathes the tissues, sweeps into its current and
+bears away the products of waste.
+
+Thus the waste occurs in the tissues and the means of repair are
+obtained from the blood. The blood is thus continually being
+impoverished by having its nourishment drained away. How, then, is the
+efficiency of the blood maintained? The answer is that while the
+ultimate purpose of the food is for the repair of the waste, its
+immediate destination is the blood.[19]
+
+129. Absorption of Food by the Blood. How does the food pass from the
+cavity of the stomach and intestinal canal into the blood-vessels?
+There are no visible openings which permit communication. It is done by
+what in physics is known as _endosmotic_ and _exosmotic_ action. That
+is, whenever there are two solutions of different densities, separated
+only by an animal membrane, an interchange will take place between them
+through the membrane.
+
+To illustrate: in the walls of the stomach and intestines there is a
+network of minute vessels filled with blood,—a liquid containing many
+substances in solution. The stomach and intestinal canal also contain
+liquid food, holding many substances in solution. A membrane, made up
+of the extremely thin walls of the blood-vessels and intestines,
+separates the liquids. An exchange takes place between the blood and
+the contents of the stomach and bowels, by which the dissolved
+substances of food pass through the separating membranes into the
+blood.
+
+Illustration: Fig. 46.—Cavities of the Mouth, Pharynx, etc. (Section in
+the middle line designed to show the mouth in its relations to the
+nasal fossæ, the pharynx, and the larynx.)
+
+
+A,  sphenoidal sinus;
+  B, internal orifice of Eustachian tube;
+  C, velum palati;
+  D, anterior pillar of soft palate;
+  E, posterior pillar of soft palate;
+  F, tonsil;
+  H, lingual portion of the pharynx;
+  K, lower portion of the pharynx;
+  L, larynx;
+  M, section of hyoid bone;
+  N, epiglottis;
+  O, palatine arch
+
+This change, by which food is made ready to pass into the blood,
+constitutes food-digestion, and the organs concerned in bringing about
+this change in the food are the digestive organs.
+
+130. The General Plan of Digestion. It is evident that the digestive
+organs will be simple or complex, according to the amount of change
+which is necessary to prepare the food to be taken up by the blood. If
+the requisite change is slight, the digestive organs will be few, and
+their structure simple. But if the food is varied and complex in
+composition, the digestive apparatus will be complex. This condition
+applies to the food and the digestion of man.
+
+Illustration: Fig. 47.—Diagram of the Structure of Secreting Glands.
+
+
+A,  simple tubular gland;
+  B, gland with mouth shut and sac formed;
+  C, gland with a coiled tube;
+  D, plan of part of a racemose gland
+
+
+The digestive apparatus of the human body consists of the alimentary
+canal and tributary organs which, although outside of this canal,
+communicate with it by ducts. The alimentary canal consists of the
+mouth, the pharynx, the œsophagus, the stomach, and the intestines.
+Other digestive organs which are tributary to this canal, and discharge
+their secretions into it, are the salivary glands,[20] the liver, and
+the pancreas.
+
+The digestive process is subdivided into three steps, which take place
+in the mouth, in the stomach, and in the intestines.
+
+131. The Mouth. The mouth is the cavity formed by the lips, the cheeks,
+the palate, and the tongue. Its bony roof is made up of the upper
+jawbone on each side, and the palate bones behind. This is the _hard
+palate_, and forms only the front portion of the roof. The continuation
+of the roof is called the _soft palate_, and is made up of muscular
+tissue covered with mucous membrane.
+
+The mouth continues behind into the throat, the separation between the
+two being marked by fleshy pillars which arch up from the sides to form
+the soft palate. In the middle of this arch there hangs from its free
+edge a little lobe called the uvula. On each side where the pillars
+begin to arch is an almond-shaped body known as the tonsil. When we
+take cold, one or both of the tonsils may become inflamed, and so
+swollen as to obstruct the passage into the throat. The mouth is lined
+with mucous membrane, which is continuous with that of the throat,
+œsophagus, stomach, and intestines (Fig. 51).
+
+132. Mastication, or Chewing. The first step of the process of
+digestion is mastication, the cutting and grinding of the food by the
+teeth, effected by the vertical and lateral movements of the lower jaw.
+While the food is thus being crushed, it is moved to and fro by the
+varied movements of the tongue, that every part of it may be acted upon
+by the teeth. The advantage of this is obvious. The more finely the
+food is divided, the more easily will the digestive fluids reach every
+part of it, and the more thoroughly and speedily will digestion ensue.
+
+The act of chewing is simple and yet important, for if hurriedly or
+imperfectly done, the food is in a condition to cause disturbance in
+the digestive process. Thorough mastication is a necessary introduction
+to the more complicated changes which occur in the later digestion.
+
+133. The Teeth. The teeth are attached to the upper and lower maxillary
+bones by roots which sink into the sockets of the jaws. Each tooth
+consists of a _crown_, the visible part, and one or more fangs, buried
+in the sockets. There are in adults 32 teeth, 16 in each jaw.
+
+Teeth differ in name according to their form and the uses to which they
+are specially adapted. Thus, at the front of the jaws, the incisors, or
+cutting teeth, number eight, two on each side. They have a single root
+and the crown is beveled behind, presenting a chisel-like edge. The
+incisors divide the food, and are well developed in rodents, as
+squirrels, rats, and beavers.
+
+Next come the canine teeth, or cuspids, two in each jaw, so called from
+their resemblance to the teeth of dogs and other flesh-eating animals.
+These teeth have single roots, but their crowns are more pointed than
+in the incisors. The upper two are often called eye teeth, and the
+lower two, stomach teeth. Next behind the canines follow, on each side,
+two bicuspids. Their crowns are broad, and they have two roots. The
+three hindmost teeth in each jaw are the molars, or grinders. These are
+broad teeth with four or five points on each, and usually each molar
+has three roots.
+
+The last molars are known as the wisdom teeth, as they do not usually
+appear until the person has reached the “years of discretion.” All
+animals that live on grass, hay, corn, and the cereals generally, have
+large grinding teeth, as the horse, ox, sheep, and elephant.
+
+The following table shows the teeth in their order:
+
+        Mo. Bi. Ca. In.     In. Ca. Bi. Mo.
+  Upper  3   2   1   2   |   2   1   2   3  = 16
+                         |                      } = 32
+  Lower  3   2   1   2   |   2   1   2   3  = 16
+
+The vertical line indicates the middle of the jaw, and shows that on
+each side of each jaw there are eight teeth.
+
+134. Development of the Teeth. The teeth just described are the
+permanent set, which succeeds the temporary or milk teeth. The latter
+are twenty in number, ten in each jaw, of which the four in the middle
+are incisors. The tooth beyond on each side is an eye tooth, and the
+next two on each side are bicuspids, or premolars.
+
+The milk teeth appear during the first and second years, and last until
+about the sixth or seventh year, from which time until the twelfth or
+thirteenth year, they are gradually pushed out, one by one, by the
+permanent teeth. The roots of the milk teeth are much smaller than
+those of the second set.
+
+Illustration: Fig. 48.—Temporary and Permanent Teeth together.
+
+_Temporary teeth:_ A, central incisors;
+  B lateral incisors;
+  C, canines;
+  D, anterior molars;
+  E, posterior molars
+
+_Permanent teeth:_
+  F, central incisors;
+  H, lateral incisors;
+  K, canines;
+  L, first bicuspids;
+  M, second biscuspids;
+  N, first molars
+
+The plan of a gradual succession of teeth is a beautiful provision of
+nature, permitting the jaws to increase in size, and preserving the
+relative position and regularity of the successive teeth.
+
+Illustration: Fig. 49.—Showing the Principal Organs of the Thorax and
+Abdomen _in situ_. (The principal muscles are seen on the left, and
+superficial veins on the right.)
+
+
+135. Structure of the Teeth. If we should saw a tooth down through its
+center we would find in the interior a cavity. This is the pulp cavity,
+which is filled with the dental pulp, a delicate substance richly
+supplied with nerves and blood-vessels, which enter the tooth by small
+openings at the point of the root. The teeth are thus nourished like
+other parts of the body. The exposure of the delicate pulp to the air,
+due to the decay of the dentine, gives rise to the pain of toothache.
+
+Surrounding the cavity on all sides is the hard substance known as the
+dentine, or tooth ivory. Outside the dentine of the root is a substance
+closely resembling bone, called cement. In fact, it is true bone, but
+lacks the Haversian canals. The root is held in its socket by a dense
+fibrous membrane which surrounds the cement as the periosteum does
+bone.
+
+Illustration: Fig. 50.—Section of Face. (Showing the parotid and
+submaxillary glands.)
+
+
+The crown of the tooth is not covered by cement, but by the hard
+enamel, which forms a strong protection for the exposed part. When the
+teeth are first “cut,” the surface of the enamel is coated with a
+delicate membrane which answers to the Scriptural phrase “the skin of
+the teeth.” This is worn off in adult life.
+
+136. Insalivation. The thorough mixture of the saliva with the food is
+called insalivation. While the food is being chewed, it is moistened
+with a fluid called saliva, which flows into the mouth from six little
+glands. There are on each side of the mouth three salivary glands,
+which secrete the saliva from the blood. The parotid is situated on the
+side of the face in front of the ear. The disease, common in childhood,
+during which this gland becomes inflamed and swollen, is known as the
+“mumps.” The submaxillary gland is placed below and to the inner side
+of the lower jaw, and the sublingual is on the floor of the mouth,
+between the tongue and the gums. Each gland opens into the mouth by a
+little duct. These glands somewhat resemble a bunch of grapes with a
+tube for a stalk.
+
+The saliva is a colorless liquid without taste or smell. Its principal
+element, besides water, is a ferment called _ptyalin_, which has the
+remarkable property of being able to change starch into a form of
+cane-sugar, known as maltose.
+
+Thus, while the food is being chewed, another process is going on by
+which starch is changed into sugar. The saliva also moistens the food
+into a mass for swallowing, and aids in speech by keeping the mouth
+moist.
+
+The activity of the salivary glands is largely regulated by their
+abundant supply of nerves. Thus, the saliva flows into the mouth, even
+at the sight, smell, or thought of food. This is popularly known as
+“making the mouth water.” The flow of saliva may be checked by nervous
+influences, as sudden terror and undue anxiety.
+
+Experiment 56. _To show the action of saliva on starch_. Saliva for
+experiment may be obtained by chewing a piece of India rubber and
+collecting the saliva in a test tube. Observe that it is colorless and
+either transparent or translucent, and when poured from one vessel to
+another is glairy and more or less adhesive. Its reaction is alkaline
+to litmus paper.
+
+
+Experiment 57.Make a thin paste from pure starch or arrowroot. Dilute a
+little of the saliva with five volumes of water, and filter it. This is
+best done through a filter perforated at its apex by a pin-hole. In
+this way all air-bubbles are avoided. Label three test tubes _A, B_,
+and _C_. In _A_, place starch paste; in _B_, saliva; and in _C_ one
+volume of saliva and three volumes of starch paste. Place them for ten
+minutes in a water bath at about 104° Fahrenheit.
+    Test portions of all three for a reducing sugar, by means of
+    Fehling’s solution or tablets.[21] _A_ and _B_ give no evidence of
+    sugar, while _C_ reduces the Fehling, giving a yellow or red
+    deposit of cuprous oxide. Therefore, starch is converted into a
+    reducing sugar by the saliva. This is done by the ferment ptyalin
+    contained in saliva.
+
+137. The Pharynx and Œsophagus. The dilated upper part of the
+alimentary canal is called the pharynx. It forms a blind sac above the
+level of the mouth. The mouth opens directly into the pharynx, and just
+above it are two openings leading into the posterior passages of the
+nose. There are also little openings, one on each side, from which
+begin the Eustachian tubes, which lead upward to the ear cavities.
+
+The windpipe opens downward from the pharynx, but this communication
+can be shut off by a little plate or lid of cartilage, the epiglottis.
+During the act of swallowing, this closes down over the entrance to the
+windpipe, like a lid, and prevents the food from passing into the
+air-passages. This tiny trap-door can be seen, by the aid of a mirror,
+if we open the mouth wide and press down the back of the tongue with
+the handle of a spoon (Figs. 46, 84, and 85).
+
+Thus, there are six openings from the pharynx; the œsophagus being the
+direct continuation from it to the stomach. If we open the mouth before
+a mirror we see through the fauces the rear wall of the pharynx. In its
+lining membrane is a large number of glands, the secretion from which
+during a severe cold may be quite troublesome.
+
+The œsophagus, or gullet, is a tube about nine inches long, reaching
+from the throat to the stomach. It lies behind the windpipe, pierces
+the diaphragm between the chest and abdomen, and opens into the
+stomach. It has in its walls muscular fibers, which, by their worm-like
+contractions, grasp the successive masses of food swallowed, and pass
+them along downwards into the stomach.
+
+138. Deglutition, or Swallowing. The food, having been well chewed and
+mixed with saliva, is now ready to be swallowed as a soft, pasty mass.
+The tongue gathers it up and forces it backwards between the pillars of
+the fauces into the pharynx.
+
+If we place the fingers on the “Adam’s apple,” and then pretend to
+swallow something, we can feel the upper part of the windpipe and the
+closing of its lid (epiglottis), so as to cover the entrance and
+prevent the passage of food into the trachea.
+
+There is only one pathway for the food to travel, and that is down the
+œsophagus. The slow descent of the food may be seen if a horse or dog
+be watched while swallowing. Even liquids do not fall or flow down the
+food passage. Hence, acrobats can drink while standing on their heads,
+or a horse with its mouth below the level of the œsophagus. The food is
+under the control of the will until it has entered the pharynx; all the
+later movements are involuntary.
+
+Illustration: Fig. 51.—A View into the Back Part of the Adult Mouth.
+(The head is represented as having been thrown back, and the tongue
+drawn forward.)
+
+
+A,  B, incisors;
+  C, canine;
+  D, E, bicuspids;
+  F, H, K, molars;
+  M, anterior pillar of the fauces;
+  N, tonsil;
+  L, uvula;
+  O, upper part of the pharynx;
+  P, tongue drawn forward;
+  R, linear ridge, or raphé.
+
+
+139. The Stomach. The stomach is the most dilated portion of the
+alimentary canal and the principal organ of digestion. Its form is not
+easily described. It has been compared to a bagpipe, which it resembles
+somewhat, when moderately distended. When empty it is flattened, and in
+some parts its opposite walls are in contact.
+
+We may describe the stomach as a pear-shaped bag, with the large end to
+the left and the small end to the right. It lies chiefly on the left
+side of the abdomen, under the diaphragm, and protected by the lower
+ribs. The fact that the large end of the stomach lies just beneath the
+diaphragm and the heart, and is sometimes greatly distended on account
+of indigestion or gas, may cause feelings of heaviness in the chest or
+palpitation of the heart. The stomach is subject to greater variations
+in size than any other organ of the body, depending on its contents.
+Just after a moderate meal it averages about twelve inches in length
+and four in diameter, with a capacity of about four pints.
+
+Illustration: Fig. 52.—The Stomach.
+
+
+A, cardiac end;
+  B, pyloric end,
+  C, lesser curvature,
+  D, greater curvature
+
+The orifice by which the food enters is called the cardiac opening,
+because it is near the heart. The other opening, by which the food
+leaves the stomach, and where the small intestine begins, is the
+pyloric orifice, and is guarded by a kind of valve, known as the
+pylorus, or gatekeeper. The concave border between the two orifices is
+called the _small curvature_, and the convex as the _great curvature_,
+of the stomach.
+
+140. Coats of Stomach. The walls of the stomach are formed by four
+coats, known successively from without as serous, muscular, sub-mucous,
+and mucous. The outer coat is the serous membrane which lines the
+abdomen,—the peritoneum (note, p. 135). The second coat is muscular,
+having three sets of involuntary muscular fibers. The outer set runs
+lengthwise from the cardiac orifice to the pylorus. The middle set
+encircles all parts of the stomach, while the inner set consists of
+oblique fibers. The third coat is the sub-mucous, made up of loose
+connective tissues, and binds the mucous to the muscular coat. Lastly
+there is the mucous coat, a moist, pink, inelastic membrane, which
+completely lines the stomach. When the stomach is not distended, the
+mucous layer is thrown into folds presenting a corrugated appearance.
+
+Illustration: Fig. 53.—Pits in the Mucous Membrane of the Stomach, and
+Openings of the Gastric Glands. (Magnified 20 diameters.)
+
+
+141. The Gastric Glands. If we were to examine with a hand lens the
+inner surface of the stomach, we would find it covered with little
+pits, or depressions, at the bottom of which would be seen dark dots.
+These dots are the openings of the gastric glands. In the form of fine,
+wavy tubes, the gastric glands are buried in the mucous membrane, their
+mouths opening on the surface. When the stomach is empty the mucous
+membrane is pale, but when food enters, it at once takes on a rosy
+tint. This is due to the influx of blood from the large number of very
+minute blood-vessels which are in the tissue between the rows of
+glands.
+
+The cells of the gastric glands are thrown into a state of greater
+activity by the increased quantity of blood supply. As a result, soon
+after food enters the stomach, drops of fluid collect at the mouths of
+the glands and trickle down its walls to mix with the food. Thus these
+glands produce a large quantity of gastric juice, to aid in the
+digestion of food.
+
+142. Digestion in the Stomach. When the food, thoroughly mixed with
+saliva, reaches the stomach, the cardiac end of that organ is closed as
+well as the pyloric valve, and the muscular walls contract on the
+contents. A spiral wave of motion begins, becoming more rapid as
+digestion goes on. Every particle of food is thus constantly churned
+about in the stomach and thoroughly mixed with the gastric juice. The
+action of the juice is aided by the heat of the parts, a temperature of
+about 99° Fahrenheit.
+
+The gastric juice is a thin almost colorless fluid with a sour taste
+and odor. The reaction is distinctly acid, normally due to free
+hydrochloric acid. Its chief constituents are two ferments called
+pepsin and rennin, free hydrochloric acid, mineral salts, and 95 per
+cent of water.
+
+Illustration: Fig. 54.—A highly magnified view of a peptic or gastric
+gland, which is represented as giving off branches. It shows the
+columnar epithelium of the surface dipping down into the duct D of the
+gland, from which two tubes branch off. Each tube is lined with
+columnar epithelial cells, and there is a minute central passage with
+the “neck” at N. Here and there are seen other special cells called
+parietal cells, P, which are supposed to produce the acid of the
+gastric juice. The principal cells are represented at C.
+
+
+Pepsin the important constituent of the gastric juice, has the power,
+in the presence of an acid, of dissolving the proteid food-stuffs. Some
+of which is converted into what are called _peptones_, both soluble and
+capable of filtering through membranes. The gastric juice has no action
+on starchy foods, neither does it act on fats, except to dissolve the
+albuminous walls of the fat cells. The fat itself is thus set free in
+the form of minute globules. The whole contents of the stomach now
+assume the appearance and the consistency of a thick soup, usually of a
+grayish color, known as chyme.
+
+It is well known that “rennet” prepared from the calf’s stomach has a
+remarkable effect in rapidly curdling milk, and this property is
+utilized in the manufacture of cheese. Now, a similar ferment is
+abundant in the gastric juice, and may be called _rennin_. It causes
+milk to clot, and does this by so acting on the casein as to make the
+milk set into a jelly. Mothers are sometimes frightened when their
+children, seemingly in perfect health, vomit masses of curdled milk.
+This curdling of the milk is, however, a normal process, and the only
+noteworthy thing is its rejection, usually due to overfeeding.
+
+Experiment 58. _To show that pepsin and acid are necessary for gastric
+digestion._ Take three beakers, or large test tubes; label them _A_,
+_B_, _C_. Put into _A_ water and a few grains of powdered pepsin. Fill
+_B_ two-thirds full of dilute hydrochloric acid (one teaspoonful to a
+pint), and fill _C_ two-thirds full of hydrochloric acid and a few
+grains of pepsin. Put into each a small quantity of well-washed fibrin,
+and place them all in a water bath at 104° Fahrenheit for half an hour.
+Examine them. In _A_, the fibrin is unchanged; in _B_, the fibrin is
+clear and swollen up; in _C_, it has disappeared, having first become
+swollen and clear, and completely dissolved, being finally converted
+into peptones. Therefore, both acid and ferment are required for
+gastric digestion.
+
+Experiment 59. Half fill with dilute hydrochloric acid three large test
+tubes, labelled _A_, _B_, _C_. Add to each a few grains of pepsin. Boil
+_B_, and make _C_ faintly alkaline with sodic carbonate. The alkalinity
+may be noted by adding previously some neutral litmus solution. Add to
+each an equal amount—a few threads—of well-washed fibrin which has been
+previously steeped for some time in dilute hydrochloric acid, so that
+it is swollen and transparent. Keep the tubes in a water-bath at about
+104° Fahrenheit for an hour and examine them at intervals of twenty
+minutes.
+    After five to ten minutes the fibrin in _A_ is dissolved and the
+    fluid begins to be turbid. In _B_ and _C_ there is no change. Even
+    after long exposure to 100° Fahrenheit there is no change in _B_
+    and _C_.
+
+After a variable time, from one to four hours, the contents of the
+stomach, which are now called chyme, begin to move on in successive
+portions into the next part of the intestinal canal. The ring-like
+muscles of the pylorus relax at intervals to allow the muscles of the
+stomach to force the partly digested mass into the small intestines.
+This action is frequently repeated, until even the indigestible masses
+which the gastric juice cannot break down are crowded out of the
+stomach into the intestines. From three to four hours after a meal the
+stomach is again quite emptied.
+
+A certain amount of this semi-liquid mass, especially the peptones,
+with any saccharine fluids, resulting from the partial conversion of
+starch or otherwise, is at once absorbed, making its way through the
+delicate vessels of the stomach into the blood current, which is
+flowing through the gastric veins to the portal vein of the liver.
+
+Illustration: Fig. 55.—A Small Portion of the Mucous Membrane of the
+Small Intestine. (Villi are seen surrounded with the openings of the
+tubular glands.) [Magnified 20 diameters.]
+
+
+143. The Small Intestine. At the pyloric end of the stomach the
+alimentary canal becomes again a slender tube called the small
+intestine. This is about twenty feet long and one inch in diameter, and
+is divided, for the convenience of description, into three parts.
+
+The first 12 inches is called the duodenum. Into this portion opens the
+bile duct from the liver with the duct from the pancreas, these having
+been first united and then entering the intestine as a common duct.
+
+The next portion of the intestine is called the jejunum, because it is
+usually empty after death.
+
+The remaining portion is named the ileum, because of the many folds
+into which it is thrown. It is the longest part of the small intestine,
+and terminates in the right iliac region, opening into the large
+intestine. This opening is guarded by the folds of the membrane forming
+the ileo-cæcal valve, which permits the passage of material from the
+small to the large intestine, but prevents its backward movement.
+
+144. The Coats of the Small Intestine. Like the stomach, the small
+intestine has four coats, the serous, muscular, sub-mucous, and mucous.
+The serous is the peritoneum.[22] The muscular consists of an outer
+layer of longitudinal, and an inner layer of circular fibers, by
+contraction of which the food is forced along the bowel. The sub-mucous
+coat is made up of a loose layer of tissue in which the blood-vessels
+and nerves are distributed. The inner, or mucous, surface has a fine,
+velvety feeling, due to a countless number of tiny, thread-like
+projections, called villi. They stand up somewhat like the “pile” of
+velvet. It is through these villi that the digested food passes into
+the blood.
+
+Illustration: Fig. 56.—Sectional View of Intestinal Villi. (Black dots
+represent the glandular openings.)
+
+
+The inner coat of a large part of the small intestine is thrown into
+numerous transverse folds called _valvulæ conniventes_. These seem to
+serve two purposes, to increase the extent of the surface of the bowels
+and to delay mechanically the progress of the intestinal contents.
+Buried in the mucous layer throughout the length, both of the small and
+large intestines, are other glands which secrete intestinal fluids.
+Thus, in the lower part of the ileum there are numerous glands in oval
+patches known as _Peyer’s patches_. These are very prone to become
+inflamed and to ulcerate during the course of typhoid fever.
+
+145. The Large Intestine. The large intestine begins in the right iliac
+region and is about five or six feet long. It is much larger than the
+small intestine, joining it obliquely at short distance from its end. A
+blind pouch, or dilated pocket is thus formed at the place of junction,
+called the cæcum. A valvular arrangement called the ileo-cæcal valve,
+which is provided with a button-hole slit, forms a kind of movable
+partition between this part of the large intestine and the small
+intestine.
+
+Illustration: Fig. 57.—Tubular Glands of the Small Intestines.
+A, B, tubular glands seen in vertical section with their orifices at C,
+opening upon the membrane between the villi, D, villus (Magnified 40
+diameters)
+
+Attached to the cæcum is a worm-shaped tube, about the size of a lead
+pencil, and from three to four inches long, called the _vermiform
+appendix_. Its use is unknown. This tube is of great surgical
+importance, from the fact that it is subject to severe inflammation,
+often resulting in an internal abscess, which is always dangerous and
+may prove fatal. Inflammation of the appendix is known as
+_appendicitis_,—a name quite familiar on account of the many surgical
+operations performed of late years for its relief.
+
+The large intestine passes upwards on the right side as the ascending
+colon, until the under side of the liver is reached, where it passes to
+the left side, as the transverse colon, below the stomach. It there
+turns downward, as the descending colon, and making an S-shaped curve,
+ends in the rectum. Thus the large intestine encircles, in the form of
+a horseshoe, the convoluted mass of small intestines.
+
+Like the small intestine, the large has four coats. The mucous coat,
+however, has no folds, or villi, but numerous closely set glands, like
+some of those of the small intestine. The longitudinal muscular fibers
+of the large intestine are arranged in three bands, or bundles, which,
+being shorter than the canal itself, produce a series of bulgings or
+pouches in its walls. This sacculation of the large bowel is supposed
+to be designed for delaying the onward flow of its contents, thus
+allowing more time for the absorption of the liquid material. The
+blood-vessels and nerves of this part of the digestive canal are very
+numerous, and are derived from the same sources as those of the small
+intestine.
+
+146. The Liver. The liver is a part of the digestive apparatus, since
+it forms the bile, one of the digestive fluids. It is a large
+reddish-brown organ, situated just below the diaphragm, and on the
+right side. The liver is the largest gland in the body, and weighs from
+50 to 60 ounces. It consists of two lobes, the right and the left, the
+right being much the larger. The upper, convex surface of the liver is
+very smooth and even; but the under surface is irregular, broken by the
+entrance and exit of the various vessels which belong to the organ. It
+is held in its place by five ligaments, four of which are formed by
+double folds of the peritoneum.
+
+The thin front edge of the liver reaches just below the bony edge of
+the ribs; but the dome-shaped diaphragm rises slightly in a horizontal
+position, and the liver passes up and is almost wholly covered by the
+ribs. In tight lacing, the liver is often forced downward out from the
+cover of the ribs, and thus becomes permanently displaced. As a result,
+other organs in the abdomen and pelvis are crowded together, and also
+become displaced.
+
+147. Minute Structure of the Liver. When a small piece of the liver is
+examined under a microscope it is found to be made up of masses of
+many-sided cells, each about 1/1000 of an inch in diameter. Each group
+of cells is called a _lobule_. When a single lobule is examined under
+the microscope it appears to be of an irregular, circular shape, with
+its cells arranged in rows, radiating from the center to the
+circumference. Minute, hair-like channels separate the cells one from
+another, and unite in one main duct leading from the lobule. It is the
+lobules which give to the liver its coarse, granular appearance, when
+torn across.
+
+Illustration: Fig. 58.—Diagrammatic Section of a Villus
+
+
+A,  layer of columnar epithelium covering the villus;
+  B, central lacteal of villus;
+  C, unstriped muscular fibers;
+  D, goblet cell
+
+
+Now there is a large vessel called the portal vein that brings to the
+liver blood full of nourishing material obtained from the stomach and
+intestines. On entering the liver this great vein conducts itself as if
+it were an artery. It divides and subdivides into smaller and smaller
+branches, until, in the form of the tiniest vessels, called
+capillaries, it passes inward among the cells to the very center of the
+hepatic lobules.
+
+148. The Bile. We have in the liver, on a grand scale, exactly the same
+conditions as obtain in the smaller and simpler glands. The thin-walled
+liver cells take from the blood certain materials which they elaborate
+into an important digestive fluid, called the bile.[23] This newly
+manufactured fluid is carried away in little canals, called _bile
+ducts_. These minute ducts gradually unite and form at last one main
+duct, which carries the bile from the liver. This is known as the
+hepatic duct. It passes out on the under side of the liver, and as it
+approaches the intestine, it meets at an acute angle the cystic duct
+which proceeds from the gall bladder and forms with it the common bile
+duct. The common duct opens obliquely into the horseshoe bend of the
+duodenum.
+
+The cystic duct leads back to the under surface of the liver, where it
+expands into a sac capable of holding about two ounces of fluid, and is
+known as the gall bladder. Thus the bile, prepared in the depths of the
+liver by the liver cells, is carried away by the bile ducts, and may
+pass directly into the intestines to mix with the food. If, however,
+digestion is not going on, the mouth of the bile duct is closed, and in
+that case the bile is carried by the cystic duct to the gall bladder.
+Here it remains until such time as it is needed.
+
+149. Blood Supply of the Liver. We must not forget that the liver
+itself, being a large and important organ, requires constant
+nourishment for the work assigned to it. The blood which is brought to
+it by the portal vein, being venous, is not fit to nourish it. The work
+is done by the arterial blood brought to it by a great branch direct
+from the aorta, known as the hepatic artery, minute branches of which
+in the form of capillaries, spread themselves around the hepatic
+lobules.
+
+The blood, having done its work and now laden with impurities, is
+picked up by minute veinlets, which unite again and again till they at
+last form one great trunk called the hepatic vein. This carries the
+impure blood from the liver, and finally empties it into one of the
+large veins of the body.
+
+After the blood has been robbed of its bile-making materials, it is
+collected by the veinlets that surround the lobules, and finds its way
+with other venous blood into the hepatic vein. In brief, blood is
+brought to the liver and distributed through its substance by two
+distinct channels,—the portal vein and the hepatic artery, but it
+leaves the liver by one distinct channel,—the hepatic vein.
+
+Illustration: Fig. 59.—Showing the Relations of the Duodenum and Other
+Intestinal Organs. (A portion of the stomach has been cut away.)
+
+
+150. Functions of the Liver. We have thus far studied the liver only as
+an organ of secretion, whose work is to elaborate bile for future use
+in the process of digestion. This is, however, only one of its
+functions, and perhaps not the most important. In fact, the functions
+of the liver are not single, but several. The bile is not wholly a
+digestive fluid, but it contains, also, materials which are separated
+from the blood to be cast out of the body before they work mischief.
+Thus, the liver ranks above all others as an organ of excretion, that
+is, it separates material of no further use to the body.
+
+Of the various ingredients of the bile, only the bile salts are of use
+in the work of digestion, for they act upon the fats in the alimentary
+canal, and aid somehow in their emulsion and absorption. They appear to
+be themselves split up into other substances, and absorbed with the
+dissolved fats into the blood stream again.
+
+The third function of the liver is very different from those already
+described. It is found that the liver of an animal well and regularly
+fed, when examined soon after death, contains a quantity of a
+carbohydrate substance not unlike starch. This substance, extracted in
+the form of a white powder, is really an animal starch. It is called
+glycogen, or liver sugar, and is easily converted into grape sugar.
+
+The hepatic cells appear to manufacture this glycogen and to store it
+up from the food brought by the portal blood. It is also thought the
+glycogen thus deposited and stored up in the liver is little by little
+changed into sugar. Then, as it is wanted, the liver disposes of this
+stored-up material, by pouring it, in a state of solution, into the
+hepatic vein. It is thus steadily carried to the tissues, as their
+needs demand, to supply them with material to be transformed into heat
+and energy.
+
+151. The Pancreas. The pancreas, or sweetbread, is much smaller than
+the liver. It is a tongue-like mass from six to eight inches long,
+weighing from three to four ounces, and is often compared in appearance
+to a dog’s tongue. It is somewhat the shape of a hammer with the handle
+running to a point.
+
+The pancreas lies behind the stomach, across the body, from right to
+left, with its large head embraced in the horseshoe bend of the
+duodenum. It closely resembles the salivary glands in structure, with
+its main duct running from one end to the other. This duct at last
+enters the duodenum in company with the common bile duct.
+
+The pancreatic juice, the most powerful in the body, is clear, somewhat
+viscid, fluid. It has a decided alkaline reaction and is not unlike
+saliva in many respects. Combined with the bile, this juice acts upon
+the large drops of fat which pass from the stomach into the duodenum
+and emulsifies them. This process consists partly in producing a fine
+subdivision of the particles of fat, called an emulsion, and partly in
+a chemical decomposition by which a kind of soap is formed. In this way
+the oils and fats are divided into particles sufficiently minute to
+permit of their being absorbed into the blood.
+
+Again, this most important digestive fluid produces on starch an action
+similar to that of saliva, but much more powerful. During its short
+stay in the mouth, very little starch is changed into sugar, and in the
+stomach, as we have seen, the action of the saliva is arrested. Now,
+the pancreatic juice takes up the work in the small intestine and
+changes the greater part of the starch into sugar. Nor is this all, for
+it also acts powerfully upon the proteids not acted upon in the
+stomach, and changes them into peptones that do not differ materially
+from those resulting from gastric digestion. The remarkable power which
+the pancreatic juice possesses of acting on all the food-stuffs appears
+to be due mainly to the presence of a specific element or ferment,
+known as _trypsin_.
+
+Experiment 60. _To show the action of pancreatic juice upon oils or
+fats._ Put two grains of Fairchild’s extract of pancreas into a
+four-ounce bottle. Add half a teaspoonful of warm water, and shake well
+for a few minutes; then add a tablespoonful of cod liver oil; shake
+vigorously.
+    A creamy, opaque mixture of the oil and water, called an emulsion,
+    will result. This will gradually separate upon standing, the
+    pancreatic extract settling in the water at the bottom. When shaken
+    it will again form an emulsion.
+
+Experiment 61. _To show the action of pancreatic juice on starch_. Put
+two tablespoonfuls of _smooth_ starch paste into a goblet, and while
+still so warm as just to be borne by the mouth, stir into it two grains
+of the extract of pancreas. The starch paste will rapidly become
+thinner, and gradually change into soluble starch, in a perfectly fluid
+solution. Within a few minutes some of the starch is converted through
+intermediary stages into maltose. Use the Fehling test for sugar.
+
+
+152. Digestion in the Small Intestines. After digestion in the stomach
+has been going on for some time, successive portions of the
+semi-digested food begin to pass into the duodenum. The pancreas now
+takes on new activity, and a copious flow of pancreatic juice is poured
+along its duct into the intestines. As the food is pushed along over
+the common opening of the bile and pancreatic ducts, a great quantity
+of bile from this reservoir, the gall bladder, is poured into the
+intestines. These two digestive fluids are now mixed with the chyme,
+and act upon it in the remarkable manner just described.
+
+Illustration: Fig. 60.—Diagrammatic Scheme of Intestinal Absorption.
+
+
+A,  mesentery;
+  B, lacteals and mesentery glands;
+  C, veins of intestines;
+  R.C, receptacle of the chyle (receptaculum chyli);
+  P V, portal vein;
+  H V, hepatic veins;
+  S.V.C, superior vena cava;
+  R.A, right auricle of the heart;
+  I.V.C, inferior vena cava.
+
+The inner surface of the small intestine also secretes a liquid called
+intestinal juice, the precise functions of which are not known. The
+chyme, thus acted upon by the different digestive fluids, resembles a
+thick cream, and is now called chyle. The chyle is propelled along the
+intestine by the worm-like contractions of its muscular walls. A
+function of the bile, not yet mentioned, is to stimulate these
+movements, and at the same time by its antiseptic properties to prevent
+putrefaction of the contents of the intestine.
+
+153. Digestion in the Large Intestines. Digestion does not occur to any
+great extent in the large intestines. The food enters this portion of
+the digestive canal through the ileo-cæcal valve, and travels through
+it slowly. Time is thus given for the fluid materials to be taken up by
+the blood-vessels of the mucous membrane. The remains of the food now
+become less fluid, and consist of undigested matter which has escaped
+the action of the several digestive juices, or withstood their
+influence. Driven onward by the contractions of the muscular walls, the
+refuse materials at last reach the rectum, from which they are
+voluntarily expelled from the body.
+
+Absorption.
+
+154. Absorption. While food remains within the alimentary canal it is
+as much outside of the body, so far as nutrition is concerned, as if it
+had never been taken inside. To be of any service the food must enter
+the blood; it must be absorbed. The efficient agents in absorption are
+the blood-vessels, the lacteals, and the lymphatics. The process
+through which the nutritious material is fitted to enter the blood, is
+called absorption. It is a process not confined, as we shall see,
+simply to the alimentary canal, but one that is going on in every
+tissue.
+
+The vessels by which the process of absorption is carried on are called
+absorbents. The story, briefly told, is this: certain food materials
+that have been prepared to enter the blood, filter through the mucous
+membrane of the intestinal canal, and also the thin walls of minute
+blood-vessels and lymphatics, and are carried by these to larger
+vessels, and at last reach the heart, thence to be distributed to the
+tissues.
+
+155. Absorption from the Mouth and Stomach. The lining of the mouth and
+œsophagus is not well adapted for absorption. That this does occur is
+shown by the fact that certain poisonous chemicals, like cyanide of
+potash, if kept in the mouth for a few moments will cause death. While
+we are chewing and swallowing our food, no doubt a certain amount of
+water and common salt, together with sugar which has been changed from
+starch by the action of the saliva, gains entrance to the blood.
+
+In the stomach, however, absorption takes place with great activity.
+The semi-liquid food is separated from the enormous supply of
+blood-vessels in the mucous membrane only by a thin porous partition.
+There is, therefore, nothing to prevent the exchange taking place
+between the blood and the food. Water, along with any substances in the
+food that have become dissolved, will pass through the partition and
+enter the blood-current. Thus it is that a certain amount of starch
+that has been changed into sugar, of salts in solution, of proteids
+converted into peptones, is taken up directly by the blood-vessels of
+the stomach.
+
+156. Absorption by the Intestines. Absorption by the intestines is a
+most active and complicated process. The stomach is really an organ
+more for the digestion than the absorption of food, while the small
+intestines are especially constructed for absorption. In fact, the
+greatest part of absorption is accomplished by the small intestines.
+They have not only a very large area of absorbing surface, but also
+structures especially adapted to do this work.
+
+157. The Lacteals. We have learned in Section 144 that the mucous
+lining of the small intestines is crowded with millions of little
+appendages called villi, meaning “tufts of hair.” These are only about
+1/30 of an inch long, and a dime will cover more than five hundred of
+them. Each villus contains a loop of blood-vessels, and another vessel,
+the lacteal, so called from the Latin word _lac_, milk, because of the
+milky appearance of the fluid it contains. The villi are adapted
+especially for the absorption of fat. They dip like the tiniest fingers
+into the chyle, and the minute particles of fat pass through their
+cellular covering and gain entrance to the lacteals. The milky material
+sucked up by the lacteals is not in a proper condition to be poured at
+once into the blood current. It is, as it were, in too crude a state,
+and needs some special preparation.
+
+The intestines are suspended to the posterior wall of the abdomen by a
+double fold of peritoneum called the mesentery. In this membrane are
+some 150 glands about the size of an almond, called mesenteric glands.
+Now the lacteals join these glands and pour in their fluid contents to
+undergo some important changes. It is not unlikely that the mesenteric
+glands may intercept, like a filter, material which, if allowed to
+enter the blood, would disturb the whole body. Thus, while the glands
+might suffer, the rest of the body might escape. This may account for
+the fact that these glands and the lymphatics may be easily irritated
+and inflamed, thus becoming enlarged and sensitive, as often occurs in
+the axilla.
+
+Having been acted upon by the mesenteric glands, and passed through
+them, the chyle flows onward until it is poured into a dilated
+reservoir for the chyle, known as the receptaculum chyli. This is a
+sac-like expansion of the lower end of the thoracic duct. Into this
+receptacle, situated at the level of the upper lumbar vertebræ, in
+front of the spinal column, are poured, not only the contents of the
+lacteals, but also of the lymphatic vessels of the lower limbs.
+
+158. The Thoracic Duct. This duct is a tube from fifteen to eighteen
+inches long, which passes upwards in front of the spine to reach the
+base of the neck, where it opens at the junction of the great veins of
+the left side of the head with those of the left arm. Thus the thoracic
+duct acts as a kind of feeding pipe to carry along the nutritive
+material obtained from the food and to pour it into the blood current.
+It is to be remembered that the lacteals are in reality lymphatics—the
+lymphatics of the intestines.
+
+Illustration: Fig. 61.—Section of a Lymphatic Gland.
+
+
+A,  strong fibrous capsule sending partitions into the gland;
+  B, partitions between the follicles or pouches of the _cortical_ or
+  outer portion;
+  C, partitions of the _medullary_ or central portion;
+  D, E, masses of protoplasmic matter in the pouches of the gland;
+  F, lymph-vessels which bring lymph _to_ the gland, passing into its
+  center;
+  G, confluence of those leading to the efferent vessel;
+  H, vessel which carries the lymph away _from_ the gland.
+
+
+159. The Lymphatics. In nearly every tissue and organ of the body there
+is a marvelous network of vessels, precisely like the lacteals, called
+the lymphatics. These are busily at work taking up and making over anew
+waste fluids or surplus materials derived from the blood and tissues
+generally. It is estimated that the quantity of fluid picked up from
+the tissues by the lymphatics and restored daily to the circulation is
+equal to the bulk of the blood in the body. The lymphatics seem to
+start out from the part in which they are found, like the rootlets of a
+plant in the soil. They carry a turbid, slightly yellowish fluid,
+called lymph, very much like blood without the red corpuscles.
+
+Now, just as the chyle was not fit to be immediately taken up by the
+blood, but was passed through the mesenteric glands to be properly
+worked over, so the lymph is carried to the lymphatic glands, where it
+undergoes certain changes to fit it for being poured into the blood.
+Nature, like a careful housekeeper, allows nothing to be wasted that
+can be of any further service in the animal economy (Figs. 63 and 64).
+
+The lymphatics unite to form larger and larger vessels, and at last
+join the thoracic duct, except the lymphatics of the right side of the
+head and chest and right arm. These open by the right lymphatic duct
+into the venous system on the right side of the neck.
+
+The whole lymphatic system may be regarded as a necessary appendage to
+the vascular system (Chapter VII.). It is convenient, however, to treat
+it under the general topic of absorption, in order to complete the
+history of food digestion.
+
+160. The Spleen and Other Ductless Glands. With the lymphatics may be
+classified, for convenience, a number of organs called ductless or
+blood glands. Although they apparently prepare materials for use in the
+body, they have no ducts or canals along which may be carried the
+result of their work. Again, they are called blood glands because it is
+supposed they serve some purpose in preparing material for the blood.
+
+The spleen is the largest of these glands. It lies beneath the
+diaphragm, and upon the left side of the stomach. It is of a deep red
+color, full of blood, and is about the size and shape of the palm of
+the hand.
+
+The spleen has a fibrous capsule from which partitions pass inwards,
+dividing it into spaces by a framework of elastic tissue, with plain
+muscular fibers. These spaces are filled with what is called the spleen
+pulp, through which the blood filters from its artery, just as a fluid
+would pass through a sponge. The functions of the spleen are not known.
+It appears to take some part in the formation of blood corpuscles. In
+certain diseases, like malarial fever, it may become remarkably
+enlarged. It may be wholly removed from an animal without apparent
+injury. During digestion it seems to act as a muscular pump, drawing
+the blood onwards with increased vigor along its large vein to the
+liver.
+
+The thyroid is another ductless gland. It is situated beneath the
+muscles of the neck on the sides of “Adam’s apple” and below it. It
+undergoes great enlargement in the disease called goitre.
+
+The thymus is also a blood gland. It is situated around the windpipe,
+behind the upper part of the breastbone. Until about the end of the
+second year it increases in size, and then it begins gradually to
+shrivel away. Like the spleen, the thyroid and thymus glands are
+supposed to work some change in the blood, but what is not clearly
+known.
+
+The suprarenal capsules are two little bodies, one perched on the top
+of each kidney, in shape not unlike that of a conical hat. Of their
+functions nothing definite is known.
+
+Experiments.
+
+The action produced by the tendency of fluids to mix, or become equally
+diffused in contact with each other, is known as _osmosis_, a form of
+molecular attraction allied to that of adhesion. The various physical
+processes by which the products of digestion are transferred from the
+digestive canal to the blood may be illustrated in a general way by the
+following simple experiments.
+
+The student must, however, understand that the necessarily crude
+experiments of the classroom may not conform in certain essentials to
+these great processes conducted in the living body, which they are
+intended to illustrate and explain.
+
+Illustration: Fig. 62.
+
+
+Experiment 62. _Simple Apparatus for Illustrating Endosmotic Action._
+“Remove carefully a circular portion, about an inch in diameter, of the
+shell from one end of an egg, which may be done without injuring the
+membranes, by cracking the shell in small pieces, which are picked off
+with forceps. A small glass tube is then introduced through an opening
+in the shell and membranes of the other end of the egg, and is secured
+in a vertical position by wax or plaster of Paris, the tube penetrating
+the yelk. The egg is then placed in a wine-glass partly filled with
+water. In the course of a few minutes, the water will have penetrated
+the exposed membrane, and the yelk will rise in the tube.”—Flint’s
+_Human Physiology_, page 293.
+
+
+Experiment 63. Stretch a piece of moist bladder across a glass tube,—a
+common lamp-chimney will do. Into this put a strong saline solution.
+Now suspend the tube in a wide mouthed vessel of water. After a short
+time it will be found that a part of the salt solution has passed
+through into the water, while a larger amount of water has passed into
+the tube and raised the height of the liquid within it.
+
+
+161. The Quantity of Food as Affected by Age. The quantity of food
+required to keep the body in proper condition is modified to a great
+extent by circumstances. Age, occupation, place of residence, climate,
+and season, as well as individual conditions of health and disease, are
+always important factors in the problem. In youth the body is not only
+growing, but the tissue changes are active. The restless energy and
+necessary growth at this time of life cannot be maintained without an
+abundance of wholesome food. This food supply for young people should
+be ample enough to answer the demands of their keen appetite and
+vigorous digestion.
+
+In adult life, when the processes of digestion and assimilation are
+active, the amount of food may without harm, be in excess of the actual
+needs of the body. This is true, however, only so long as active
+muscular exercise is taken.
+
+In advanced life the tissue changes are slow, digestion is less active,
+and the ability to assimilate food is greatly diminished. Growth has
+ceased, the energy which induced activity is gone, and the proteids are
+no longer required to build up worn-out tissues. Hence, as old age
+approaches, the quantity of nitrogenous foods should be steadily
+diminished.
+
+Experiment 64. Obtain a sheep’s bladder and pour into it a heavy
+solution of sugar or some colored simple elixir, found at any drug
+store. Tie the bladder carefully and place it in a vessel containing
+water. After a while it will be found that an interchange has occurred,
+water having passed into the bladder and the water outside having
+become sweet.
+
+
+Experiment 65. Make a hole about as big as a five-cent piece in the
+large end of an egg. That is, break the shell carefully and snip the
+outer shell membrane, thus opening the space between the outer and
+inner membranes. Now put the egg into a glass of water, keeping it in
+an upright position by resting on a napkin-ring. There is only the
+inner shell membrane between the liquid white of the egg (albumen) and
+the water.
+    An interchange takes place, and the water passes towards the
+    albumen. As the albumen does not pass out freely towards the water,
+    the membrane becomes distended, like a little bag at the top of the
+    egg.
+
+162. Ill Effects of a too Generous Diet. A generous diet, even of those
+who take active muscular exercise, should be indulged in only with
+vigilance and discretion. Frequent sick or nervous headaches, a sense
+of fullness, bilious attacks, and dyspepsia are some of the
+after-effects of eating more food than the body actually requires. The
+excess of food is not properly acted upon by the digestive juices, and
+is liable to undergo fermentation, and thus to become a source of
+irritation to the stomach and the intestines. If too much and too rich
+food be persistently indulged in, the complexion is apt to become
+muddy, the skin, especially of the face, pale and sallow, and more or
+less covered with blotches and pimples; the breath has an unpleasant
+odor, and the general appearance of the body is unwholesome.
+
+An excess of any one of the different classes of foods may lead to
+serious results. Thus a diet habitually too rich in proteids, as with
+those who eat meat in excess, often over-taxes the kidneys to get rid
+of the excess of nitrogenous waste, and the organs of excretion are not
+able to rid the tissues of waste products which accumulate in the
+system. From the blood, thus imperfectly purified, may result kidney
+troubles and various diseases of the liver and the stomach.
+
+163. Effect of Occupation. Occupation has an important influence upon
+the quantity of food demanded for the bodily support. Those who work
+long and hard at physical labor, need a generous amount of nutritious
+food. A liberal diet of the cereals and lean meat, especially beef,
+gives that vigor to the muscles which enables one to undergo laborious
+and prolonged physical exertion. On the other hand, those who follow a
+sedentary occupation do not need so large a quantity of food.
+Brain-workers who would work well and live long, should not indulge in
+too generous a diet. The digestion of heavy meals involves a great
+expenditure of nervous force. Hence, the forces of the brain-worker,
+being required for mental exertion, should not be expended to an
+unwarranted extent on the task of digestion.
+
+164. Effect of Climate. Climate also has a marked influence on the
+quantity of food demanded by the system. Much more food of all kinds is
+consumed in cold than in warm climates. The accounts by travelers of
+the quantity of food used by the inhabitants of the frigid zone are
+almost beyond belief. A Russian admiral gives an instance of a man who,
+in his presence, ate at a single meal 28 pounds of rice and butter. Dr.
+Hayes, the Arctic traveler, states from personal observation that the
+daily ration of the Eskimos is 12 to 15 pounds of meat. With the
+thermometer ranging from 60 to 70° F. below zero, there was a
+persistent craving for strong animal diet, especially fatty foods.[24]
+
+Illustration: Fig. 63.—Lymphatics and Lymphatic Glands of the Axilla.
+
+The intense cold makes such a drain upon the heat-producing power of
+the body that only food containing the largest proportion of carbon is
+capable of making up for the loss. In tropical countries, on the other
+hand, the natives crave and subsist mainly upon fruits and vegetables.
+
+165. The Kinds of Food Required. An appetite for plain, well-cooked
+food is a safe guide to follow. Every person in good health, taking a
+moderate amount of daily exercise, should have a keen appetite for
+three meals a day and enjoy them. Food should be both nutritious and
+digestible. It is nutritious in proportion to the amount of material it
+furnishes for the nourishment of the tissues. It is digestible in a
+greater or less degree in respect to the readiness with which it yields
+to the action of the digestive fluids, and is prepared to be taken up
+by the blood. This digestibility depends partly upon the nature of the
+food in its raw state, partly upon the effect produced upon it by
+cooking, and to some extent upon its admixture with other foods.
+Certain foods, as the vegetable albumens, are both nutritious and
+digestible. A hard-working man may grow strong and maintain vigorous
+health on most of them, even if deprived of animal food.
+
+While it is true that the vegetable albumens furnish all that is really
+needed for the bodily health, animal food of some kind is an economical
+and useful addition to the diet. Races of men who endure prolonged
+physical exertion have discovered for themselves, without the teaching
+of science, the great value of meat. Hence the common custom of eating
+meat with bread and vegetables is a sound one. It is undoubtedly true
+that the people of this country, as a rule, eat meat too often and too
+much at a time. The judicious admixture of different classes of foods
+greatly aids their digestibility.
+
+The great abundance and variety of food in this country, permit this
+principle to be put into practice. A variety of mixed foods, as milk,
+eggs, bread, and meat, are almost invariably associated to a greater or
+less extent at every meal.
+
+Oftentimes where there is of necessity a sameness of diet, there arises
+a craving for special articles of food. Thus on long voyages, and
+during long campaigns in war, there is an almost universal craving for
+onions, raw potatoes, and other vegetables.
+
+166. Hints about Meals. On an average, three meals each day, from five
+to six hours apart, is the proper number for adults. Five hours is by
+no means too long a time to intervene between consecutive meals, for it
+is not desirable to introduce new food into the stomach, until the
+gastric digestion of the preceding meal has been completed, and until
+the stomach has had time to rest, and is in condition to receive fresh
+material. The stomach, like other organs, does its work best at regular
+periods.[25]
+
+Eating out of mealtimes should be strictly avoided, for it robs the
+stomach of its needed rest. Food eaten when the body and mind are
+wearied is not well digested. Rest, even for a few minutes, should be
+taken before eating a full meal. It is well to lie down, or sit quietly
+and read, fifteen minutes before eating, and directly afterwards, if
+possible.
+
+Severe exercise and hard study just after a full meal, are very apt to
+delay or actually arrest digestion, for after eating heartily, the
+vital forces of the body are called upon to help the stomach digest its
+food. If our bodily energies are compelled, in addition to this, to
+help the muscles or brain, digestion is retarded, and a feeling of
+dullness and heaviness follows. Fermentative changes, instead of the
+normal digestive changes, are apt to take place in the food.
+
+167. Practical Points about Eating. We should not eat for at least two
+or three hours before going to bed. When we are asleep, the vital
+forces are at a low ebb, the process of digestion is for the time
+nearly suspended, and the retention of incompletely digested food in
+the stomach may cause bad dreams and troubled sleep. But in many cases
+of sleeplessness, a trifle of some simple food, especially if the
+stomach seems to feel exhausted, often appears to promote sleep and
+rest.
+
+Note. The table below shows the results of many experiments to
+illustrate the time taken for the gastric digestion of a number of the
+more common solid foods. There are a good many factors of which the
+table takes no account, such as the interval since the last meal, state
+of the appetite, amount of work and exercise, method of cooking, and
+especially the quantity of food.
+
+Table Showing the Digestibility of the More Common Solid Foods.
+
+Food     How Cooked     Time in Stomach, Hours
+Apples, sweet and mellow     Raw     1½
+Apples, sour and hard     ”     2½
+Apple Dumpling     Boiled     3
+Bass, striped, fresh     Broiled     3
+Beans, pod     Boiled     2½
+Beef, with salt only     ”     2¾
+”    fresh, lean     Raw     3
+”    ”    ”     Fried     4
+”    ”    ”     Roasted     3½
+”    old, hard, salted     Boiled     4¼
+Beefsteak     Broiled     3
+Beets     Boiled     3¾
+Bread, corn     Baked     3¼
+”    wheat, fresh     ”     3½
+Butter     Melted     3½
+Cabbage, with vinegar     Raw     2
+”    ”    ”     Boiled     4½
+”    heads     Raw     2½
+Carrots     Boiled     3¼
+Cheese, old, strong     Raw     3½
+Chicken, full-grown     Fricassee     2¾
+”    soup     Boiled     3
+Codfish, cured, dried     ”     2
+Corncake     Baked     2¾
+Custard     ”     2¾
+Duck, domestic     Roasted     4
+”    wild     ”     4½
+Eggs, fresh, whipped     Raw     1½
+”     ”     2
+”    soft-boiled     Boiled     3
+”    hard-boiled     ”     3½
+”     Fried     3½
+Fowl, domestic     Boiled     4
+”    ”     Roasted     4
+Gelatin     Boiled     2½
+Goose     Roasted     2½
+Green corn and beans     Boiled     3¾
+Hash, meat and vegetables     Warmed     2½
+Lamb     Broiled     2½
+Liver     ”     2
+Milk     Boiled     2
+”     Raw     2¼
+Mutton, fresh     Broiled     3
+”    ”     Boiled     3
+”    ”     Roasted     3¼
+Oysters, fresh     Raw     2½
+”    ”     Roasted     3¼
+”    ”     Stewed     3½
+Parsnips     Boiled     2½
+Pig     Roasted     2½
+Pig’s feet, soused     Boiled     1
+Pork, recently salted     ”     4½
+”     Fried     4¼
+”     Raw     3
+”    steaks     Fried     3¼
+”     Stewed     3
+”    fat or lean     Roasted     5¼
+Potatoes     Baked     2½
+”     Boiled     3½
+”     Roasted     2½
+Rice     Boiled     1
+Sago     ”     1¾
+Salmon, salted     ”     4
+Soup, barley     ”     1½
+”    beans     ”     3
+”    beef, vegetables, bread     ”     4
+”    marrow bone     ”     4½
+”    mutton     ”     3½
+Sponge Cake     Baked     2½
+Suet, beef, fresh     Boiled     5⅓
+”    mutton     ”     4½
+Tapioca     ”     2
+Tripe, soused     ”     1
+Trout, salmon, fresh     ”     1½
+”    ”    ”     Fried     1½
+Turkey, wild     Roasted     2¼
+”    domestic     Boiled     2¼
+”    ”     Roasted     2½
+Turnips     Boiled     3½
+Veal     Roasted     4
+”     Fried     4½
+Venison, steaks     Broiled     1½
+
+The state of mind has much to do with digestion. Sudden fear or joy, or
+unexpected news, may destroy the appetite at once. Let a hungry person
+be anxiously awaiting a hearty meal, when suddenly a disastrous
+telegram is brought him; all appetite instantly disappears, and the
+tempting food is refused. Hence we should laugh and talk at our meals,
+and drive away anxious thoughts and unpleasant topics of discussion.
+
+The proper chewing of the food is an important element in digestion.
+Hence, eat slowly, and do not “bolt” large fragments of food. If
+imperfectly chewed, it is not readily acted upon by the gastric juice,
+and often undergoes fermentative changes which result in sour stomach,
+gastric pain, and other digestive disturbance.
+
+If we take too much drink with our meals, the flow of the saliva is
+checked, and digestion is hindered. It is not desireable to dilute the
+gastric juice, nor to chill the stomach with large amount of cold
+liquid.
+
+Do not take food and drink too hot or too cold. If they are taken too
+cold, the stomach is chilled, and digestion delayed. If we drink freely
+of ice-water, it may require half an hour or more for the stomach to
+regain its natural heat.
+
+It is a poor plan to stimulate a flagging appetite with highly spiced
+food and bitter drinks. An undue amount of pepper, mustard,
+horseradish, pickles, and highly seasoned meat-sauces may stimulate
+digestion for the time, but they soon impair it.
+
+Note. The process of gastric digestion was studied many years ago by
+Dr. Beaumont and others, in the remarkable case of Alexis St. Martin, a
+French-Canadian, who met with a gun-shot wound which left a permanent
+opening into his stomach, guarded by a little valve of mucous membrane.
+Through this opening the lining of the stomach could be seen, the
+temperature ascertained, and numerous experiments made as to the
+digestibility of various kinds of food.
+    It was by these careful and convincing experiments that the
+    foundation of our exact knowledge of the composition and action of
+    gastric juice was laid. The modest book in which Dr. Beaumont
+    published his results is still counted among the classics of
+    physiology. The production of artificial fistulæ in animals, a
+    method that has since proved so fruitful, was first suggested by
+    his work.
+
+It cannot be too strongly stated that food of a simple character, well
+cooked and neatly served, is more productive of healthful living than a
+great variety of fancy dishes which unduly stimulate the digestive
+organs, and create a craving for food in excess of the bodily needs.
+
+168. The Proper Care of the Teeth. It is our duty not only to take the
+very best care of our teeth, but to retain them as long as possible.
+Teeth, as we well know, are prone to decay. We may inherit poor and
+soft teeth: our mode of living may make bad teeth worse. If an ounce of
+prevention is ever worth a pound of cure, it is in keeping the teeth in
+good order. Bad teeth and toothless gums mean imperfect chewing of the
+food and, hence, impaired digestion. To attain a healthful old age, the
+power of vigorous mastication must be preserved.
+
+One of the most frequent causes of decay of the teeth is the retention
+of fragments of food between and around them. The warmth and moisture
+of the mouth make these matters decompose quickly. The acid thus
+generated attacks the enamel of the teeth, causing decay of the
+dentine. Decayed teeth are often the cause of an offensive breath and a
+foul stomach.
+
+Illustration: Fig. 64.—Lymphatics on the Inside of the Right Hand.
+
+To keep the teeth clean and wholesome, they should be thoroughly
+cleansed at bedtime and in the morning with a soft brush and warm
+water. Castile soap, and some prepared tooth-powder without grit,
+should be used, and the brush should be applied on both sides of the
+teeth.
+
+The enamel, once broken through, is never renewed. The tooth decays,
+slowly but surely: hence we must guard against certain habits which
+injure the enamel, as picking the teeth with pins and needles. We
+should never crack nuts, crush hard candy, or bite off stout thread
+with the teeth. Stiff tooth-brushes, gritty and cheap tooth-powders,
+and hot food and drink, often injure the enamel.
+
+To remove fragments of food which have lodged between adjacent teeth, a
+quill or wooden toothpick should be used. Even better than these is the
+use of surgeon’s floss, or silk, which when drawn between the teeth,
+effectually dislodges retained particles. If the teeth are not
+regularly cleansed they become discolored, and a hard coating known as
+_tartar_ accumulates on them and tends to loosen them. It is said that
+after the age of thirty more teeth are lost from this deposit than from
+all other causes combined. In fact decay and tartar are the two great
+agents that furnish work for the dentist.[26]
+
+169. Hints about Saving Teeth. We should exercise the greatest care in
+saving the teeth. The last resort of all is to lose a tooth by
+extraction. The skilled dentist will save almost anything in the shape
+of a tooth.
+
+People are often urged and consent to have a number of teeth extracted
+which, with but little trouble and expense, might be kept and do good
+service for years. The object is to replace the teeth with an
+artificial set. Very few plates, either partial or entire, are worn
+with real comfort. They should always be removed before going to sleep,
+as there is danger of their being swallowed.
+
+The great majority of drugs have no injurious effect upon the teeth.
+Some medicines, however, must be used with great care. The acids used
+in the tincture of iron have a great affinity for the lime salts of the
+teeth. As this form of iron is often used, it is not unusual to see
+teeth very badly stained or decayed from the effects of this drug. The
+acid used in the liquid preparations of quinine may destroy the teeth
+in a comparatively short time. After taking such medicines the mouth
+should be thoroughly rinsed with a weak solution of common soda, and
+the teeth cleansed.
+
+170. Alcohol and Digestion. The influence of alcoholic drinks upon
+digestion is of the utmost importance. Alcohol is not, and cannot be
+regarded from a physiological point of view as a true food. The
+reception given to it by the stomach proves this very plainly. It is
+obviously an unwelcome intruder. It cannot, like proper foods, be
+transformed into any element or component of the human body, but passes
+on, innutritious and for the most part unappropriated. Taken even into
+the mouth, by any person not hardened to its use, its effect is so
+pungent and burning as at once to demand its rejection. But if allowed
+to pass into the stomach, that organ immediately rebels against its
+intrusion, and not unfrequently ejects it with indignant emphasis. The
+burning sensation it produces there, is only an appeal for water to
+dilute it.
+
+The stomach meanwhile, in response to this fiery invitation, secretes
+from its myriad pores its juices and watery fluids, to protect itself
+as much as possible from the invading liquid. It does not digest
+alcoholic drinks; we might say it does not attempt to, because they are
+not material suitable for digestion, and also because no organ can
+perform its normal work while smarting under an unnatural irritation.
+
+Even if the stomach does not at once eject the poison, it refuses to
+adopt it as food, for it does not pass along with the other food
+material, as chyme, into the intestines, but is seized by the
+absorbents, borne into the veins, which convey it to the heart, whence
+the pulmonary artery conveys it to the lungs, where its presence is
+announced in the breath. But wherever alcohol is carried in the
+tissues, it is always an irritant, every organ in turn endeavoring to
+rid itself of the noxious material.
+
+171. Effect of Alcoholic Liquor upon the Stomach. The methods by which
+intoxicating drinks impair and often ruin digestion are various. We
+know that a piece of animal food, as beef, if soaked in alcohol for a
+few hours, becomes hard and tough, the fibers having been compacted
+together because of the abstraction of their moisture by the alcohol,
+which has a marvelous affinity for water. In the same way alcohol
+hardens and toughens animal food in the stomach, condensing its fibers,
+and rendering it indigestible, thus preventing the healthful nutrition
+of the body. So, if alcohol be added to the clear, liquid white of an
+egg, it is instantly coagulated and transformed into hard albumen. As a
+result of this hardening action, animal food in contact with alcoholic
+liquids in the stomach remains undigested, and must either be detained
+there so long as to become a source of gastric disturbance, or else be
+allowed to pass undigested through the pyloric gate, and then may
+become a cause of serious intestinal disturbance.[27]
+
+This peculiar property of alcohol, its greedy absorption of water from
+objects in contact with it, acts also by absorbing liquids from the
+surface of the stomach itself, thus hardening the delicate glands,
+impairing their ability to absorb the food-liquids, and so inducing
+gastric dyspepsia. This local injury inflicted upon the stomach by all
+forms of intoxicants, is serious and protracted. This organ is, with
+admirable wisdom, so constructed as to endure a surprising amount of
+abuse, but it was plainly not intended to thrive on alcoholic liquids.
+The application of fiery drinks to its tender surface produces at first
+a marked congestion of its blood-vessels, changing the natural pink
+color, as in the mouth, to a bright or deep red.
+
+If the irritation be not repeated, the lining membrane soon recovers
+its natural appearance. But if repeated and continued, the congestion
+becomes more intense, the red color deeper and darker; the entire
+surface is the subject of chronic inflammation, its walls are
+thickened, and sometimes ulcerated. In this deplorable state, the organ
+is quite unable to perform its normal work of digestion.[28]
+
+172. Alcohol and the Gastric Juice. But still another destructive
+influence upon digestion appears in the singular fact that alcohol
+diminishes the power of the gastric juice to do its proper work.
+Alcohol coagulates the pepsin, which is the dissolving element in this
+important gastric fluid. A very simple experiment will prove this.
+Obtain a small quantity of gastric juice from the fresh stomach of a
+calf or pig, by gently pressing it in a very little water. Pour the
+milky juice into a clear glass vessel, add a little alcohol, and a
+white deposit will presently settle to the bottom. This deposit
+contains the pepsin of the gastric juice, the potent element by which
+it does its special work of digestion. The ill effect of alcohol upon
+it is one of the prime factors in the long series of evil results from
+the use of intoxicants.
+
+173. The Final Results upon Digestion. We have thus explained three
+different methods by which alcoholic drinks exercise a terrible power
+for harm; they act upon the food so as to render it less digestible;
+they injure the stomach so as seriously to impair its power of
+digestion; and they deprive the gastric juice of the one principal
+ingredient essential to its usefulness.
+
+Alcoholic drinks forced upon the stomach are a foreign substance; the
+stomach treats them as such, and refuses to go on with the process of
+digestion till it first gets rid of the poison. This irritating
+presence and delay weaken the stomach, so that when proper food
+follows, the enfeebled organ is ill prepared for its work. After
+intoxication, there occurs an obvious reaction of the stomach, and
+digestive organs, against the violent and unnatural disturbance. The
+appetite is extinguished or depraved, and intense headache racks the
+frame, the whole system is prostrated, as from a partial paralysis (all
+these results being the voice of Nature’s sharp warning of this great
+wrong), and a rest of some days is needed before the system fully
+recovers from the injury inflicted.
+
+It is altogether an error to suppose the use of intoxicants is
+necessary or even desirable to promote appetite or digestion. In
+health, good food and a stomach undisturbed by artificial interference
+furnish all the conditions required. More than these is harmful. If it
+may sometimes seem as if alcoholic drinks arouse the appetite and
+invigorate digestion, we must not shut our eyes to the fact that this
+is only a seeming, and that their continued use will inevitably ruin
+both. In brief, there is no more sure foe to good appetite and normal
+digestion than the habitual use of alcoholic liquors.
+
+174. Effect of Alcoholic Drinks upon the Liver. It is to be noted that
+the circulation of the liver is peculiar; that the capillaries of the
+hepatic artery unite in the lobule with those of the portal vein, and
+thus the blood from both sources is combined; and that the portal vein
+brings to the liver the blood from the stomach, the intestines, and the
+spleen. From the fact that alcohol absorbed from the stomach enters the
+portal vein, and is borne directly to the liver, we would expect to
+find this organ suffering the full effects of its presence. And all the
+more would this be true, because we have just learned that the liver
+acts as a sort of filter to strain from the blood its impurities. So
+the liver is especially liable to diseases produced by alcoholics. Post
+mortems of those who have died while intoxicated show a larger amount
+of alcohol in the liver than in any other organ. Next to the stomach
+the liver is an early and late sufferer, and this is especially the
+case with hard drinkers, and even more moderate drinkers in hot
+climates. Yellow fever occurring in inebriates is always fatal.
+
+The effects produced in the liver are not so much functional as
+organic; that is, not merely a disturbed mode of action, but a
+destruction of the fabric of the organ itself. From the use of
+intoxicants, the liver becomes at first irritated, then inflamed, and
+finally seriously diseased. The fine bands, or septa, which serve as
+partitions between the hepatic lobules, and so maintain the form and
+consistency of the organ, are the special subjects of the inflammation.
+Though the liver is at first enlarged, it soon becomes contracted; the
+secreting cells are compressed, and are quite unable to perform their
+proper work, which indeed is a very important one in the round of the
+digestion of food and the purification of the blood. This contraction
+of the septa in time gives the whole organ an irregularly puckered
+appearance, called from this fact a hob-nail liver or, popularly, gin
+liver. The yellowish discoloration, usually from retained or perverted
+bile, gives the disease the medical name of cirrhosis.[29] It is
+usually accompanied with dropsy in the lower extremities, caused by
+obstruction to the return of the circulation from the parts below the
+liver. This disease is always fatal.
+
+175. Fatty Degeneration Due to Alcohol. Another form of destructive
+disease often occurs. There is an increase of fat globules deposited in
+the liver, causing notable enlargement and destroying its function.
+This is called fatty degeneration, and is not limited to the liver, but
+other organs are likely to be similarly affected. In truth, this
+deposition of fat is a most significant occurrence, as it means actual
+destruction of the liver tissues,—nothing less than progressive death
+of the organ. This condition always leads to a fatal issue. Still other
+forms of alcoholic disease of the liver are produced, one being the
+excessive formation of sugar, constituting what is known as a form of
+diabetes.
+
+176. Effect of Tobacco on Digestion. The noxious influence of tobacco
+upon the process of digestion is nearly parallel to the effects of
+alcohol, which it resembles in its irritant and narcotic character.
+Locally, it stimulates the secretion of saliva to an unnatural extent,
+and this excess of secretion diminishes the amount available for normal
+digestion.
+
+Tobacco also poisons the saliva furnished for the digestion of food,
+and thus at the very outset impairs, in both of these particulars, the
+general digestion, and especially the digestion of the starchy portions
+of the food. For this reason the amount of food taken, fails to nourish
+as it should, and either more food must be taken, or the body becomes
+gradually impoverished.
+
+The poisonous _nicotine_, the active element of tobacco, exerts a
+destructive influence upon the stomach digestion, enfeebling the vigor
+of the muscular walls of that organ. These effects combined produce
+dyspepsia, with its weary train of baneful results.
+The tobacco tongue never presents the natural, clear, pink color, but
+rather a dirty yellow, and is usually heavily coated, showing a
+disordered stomach and impaired digestion. Then, too, there is dryness
+of the mouth, an unnatural thirst that demands drink. But pure water is
+stale and flat to such a mouth: something more emphatic is needed. Thus
+comes the unnatural craving for alcoholic liquors, and thus are taken
+the first steps on the downward grade.
+
+“There is no doubt that tobacco predisposes to neuralgia, vertigo,
+indigestion, and other affections of the nervous, circulatory and
+digestive organs.”—W. H. Hammond, the eminent surgeon of New York city
+and formerly Surgeon General, U.S.A.
+
+Drs. Seaver of Yale University and Hitchcock of Amherst College,
+instructors of physical education in these two colleges, have clearly
+demonstrated by personal examination and recorded statistics that the
+use of tobacco among college students checks growth in weight, height,
+chest-girth, and, most of all, in lung capacity.
+
+Additional Experiments.
+
+Experiment 66. Test a portion of _C_ (Experiment 57) with solution of
+iodine; no blue color is obtained, as all the starch has disappeared,
+having been converted into a reducing sugar, or maltose.
+
+Experiment 67. Make a thick starch paste; place some in test tubes,
+labeled _A_ and _B_. Keep _A_ for comparison, and to _B_ add saliva,
+and expose both to about 104° F. _A_ is unaffected, while _B_ soon
+becomes fluid—within two minutes—and loses its opalescence; this
+liquefaction is a process quite antecedent to the saccharifying process
+which follows.
+
+Experiment 68. _To show the action of gastric juice on milk_. Mix two
+teaspoonfuls of fresh milk in a test tube with a few drops of neutral
+artificial gastric juice;[30] keep at about 100° F. In a short time the
+milk curdles, so that the tube can be inverted without the curd falling
+out. By and by _whey_ is squeezed out of the clot. The curdling of milk
+by the rennet ferment present in the gastric juice, is quite different
+from that produced by the “souring of milk,” or by the precipitation of
+caseinogen by acids. Here the casein (carrying with it most of the
+fats) is precipitated in a neutral fluid.
+
+
+Experiment 69. To the test tube in the preceding experiment, add two
+teaspoonfuls of dilute hydrochloric acid, and keep at 100° F. for two
+hours. The pepsin in the presence of the acid digests the casein,
+gradually dissolving it, forming a straw-colored fluid containing
+peptones. The peptonized milk has a peculiar odor and bitter taste.
+
+Experiment 70. _To show the action of rennet on milk_. Place milk in a
+test tube, add a drop or two of commercial rennet, and place the tube
+in a water-bath at about 100° F. The milk becomes solid in a few
+minutes, forming a _curd_, and by and by the curd of casein contracts,
+and presses out a fluid,—the _whey_.
+
+
+Experiment 71. Repeat the experiment, but previously boil the rennet.
+No such result is obtained as in the preceding experiment, because the
+rennet ferment is destroyed by heat.
+
+
+Experiment 72. _To show the effect of the pancreatic ferment (trypsin)
+upon albuminous matter_. Half fill three test tubes, _A, B, C_, with
+one-per-cent solution of sodium carbonate, and add 5 drops of liquor
+pancreaticus, or a few grains of Fairchild’s extract of pancreas, in
+each. Boil _B_, and make _C_ acid with dilute hydrochloric acid. Place
+in each tube an equal amount of well-washed fibrin, plug the tubes with
+absorbent cotton, and place all in a water-bath at about 100° F.
+
+
+Experiment 73. Examine from time to time the three test tubes in the
+preceding experiment. At the end of one, two, or three hours, there is
+no change in _B_ and _C_, while in _A_ the fibrin is gradually being
+eroded, and finally disappears; but it does not swell up, and the
+solution at the same time becomes slightly turbid. After three hours,
+still no change is observable in _B_ and _C_.
+
+
+Experiment 74. Filter _A_, and carefully neutralize the filtrate with
+very dilute hydrochloric or acetic acid, equal to a precipitate of
+alkali-albumen. Filter off the precipitate, and on testing the
+filtrate, peptones are found. The intermediate bodies, the albumoses,
+are not nearly so readily obtained from pancreatic as from gastric
+digests.
+
+
+Experiment 75. Filter _B_ and _C_, and carefully neutralize the
+filtrates. They give no precipitate. No peptones are found.
+
+
+Experiment 76. _To show the action of pancreatic juice upon the
+albuminous ingredients (casein) of milk_. Into a four-ounce bottle put
+two tablespoonfuls of cold water; add one grain of Fairchild’s extract
+of pancreas, and as much baking soda as can be taken up on the point of
+a penknife. Shake well, and add four tablespoonfuls of cold, fresh
+milk. Shake again.
+    Now set the bottle into a basin of hot water (as hot as one can
+    bear the hand in), and let it stand for about forty-five minutes.
+    While the milk is digesting, take a small quantity of milk in a
+    goblet, and stir in ten drops or more of vinegar. A thick curd of
+    casein will be seen.
+    Upon applying the same test to the digested milk, no curd will be
+    made. This is because the pancreatic ferment (trypsin) has digested
+    the casein into “peptone,” which does not curdle. This digested
+    milk is therefore called “peptonized milk.”
+
+
+Experiment 77. _To show the action of bile_. Obtain from the butcher
+some ox bile. Note its bitter taste, peculiar odor, and greenish color.
+It is alkaline or neutral to litmus paper. Pour it from one vessel to
+another, and note that strings of mucin (from the lining membrane of
+the gall bladder) connect one vessel with the other. It is best to
+precipitate the mucin by acetic acid before making experiments; and to
+dilute the clear liquid with a little distilled water.
+
+
+Experiment 78. _Test for bile pigments_. Place a few drops of bile on a
+white porcelain slab. With a glass rod place a drop or two of strong
+nitric acid containing nitrous acid near the drop of bile; bring the
+acid and bile into contact. Notice the succession of colors, beginning
+with green and passing into blue, red, and yellow.
+
+
+Experiment 79. _To show the action of bile on fats_. Mix three
+teaspoonfuls of bile with one-half a teaspoonful of almond oil, to
+which some oleic acid is added. Shake well, and keep the tube in a
+water-bath at about 100° F. A very good emulsion is obtained.
+
+
+Experiment 80. _To show that bile favors filtration and the absorption
+of fats_. Place two small funnels of exactly the same size in a filter
+stand, and under each a beaker. Into each funnel put a filter paper;
+moisten the one with water (_A_) and the other with bile (_B_). Pour
+into each an equal volume of almond oil; cover with a slip of glass to
+prevent evaporation. Set aside for twelve hours, and note that the oil
+passes through _B_, but scarcely any through _A_. The oil filters much
+more readily through the one moistened with bile, than through the one
+moistened with water.
+
+Experiments with the Fats.
+
+Experiment 81. Use olive oil or lard. Show by experiment that they are
+soluble in ether, chloroform and hot water, but insoluble in water
+alone.
+
+
+Experiment 82. Dissolve a few drops of oil or fat in a teaspoonful of
+ether. Let a drop of the solution fall on a piece of tissue or rice
+paper. Note the greasy stain, which does not disappear with the heat.
+
+
+Experiment 83. Pour a little cod-liver oil into a test tube; add a few
+drops of a dilute solution of sodium carbonate. The whole mass becomes
+white, making an emulsion.
+
+Experiment 84. Shake up olive oil with a solution of albumen in a test
+tube. Note that an emulsion is formed.
+
+
+
+
+Chapter VII.
+The Blood and Its Circulation.
+
+
+177. The Circulation. All the tissues of the body are traversed by
+exceedingly minute tubes called capillaries, which receive the blood
+from the arteries, and convey it to the veins. These capillaries form a
+great system of networks, the meshes of which are filled with the
+elements of the various tissues. That is, the capillaries are closed
+vessels, and the tissues lie outside of them, as asbestos packing may
+be used to envelop hot-water pipes. The space between the walls of the
+capillaries and the cells of the tissues is filled with lymph. As the
+blood flows along the capillaries, certain parts of the plasma of the
+blood filter through their walls into the lymph, and certain parts of
+the lymph filter through the cell walls of the tissues and mingle with
+the blood current. The lymph thus acts as a medium of exchange, in
+which a transfer of material takes place between the blood in the
+capillaries and the lymph around them. A similar exchange of material
+is constantly going on between the lymph and the tissues themselves.
+
+This, then, we must remember,—that in every tissue, so long as the
+blood flows, and life lasts, this exchange takes place between the
+blood within the capillaries and the tissues without.
+
+The stream of blood _to_ the tissues carries to them the material,
+including the all-important oxygen, with which they build themselves up
+and do their work. The stream _from_ the tissues carries into the blood
+the products of certain chemical changes which have taken place in
+these tissues. These products may represent simple waste matter to be
+cast out or material which may be of use to some other tissue.
+
+In brief, the tissues by the help of the lymph live on the blood. Just
+as our bodies, as a whole, live on the things around us, the food and
+the air, so do the bodily tissues live on the blood which bathes them
+in an unceasing current, and which is their immediate air and food.
+
+178. Physical Properties of Blood. The blood has been called the life
+of the body from the fact that upon it depends our bodily existence.
+The blood is so essentially the nutrient element that it is called
+sometimes very aptly “liquid flesh.” It is a red, warm, heavy, alkaline
+fluid, slightly salt in taste, and has a somewhat fetid odor. Its color
+varies from bright red in the arteries and when exposed to the air, to
+various tints from dark purple to red in the veins. The color of the
+blood is due to the coloring constituent of the red corpuscles,
+_hæmoglobin_, which is brighter or darker as it contains more or less
+oxygen.
+
+Illustration: Fig. 65.—Blood Corpuscles of Various Animals. (Magnified
+to the same scale.)
+
+
+A,  from proteus, a kind of newt;
+  B, salamander;
+  C, frog;
+  D, frog after addition of acetic acid, showing the central nucleus;
+  E, bird;
+  F, camel;
+  G, fish;
+  H, crab or other invertebrate animal
+
+The temperature of the blood varies slightly in different parts of the
+circulation. Its average heat near the surface is in health about the
+same, _viz_. 98½° F. Blood is alkaline, but outside of the body it soon
+becomes neutral, then acid. The chloride of sodium, or common salt,
+which the blood contains, gives it a salty taste. In a hemorrhage from
+the lungs, the sufferer is quick to notice in the mouth the warm and
+saltish taste. The total amount of the blood in the body was formerly
+greatly overestimated. It is about 1/13 of the total weight of the
+body, and in a person weighing 156 pounds would amount to about 12
+pounds.
+
+179. Blood Corpuscles. If we put a drop of blood upon a glass slide,
+and place upon it a cover of thin glass, we can flatten it out until
+the color almost disappears. If we examine this thin film with a
+microscope, we see that the blood is not altogether fluid. We find that
+the liquid part, or plasma, is of a light straw color, and has floating
+in it a multitude of very minute bodies, called corpuscles. These are
+of two kinds, the red and the colorless. The former are much more
+numerous, and have been compared somewhat fancifully to countless
+myriads of tiny fishes in a swiftly flowing stream.
+
+180. Red Corpuscles. The red corpuscles are circular disks about 1/3200
+of an inch in diameter, and double concave in shape. They tend to
+adhere in long rolls like piles of coins. They are soft, flexible, and
+elastic, readily squeezing through openings and passages narrower than
+their own diameter, then at once resuming their own shape.
+
+The red corpuscles are so very small, that rather more than ten
+millions of them will lie on a surface one inch square. Their number is
+so enormous that, if all the red corpuscles in a healthy person could
+be arranged in a continuous line, it is estimated that they would reach
+four times around the earth! The principal constituent of these
+corpuscles, next to water, and that which gives them color is
+_hæmoglobin_, a compound containing iron. As all the tissues are
+constantly absorbing oxygen, and giving off carbon dioxid, a very
+important office of the red corpuscles is to carry oxygen to all parts
+of the body.
+
+181. Colorless Corpuscles. The colorless corpuscles are larger than the
+red, their average diameter being about 1/2500 of an inch. While the
+red corpuscles are regular in shape, and float about, and tumble freely
+over one another, the colorless are of irregular shape, and stick close
+to the glass slide on which they are placed. Again, while the red
+corpuscles are changed only by some influence from without, as pressure
+and the like, the colorless corpuscles spontaneously undergo active and
+very curious changes of form, resembling those of the amœba, a very
+minute organism found in stagnant water (Fig. 2).
+
+The number of both red and colorless corpuscles varies a great deal
+from time to time. For instance, the number of the latter increases
+after meals, and quickly diminishes. There is reason to think both
+kinds of corpuscles are continually being destroyed, their place being
+supplied by new ones. While the action of the colorless corpuscles is
+important to the lymph and the chyle, and in the coagulation of the
+blood, their real function has not been ascertained.
+
+Illustration: Fig. 66.—Blood Corpuscles of Man.
+
+
+A,  red corpuscles;
+  B, the same seen edgeways;
+  C, the same arranged in rows;
+  D, white corpuscles with nuclei.
+
+
+Experiment 85. _To show the blood corpuscles_. A moderately powerful
+microscope is necessary to examine blood corpuscles. Let a small drop
+of blood (easily obtained by pricking the finger with a needle) be
+placed upon a clean slip of glass, and covered with thin glass, such as
+is ordinarily used for microscopic purposes.
+
+The blood is thus spread out into a film and may be readily examined.
+At first the red corpuscles will be seen as pale, disk-like bodies
+floating in the clear fluid. Soon they will be observed to stick to
+each other by their flattened faces, so as to form rows. The colorless
+corpuscles are to be seen among the red ones, but are much less
+numerous.
+
+182. The Coagulation of the Blood. Blood when shed from the living body
+is as fluid as water. But it soon becomes viscid, and flows less
+readily from one vessel to another. Soon the whole mass becomes a
+nearly solid jelly called a clot. The vessel containing it even can be
+turned upside down, without a drop of blood being spilled. If carefully
+shaken out, the mass will form a complete mould of the vessel.
+
+At first the clot includes the whole mass of blood, takes the shape of
+the vessel in which it is contained, and is of a uniform color. But in
+a short time a pale yellowish fluid begins to ooze out, and to collect
+on the surface. The clot gradually shrinks, until at the end of a few
+hours it is much firmer, and floats in the yellowish fluid. The white
+corpuscles become entangled in the upper portion of clot, giving it a
+pale yellow look on the top, known as the _buffy coat_. As the clot is
+attached to the sides of the vessel, the shrinkage is more pronounced
+toward the center, and thus the surface of the clot is hollowed or
+_cupped_, as it is called. This remarkable process is known as
+coagulation, or the clotting of blood; and the liquid which separates
+from the clot is called serum. The serum is almost entirely free from
+corpuscles, these being entangled in the fibrin.
+
+Illustration: Fig. 67.—Diagram of Clot with Buffy Coat.
+
+
+A,  serum;
+  B, cupped upper surface of clot;
+  C, white corpuscles in upper layer of clot;
+  D, lower portion of clot with red corpuscles.
+
+
+This clotting of the blood is due to the formation in the blood, after
+it is withdrawn from the living body, of a substance called fibrin.[31]
+It is made up of a network of fine white threads, running in every
+direction through the plasma, and is a proteid substance. The
+coagulation of the blood may be retarded, and even prevented, by a
+temperature below 40° F., or a temperature above 120° F. The addition
+of common salt also prevents coagulation. The clotting of the blood may
+be hastened by free access to air, by contact with roughened surfaces,
+or by keeping it at perfect rest.
+
+This power of coagulation is of the most vital importance. But for
+this, a very small cut might cause bleeding sufficient to empty the
+blood-vessels, and death would speedily follow. In slight cuts, Nature
+plugs up the wound with clots of blood, and thus prevents excessive
+bleeding. The unfavorable effects of the want of clotting are
+illustrated in some persons in whom bleeding from even the slightest
+wounds continues till life is in danger. Such persons are called
+“bleeders,” and surgeons hesitate to perform on them any operation,
+however trivial, even the extraction of a tooth being often followed by
+an alarming loss of blood.
+
+Experiment 86. A few drops of fresh blood may be easily obtained to
+illustrate important points in the physiology of blood, by tying a
+string tight around the finger, and piercing it with a clean needle.
+The blood runs freely, is red and opaque. Put two or three drops of
+fresh blood on a sheet of white paper, and observe that it looks
+yellowish.
+
+Experiment 87. Put two or three drops of fresh blood on a white
+individual butter plate inverted in a saucer of water. Cover it with an
+inverted goblet. Take off the cover in five minutes, and the drop has
+set into a jelly-like mass. Take it off in half an hour, and a little
+clot will be seen in the watery serum.
+
+Experiment 88. _To show the blood-clot._ Carry to the slaughter house a
+clean, six or eight ounce, wide-mouthed bottle. Fill it with fresh
+blood. Carry it home with great care, and let it stand over night. The
+next day the clot will be seen floating in the nearly colorless serum.
+
+Experiment 89. Obtain a pint of fresh blood; put it into a bowl, and
+whip it briskly for five minutes, with a bunch of dry twigs. Fine white
+threads of fibrin collect on the twigs, the blood remaining fluid. This
+is “whipped” or defibrinated blood, which has lost the power of
+coagulating spontaneously.
+
+183. General Plan of Circulation. All the tissues of the body depend
+upon the blood for their nourishment. It is evident then that this
+vital fluid must be continually renewed, else it would speedily lose
+all of its life-giving material. Some provision, then, is necessary not
+only to have the blood renewed in quantity and quality, but also to
+enable it to carry away impurities.
+
+So we must have an apparatus of circulation. We need first a central
+pump from which branch off large pipes, which divide into smaller and
+smaller branches until they reach the remotest tissues. Through these
+pipes the blood must be pumped and distributed to the whole body. Then
+we must have a set of return pipes by which the blood, after it has
+carried nourishment to the tissues, and received waste matters from
+them, shall be brought back to the central pumping station, to be used
+again. We must have also some apparatus to purify the blood from the
+waste matter it has collected.
+
+Illustration: Fig. 68.—Anterior View of the Heart.
+
+
+A,  superior vena cava;
+  B, right auricle;
+  C, right ventricle;
+  D, left ventricle;
+  E, left auricle;
+  F, pulmonary vein;
+  H, pulmonary artery;
+  K, aorta;
+  L, right subclavian artery;
+  M, right common carotid artery;
+  N, left common carotid artery.
+
+This central pump is the heart. The pipes leading from it and gradually
+growing smaller and smaller are the arteries. The very minute vessels
+into which they are at last subdivided are capillaries. The pipes which
+convey the blood back to the heart are the veins. Thus, the arteries
+end in the tissues in fine, hair-like vessels, the capillaries; and the
+veins begin in the tissues in exceedingly small tubes,—the capillaries.
+Of course, there can be no break in the continuity between the arteries
+and the vein. The apparatus of circulation is thus formed by the heart,
+the arteries, the capillaries, and the veins.
+
+184. The Heart. The heart is a pear-shaped, muscular organ roughly
+estimated as about the size of the persons closed fist. It lies in the
+chest behind the breastbone, and is, lodged between the lobes of the
+lungs, which partly cover it. In shape the heart resembles a cone, the
+base of which is directed upwards, a little backwards, and to the right
+side, while the apex is pointed downwards, forwards, and to the left
+side. During life, the apex of the heart beats against the chest wall
+in the space between the fifth and sixth ribs, and about an inch and a
+half to the left of the middle line of the body. The beating of the
+heart can be readily felt, heard, and often seen moving the chest wall
+as it strikes against it.
+
+Illustration: Fig. 69.—Diagram illustrating the Structure of a Serous
+Membrane.
+
+
+A,  the viscus, or organ, enveloped by serous membrane;
+  B, layer of membrane lining cavity;
+  C, membrane reflected to envelop viscus;
+  D, outer layer of viscus, with blood-vessels at
+  E communicating with the general circulation.
+
+
+The heart does not hang free in the chest, but is suspended and kept in
+position to some extent by the great vessels connected with it. It is
+enclosed in a bell-shaped covering called the pericardium. This is
+really double, with two layers, one over another. The inner or serous
+layer covers the external surface of the heart, and is reflected back
+upon itself in order to form, like all membranes of this kind, a sac
+without an opening.[32] The heart is thus covered by the pericardial
+sac, but is not contained inside its cavity. The space between the two
+membranes is filled with serous fluid. This fluid permits the heart and
+the pericardium to glide upon one another with the least possible
+amount of friction.[33]
+
+The heart is a hollow organ, but the cavity is divided into two parts
+by a muscular partition forming a left and a right side, between which
+there is no communication. These two cavities are each divided by a
+horizontal partition into an upper and a lower chamber. These
+partitions, however, include a set of valves which open like folding
+doors between the two rooms. If these doors are closed there are two
+separate rooms, but if open there is practically only one room. The
+heart thus has four chambers, two on each side. The two upper chambers
+are called auricles from their supposed resemblance to the ear. The two
+lower chambers are called ventricles, and their walls form the chief
+portion of the muscular substance of the organ. There are, therefore,
+the right and left auricles, with their thin, soft walls, and the right
+and left ventricles, with their thick and strong walls.
+
+185. The Valves of the Heart. The heart is a valvular pump, which works
+on mechanical principles, the motive power being supplied by the
+contraction of its muscular fibers. Regarding the heart as a pump, its
+valves assume great importance. They consist of thin, but strong,
+triangular folds of tough membrane which hang down from the edges of
+the passages into the ventricles. They may be compared to swinging
+curtains which, by opening only one way, allow the blood to flow from
+the auricles to the ventricles, but by instantly folding back prevent
+its return.
+
+Illustration: Fig. 70.—Lateral Section of the Right Chest. (Showing the
+relative position of the heart and its great vessels, the œsophagus and
+trachea.)
+
+
+A,  inferior constrictor muscle (aids in conveying food down the
+œsophagus);
+  B, œsophagus;
+  C, section of the right bronchus;
+  D, two right pulmonary veins;
+  E, great azygos vein crossing œsophagus and right bronchus to empty
+  into the superior vena cava;
+  F, thoracic duct;
+  H, thoracic aorta;
+  K, lower portion of œsophagus passing through the diaphragm;
+  L, diaphragm as it appears in sectional view, enveloping the heart;
+  M, inferior vena cava passing through diaphragm and emptying into
+  auricle;
+  N, right auricle;
+  O, section of right branch of the pulmonary artery;
+  P, aorta;
+  R, superior vena cava;
+  S, trachea.
+
+The valve on the right side is called the tricuspid, because it
+consists of three little folds which fall over the opening and close
+it, being kept from falling too far by a number of slender threads
+called chordæ tendinæ. The valve on the left side, called the mitral,
+from its fancied resemblance to a bishop’s mitre, consists of two folds
+which close together as do those of the tricuspid valve.
+
+The slender cords which regulate the valves are only just long enough
+to allow the folds to close together, and no force of the blood pushing
+against the valves can send them farther back, as the cords will not
+stretch The harder the blood in the ventricles pushes back against the
+valves, the tighter the cords become and the closer the folds are
+brought together, until the way is completely closed.
+
+From the right ventricle a large vessel called the pulmonary artery
+passes to the lungs, and from the left ventricle a large vessel called
+the aorta arches out to the general circulation of the body. The
+openings from the ventricles into these vessels are guarded by the
+semilunar valves. Each valve has three folds, each half-moon-shaped,
+hence the name semilunar. These valves, when shut, prevent any backward
+flow of the blood on the right side between the pulmonary artery and
+the right ventricle, and on the left side between the aorta and the
+left ventricle.
+
+Illustration: Fig. 71.—Right Cavities of the Heart.
+
+
+A,  aorta;
+  B, superior vena cava;
+  C, C, right pulmonary veins;
+  D, inferior vena cava;
+  E, section of coronary vein;
+  F, right ventricular cavity;
+  H, posterior curtain of the tricuspid valve;
+  K, right auricular cavity;
+  M, fossa ovalis, oval depression, partition between the auricles
+  formed after birth.
+
+
+186. General Plan of the Blood-vessels Connected with the Heart. There
+are numerous blood-vessels connected with the heart, the relative
+position and the use of which must be understood. The two largest veins
+in the body, the superior vena cava and the inferior vena cava, open
+into the right auricle. These two veins bring venous blood from all
+parts of the body, and pour it into the right auricle, whence it passes
+into the right ventricle.
+
+From the right ventricle arises one large vessel, the pulmonary artery,
+which soon divides into two branches of nearly equal size, one for the
+right lung, the other for the left. Each branch, having reached its
+lung, divides and subdivides again and again, until it ends in
+hair-like capillaries, which form a very fine network in every part of
+the lung. Thus the blood is pumped from the right ventricle into the
+pulmonary artery and distributed throughout the two lungs (Figs. 86 and
+88).
+
+We will now turn to the left side of the heart, and notice the general
+arrangement of its great vessels. Four veins, called the pulmonary
+veins, open into the left auricle, two from each lung. These veins
+start from very minute vessels the continuation of the capillaries of
+the pulmonary artery. They form larger and larger vessels until they
+become two large veins in each lung, and pour their contents into the
+left auricle. Thus the pulmonary artery carries venous blood from the
+right ventricle _to_ the lungs, as the pulmonary veins carry arterial
+blood _from_ the lungs to the left auricle.
+
+From the left ventricle springs the largest arterial trunk in the body,
+over one-half of an inch in diameter, called the aorta. From the aorta
+other arteries branch off to carry the blood to all parts of the body,
+only to be again brought back by the veins to the right side, through
+the cavities of the ventricles. We shall learn in Chapter VIII. that
+the main object of pumping the blood into the lungs is to have it
+purified from certain waste matters which it has taken up in its course
+through the body, before it is again sent on its journey from the left
+ventricle.
+
+187. The Arteries. The blood-vessels are flexible tubes through which
+the blood is borne through the body. There are three kinds,—the
+arteries, the veins, and the capillaries, and these differ from one
+another in various ways.
+
+The arteries are the highly elastic and extensible tubes which carry
+the pure, fresh blood outwards from the heart to all parts of the body.
+They may all be regarded as branches of the aorta. After the aorta
+leaves the left ventricle it rises towards the neck, but soon turns
+downwards, making a curve known as the arch of the aorta.
+
+From the arch are given off the arteries which supply the head and arms
+with blood. These are the two carotid arteries, which run up on each
+side of the neck to the head, and the two subclavian arteries, which
+pass beneath the collar bone to the arms. This great arterial trunk now
+passes down in front of the spine to the pelvis, where it divides into
+two main branches, which supply the pelvis and the lower limbs.
+
+The descending aorta, while passing downwards, gives off arteries to
+the different tissues and organs. Of these branches the chief are the
+cœliac artery, which subdivides into three great branches,—one each to
+supply the stomach, the liver, and the spleen; then the renal arteries,
+one to each kidney; and next two others, the mesenteric arteries, to
+the intestines. The aorta at last divides into two main branches, the
+common iliac arteries, which, by their subdivisions, furnish the
+arterial vessels for the pelvis and the lower limbs.
+
+Illustration: Fig. 72.—Left Cavities of the Heart.
+
+
+A,  B, right pulmonary veins;
+  with S, openings of the veins;
+  E, D, C, aortic valves;
+  R, aorta;
+  P, pulmonary artery;
+  O, pulmonic valves;
+  H, mitral valve;
+  K, columnæ carnoeæ;
+  M, right ventricular cavity;
+  N, interventricular septum.
+
+The flow of blood in the arteries is caused by the muscular force of
+the heart, aided by the elastic tissues and muscular fibers of the
+arterial walls, and to a certain extent by the muscles themselves. Most
+of the great arterial trunks lie deep in the fleshy parts of the body;
+but their branches are so numerous and become so minute that, with a
+few exceptions, they penetrate all the tissues of the body,—so much so,
+that the point of the finest needle cannot be thrust into the flesh
+anywhere without wounding one or more little arteries and thus drawing
+blood.
+
+188. The Veins. The veins are the blood-vessels which carry the impure
+blood from the various tissues of the body to the heart. They begin in
+the minute capillaries at the extremities of the four limbs, and
+everywhere throughout the body, and passing onwards toward the heart,
+receive constantly fresh accessions on the way from myriad other veins
+bringing blood from other wayside capillaries, till the central veins
+gradually unite into larger and larger vessels until at length they
+form the two great vessels which open into the right auricle of the
+heart.
+
+These two great venous trunks are the inferior vena cava, bringing the
+blood from the trunk and the lower limbs, and the superior vena cava,
+bringing the blood from the head and the upper limbs. These two large
+trunks meet as they enter the right auricle. The four pulmonary veins,
+as we have learned, carry the arterial blood from the lungs to the left
+auricle.
+
+Illustration: Fig. 73.
+
+
+A,  part of a vein laid open, with two pairs of valves;
+  B, longitudinal section of a vein, showing the valves closed.
+
+A large vein generally accompanies its corresponding artery, but most
+veins lie near the surface of the body, just beneath the skin. They may
+be easily seen under the skin of the hand and forearm, especially in
+aged persons. If the arm of a young person is allowed to hang down a
+few moments, and then tightly bandaged above the elbow to retard the
+return of the blood, the veins become large and prominent.
+
+The walls of the larger veins, unlike arteries, contain but little of
+either elastic or muscular tissue; hence they are thin, and when empty
+collapse. The inner surfaces of many of the veins are supplied with
+pouch-like folds, or pockets, which act as valves to impede the
+backward flow of the blood, while they do not obstruct blood flowing
+forward toward the heart. These valves can be shown by letting the
+forearm hang down, and sliding the finger upwards over the veins (Fig.
+73).
+
+The veins have no force-pump, like the arteries, to propel their
+contents towards their destination. The onward flow of the blood in
+them is due to various causes, the chief being the pressure behind of
+the blood pumped into the capillaries. Then as the pocket-like valves
+prevent the backward flow of the blood, the pressure of the various
+muscles of the body urges along the blood, and thus promotes the onward
+flow.
+
+The forces which drive the blood through the arteries are sufficient to
+carry the blood on through the capillaries. It is calculated that the
+onward flow in the capillaries is about 1/50 to 1/33 of an inch in a
+second, while in the arteries the blood current flows about 16 inches
+in a second, and in the great veins about 4 inches every second.
+
+Illustration: Fig. 74.—The Structure of Capillaries.
+Capillaries of various sizes, showing cells with nuclei
+
+
+189. The Capillaries. The capillaries are the minute, hair-like tubes,
+with very thin walls, which form the connection between the ending of
+the finest arteries and the beginning of the smallest veins. They are
+distributed through every tissue of the body, except the epidermis and
+its products, the epithelium, the cartilages, and the substance of the
+teeth. In fact, the capillaries form a network of the tiniest
+blood-vessels, so minute as to be quite invisible, at least one-fourth
+smaller than the finest line visible to the naked eye.
+
+The capillaries serve as a medium to transmit the blood from the
+arteries to the veins; and it is through them that the blood brings
+nourishment to the surrounding tissues. In brief, we may regard the
+whole body as consisting of countless groups of little islands
+surrounded by ever-flowing streams of blood. The walls of the
+capillaries are of the most delicate structure, consisting of a single
+layer of cells loosely connected. Thus there is allowed the most free
+interchange between the blood and the tissues, through the medium of
+the lymph.
+
+The number of the capillaries is inconceivable. Those in the lungs
+alone, placed in a continuous line, would reach thousands of miles. The
+thin walls of the capillaries are admirably adapted for the important
+interchanges that take place between the blood and the tissues.
+
+190. The Circulation of the Blood. It is now well to study the
+circulation as a whole, tracing the course of the blood from a certain
+point until it returns to the same point. We may conveniently begin
+with the portion of blood contained at any moment in the right auricle.
+The superior and inferior venæ cavæ are busily filling the auricle with
+dark, impure blood. When it is full, it contracts. The passage leading
+to the right ventricle lies open, and through it the blood pours till
+the ventricle is full. Instantly this begins, in its turn, to contract.
+The tricuspid valve at once closes, and blocks the way backward. The
+blood is now forced through the open semilunar valves into the
+pulmonary artery.
+
+The pulmonary artery, bringing venous blood, by its alternate expansion
+and recoil, draws the blood along until it reaches the pulmonary
+capillaries. These tiny tubes surround the air cells of the lungs, and
+here an exchange takes place. The impure, venous blood here gives up
+its _débris_ in the shape of carbon dioxid and water, and in return
+takes up a large amount of oxygen. Thus the blood brought to the lungs
+by the pulmonary arteries leaves the lungs entirely different in
+character and appearance. This part of the circulation is often called
+the lesser or pulmonic circulation.
+
+The four pulmonary veins bring back bright, scarlet blood, and pour it
+into the left auricle of the heart, whence it passes through the mitral
+valve into the left ventricle. As soon as the left ventricle is full,
+it contracts. The mitral valve instantly closes and blocks the passage
+backward into the auricle; the blood, having no other way open, is
+forced through the semilunar valves into the aorta. Now red in color
+from its fresh oxygen, and laden with nutritive materials, it is
+distributed by the arteries to the various tissues of the body. Here it
+gives up its oxygen, and certain nutritive materials to build up the
+tissues, and receives certain products of waste, and, changed to a
+purple color, passes from the capillaries into the veins.
+
+Illustration: Fig. 75.—Diagram illustrating the Circulation.
+
+  1, right auricle;
+  2, left auricle;
+  3, right ventricle;
+  4, left ventricle;
+  5, vena cava superior;
+  6, vena cava inferior;
+  7, pulmonary arteries;
+  8, lungs;
+  9, pulmonary veins;
+  10, aorta;
+  11, alimentary canal;
+  12, liver;
+  13, hepatic artery;
+  14, portal vein;
+  15, hepatic vein.
+
+All the veins of the body, except those from the lungs and the heart
+itself, unite into two large veins, as already described, which pour
+their contents into the right auricle of the heart, and thus the grand
+round of circulation is continually maintained. This is called the
+systemic circulation. The whole circuit of the blood is thus divided
+into two portions, very distinct from each other.
+
+191. The Portal Circulation. A certain part of the systemic or greater
+circulation is often called the portal circulation, which consists of
+the flow of the blood from the abdominal viscera through the portal
+vein and liver to the hepatic vein. The blood brought to the
+capillaries of the stomach, intestines, spleen, and pancreas is
+gathered into veins which unite into a single trunk called the portal
+vein. The blood, thus laden with certain products of digestion, is
+carried to the liver by the portal vein, mingling with that supplied to
+the capillaries of the same organ by the hepatic artery. From these
+capillaries the blood is carried by small veins which unite into a
+large trunk, the hepatic vein, which opens into the inferior vena cava.
+The portal circulation is thus not an independent system, but forms a
+kind of loop on the systemic circulation.
+
+The lymph-current is in a sense a slow and stagnant side stream of the
+blood circulation; for substances are constantly passing from the
+blood-vessels into the lymph spaces, and returning, although after a
+comparatively long interval, into the blood by the great lymphatic
+trunks.
+
+Experiment 90. _To illustrate the action of the heart, and how it pumps
+the blood in only one direction_. Take a Davidson or Household rubber
+syringe. Sink the suction end into water, and press the bulb. As you
+let the bulb expand, it fills with water; as you press it again, a
+valve prevents the water from flowing back, and it is driven out in a
+jet along the other pipe. The suction pipe represents the veins; the
+bulb, the heart; and the tube end, out of which the water flows, the
+arteries.
+
+Note. The heart is not nourished by the blood which passes through it.
+The muscular substance of the heart itself is supplied with nourishment
+by two little arteries called the _coronary arteries_, which start from
+the aorta just above two of the semilunar valves. The blood is returned
+to the right auricle (not to either of the venæ cavæ) by the _coronary
+vein_.
+    The longest route a portion of blood may take from the moment it
+    leaves the left ventricle to the moment it returns to it, is
+    through the portal circulation. The shortest possible route is
+    through the substance of the heart itself. The mean time which the
+    blood requires to make a complete circuit is about 23 seconds.
+
+
+192. The Rhythmic Action of the Heart. To maintain a steady flow of
+blood throughout the body the action of the heart must be regular and
+methodical. The heart does not contract as a whole. The two auricles
+contract at the same time, and this is followed at once by the
+contraction of the two ventricles. While the ventricles are
+contracting, the auricles begin to relax, and after the ventricles
+contract they also relax. Now comes a pause, or rest, after which the
+auricles and ventricles contract again in the same order as before, and
+their contractions are followed by the same pause as before. These
+contractions and relaxations of the various parts of the heart follow
+one another so regularly that the result is called the rhythmic action
+of the heart.
+
+The average number of beats of the heart, under normal conditions, is
+from 65 to 75 per minute. Now the time occupied from the instant the
+auricles begin to contract until after the contraction of the
+ventricles and the pause, is less than a second. Of this time one-fifth
+is occupied by the contraction of the auricles, two-fifths by the
+contraction of the ventricles, and the time during which the whole
+heart is at rest is two-fifths of the period.
+
+193. Impulse and Sounds of the Heart. The rhythmic action of the heart
+is attended with various occurrences worthy of note. If the hand be
+laid flat over the chest wall on the left, between the fifth and sixth
+ribs, the heart will be felt beating. This movement is known as the
+beat or impulse of the heart, and can be both seen and felt on the left
+side. The heart-beat is unusually strong during active bodily exertion,
+and under mental excitement.
+
+The impulse of the heart is due to the striking of the lower, tense
+part of the ventricles—the apex of the heart—against the chest wall at
+the moment of their vigorous contraction. It is important for the
+physician to know the exact place where the heart-beat should be felt,
+for the heart may be displaced by disease, and its impulse would
+indicate its new position.
+
+Sounds also accompany the heart’s action. If the ear be applied over
+the region of the heart, two distinct sounds will be heard following
+one another with perfect regularity. Their character may be tolerably
+imitated by pronouncing the syllables _lubb_, _dŭp_. One sound is heard
+immediately after the other, then there is a pause, then come the two
+sounds again. The first is a dull, muffled sound, known as the “first
+sound,” followed at once by a short and sharper sound, known as the
+“second sound” of the heart.
+
+The precise cause of the first sound is still doubtful, but it is made
+at the moment the ventricles contract. The second sound is, without
+doubt, caused by the sudden closure of the semilunar valves of the
+pulmonary artery and the aorta, at the moment when the contraction of
+the ventricles is completed.
+
+Illustration: Fig. 76.—Muscular Fibers of the Ventricles.
+
+
+A,  superficial fibers common to both ventricles;
+  B, fibers of the left ventricle;
+  C, deep fibers passing upwards toward the base of the heart;
+  D, fibers penetrating the left ventricle
+
+The sounds of the heart are modified or masked by blowing “murmurs”
+when the cardiac orifices or valves are roughened, dilated, or
+otherwise affected as the result of disease. Hence these new sounds may
+often afford indications of the greatest importance to physicians in
+the diagnosis of heart-disease.
+
+194. The Nervous Control of the Heart. The regular, rhythmic movement
+of the heart is maintained by the action of certain nerves. In various
+places in the substance of the heart are masses of nerve matter, called
+ganglia. From these ganglia there proceed, at regular intervals,
+discharges of nerve energy, some of which excite movement, while others
+seem to restrain it. The heart would quickly become exhausted if the
+exciting ganglia had it all their own way, while it would stand still
+if the restraining ganglia had full sway. The influence of one,
+however, modifies the other, and the result is a moderate and regular
+activity of the heart.
+
+The heart is also subject to other nerve influences, but from outside
+of itself. Two nerves are connected with the heart, the pneumogastric
+and the sympathetic (secs. 271 and 265). The former appears to be
+connected with the restraining ganglia; the latter with the exciting
+ganglia. Thus, if a person were the subject of some emotion which
+caused fainting, the explanation would be that the impression had been
+conveyed to the brain, and from the brain to the heart by the
+pneumogastric nerves. The result would be that the heart for an instant
+ceases to beat. Death would be the result if the nerve influence were
+so great as to restrain the movements of the heart for any appreciable
+time.
+
+Again, if the person were the subject of some emotion by which the
+heart were beating faster than usual, it would mean that there was sent
+from the brain to the heart by the sympathetic nerves the impression
+which stimulated it to increased activity.
+
+195. The Nervous Control of the Blood-vessels. The tone and caliber of
+the blood-vessels are controlled by certain vaso-motor nerves, which
+are distributed among the muscular fibers of the walls. These nerves
+are governed from a center in the medulla oblongata, a part of the
+brain (sec. 270). If the nerves are stimulated more than usual, the
+muscular walls contract, and the quantity of the blood flowing through
+them and the supply to the part are diminished. Again, if the stimulus
+is less than usual, the vessels dilate, and the supply to the part is
+increased.
+
+Now the vaso-motor center may be excited to increased activity by
+influences reaching it from various parts of the body, or even from the
+brain itself. As a result, the nerves are stimulated, and the vessels
+contract. Again, the normal influence of the vaso-motor center may be
+suspended for a time by what is known as the inhibitory or restraining
+effect. The result is that the tone of the blood-vessels becomes
+diminished, and their channels widen.
+
+The effect of this power of the nervous system is to give it a certain
+control over the circulation in particular parts. Thus, though the
+force of the heart and the general average blood-pressure remain the
+same, the state of the circulation may be very different in different
+parts of the body. The importance of this local control over the
+circulation is of the utmost significance. Thus an organ at work needs
+to be more richly supplied with blood than when at rest. For example,
+when the salivary glands need to secrete saliva, and the stomach to
+pour out gastric juice, the arteries that supply these organs are
+dilated, and so the parts are flushed with an extra supply of blood,
+and thus are aroused to greater activity.
+
+Again, the ordinary supply of blood to a part may be lessened, so that
+the organ is reduced to a state of inactivity, as occurs in the case of
+the brain during sleep. We have in the act of blushing a visible
+example of sudden enlargement of the smaller arteries of the face and
+neck, called forth by some mental emotion which acts on the vaso-motor
+center and diminishes its activity. The reverse condition occurs in the
+act of turning pale. Then the result of the mental emotion is to cause
+the vaso-motor nerves to exercise a more powerful control over the
+capillaries, thereby closing them, and thus shutting off the flow of
+blood.
+
+Experiment 91. Hold up the ear of a white rabbit against the light
+while the animal is kept quiet and not alarmed. The red central artery
+can be seen coursing along the translucent organ, giving off branches
+which by subdivision become too small to be separately visible, and the
+whole ear has a pink color and is warm from the abundant blood flowing
+through it. Attentive observation will show also that the caliber of
+the main artery is not constant; at somewhat irregular periods of a
+minute or more it dilates and contracts a little.
+
+Illustration: Fig. 77.—Some of the Principal Organs of the Chest and
+Abdomen. (Blood vessels on the left, muscles on the right.)
+
+In brief, all over the body, the nervous system, by its vaso-motor
+centers, is always supervising and regulating the distribution of blood
+in the body, sending now more and now less to this or that part.
+
+Illustration: Fig. 78.—Capillary Blood-Vessels in the Web of a Frog’s
+Foot, as seen with the Microscope.
+
+
+196. The Pulse. When the finger is placed on any part of the body where
+an artery is located near the surface, as, for example, on the radial
+artery near the wrist, there is felt an intermittent pressure,
+throbbing with every beat of the heart. This movement, frequently
+visible to the eye, is the result of the alternate expansion of the
+artery by the wave of blood, and the recoil of the arterial walls by
+their elasticity. In other words, it is the wave produced by throwing a
+mass of blood into the arteries already full. The blood-wave strikes
+upon the elastic walls of the arteries, causing an increased
+distention, followed at once by contraction. This regular dilatation
+and rigidity of the elastic artery answering to the beats of the heart,
+is known as the pulse.
+
+The pulse may be easily found at the wrist, the temple, and the inner
+side of the ankle. The throb of the two carotid arteries may be plainly
+felt by pressing the thumb and finger backwards on each side of the
+larynx. The progress of the pulse-wave must not be confused with the
+actual current of the blood itself. For instance, the pulse-wave
+travels at the rate of about 30 feet a second, and takes about 1/10 of
+a second to reach the wrist, while the blood itself is from 3 to 5
+seconds in reaching the same place.
+
+The pulse-wave may be compared to the wave produced by a stiff breeze
+on the surface of a slowly moving stream, or the jerking throb sent
+along a rope when shaken. The rate of the pulse is modified by age,
+fatigue, posture, exercise, stimulants, disease, and many other
+circumstances. At birth the rate is about 140 times a minute, in early
+infancy, 120 or upwards, in the healthy adult between 65 and 75, the
+most common number being 72. In the same individual, the pulse is
+quicker when standing than when lying down, is quickened by excitement,
+is faster in the morning, and is slowest at midnight. In old age the
+pulse is faster than in middle life; in children it is quicker than in
+adults.
+
+Illustration: Fig. 79.—Circulation in the Capillaries, as seen with the
+Microscope.
+
+As the pulse varies much in its rate and character in disease, it is to
+the skilled touch of the physician an invaluable help in the diagnosis
+of the physical condition of his patient.
+
+Experiment 92. _To find the pulse_. Grasp the wrist of a friend,
+pressing with three fingers over the radius. Press three fingers over
+the radius in your own wrist, to feel the pulse.
+    Count by a watch the rate of your pulse per minute, and do the same
+    with a friend’s pulse. Compare its characters with your own pulse.
+    Observe how the character and frequency of the pulse are altered by
+    posture, muscular exercise, a prolonged, sustained, deep
+    inspiration, prolonged expiration, and other conditions.
+
+197. Effect of Alcoholic Liquors upon the Organs of Circulation.
+Alcoholic drinks exercise a destructive influence upon the heart, the
+circulation, and the blood itself. These vicious liquids can reach the
+heart only indirectly, either from the stomach by the portal vein to
+the liver, and thence to the heart, or else by way of the lacteals, and
+so to the blood through the thoracic duct. But by either course the
+route is direct enough, and speedy enough to accomplish a vast amount
+of ruinous work.
+
+The influence of alcohol upon the heart and circulation is produced
+mainly through the nervous system. The inhibitory nerves, as we have
+seen, hold the heart in check, exercise a restraining control over it,
+very much as the reins control an active horse. In health this
+inhibitory influence is protective and sustaining. But now comes the
+narcotic invasion of alcoholic drinks, which paralyze the inhibitory
+nerves, with the others, and at once the uncontrolled heart, like the
+unchecked steed, plunges on to violent and often destructive results.
+
+Illustration: Fig. 80.—Two Principal Arteries of the Front of the Leg
+(Anterior Tibial and Dorsalis Pedis).
+
+This action, because it is quicker, has been considered also a stronger
+action, and the alcohol has therefore been supposed to produce a
+stimulating effect. But later researches lead to the conclusion that
+the effect of alcoholic liquors is not properly that of a stimulant,
+but of a narcotic paralyzant, and that while it indeed quickens, it
+also really weakens the heart’s action. This view would seem sustained
+by the fact that the more the intoxicants are pushed, the deeper are
+the narcotic and paralyzing effects. After having obstructed the
+nutritive and reparative functions of the vital fluid for many years,
+their effects at last may become fatal.
+
+This relaxing effect involves not only the heart, but also the
+capillary system, as is shown in the complexion of the face and the
+color of the hands. In moderate drinkers the face is only flushed, but
+in drunkards it is purplish. The flush attending the early stages of
+drinking is, of course, not the flush of health, but an indication of
+disease.[34]
+
+198. Effect upon the Heart. This forced overworking of the heart which
+drives it at a reckless rate, cuts short its periods of rest and
+inevitably produces serious heart-exhaustion. If repeated and
+continued, it involves grave changes of the structure of the heart. The
+heart muscle, endeavoring to compensate for the over-exertion, may
+become much thickened, making the ventricles smaller, and so fail to do
+its duty in properly pumping forward the blood which rushes in from the
+auricle. Or the heart wall may by exhaustion become thinner, making the
+ventricles much too large, and unable to send on the current. In still
+other cases, the heart degenerates with minute particles of fat
+deposited in its structures, and thus loses its power to propel the
+nutritive fluid. All three of these conditions involve organic disease
+of the valves, and all three often produce fatal results.
+
+199. Effect of Alcohol on the Blood-vessels. Alcoholic liquors injure
+not only the heart, but often destroy the blood-vessels, chiefly the
+larger arteries, as the arch of the aorta or the basilar artery of the
+brain. In the walls of these vessels may be gradually deposited a
+morbid product, the result of disordered nutrition, sometimes chalky,
+sometimes bony, with usually a dangerous dilatation of the tube.
+
+In other cases the vessels are weakened by an unnatural fatty deposit.
+Though these disordered conditions differ somewhat, the morbid results
+in all are the same. The weakened and stiffened arterial walls lose the
+elastic spring of the pulsing current. The blood fails to sweep on with
+its accustomed vigor. At last, owing perhaps to the pressure, against
+the obstruction of a clot of blood, or perhaps to some unusual strain
+of work or passion, the enfeebled vessel bursts, and death speedily
+ensues from a form of apoplexy.
+
+Illustration: Fig. 81.—Showing the Carotid Artery and Jugular Vein on
+the Right Side, with Some of their Main Branches. (Some branches of the
+cervical plexus, and the hypoglossal nerve are also shown.)
+
+
+Note. “An alcoholic heart loses its contractile and resisting power,
+both through morbid changes in its nerve ganglia and in its muscle
+fibers. In typhoid fever, muscle changes are evidently the cause of the
+heart-enfeeblement; while in diphtheria, disturbances in innervation
+cause the heart insufficiency. ‘If the habitual use of alcohol causes
+the loss of contractile and resisting power by impairment of both the
+nerve ganglia and muscle fibers of the heart, how can it act as a heart
+tonic?’”—Dr. Alfred L. Loomis, Professor of Medicine in the Medical
+Department of the University of the City of New York.
+
+
+200. Other Results from the Use of Intoxicants. Other disastrous
+consequences follow the use of intoxicants, and these upon the blood.
+When any alcohol is present in the circulation, its greed for water
+induces the absorption of moisture from the red globules of the blood,
+the oxygen-carriers. In consequence they contract and harden, thus
+becoming unable to absorb, as theretofore, the oxygen in the lungs.
+Then, in turn, the oxidation of the waste matter in the tissues is
+prevented; thus the corpuscles cannot convey carbon dioxid from the
+capillaries, and this fact means that some portion of refuse material,
+not being thus changed and eliminated, must remain in the blood,
+rendering it impure and unfit for its proper use in nutrition. Thus,
+step by step, the use of alcoholics impairs the functions of the blood
+corpuscles, perverts nutrition, and slowly poisons the blood.
+
+Illustration: Fig. 82.—The Right Axillary and Brachial Arteries, with
+Some of their Main Branches.
+
+
+Note. “Destroy or paralyze the inhibitory nerve center, and instantly
+its controlling effect on the heart mechanism is lost, and the
+accelerating agent, being no longer under its normal restraint, runs
+riot. The heart’s action is increased, the pulse is quickened, an
+excess of blood is forced into the vessels, and from their becoming
+engorged and dilated the face gets flushed, all the usual concomitants
+of a general engorgement of the circulation being the result.”—Dr.
+George Harley, F.R.S., an eminent English medical author.
+    “The habitual use of alcohol produces a deleterious influence upon
+    the whole economy. The digestive powers are weakened, the appetite
+    is impaired, and the muscular system is enfeebled. The blood is
+    impoverished, and nutrition is imperfect and disordered, as shown
+    by the flabbiness of the skin and muscles, emaciation, or an
+    abnormal accumulation of fat.”—Dr. Austin Flint, Senior, formerly
+    Professor of the Practice of Medicine in Bellevue Medical College,
+    and author of many standard medical works.
+    “The immoderate use of the strong kind of tobacco, which soldiers
+    affect, is often very injurious to them, especially to very young
+    soldiers. It renders them nervous and shaky, gives rise to
+    palpitation, and is a factor in the production of the irritable or
+    so-called “trotting-heart” and tends to impair the appetite and
+    digestion.”—London _Lancet_.
+    “I never smoke because I have seen the most efficient proofs of the
+    injurious effects of tobacco on the nervous system.”—Dr.
+    Brown-Sequard, the eminent French physiologist.
+    “Tobacco, and especially cigarettes, being a depressant upon the
+    heart, should be positively forbidden.”—Dr. J. M. Keating, on
+    “Physical Development,” in _Cyclopœdia of the Diseases of
+    Children_.
+
+
+201. Effect of Tobacco upon the Heart. While tobacco poisons more or
+less almost every organ of the body, it is upon the heart that it works
+its most serious wrong. Upon this most important organ its destructive
+effect is to depress and paralyze. Especially does this apply to the
+young, whose bodies are not yet knit into the vigor that can brave
+invasion.
+
+The _nicotine_ of tobacco acts through the nerves that control the
+heart’s action. Under its baneful influence the motions of the heart
+are irregular, now feeble and fluttering, now thumping with apparently
+much force: but both these forms of disturbed action indicate an
+abnormal condition. Frequently there is severe pain in the heart, often
+dizziness with gasping breath, extreme pallor, and fainting.
+
+The condition of the pulse is a guide to this state of the heart. In
+this the physician reads plainly the existence of the “tobacco heart,”
+an affection as clearly known among medical men as croup or measles.
+There are few conditions more distressing than the constant and
+impending suffering attending a tumultuous and fluttering heart. It is
+stated that one in every four of tobacco-users is subject, in some
+degree, to this disturbance. Test examinations of a large number of
+lads who had used cigarettes showed that only a very small percentage
+escaped cardiac trouble. Of older tobacco-users there are very few but
+have some warning of the hazard they invoke. Generally they suffer more
+or less from the tobacco heart, and if the nervous system or the heart
+be naturally feeble, they suffer all the more speedily and intensely.
+
+Additional Experiments.
+
+Experiment 93. Touch a few drops of blood fresh from the finger, with a
+strip of dry, smooth, neutral litmus paper, highly glazed to prevent
+the red corpuscles from penetrating into the test paper. Allow the
+blood to remain a short time; then wash it off with a stream of
+distilled water, when a blue spot upon a red or violet ground will be
+seen, indicating its _alkaline_ reaction, due chiefly to the sodium
+phosphate and sodium carbonate.
+
+Experiment 94. Place on a glass slide a thin layer of defibrinated
+blood; try to read printed matter through it. This cannot be done.
+
+Experiment 95. _To make blood transparent or laky_. Place in each of
+three test tubes two or three teaspoonfuls of defibrinated blood,
+obtained from Experiment 89, labeled _A, B_, and _C. A_ is for
+comparison. To _B_ add five volumes of water, and warm slightly, noting
+the change of color by reflected and transmitted light. By reflected
+light it is much darker,—it looks almost black; but by transmitted
+light it is transparent. Test this by looking at printed matter as in
+Experiment 94.
+
+Experiment 96. To fifteen or twenty drops of defibrinated blood in a
+test tube (labeled _D_) add five volumes of a 10-per-cent solution of
+common salt. It changes to a very bright, florid, brick-red color.
+Compare its color with _A, B_, and _C_. It is opaque.
+
+Experiment 97. Wash away the coloring matter from the twigs (see
+Experiment 89) with a stream of water until the fibrin becomes quite
+white. It is white, fibrous, and elastic. Stretch some of the fibers to
+show their extensibility; on freeing them, they regain their
+elasticity.
+
+Experiment 98. Take some of the serum saved from Experiment 88 and note
+that it does not coagulate spontaneously. Boil a little in a test tube
+over a spirit lamp, and the albumen will coagulate.
+
+Experiment 99. _To illustrate in a general way that blood is really a
+mass of red bodies which give the red color to the fluid in which they
+float._ Fill a clean white glass bottle two-thirds full of little red
+beads, and then fill the bottle full of water. At a short distance the
+bottle appears to be rilled with a uniformly red liquid.
+
+Experiment 100. _To show how blood holds a mineral substance in
+solution_. Put an egg-shell crushed fine, into a glass of water made
+acid by a teaspoonful of muriatic acid. After an hour or so the
+egg-shell will disappear, having been dissolved in the acid water. In
+like manner the blood holds various minerals in solution.
+
+Experiment 101. _To hear the sounds of the heart_. Locate the heart
+exactly. Note its beat. Borrow a stethoscope from some physician.
+Listen to the heart-beat of some friend. Note the sounds of your own
+heart in the same way.
+
+Experiment 102. _To show how the pulse may be studied_.“The movements
+of the artery in the human body as the pulse-wave passes through it may
+be shown to consist in a sudden dilatation, followed by a slow
+contraction, interrupted by one or more secondary dilatations. This
+demonstration may be made by pressing a small piece of looking-glass
+about one centimeter square (⅔ of an inch) upon the wrist over the
+radial artery, in such a way that with each pulse beat the mirror may
+be slightly tilted. If the wrist be now held in such a position that
+sunlight will fall upon the mirror, a spot of light will be reflected
+on the opposite side of the room, and its motion upon the wall will
+show that the expansion of the artery is a sudden movement, while the
+subsequent contraction is slow and interrupted.”—Bowditch’s _Hints for
+Teachers of Physiology_.
+
+Illustration: Fig. 83.—How the Pulse may be studied by Pressing a
+Mirror over the Radial Artery.
+
+
+Experiment 103. _To illustrate the effect of muscular exercise in
+quickening the pulse_. Run up and down stairs several times. Count the
+pulse both before and after. Note the effect upon the rate.
+
+Experiment 104. _To show the action of the elastic walls of the
+arteries._ Take a long glass or metal tube of small caliber. Fasten one
+end to the faucet of a water-pipe (one in a set bowl preferred) by a
+very short piece of rubber tube. Turn the water on and off alternately
+and rapidly, to imitate the intermittent discharge of the ventricles.
+The water will flow from the other end of the rubber pipe in jets, each
+jet ceasing the moment the water is shut off.
+    The experiment will be more successful if the rubber bulb attached
+    to an ordinary medicine-dropper be removed, and the tapering glass
+    tube be slipped on to the outer end of the rubber tube attached to
+    the faucet.
+
+Experiment 105. Substitute a piece of rubber tube for the glass tube,
+and repeat the preceding experiment. Now it will be found that a
+continuous stream flows from the tube. The pressure of water stretches
+the elastic tube, and when the stream is turned off, the rubber recoils
+on the water, and the intermittent flow is changed into a continuous
+stream.
+
+Experiment 106. _To illustrate some of the phenomena of circulation._
+Take a common rubber bulb syringe, of the Davidson, Household, or any
+other standard make. Attach a piece of rubber tube about six or eight
+feet long to the delivery end of the syringe.
+    To represent the resistance made by the capillaries to the flow of
+    blood, slip the large end of a common glass medicine-dropper into
+    the outer end of the rubber tube. This dropper has one end tapered
+    to a fine point.
+    Place the syringe flat, without kinks or bends, on a desk or table.
+    Press the bulb slowly and regularly. The water is thus pumped into
+    the tube in an intermittent manner, and yet it is forced out of the
+    tapering end of the glass tube in a steady flow.
+
+Experiment 107. Take off the tapering glass tube, or, in the place of
+one long piece of rubber tube, substitute several pieces of glass
+tubing connected together by short pieces of rubber tubes. The obstacle
+to the flow has thus been greatly lessened, and the water flows out in
+intermittent jets to correspond to the compression of the bulb.
+
+
+
+
+Chapter VIII.
+Respiration.
+
+
+202. Nature and Object of Respiration. The blood, as we have learned,
+not only provides material for the growth and activity of all the
+tissues of the body, but also serves as a means of removing from them
+the products of their activity. These are waste products, which if
+allowed to remain, would impair the health of the tissues. Thus the
+blood becomes impoverished both by the addition of waste material, and
+from the loss of its nutritive matter.
+
+We have shown, in the preceding chapter, how the blood carries to the
+tissues the nourishment it has absorbed from the food. We have now to
+consider a new source of nourishment to the blood, _viz._, that which
+it receives from the oxygen of the air. We are also to learn one of the
+methods by which the blood gets rid of poisonous waste matters. In
+brief, we are to study the set of processes known as respiration, by
+which oxygen is supplied to the various tissues, and by which the
+principal waste matters, or chief products of oxidation, are removed.
+
+Now, the tissues are continually feeding on the life-giving oxygen, and
+at the same time are continually producing carbon dioxid and other
+waste products. In fact, the life of the tissues is dependent upon a
+continual succession of oxidations and deoxidations. When the blood
+leaves the tissues, it is poorer in oxygen, is burdened with carbon
+dioxid, and has had its color changed from bright scarlet to purple
+red. This is the change from the arterial to venous conditions which
+has been described in the preceding chapter.
+
+Now, as we have seen, the change from venous to arterial blood occurs
+in the capillaries of the lungs, the only means of communication
+between the pulmonary arteries and the pulmonary veins. The blood in
+the pulmonary capillaries is separated from the air only by a delicate
+tissue formed of its own wall and the pulmonary membrane. Hence a
+gaseous interchange, the essential step in respiration, very readily
+takes place between the blood and the air, by which the latter gains
+moisture and carbon dioxid, and loses its oxygen. These changes in the
+lungs also restore to the dark blood its rosy tint.
+
+The only condition absolutely necessary to the purification of the
+blood is an organ having a delicate membrane, on one side of which is a
+thin sheet of blood, while the other side is in such contact with the
+air that an interchange of gases can readily take place. The demand for
+oxygen is, however, so incessant, and the accumulation of carbon dioxid
+is so rapid in every tissue of the human body, that an All-Wise Creator
+has provided a most perfect but complicated set of machinery to effect
+this wonderful purification of the blood.
+
+We are now ready to begin the study of the arrangement and working of
+the respiratory apparatus. With its consideration, we complete our view
+of the sources of supply to the blood, and begin our study of its
+purification.
+
+Illustration: Fig. 84.—The Epiglottis.
+
+
+203. The Trachea, or Windpipe. If we look into the mouth of a friend,
+or into our own with a mirror, we see at the back part an arch which is
+the boundary line of the mouth proper. There is just behind this a
+similar limit for the back part of the nostrils. The funnel-shaped
+cavity beyond, into which both the mouth and the posterior nasal
+passages open, is called the pharynx. In its lower part are two
+openings; the trachea, or windpipe, in front, and the œsophagus behind.
+
+The trachea is surmounted by a box-like structure of cartilage, about
+four and one-half inches long, called the larynx. The upper end of the
+larynx opens into the pharynx or throat, and is provided with a lid,—
+the epiglottis,—which closes under certain circumstances (secs. 137 and
+349). The larynx contains the organ of voice, and is more fully
+described in Chapter XII.
+
+The continuation of the larynx is the trachea, a tube about
+three-fourths of an inch in diameter, and about four inches long. It
+extends downwards along the middle line of the neck, where it may
+readily be felt in front, below the Adam’s apple.
+
+Illustration: Fig. 85.—Larynx, Trachea, and the Bronchi. (Front view.)
+
+
+A,  epiglottis;
+  B, thyroid cartilage;
+  C, cricoid-thyroid membrane, connecting with the cricoid cartilage
+  below, all forming the larynx;
+  D, one of the rings of the trachea.
+
+The walls of the windpipe are strengthened by a series of cartilaginous
+rings, each somewhat the shape of a horseshoe or like the letter C,
+being incomplete behind, where they come in contact with the œsophagus.
+Thus the trachea, while always open for the passage of air, admits of
+the distention of the food-passage.
+
+204. The Bronchial Tubes. The lower end of the windpipe is just behind
+the upper part of the sternum, and there it divides into two branches,
+called bronchi. Each branch enters the lung of its own side, and breaks
+up into a great number of smaller branches, called bronchial tubes.
+These divide into smaller tubes, which continue subdividing till the
+whole lung is penetrated by the branches, the extremities of which are
+extremely minute. To all these branches the general name of bronchial
+tubes is given. The smallest are only about one-fiftieth of an inch in
+diameter.
+
+Illustration: Fig. 86.—Relative Position of the Lungs, Heart, and its
+Great Vessels.
+
+
+A,  left ventricle;
+  B, right ventricle;
+  C, left auricle;
+  D, right auricle;
+  E, superior vena cava;
+  F, pulmonary artery;
+  G, aorta;
+  H, arch of the aorta;
+  K, innominate artery;
+  L, right common carotid artery;
+  M, right subclavian artery;
+  N, thyroid cartilage forming upper portion of the larynx;
+  O, trachea.
+
+Now the walls of the windpipe, and of the larger bronchial tubes would
+readily collapse, and close the passage for air, but for a wise
+precaution. The horseshoe-shaped rings of cartilage in the trachea and
+the plates of cartilage in the bronchial tubes keep these passages
+open. Again, these air passages have elastic fibers running the length
+of the tubes, which allow them to stretch and bend readily with the
+movements of the neck.
+
+205. The Cilia of the Air Passages. The inner surfaces of the windpipe
+and bronchial tubes are lined with mucous membrane, continuous with
+that of the throat, the mouth, and the nostrils, the secretion from
+which serves to keep the parts moist.
+
+Delicate, hair-like filaments, not unlike the pile on velvet, called
+cilia, spring from the epithelial lining of the air tubes. Their
+constant wavy movement is always upwards and outwards, towards the
+mouth. Thus any excessive secretion, as of bronchitis or catarrh, is
+carried upwards, and finally expelled by coughing. In this way, the
+lungs are kept quite free from particles of foreign matter derived from
+the air. Otherwise we should suffer, and often be in danger from the
+accumulation of mucus and dust in the air passages. Thus these tiny
+cilia act as dusters which Nature uses to keep the air tubes free and
+clean (Fig. 5).
+
+Illustration: Fig. 87.—Bronchial tube, with its Divisions and
+Subdivisions. (Showing groups of air cells at the termination of minute
+bronchial tubes.)
+
+
+206. The Lungs. The lungs, the organs of respiration, are two pinkish
+gray structures of a light, spongy appearance, that fill the chest
+cavity, except the space taken up by the heart and large vessels.
+Between the lungs are situated the large bronchi, the œsophagus, the
+heart in its pericardium, and the great blood-vessels. The base of the
+lungs rests on the dome-like diaphragm, which separates the chest from
+the abdomen. This partly muscular and partly tendinous partition is a
+most important factor in breathing.
+
+Each lung is covered, except at one point, with an elastic serous
+membrane in a double layer, called the pleura. One layer closely
+envelops the lung, at the apex of which it is reflected to the wall of
+the chest cavity of its own side, which it lines. The two layers thus
+form between them a Closed Sac a serous cavity (see Fig. 69, also note,
+p. 176).
+
+Illustration: Fig. 88.—The Lungs with the Trachea, Bronchi, and Larger
+Bronchial Tubes exposed. (Posterior view.)
+
+
+A,  division of left bronchus to upper lobe;
+  B, left branch of the Pulmonary artery;
+  C, left bronchus;
+  D, left superior pulmonary vein;
+  E, left inferior pulmonary vein;
+  F, left auricle;
+  K, inferior vena cava;
+  L, division of right bronchus to lower lobe;
+  M, right inferior pulmonary vein;
+  N, right superior pulmonary vein;
+  O, right branch of the pulmonary artery;
+  P, division of right bronchus to upper lobe;
+  R, left ventricle;
+  S, right ventricle.
+
+In health the two pleural surfaces of the lungs are always in contact,
+and they secrete just enough serous fluid to allow the surfaces to
+glide smoothly upon each other. Inflammation of this membrane is called
+_pleurisy_. In this disease the breathing becomes very painful, as the
+secretion of glairy serum is suspended, and the dry and inflamed
+surfaces rub harshly upon each other.
+
+The root of the lung, as it is called, is formed by the bronchi, two
+pulmonary arteries, and two pulmonary veins. The nerves and lymphatic
+vessels of the lung also enter at the root. If we only remember that
+all the bronchial tubes, great and small, are hollow, we may compare
+the whole system to a short bush or tree growing upside down in the
+chest, of which the trachea is the trunk, and the bronchial tubes the
+branches of various sizes.
+
+207. Minute Structure of the Lungs. If one of the smallest bronchial
+tubes be traced in its tree-like ramifications, it will be found to end
+in an irregular funnel-shaped passage wider than itself. Around this
+passage are grouped a number of honeycomb-like sacs, the air cells[35]
+or alveoli of the lungs. These communicate freely with the passage, and
+through it with the bronchial branches, but have no other openings. The
+whole arrangement of passages and air cells springing from the end of a
+bronchial tube, is called an ultimate lobule. Now each lobule is a very
+small miniature of a whole lung, for by the grouping together of these
+lobules another set of larger lobules is formed.
+
+Illustration: Fig. 89.
+
+
+A,  diagrammatic representation of the ending of a bronchial tube in
+air sacs or alveoli;
+  B, termination of two bronchial tubes in enlargement beset with air
+  sacs (_Huxley_);
+  C, diagrammatic view of an air sac.
+
+  a lies within sac and points to epithelium lining wall;
+  b, partition between two adjacent sacs, in which run capillaries;
+  c, elastic connective tissue (_Huxley_).
+
+In like manner countless numbers of these lobules, bound together by
+connective tissue, are grouped after the same fashion to form by their
+aggregation the lobes of the lung. The right lung has three such lobes;
+and the left, two. Each lobule has a branch of the pulmonary artery
+entering it, and a similar rootlet of the pulmonary vein leaving it. It
+also receives lymphatic vessels, and minute twigs of the pulmonary
+plexus of nerves.
+
+Illustration: Fig. 90.—Diagram to illustrate the Amounts of Air
+contained by the Lungs in Various Phases of Ordinary and of Forced
+Respiration.
+
+The walls of the air cells are of extreme thinness, consisting of
+delicate elastic and connective tissue, and lined inside by a single
+layer of thin epithelial cells. In the connective tissue run capillary
+vessels belonging to the pulmonary artery and veins. Now these delicate
+vessels running in the connective tissue are surrounded on all sides by
+air cells. It is evident, then, that the blood flowing through these
+capillaries is separated from the air within the cells only by the thin
+walls of the vessels, and the delicate tissues of the air cells.
+
+This arrangement is perfectly adapted for an interchange between the
+blood in the capillaries and the air in the air cells. This will be
+more fully explained in sec. 214.
+
+208. Capacity of the Lungs. In breathing we alternately take into and
+expel from the lungs a certain quantity of air. With each quiet
+inspiration about 30 cubic inches of air enter the lungs, and 30 cubic
+inches pass out with each expiration. The air thus passing into and out
+of the lungs is called tidal air. After an ordinary inspiration, the
+lungs contain about 230 cubic inches of air. By taking a deep
+inspiration, about 100 cubic inches more can be taken in. This extra
+amount is called complemental air.
+
+After an ordinary expiration, about 200 cubic inches are left in the
+lungs, but by forced expiration about one-half of this may be driven
+out. This is known as supplemental air. The lungs can never be entirely
+emptied of air, about 75 to 100 cubic inches always remaining. This is
+known as the residual air.
+
+The air that the lungs of an adult man are capable of containing is
+thus composed:
+
+Complemental air     100     cubic inches.
+Tidal     30         ”     ”
+Supplemental     100         ”     ”
+Residual     100         ”     ”
+Total capacity of lungs     330         ”     ”
+
+If, then, a person proceeds, after taking the deepest possible breath, to breath out as much as he can, he expels:
+Complemental air     100     cubic inches.
+Tidal     30         ”     ”
+Supplemental     100         ”     ”
+230     
+
+209. The Movements of Breathing. The act of breathing consists of a
+series of rhythmical movements, succeeding one another in regular
+order. In the first movement, inspiration, the chest rises, and there
+is an inrush of fresh air; this is at once followed by expiration, the
+falling of the chest walls, and the output of air. A pause now occurs,
+and the same breathing movements are repeated.
+
+The entrance and the exit of air into the respiratory passages are
+accompanied with peculiar sounds which are readily heard on placing the
+ear at the chest wall. These sounds are greatly modified in various
+pulmonary diseases, and hence are of great value to the physician in
+making a correct diagnosis.
+
+In a healthy adult, the number of respirations should be from 16 to 18
+per minute, but they vary with age, that of a newly born child being 44
+for the same time. Exercise increases the number, while rest diminishes
+it. In standing, the rate is more than when lying at rest. Mental
+emotion and excitement quicken the rate. The number is smallest during
+sleep. Disease has a notable effect upon the frequency of respirations.
+In diseases involving the lungs, bronchial tubes, and the pleura, the
+rate may be alarmingly increased, and the pulse is quickened in
+proportion.
+
+210. The Mechanism of Breathing. The chest is a chamber with bony
+walls, the ribs connecting in front with the breastbone, and behind
+with the spine. The spaces between the ribs are occupied by the
+intercostal muscles, while large muscles clothe the entire chest. The
+diaphragm serves as a movable floor to the chest, which is an air-tight
+chamber with movable walls and floor. In this chamber are suspended the
+lungs, the air cells of which communicate with the outside through the
+bronchial passages, but have no connection with the chest cavity. The
+thin space between the lungs and the rib walls, called the pleural
+cavity, is in health a vacuum.
+
+Now, when the diaphragm contracts, it descends and thus increases the
+depth of the chest cavity. A quantity of air is now drawn into the
+lungs and causes them to expand, thus filling up the increased space.
+As soon as the diaphragm relaxes, returning to its arched position and
+reducing the size of the chest cavity, the air is driven from the
+lungs, which then diminish in size. After a short pause, the diaphragm
+again contracts, and the same round of operation is constantly
+repeated.
+
+The walls of the chest being movable, by the contractions of the
+intercostals and other muscles, the ribs are raised and the breastbone
+pushed forward. The chest cavity is thus enlarged from side to side and
+from behind forwards. Thus, by the simultaneous descent of the
+diaphragm and the elevation of the ribs, the cavity of the chest is
+increased in three directions,—downwards, side-ways, and from behind
+forwards.
+
+It is thus evident that inspiration is due to a series of muscular
+contractions. As soon as the contractions cease, the elastic lung
+tissue resumes its original position, just as an extended rubber band
+recovers itself. As a result, the original size of the chest cavity is
+restored, and the inhaled air is driven from the lungs. Expiration may
+then be regarded as the result of an elastic recoil, and not of active
+muscular contractions.
+
+Illustration: Fig. 91.—Diagrammatic Section of the Trunk. (Showing the
+expansion of the chest and the movement of the ribs by action of the
+lungs.) [The dotted lines indicate the position during inspiration.]
+
+
+211. Varieties of Breathing. This is the mechanism of quiet, normal
+respiration. When the respiration is difficult, additional forces are
+brought into play. Thus when the windpipe and bronchial tubes are
+obstructed, as in croup, asthma, or consumption, many additional
+muscles are made use of to help the lungs to expand. The position which
+asthmatics often assume, with arms raised to grasp something for
+support, is from the need of the sufferer to get a fixed point from
+which the muscles of the arm and chest may act forcibly in raising the
+ribs, and thus securing more comfortable breathing.
+
+The visible movements of breathing vary according to circumstances. In
+infants the action of the diaphragm is marked, and the movements of the
+abdomen are especially obvious. This is called abdominal breathing. In
+women the action of the ribs as they rise and fall, is emphasized more
+than in men, and this we call costal breathing. In young persons and in
+men, the respiration not usually being impeded by tight clothing, the
+breathing is normal, being deep and abdominal.
+
+Disease has a marked effect upon the mode of breathing. Thus, when
+children suffer from some serious chest disease, the increased
+movements of the abdominal walls seem distressing. So in fracture of
+the ribs, the surgeon envelops the overlying part of the chest with
+long strips of firm adhesive plaster to restrain the motions of chest
+respiration, that they may not disturb the jagged ends of the broken
+bones. Again, in painful diseases of the abdomen, the sufferer
+instinctively suspends the abdominal action and relies upon the chest
+breathing. These deviations from the natural movements of respiration
+are useful to the physician in ascertaining the seat of disease.
+
+212. The Nervous Control of Respiration. It is a matter of common
+experience that one’s breath may be held for a short time, but the need
+of fresh air speedily gets the mastery, and a long, deep breath is
+drawn. Hence the efforts of criminals to commit suicide by persistent
+restraint of their breathing, are always a failure. At the very worst,
+unconsciousness ensues, and then respiration is automatically resumed.
+Thus a wise Providence defeats the purpose of crime. The movements of
+breathing go on without our attention. In sleep the regularity of
+respiration is even greater than when awake. There is a particular part
+of the nervous system that presides over the breathing function. It is
+situated in that part of the brain called the medulla oblongata, and is
+fancifully called the “vital knot” (sec. 270). It is injury to this
+respiratory center which proves fatal in cases of broken neck.
+
+From this nerve center there is sent out to the nerves that supply the
+diaphragm and other muscles of breathing, a force which stimulates them
+to regular contraction. This breathing center is affected by the
+condition of the blood. It is stimulated by an excess of carbon dioxid
+in the blood, and is quieted by the presence of oxygen.
+
+Experiment 108. _To locate the lungs_. Mark out the boundaries of the
+lungs by “sounding” them; that is, by _percussion_, as it is called.
+This means to put the forefinger of the left hand across the chest or
+back, and to give it a quick, sharp rap with two or three fingers. Note
+where it sounds hollow, resonant. This experiment can be done by the
+student with only imperfect success, until practice brings some skill.
+
+Experiment 109. Borrow a stethoscope, and listen to the respiration
+over the chest on the right side. This is known as _auscultation_. Note
+the difference of the sounds in inspiration and in expiration. Do not
+confuse the heart sounds with those of respiration. The respiratory
+murmurs may be heard fairly well by applying the ear flat to the chest,
+with only one garment interposed.
+
+Experiment 110. Get a sheep’s lungs, with the windpipe attached. Ask
+for the heart and lungs all in one mass. Take pains to examine the
+specimen first, and accept only a good one. Parts are apt to be hastily
+snipped or mangled. Examine the windpipe. Note the horseshoe-shaped
+rings of cartilage in front, which serve to keep it open.
+
+Experiment 111. Examine one bronchus, carefully dissecting away the
+lung tissue with curved scissors. Follow along until small branches of
+the bronchial tubes are reached. Take time for the dissection, and save
+the specimen in dilute alcohol. Put pieces of the lung tissue in a
+basin of water, and note that they float.
+
+The labored breathing of suffocation and of lung diseases is due to the
+excessive stimulation of this center, caused by the excess of carbon
+dioxid in the blood. Various mental influences from the brain itself,
+as the emotions of alarm or joy or distress, modify the action of the
+respiratory center.
+
+Again, nerves of sensation on the surface of the body convey influences
+to this nerve center and lead to its stimulation, resulting in a
+vigorous breathing movement. Thus a dash of cold water on the face or
+neck of a fainting person instantly produces a deep, long-drawn breath.
+Certain drugs, as opium, act to reduce the activity of this nerve
+center. Hence, in opium poisoning, special attention should be paid to
+keeping up the respiration. The condition of the lungs themselves is
+made known to the breathing center, by messages sent along the branches
+of the great pneumogastric nerve (page 276), leading from the lungs to
+the medulla oblongata.
+
+213. Effects of Respiration upon the Blood. The blood contains three
+gases, partly dissolved in it and partly in chemical union with certain
+of its constituents. These are oxygen, carbon dioxid, and nitrogen. The
+latter need not be taken into account. The oxygen is the nourishing
+material which the tissues require to carry on their work. The carbon
+dioxid is a waste substance which the tissues produce by their
+activity, and which the blood carries away from them.
+
+As before shown, the blood as it flows through the tissues loses most
+of its oxygen, and carbon dioxid takes its place. Now if the blood is
+to maintain its efficiency in this respect, it must always be receiving
+new supplies of oxygen, and also have some mode of throwing off its
+excess of carbon dioxid. This, then, is the double function of the
+process of respiration. Again, the blood sent out from the left side of
+the heart is of a bright scarlet color. After its work is done, and the
+blood returns to the right side of the heart, it is of a dark purple
+color. This change in color takes place in the capillaries, and is due
+to the fact that there the blood gives up most of its oxygen to the
+tissues and receives from them a great deal of carbon dioxid.
+
+In brief, while passing through the capillaries of the lungs the blood
+has been changed from the venous to the arterial blood. That is to say,
+the blood in its progress through the lungs has rid itself of its
+excess of carbon dioxid and obtained a fresh supply of oxygen.[36]
+
+214. Effects of Respiration upon the Air in the Lungs. It is well known
+that if two different liquids be placed in a vessel in contact with
+each other and left undisturbed, they do not remain separate, but
+gradually mix, and in time will be perfectly combined. This is called
+diffusion of liquids. The same thing occurs with gases, though the
+process is not visible. This is known as the diffusion of gases. It is
+also true that two liquids will mingle when separated from each other
+by a membrane (sec. 129). In a similar manner two gases, especially if
+of different densities, may mingle even when separated from each other
+by a membrane.
+
+In a general way this explains the respiratory changes that occur in
+the blood in the lungs. Blood containing oxygen and carbon dioxid is
+flowing in countless tiny streams through the walls of the air cells of
+the lungs. The air cells themselves contain a mixture of the same two
+gases. A thin, moist membrane, well adapted to allow gaseous diffusion,
+separates the blood from the air. This membrane is the delicate wall of
+the capillaries and the epithelium of the air cells. By experiment it
+has been found that the pressure of oxygen in the blood is less than
+that in the air cells, and that the pressure of carbon dioxid gas in
+the blood is greater than that in the air cells. As a result, a
+diffusion of gases ensues. The blood gains oxygen and loses carbon
+dioxid, while the air cells lose oxygen and gain the latter gas.
+
+Illustration: Fig. 92.—Capillary Network of the Air Cells and Origin of
+the Pulmonary Veins.
+
+
+A,  small branch of pulmonary artery;
+  B, twigs of the pulmonary artery anastomosing to form peripheral
+  network of the primitive air cells;
+  C, capillary network around the walls of the air sacs;
+  D, branches of network converging for form the veinlets of the
+  pulmonary veins.
+
+The blood thus becomes purified and reinvigorated, and at the same time
+is changed in color from purple to scarlet, from venous to arterial. It
+is now evident that if this interchange is to continue, the air in the
+cells must be constantly renewed, its oxygen restored, and its excess
+of carbon dioxid removed. Otherwise the process just described would be
+reversed, making the blood still more unfit to nourish the tissues, and
+more poisonous to them than before.
+
+215. Change in the Air in Breathing. The air which we exhale during
+respiration differs in several important particulars from the air we
+inhale. Both contain chiefly the three gases, though in different
+quantities, as the following table shows.
+
+                                      Oxygen.      Nitrogen.     Carbon
+    Dioxid. Inspired air contains      20.81        79.15          .04
+    Expired air contains               16.03        79.58         4.38
+                               
+That is, expired air contains about five per cent less oxygen and five
+per cent more carbon dioxid than inspired air.
+
+The temperature of expired air is variable, but generally is higher
+than that of inspired air, it having been in contact with the warm air
+passages. It is also loaded with aqueous vapor, imparted to it like the
+heat, not in the depth of the lungs, but in the upper air passages.
+
+Expired air contains, besides carbon dioxid, various impurities, many
+of an unknown nature, and all in small amounts. When the expired air is
+condensed in a cold receiver, the aqueous product is found to contain
+organic matter, which, from the presence of _micro-organisms_,
+introduced in the inspired air, is apt to putrefy rapidly. Some of
+these organic substances are probably poisonous, either so in
+themselves, as produced in some manner in the breathing apparatus, or
+poisonous as being the products of decomposition. For it is known that
+various animal substances give rise, by decomposition, to distinct
+poisonous products known as _ptomaines_. It is possible that some of
+the constituents of the expired air are of an allied nature. See under
+“Bacteria” (Chapter XIV).
+
+At all events, these substances have an injurious action, for an
+atmosphere containing simply one per cent of pure carbon dioxid has
+very little hurtful effect on the animal economy, but an atmosphere in
+which the carbon dioxid has been raised one per cent by breathing is
+highly injurious.
+
+The quantity of oxygen removed from the air by the breathing of an
+adult person at rest amounts daily to about 18 cubic feet. About the
+same amount of carbon dioxid is expelled, and this could be represented
+by a piece of pure charcoal weighing 9 ounces. The quantity of carbon
+dioxid, however, varies with the age, and is increased also by external
+cold and by exercise, and is affected by the kind of food. The amount
+of water, exhaled as vapor, varies from 6 to 20 ounces daily. The
+average daily quantity is about one-half a pint.
+
+216. Modified Respiratory Movements. The respiratory column of air is
+often used in a mechanical way to expel bodies from the upper air
+passages. There are also, in order to secure special ends, a number of
+modified movements not distinctly respiratory. The following peculiar
+respiratory acts call for a few words of explanation.
+
+A sigh is a rapid and generally audible expiration, due to the elastic
+recoil of the lungs and chest walls. It is often caused by depressing
+emotions. Yawning is a deep inspiration with a stretching of the
+muscles of the face and mouth, and is usually excited by fatigue or
+drowsiness, but often occurs from a sort of contagion.
+
+Hiccough is a sudden jerking inspiration due to the spasmodic
+contraction of the diaphragm and of the glottis, causing the air to
+rush suddenly through the larynx, and produce this peculiar sound.
+Snoring is caused by vibration of the soft palate during sleep, and is
+habitual with some, although it occurs with many when the system is
+unusually exhausted and relaxed.
+
+Laughing consists of a series of short, rapid, spasmodic expirations
+which cause the peculiar sounds, with characteristic movements of the
+facial muscles. Crying, caused by emotional states, consists of sudden
+jerky expirations with long inspirations, with facial movements
+indicative of distress. In sobbing, which often follows long-continued
+crying, there is a rapid series of convulsive inspirations, with sudden
+involuntary contractions of the diaphragm. Laughter, and sometimes
+sobbing, like yawning, may be the result of involuntary imitation.
+
+Experiment 112. _Simple Apparatus to Illustrate the Movements of the
+Lungs in the Chest_.—T is a bottle from which the bottom has been
+removed; D, a flexible and elastic membrane tied on the bottle, and
+capable of being pulled out by the string S, so as to increase the
+capacity of the bottle. L is a thin elastic bag representing the lungs.
+It communicates with the external air by a glass tube fitted air-tight
+through a cork in the neck of the bottle. When D is drawn down, the
+pressure of the external air causes L to expand. When the string is let
+go, L contracts again, by virtue of its elasticity.
+
+Illustration: Fig. 93.
+
+Coughing is produced by irritation in the upper part of the windpipe
+and larynx. A deep breath is drawn, the opening of the windpipe is
+closed, and immediately is burst open with a violent effort which sends
+a blast of air through the upper air passages. The object is to
+dislodge and expel any mucus or foreign matter that is irritating the
+air passages.
+
+Sneezing is like coughing; the tongue is raised against the soft
+palate, so the air is forced through the nasal passages. It is caused
+by an irritation of the nostrils or eyes. In the beginning of a cold in
+the head, for instance, the cold air irritates the inflamed mucous
+membrane of the nose, and causes repeated attacks of sneezing.
+
+217. How the Atmosphere is Made Impure. The air around us is constantly
+being made impure in a great variety of ways. The combustion of fuel,
+the respiration of men and animals, the exhalations from their bodies,
+the noxious gases and effluvia of the various industries, together with
+the changes of fermentation and decomposition to which all organized
+matter is liable,—all tend to pollute the atmosphere.
+
+The necessity of external ventilation has been foreseen for us. The
+forces of nature,—the winds, sunlight, rain, and growing
+vegetation,—all of great power and universal distribution and
+application, restore the balance, and purify the air. As to the
+principal gases, the air of the city does not differ materially from
+that of rural sections. There is, however, a vastly greater quantity of
+dust and smoke in the air of towns. The breathing of this dust, to a
+greater or less extent laden with bacteria, fungi, and the germs of
+disease, is an ever-present and most potent menace to public and
+personal health. It is one of the main causes of the excess of
+mortality in towns and cities over that of country districts.
+
+This is best shown in the overcrowded streets and houses of great
+cities, which are deprived of the purifying influence of sun and air.
+The fatal effect of living in vitiated air is especially marked in the
+mortality among infants and children living in the squalid and
+overcrowded sections of our great cities. The salutary effect of
+sunshine is shown by the fact that mortality is usually greater on the
+shady side of the street.
+
+218. How the Air is Made Impure by Breathing. It is not the carbon
+dioxid alone that causes injurious results to health, it is more
+especially the organic matter thrown off in the expired air. The carbon
+dioxid which accompanies the organic matter is only the index. In
+testing the purity of air it is not difficult to ascertain the amount
+of carbon dioxid present, but it is no easy problem to measure the
+amount of organic matter. Hence it is the former that is looked for in
+factories, churches, schoolrooms, and when it is found to exceed .07
+per cent it is known that there is a hurtful amount of organic matter
+present.
+
+The air as expelled from the lungs contains, not only a certain amount
+of organic matter in the form of vapor, but minute solid particles of
+_débris_ and bacterial micro-organisms (Chap. XIV). The air thus
+already vitiated, after it leaves the mouth, putrefies very rapidly. It
+is at once absorbed by clothing, curtains, carpets, porous walls, and
+by many other objects. It is difficult to dislodge these enemies of
+health even by free ventilation. The close and disagreeable odor of a
+filthy or overcrowded room is due to these organic exhalations from the
+lungs, the skin, and the unclean clothing of the occupants.
+
+The necessity of having a proper supply of fresh air in enclosed
+places, and the need of removal of impure air are thus evident. If a
+man were shut up in a tightly sealed room containing 425 cubic feet of
+air, he would be found dead or nearly so at the end of twenty-four
+hours. Long before this time he would have suffered from nausea,
+headache, dizziness, and other proofs of blood-poisoning. These
+symptoms are often felt by those who are confined for an hour or more
+in a room where the atmosphere has been polluted by a crowd of people.
+The unpleasant effects rapidly disappear on breathing fresh air.
+
+219. The Effect on the Health of Breathing Foul Air. People are often
+compelled to remain indoors for many hours, day after day, in shops,
+factories, or offices, breathing air perhaps only slightly vitiated,
+but still recognized as “stuffy.” Such persons often suffer from ill
+health. The exact form of the disturbance of health depends much upon
+the hereditary proclivity and physical make-up of the individual. Loss
+of appetite, dull headache, fretfulness, persistent weariness,
+despondency, followed by a general weakness and an impoverished state
+of blood, often result.
+
+Persons in this lowered state of health are much more prone to surfer
+from colds, catarrhs, bronchitis, and pneumonia than if they were
+living in the open air, or breathing only pure air. Thus, in the
+Crimean War, the soldiers who lived in tents in the coldest weather
+were far more free from colds and lung troubles than those who lived in
+tight and ill-ventilated huts. In the early fall when typhoid fever is
+prevalent, the grounds of large hospitals are dotted with canvas tents,
+in which patients suffering from this fever do much better than in the
+wards.
+
+This tendency to inflammatory diseases of the air passages is
+aggravated by the overheated and overdried condition of the air in the
+room occupied. This may result from burning gas, from overheated
+furnaces and stoves, hot-water pipes, and other causes. Serious lung
+diseases, such as consumption, are more common among those who live in
+damp, overcrowded, or poorly ventilated homes.
+
+220. The Danger from Pulmonary Infection. The germ of pulmonary
+consumption, known as the bacillus tuberculosis, is contained in the
+breath and the sputa from the lungs of its victims. It is not difficult
+to understand how these bacilli may be conveyed through the air from
+the lungs of the sick to those of apparently healthy people. Such
+persons may, however, be predisposed, either constitutionally or by
+defective hygienic surroundings, to fall victims to this dreaded
+disease. Overcrowding, poor ventilation, and dampness all tend to
+increase the risk of pulmonary infection.
+
+It must not be supposed that the tubercle bacillus is necessarily
+transmitted directly through the air from the lungs of the sick to be
+implanted in the lungs of the healthy. The germs may remain for a time
+in the dust turn and _débris_ of damp, filthy, and overcrowded houses.
+In this congenial soil they retain their vitality for a long time, and
+possibly may take on more virulent infective properties than they
+possessed when expelled from the diseased lungs.[37]
+
+Illustration: Fig. 94. Example of a Micro-Organism—Bacillus
+Tuberculosis in Sputum. (Magnified about 500 diameters.)
+
+
+221. Ventilation. The question of a practicable and economical system
+of ventilation for our homes, schoolrooms, workshops, and public places
+presents many difficult and perplexing problems. It is perhaps due to
+the complex nature of the subject, that ventilation, as an ordinary
+condition of daily health, has been so much neglected. The matter is
+practically ignored in building ordinary houses. The continuous renewal
+of air receives little if any consideration, compared with the
+provision made to furnish our homes with heat, light, and water. When
+the windows are closed we usually depend for ventilation upon mere
+chance,—on the chimney, the fireplace, and the crevices of doors and
+windows. The proper ventilation of a house and its surroundings should
+form as prominent a consideration in the plans of builders and
+architects as do the grading of the land, the size of the rooms, and
+the cost of heating.
+
+The object of ventilation is twofold: First, to provide for the removal
+of the impure air; second, for a supply of pure air. This must include
+a plan to provide fresh air in such a manner that there shall be no
+draughts or exposure of the occupants of the rooms to undue
+temperature. Hence, what at first might seem an easy thing to do, is,
+in fact, one of the most difficult of sanitary problems.
+
+222. Conditions of Efficient Ventilation. To secure proper ventilation
+certain conditions must be observed. The pure air introduced should not
+be far below the temperature of the room, or if so, the entering
+current should be introduced towards the ceiling, that it may mix with
+the warm air.
+
+Draughts must be avoided. If the circuit from entrance to exit is
+short, draughts are likely to be produced, and impure air has less
+chance of mixing by diffusion with the pure air. The current of air
+introduced should be constant, otherwise the balance may occasionally
+be in favor of vitiated air. If a mode of ventilation prove successful,
+it should not be interfered with by other means of entrance. Thus, an
+open door may prevent the incoming air from passing through its proper
+channels. It is desirable that the inlet be so arranged that it can be
+diminished in size or closed altogether. For instance, when the outer
+air is very cold, or the wind blows directly into the inlet, the amount
+of cold air entering it may lower the temperature of the room to an
+undesirable degree.
+
+In brief, it is necessary to have a thorough mixing of pure and impure
+air, so that the combination at different parts of the room may be
+fairly uniform. To secure these results, the inlets and outlets should
+be arranged upon principles of ventilation generally accepted by
+authorities on public health. It seems hardly necessary to say that due
+attention must be paid to the source from which the introduced air is
+drawn. If it be taken from foul cellars, or from dirty streets, it may
+be as impure as that which it is designed to replace.
+
+Animal Heat.
+
+223. Animal or Vital Heat. If a thermometer, made for the purpose, be
+placed for five minutes in the armpit, or under the tongue, it will
+indicate a temperature of about 98½° F., whether the surrounding
+atmosphere be warm or cold. This is the natural heat of a healthy
+person, and in health it rarely varies more than a degree or two. But
+as the body is constantly losing heat by radiation and conduction, it
+is evident that if the standard temperature be maintained, a certain
+amount of heat must be generated within the body to make up for the
+loss externally. The heat thus produced is known as animal or vital
+heat.
+This generation of heat is common to all living organisms. When the
+mass of the body is large, its heat is readily perceptible to the touch
+and by its effect upon the thermometer. In mammals and birds the
+heat-production is more active than in fishes and reptiles, and their
+temperatures differ in degree even in different species of the same
+class, according to the special organization of the animal and the
+general activity of its functions. The temperature of the frog may be
+85° F. in June and 41° F. in January. The structure of its tissues is
+unaltered and their vitality unimpaired by such violent fluctuations.
+But in man it is necessary not only for health, but even for life, that
+the temperature should vary only within narrow limits around the mean
+of 98½° F.
+
+We are ignorant of the precise significance of this constancy of
+temperature in warm-blooded animals, which is as important and peculiar
+as their average height, Man, undoubtedly, must possess a superior
+delicacy of organization, hardly revealed by structure, which makes it
+necessary that he should be shielded from the shocks and jars of
+varying temperature, that less highly endowed organisms endure with
+impunity.
+
+224. Sources of Bodily Heat. The heat of the body is generated by the
+chemical changes, generally spoken of as those of oxidation, which are
+constantly going on in the tissues. Indeed, whenever protoplasmic
+materials are being oxidized (the process referred to in sec. 15 as
+katabolism) heat is being set free. These chemical changes are of
+various kinds, but the great source of heat is the katabolic process,
+known as oxidation.
+
+The vital part of the tissues, built up from the complex classes of
+food, is oxidized by means of the oxygen carried by the arterial blood,
+and broken down into simpler bodies which at last result in urea,
+carbon dioxid, and water. Wherever there is life, this process of
+oxidation is going on, but more energetically in some tissues and
+organs than in others. In other words, the minutest tissue in the body
+is a source of heat in proportion to the activity of its chemical
+changes. The more active the changes, the greater is the heat produced,
+and the greater the amount of urea, carbon dioxid, and water
+eliminated. The waste caused by this oxidation must be made good by a
+due supply of food to be built up into protoplasmic material. For the
+production of heat, therefore, food is necessary. But the oxidation
+process is not as simple and direct as the statement of it might seem
+to indicate. Though complicated in its various stages, the ultimate
+result is as simple as in ordinary combustion outside of the body, and
+the products are the same.
+
+The continual chemical changes, then, chiefly by oxidation of
+combustible materials in the tissues, produce an amount of heat which
+is efficient to maintain the temperature of the living body at about
+98½° F. This process of oxidation provides not only for the heat of the
+body, but also for the energy required to carry on the muscular work of
+the animal organism.
+
+225. Regulation of the Bodily Temperature. While bodily heat is being
+continually produced, it is also as continually being lost by the
+lungs, by the skin, and to some extent, by certain excretions. The
+blood, in its swiftly flowing current, carries warmth from the tissues
+where heat is being rapidly generated, to the tissues or organs in
+which it is being lost by radiation, conduction, or evaporation. Were
+there no arrangement by which heat could be distributed and regulated,
+the temperature of the body would be very unequal in different parts,
+and would vary at different times.
+
+The normal temperature is maintained with slight variations throughout
+life. Indeed a change of more than a degree above or below the average,
+indicates some failure in the organism, or some unusual influence. It
+is evident, then, that the mechanisms which regulate the temperature of
+the body must be exceedingly sensitive.
+
+The two chief means of regulating the temperature of the body are the
+lungs and the skin. As a means of lowering the temperature, the lungs
+and air passages are very inferior to the skin; although, by giving
+heat to the air we breathe, they stand next to the skin in importance.
+As a regulating power they are altogether subordinate to the skin.
+
+Experiment 113. _To show the natural temperature of the body_. Borrow a
+physician’s clinical thermometer, and take your own temperature, and
+that of several friends, by placing the instrument under the tongue,
+closing the mouth, and holding it there for five minutes. It should be
+thoroughly cleansed after each use.
+
+226. The Skin as a Heat-regulator. The great regulator of the bodily
+temperature is, undoubtedly, the skin, which performs this function by
+means of a self-regulating apparatus with a more or less double action.
+First, the skin regulates the loss of heat by means of the vaso-motor
+mechanism. The more blood passes through the skin, the greater will be
+the loss of heat by conduction, radiation, and evaporation. Hence, any
+action of the vaso-motor mechanism which causes dilatation of the
+cutaneous capillaries, leads to a larger flow of blood through the
+skin, and will tend to cool the body. On the other hand, when by the
+same mechanism the cutaneous vessels are constricted, there will be a
+smaller flow of blood through the skin, which will serve to check the
+loss of heat from the body (secs. 195 and 270).
+
+Again, the special nerves of perspiration act directly as regulators of
+temperature. They increase the loss of heat when they promote the
+secretion of the skin, and diminish the loss when they cease to promote
+it.
+
+The practical working of this heat-regulating mechanism is well shown
+by exercise. The bodily temperature rarely rises so much as a degree
+during vigorous exercise. The respiration is increased, the cutaneous
+capillaries become dilated from the quickened circulation, and a larger
+amount of blood is circulating through the skin. Besides this, the skin
+perspires freely. A large amount of heat is thus lost to the body,
+sufficient to offset the addition caused by the muscular contractions.
+
+It is owing to the wonderful elasticity of the sweat-secreting
+mechanism, and to the increase in respiratory activity, and the
+consequent increase in the amount of watery vapor given off by the
+lungs, that men are able to endure for days an atmosphere warmer than
+the blood, and even for a short time at a temperature above that of
+boiling water. The temperature of a Turkish bath may be as high as 150°
+to 175° F. But an atmospheric temperature may be considerably below
+this, and yet if long continued becomes dangerous to life. In August,
+1896, for instance, hundreds of persons died in this country, within a
+few days, from the effects of the excessive heat.
+
+A much higher temperature may be borne in dry air than in humid air, or
+that which is saturated with watery vapor. Thus, a shade temperature of
+100° F. in the dry air of a high plain may be quite tolerable, while a
+temperature of 80° F. in the moisture-laden atmosphere of less elevated
+regions, is oppressive. The reason is that in dry air the sweat
+evaporates freely, and cools the skin. In saturated air at the bodily
+temperature there is little loss of heat by perspiration, or by
+evaporation from the bodily surface.
+
+This topic is again discussed in the description of the skin as a
+regulator of the bodily temperature (sec. 241).
+
+227. Voluntary Means of Regulating the Temperature. The voluntary
+factor, as a means of regulating the heat loss in man, is one of great
+importance. Clothing retards the loss of heat by keeping in contact
+with it a layer of still air, which is an exceedingly bad conductor.
+When a man feels too warm and throws off his coat, he removes one of
+the badly conducting layers of air, and increases the heat loss by
+radiation and conduction. The vapor next the skin is thus allowed a
+freer access to the surface, and the loss of heat by evaporation of the
+sweat becomes greater. This voluntary factor by which the equilibrium
+is maintained must be regarded as of great importance. This power also
+exists in the lower animals, but to a much smaller extent. Thus a dog,
+on a hot day, runs out his tongue and stretches his limbs so as to
+increase the surface from which heat is radiated and conducted.
+
+The production, like the loss, of heat is to a certain extent under the
+control of the will. Work increases the production of heat, and rest,
+especially sleep, lessens it. Thus the inhabitants of very hot
+countries seek relief during the hottest part of the day by a siesta.
+The quantity and quality of food also influence the production of heat.
+A larger quantity of food is taken in winter than in summer. Among the
+inhabitants of the northern and Arctic regions, the daily consumption
+of food is far greater than in temperate and tropical climates.
+
+228. Effect of Alcohol upon the Lungs. It is a well recognized fact
+that alcohol when taken into the stomach is carried from that organ to
+the liver, where, by the baneful directness of its presence, it
+produces a speedy and often disastrous effect. But the trail of its
+malign power does not disappear there. From the liver it passes to the
+right side of the heart, and thence to the lungs, where its influence
+is still for harm.
+
+In the lungs, alcohol tends to check and diminish the breathing
+capacity of these organs. This effect follows from the partial
+paralyzing influence of the stupefying agent upon the sympathetic
+nervous system, diminishing its sensibility to the impulse of healthful
+respiration. This diminished capacity for respiration is clearly shown
+by the use of the _spirometer_, a simple instrument which accurately
+records the cubic measure of the lungs, and proves beyond denial the
+decrease of the lung space.
+
+“Most familiar and most dangerous is the drinking man’s inability to
+resist lung diseases.”—Dr. Adoph Frick, the eminent German physiologist
+of Zurich.
+    “Alcohol, instead of preventing consumption, as was once believed,
+    reduces the vitality so much as to render the system unusually
+    susceptible to that fatal disease.”—R. S. Tracy, M.D., Sanitary
+    Inspector of the N. Y. City Health Dept.
+    “In thirty cases in which alcoholic phthisis was present a dense,
+    fibroid, pigmented change was almost invariably present in some
+    portion of the lung far more frequently than in other cases of
+    phthisis.”—_Annual of Medical Sciences_.
+    “There is no form of consumption so fatal as that from alcohol.
+    Medicines affect the disease but little, the most judicious diet
+    fails, and change of air accomplishes but slight real good.... In
+    plain terms, there is no remedy whatever for alcoholic phthisis. It
+    may be delayed in its course, but it is never stopped; and not
+    infrequently, instead of being delayed, it runs on to a fatal
+    termination more rapidly than is common in any other type of the
+    disorder.”—Dr. B. W. Richardson in _Diseases of Modern Life_
+
+
+229. Other Results of Intoxicants upon the Lungs. But a more potent
+injury to the lungs comes from another cause. The lungs are the arena
+where is carried on the ceaseless interchange of elements that is
+necessary to the processes of life. Here the dark venous blood, loaded
+with effete material, lays down its carbon burden and, with the
+brightening company of oxygen, begins again its circuit. But the enemy
+intrudes, and the use of alcohol tends to prevent this benign
+interchange.
+
+The continued congestion of the lung tissue results in its becoming
+thickened and hardened, thus obstructing the absorption of oxygen, and
+the escape of carbon dioxid. Besides this, alcohol destroys the
+integrity of the red globules, causing them to shrink and harden, and
+impairing their power to receive oxygen. Thus the blood that leaves the
+lungs conveys an excess of the poisonous carbon dioxid, and a
+deficiency of the needful oxygen. This is plainly shown in the purplish
+countenance of the inebriate, crowded with enlarged veins. This
+discoloration of the face is in a measure reproduced upon the congested
+mucous membrane of the lungs. It is also proved beyond question by the
+decreased amount of carbon dioxid thrown off in the expired breath of
+any person who has used alcoholics.
+
+The enfeebled respiration explains (though it is only one of the
+reasons) why inebriates cannot endure vigorous and prolonged exertion
+as can a healthy person. The hurried circulation produced by
+intoxicants involves in turn quickened respiration, which means more
+rapid exhaustion of the life forces. The use of intoxicants involves a
+repeated dilatation of the capillaries, which steadily diminishes their
+defensive power, rendering the person more liable to yield to the
+invasion of pulmonary diseases.[38]
+
+230. Effect of Alcoholics upon Disease. A theory has prevailed, to a
+limited extent, that the use of intoxicants may act as a preventive of
+consumption. The records of medical science fail to show any proof
+whatever to support this impression. No error could be more serious or
+more misleading, for the truth is in precisely the opposite direction.
+Instead of preventing, alcohol tends to develop consumption. Many
+physicians of large experience record the existence of a distinctly
+recognized alcoholic consumption, attacking those constitutions broken
+down by dissipation. This form of consumption is steadily progressive,
+and always fatal.
+
+The constitutional debility produced by the habit of using alcoholic
+beverages tends to render one a prompt victim to the more severe
+diseases, as pneumonia, and especially epidemical diseases, which sweep
+away vast numbers of victims every year.
+
+231. Effect of Tobacco upon the Respiratory Passages. The effects of
+tobacco upon the throat and lungs are frequently very marked and
+persistent. The hot smoke must very naturally be an irritant, as the
+mouth and nostrils were not made as a chimney for heated and narcotic
+vapors. The smoke is an irritant, both by its temperature and from its
+destructive ingredients, the carbon soot and the ammonia which it
+conveys. It irritates and dries the mucous membrane of the mouth and
+throat, producing an unnatural thirst which becomes an enticement to
+the use of intoxicating liquors. The inflammation of the mouth and
+throat is apt to extend up the Eustachian tube, thus impairing the
+sense of hearing.
+
+But even these are not all the bad effects of tobacco. The inhalation
+of the poisonous smoke produces unhealthful effects upon the delicate
+mucous membrane of the bronchial tubes and of the lungs. Upon the
+former the effect is to produce an irritating cough, with short breath
+and chronic bronchial catarrh. The pulmonary membrane is congested,
+taking cold becomes easy, and recovery from it tedious. Frequently the
+respiration is seriously disturbed, thus the blood is imperfectly
+aërated, and so in turn the nutrition of the entire system is impaired.
+The cigarette is the defiling medium through which these direful
+results frequently invade the system, and the easily moulded condition
+of youth yields readily to the destructive snare.
+
+“The first effect of a cigar upon any one demonstrates that tobacco can
+poison by its smoke and through the lungs.”—London _Lancet_.
+    “The action of the heart and lungs is impaired by the influence of
+    the narcotic on the nervous system, but a morbid state of the
+    larynx, trachea, and lungs results from the direct action of the
+    smoke.”—Dr. Laycock, Professor of Medicine in the University of
+    Edinburgh.
+
+Additional Experiments.
+
+Experiment 114. _To illustrate the arrangement of the lungs and the two
+pleuræ._ Place a large sponge which will represent the lungs in a thin
+paper bag which just fits it; this will represent the pulmonary layer
+of the pleura. Place the sponge and paper bag inside a second paper
+bag, which will represent the parietal layer of the pleura. Join the
+mouths of the two bags. The two surfaces of the bags which are now in
+contact will represent the two moistened surfaces of the pleuræ, which
+rub together in breathing.
+
+Experiment 115. _To show how the lungs may be filled with air._ Take
+one of the lungs saved from Experiment 110. Tie a glass tube six inches
+long into the larynx. Attach a piece of rubber to one end of the glass
+tube. Now inflate the lung several times, and let it collapse. When
+distended, examine every part of it.
+
+Experiment 116. _To take your own bodily temperature or that of a
+friend._ If you cannot obtain the use of a physician’s clinical
+thermometer, unfasten one of the little thermometers found on so many
+calendars and advertising sheets. Hold it for five minutes under the
+tongue with the lips closed. Read it while in position or the instant
+it is removed. The natural temperature of the mouth is about 98½° F.
+
+Experiment 117. _To show the vocal cords._ Get a pig’s windpipe in
+perfect order, from the butcher, to show the vocal cords. Once secured,
+it can be kept for an indefinite time in glycerine and water or dilute
+alcohol.
+
+Experiment 118. _To show that the air we expire is warm._ Breathe on a
+thermometer for a few minutes. The mercury will rise rapidly.
+
+Experiment 119. _To show that expired air is moist_. Breathe on a
+mirror, or a knife blade, or any polished metallic surface, and note
+the deposit of moisture.
+
+Experiment 120. _To show that the expired air contains carbon dioxid_.
+Put a glass tube into a bottle of lime water and breathe through the
+tube. The A liquid will soon become cloudy, because the carbon dioxid
+of the expired air throws down the lime held in solution.
+
+Experiment 121. “A substitute for a clinical thermometer may be readily
+contrived by taking an ordinary house thermometer from its tin case,
+and cutting off the lower part of the scale so that the bulb may
+project freely. With this instrument the pupils may take their own and
+each other’s temperatures, and it will be found that whatever the
+season of the year or the temperature of the room, the thermometer in
+the mouth will record about 99° F. Care must, of course, be taken to
+keep the thermometer in the mouth till it ceases to rise, and to read
+while it is still in position.”—Professor H. P. Bowditch.
+
+Experiment 122. _To illustrate the manner in which the movements of
+inspiration cause the air to enter the lungs._ Fit up an apparatus, as
+represented in Fig. 95, in which a stout glass tube is provided with a
+sound cork, B, and also an air-tight piston, D, resembling that of an
+ordinary syringe. A short tube, A, passing through the cork, has a
+small India-rubber bag, C, tied to it. Fit the cork in the tube while
+the piston is near the top. Now, by lowering the piston we increase the
+capacity of the cavity containing the bag. The pressure outside the bag
+is thus lowered, and air rushes into it through the tube, A, till a
+balance is restored. The bag is thus stretched. As soon as we let go
+the piston, the elasticity of the bag, being free to act, Movements of
+drives out the air just taken in, and the piston returns to its former
+place.
+
+Illustration: Fig. 95. Apparatus for Illustrating the Movements of
+Respiration.
+
+
+It will be noticed that in this experiment the elastic bag and its tube
+represent the lungs and trachea; and the glass vessel enclosing it, the
+thorax.
+
+For additional experiments on the mechanics of respiration, see Chapter
+XV.
+
+
+
+
+Chapter IX.
+The Skin and the Kidneys.
+
+
+232. The Elimination of Waste Products. We have traced the food from
+the alimentary canal into the blood. We have learned that various food
+materials, prepared by the digestive processes, are taken up by the
+branches of the portal vein, or by the lymphatics, and carried into the
+blood current. The nutritive material thus absorbed is conveyed by the
+blood plasma and the lymph to the various tissues to provide them with
+nourishment.
+
+We have learned also that oxygen, taken up in the air cells of the
+lungs, is being continually carried to the tissues, and that the blood
+is purified by being deprived in the lungs of its excess of carbon
+dioxid. From this tissue activity, which is mainly oxidation, are
+formed certain waste products which, as we have seen, are absorbed by
+the capillaries and lymphatics and carried into the venous circulation.
+
+In their passage through the blood and tissues, the albumens, sugars,
+starches, and fats are converted into carbon dioxid, water, and urea,
+or some closely allied body. Certain articles of food also contain
+small amounts of sulphur and phosphorus, which undergo oxidation into
+sulphates and phosphates. We speak, then, of carbon dioxid, salts, and
+water as waste products of the animal economy. These leave the body by
+one of the three main channels,—the lungs, the skin, or the kidneys.
+
+The elimination of these products is brought about by a special
+apparatus called organs of excretion. The worn-out substances
+themselves are called excretions, as opposed to secretions, which are
+elaborated for use in the body. (See note, p. 121.) As already shown,
+the lungs are the main channels for the elimination of carbon dioxid,
+and of a portion of water as vapor. By the skin the body gets rid of a
+small portion of salts, a little carbon dioxid, and a large amount of
+water in the form of perspiration. From the kidneys are eliminated
+nearly all the urea and allied bodies, the main portion of the salts,
+and a large amount of water. In fact, practically all the nitrogenous
+waste leaves the body by the kidneys.
+
+Illustration: Fig. 96.—Diagrammatic Scheme to illustrate in a very
+General Way Absorption and Excretion.
+
+
+A,  represents the alimentary canal;
+  L, the pulmonary surface;
+  K, the surface of the renal epithelium;
+  S, the skin;
+  o, oxygen;
+  h, hydrogen;
+  n, nitrogen.
+
+
+233. The Skin. The skin is an important and unique organ of the body.
+It is a blood-purifying organ as truly as are the lungs and the
+kidneys, while it also performs other and complex duties. It is not
+merely a protective covering for the surface of the body. This is
+indeed the most apparent, but in some respectes, the lest important, of
+its functions. This protective duty is necessary and efficient, as is
+proved by the familiar experience of the pain when a portion of the
+outer skin has been removed.
+
+The skin, being richly supplied with nerves, is an important organ of
+sensibility and touch. In some parts it is closely attached to the
+structures beneath, while in others it is less firmly adherent and
+rests upon a variable amount of fatty tissue. It thus assists in
+relieving the abrupt projections and depressions of the general
+surface, and in giving roundness and symmetry to the entire body. The
+thickness of the skin varies in different parts of the body. Where
+exposed to pressure and friction, as on the soles of the feet and in
+the palms of the hands, it is much thickened.
+
+The true skin is 1/12 to ⅛ of an inch in thickness, but in certain
+parts, as in the lips and ear passages, it is often not more than 1/100
+of an inch thick. At the orifices of the body, as at the mouth, ears,
+and nose, the skin gradually passes into mucous membrane, the structure
+of the two being practically identical. As the skin is an outside
+covering, so is the mucous membrane a more delicate inside lining for
+all cavities into which the apertures open, as the alimentary canal and
+the lungs.
+
+Illustration: Fig. 97.—A Layer of the Cuticle from the Palm of the
+Hand. (Detached by maceration.)
+
+The skin ranks as an important organ of excretion, its product being
+sweat, excreted by the sweat glands. The amount of this excretion
+evaporated from the general surface is very considerable, and is
+modified as becomes necessary from the varied conditions of the
+temperature. The skin also plays an important part in regulating the
+bodily temperature(sec. 241).
+
+234. The Cutis Vera, or True Skin. The skin is remarkably complex in
+its structure, and is divided into two distinct layers, which may be
+readily separated: the deeper layer,—the true skin, dermis, or corium;
+and the superficial layer, or outer skin,—the epidermis, cuticle, or
+scarf skin.
+
+The true skin consists of elastic and white fibrous tissue, the bundles
+of which interlace in every direction. Throughout this feltwork
+structure which gradually passes into areolar tissue are numerous
+muscular fibers, as about the hair-follicles and the oil glands. When
+these tiny muscles contract from cold or by mental emotion, the
+follicles project upon the surface, producing what is called “goose
+flesh.”
+
+The true skin is richly supplied with blood-vessels and nerves, as when
+cut it bleeds freely, and is very sensitive. The surface of the true
+skin is thrown into a series of minute elevations called the papillæ,
+upon which the outer skin is moulded. These abound in blood-vessels,
+lymphatics, and peculiar nerve-endings, which will be described in
+connection with the organ of touch (sec. 314). The papillæ are large
+and numerous in sensitive places, as the palms of the hands, the soles
+of the feet, and the fingers. They are arranged in parallel curved
+lines, and form the elevated ridges seen on the surface of the outer
+skin (Fig. 103).
+
+235. The Epidermis, or Cuticle. Above the true skin is the epidermis.
+It is semi-transparent, and under the microscope resembles the scales
+of a fish. It is this layer that is raised by a blister.
+
+As the epidermis has neither blood-vessels, nerves, nor lymphatics, it
+may be cut without bleeding or pain. Its outer surface is marked with
+shallow grooves which correspond to the deep furrows between the
+papillæ of the true skin. The inner surface is applied directly to the
+papillary layer of the true skin, and follows closely its inequalities.
+The outer skin is made up of several layers of cells, which next to the
+true skin are soft and active, but gradually become harder towards the
+surface, where they are flattened and scale-like. The upper scales are
+continually being rubbed off, and are replaced by deeper cells from
+beneath. There are new cells continually being produced in the deeper
+layer, which push upward the cells already existing, then gradually
+become dry, and are cast off as fine, white dust. Rubbing with a coarse
+towel after a hot bath removes countless numbers of these dead cells of
+the outer skin. During and after an attack of scarlet fever the patient
+“peels,” that is, sheds an unusual amount of the seal; cells of the
+cuticle.
+
+The deeper and more active layer of the epidermis, the _mucosum_, is
+made up of cells some of which contain minute granules of pigment, or
+coloring matter, that give color to the skin. The differences in the
+tint, as brunette, fair, and blond, are due mainly to the amount of
+coloring matter in these pigment cells. In the European this amount is
+generally small, while in other peoples the color cells may be brown,
+yellow, or even black. The pinkish tint of healthy skin, and the
+rosy-red after a bath are due, not to the pigment cells, but to the
+pressure of capillaries in the true skin, the color of the blood being
+seen through the semi-transparent outer skin.
+
+Illustration: Fig. 98.—Surface of the Palm of the Hand, showing the
+Openings of the Sweat Glands and the Grooves between the Papillæ of the
+Skin. (Magnified 4 diameters.) [In the smaller figure the same
+epidermal surface is shown, as seen with the naked eye.]
+
+
+Experiment 123. Of course the living skin can be examined only in a
+general way. Stretch and pull it, and notice that it is elastic. Note
+any liver spots, white scars, moles, warts, etc. Examine the outer skin
+carefully with a strong magnifying glass. Study the papillæ on the
+palms. Scrape off with a sharp knife a few bits of the scarf skin, and
+examine them with the microscope.
+
+236. The Hair. Hairs varying in size cover nearly the entire body,
+except a few portions, as the upper eyelids, the palms of the hands,
+and the soles of the feet.
+
+The length and diameter of the hairs vary in different persons,
+especially in the long, soft hairs of the head and beard. The average
+number of hairs upon a square inch of the scalp is about 1000, and the
+number upon the entire head is estimated as about 120,000.
+
+Healthy hair is quite elastic, and may be stretched from one-fifth to
+one-third more than its original length. An ordinary hair from the head
+will support a weight of six to seven ounces. The hair may become
+strongly electrified by friction, especially when brushed vigorously in
+cold, dry weather. Another peculiarity of the hair is that it readily
+absorbs moisture.
+
+237. Structure of the Hair. The hair and the nails are structures
+connected with the skin, being modified forms of the epidermis. A hair
+is formed by a depression, or furrow, the inner walls of which consist
+of the infolded outer skin. This depression takes the form of a sac and
+is called the hair-follicle, in which the roots of the hair are
+embedded. At the bottom of the follicle there is an upward projection
+of the true skin, a papilla, which contains blood-vessels and nerves.
+It is covered with epidermic cells which multiply rapidly, thus
+accounting for the rapid growth of the hair. Around each papilla is a
+bulbous expansion, the hair bulb, from which the hair begins to grow.
+
+Illustration: Fig. 99.—Epidermis of the Foot.
+
+It will be noticed that there are only a few orifices of the sweat
+glands in this region. (Magnified 8 diameters.)
+
+The cells on the papillæ are the means by which the hairs grow. As
+these are pushed upwards by new ones formed beneath, they are
+compressed, and the shape of the follicle determines their cylindrical
+growth, the shaft of the hair. So closely are these cells welded to
+form the cylinder, that even under a microscope the hair presents only
+a fibrous appearance, except in the center, where the cells are larger,
+forming the medulla, or pith (Fig. 106).
+
+The medulla of the hair contains the pigment granules or coloring
+matter, which may be of any shade between a light yellow and an intense
+black. It is this that gives the great variety in color. Generally with
+old people the pigment is absent, the cells being occupied by air;
+hence the hair becomes gray or white. The thin, flat scales on the
+surface of the hair overlap like shingles. Connected with the
+hair-follicles are small bundles of muscular fibers, which run
+obliquely in the skin and which, on shortening, may cause the hairs to
+become more upright, and thus are made to “stand on end.” The bristling
+back of an angry cat furnishes a familiar illustration of this muscular
+action.
+
+Illustration: Fig. 100.—Hair and Hair-Follicle.
+
+
+A,  root of hair;
+  B, bulb of the hair;
+  C, internal root sheath;
+  D, external root sheath;
+  E, external membrane of follicle;
+  F, muscular fibers attached to the follicle;
+  H, compound sebaceous gland with its duct;
+  K, L, simple sebaceous gland;
+  M, opening of the hair-follicle.
+
+Opening into each hair-follicle are usually one or more sebaceous, or
+oil, glands. These consist of groups of minute pouches lined with cells
+producing an oily material which serves to oil the hair and keep the
+skin moist and pliant.
+
+238. The Nails. The nails are also formed of epidermis cells which have
+undergone compression, much like those forming the shaft of a hair. In
+other words, a nail is simply a thick layer of horny scales built from
+the outer part of the scarf skin. The nail lies upon very fine and
+closely set papillæ, forming its matrix, or bed. It is covered at its
+base with a fold of the true skin, called its root, from beneath which
+it seems to grow.
+
+The growth of the nail, like that of the hair and the outer skin, is
+effected by the production of new cells at the root and under surface.
+The growth of each hair is limited; in time it falls out and is
+replaced by a new one. But the nail is kept of proper size simply by
+the removal of its free edge.
+
+239. The Sweat Glands. Deep in the substance of the true skin, or in
+the fatty tissue beneath it, are the sweat glands. Each gland consists
+of a single tube with a blind end, coiled in a sort of ball about 1/60
+of an inch in diameter. From this coil the tube passes upwards through
+the dermis in a wavy course until it reaches the cuticle, which it
+penetrates with a number of spiral turns, at last opening on the
+surface. The tubes consist of delicate walls of membrane lined with
+cells. The coil of the gland is enveloped by minute blood-vessels. The
+cells of the glands are separated from the blood only by a fine
+partition, and draw from it whatever supplies they need for their
+special work.
+
+Illustration: Fig. 101.—Concave or Adherent Surface of the Nail.
+
+
+A,  border of the root;
+  B, whitish portion of semilunar shape (the lunula);
+  C, body of nail. The continuous line around border represents the
+  free edge.
+
+Illustration: Fig. 102.—Nail in Position.
+
+
+A,  section of cutaneous fold (B) turned back to show the root of the
+nail;
+  B, cutaneous fold covering the root of the nail;
+  C, semi lunar whitish portion (lunula);
+  D, free border.
+
+With few exceptions every portion of the skin is provided with sweat
+glands, but they are not equally distributed over the body. They are
+fewest in the back and neck, where it is estimated they average 400 to
+the square inch. They are thickest in the palms of the hands, where
+they amount to nearly 3000 to each square inch. These minute openings
+occur in the ridges of the skin, and may be easily seen with a hand
+lens. The length of a tube when straightened is about 1/4 of an inch.
+The total number in the body is estimated at about 2,500,000, thus
+making the entire length of the tubes devoted to the secretion of sweat
+about 10 miles.
+
+240. Nature and Properties of Sweat. The sweat is a turbid, saltish
+fluid with a feeble but characteristic odor due to certain volatile
+fatty acids. Urea is always present in small quantities, and its
+proportion may be largely increased when there is deficiency of
+elimination by the kidneys. Thus it is often observed that the sweat is
+more abundant when the kidneys are inactive, and the reverse is true.
+This explains the increased excretion of the kidneys in cold weather.
+Of the inorganic constituents of sweat, common salt is the largest and
+most important. Some carbon dioxid passes out through the skin, but not
+more than 1/50 as much as escapes by the lungs.
+
+The sweat ordinarily passes off as vapor. If there is no obvious
+perspiration we must not infer that the skin is inactive, since sweat
+is continually passing from the surface, though often it may not be
+apparent. On an average from 1½ to 4 pounds of sweat are eliminated
+daily from the skin in the form of vapor. This is double the amount
+excreted by the lungs, and averages about 1/67 of the weight of the
+body.
+
+The visible sweat, or sensible perspiration, becomes abundant during
+active exercise, after copious drinking of cold water, on taking
+certain drugs, and when the body is exposed to excessive warmth.
+Forming more rapidly than it evaporates it collects in drops on the
+surface. The disagreeable sensations produced by humid weather result
+from the fact that the atmosphere is so loaded with vapor that the
+moisture of the skin is slowly removed by evaporation.
+
+Experiment 124. Study the openings of the sweat glands with the aid of
+a strong magnifying glass. They are conveniently examined on the palms.
+
+A man’s weight may be considerably reduced within a short time by loss
+through the perspiration alone. This may explain to some extent the
+weakening effect of profuse perspiration, as from night sweats of
+consumption, convalescence from typhoid fever, or the artificial
+sweating from taking certain drugs.
+
+241. The Skin as a Regulator of the Temperature of the Body. We thus
+learn that the skin covers and protects the more delicate structures
+beneath it; and that it also serves as an important organ of excretion.
+By means of the sweat the skin performs a third and a most important
+function, _viz_., that of regulating the temperature of the body.
+
+The blood-vessels of the skin, like those of other parts of the body,
+are under the control of the nervous system, which regulates their
+diameter. If the nervous control be relaxed, the blood-vessels dilate,
+more blood flows through them, and more material is brought to the
+glands of the skin to be acted upon. External warmth relaxes the skin
+and its blood-vessels. There results an increased flow of blood to the
+skin, with increased perspiration. External cold, on the other hand,
+contracts the skin and its blood-vessels, producing a diminished supply
+of blood and a diminished amount of sweat.
+
+Now, it is a law of physics that the change from liquid to vapor
+involves a loss of heat. A few drops of ether or of any volatile liquid
+placed on the skin, produce a marked sense of coldness, because the
+heat necessary to change the liquid into vapor has been drawn rapidly
+from the skin. This principle holds good for every particle of sweat
+that reaches the mouth of a sweat gland. As the sweat evaporates, it
+absorbs a certain amount of heat, and cools the body to that extent.
+
+242. How the Action of the Skin may be Modified. After profuse sweating
+we feel chilly from the evaporation of a large amount of moisture,
+which rapidly cools the surface. When the weather is very warm the
+evaporation tends to prevent the bodily temperature from rising. On the
+other hand, if the weather be cold, much less sweat is produced, the
+loss of heat from the body is greatly lessened, and its temperature
+prevented from falling. Thus it is plain why medicine is given and
+other efforts are made to sweat the fever patient. The increased
+activity of the skin helps to reduce the bodily heat.
+
+The sweat glands are under the control of certain nerve fibers
+originating in the spinal cord, and are not necessarily excited to
+action by an increased flow of blood through the skin. In other words,
+the sweat glands may be stimulated to increased action both by an
+increased flow of blood, and also by reflex action upon the
+vaso-dilator nerves of the parts. These two agencies, while working in
+harmony through the vaso-dilators, produce phenomena which are
+essentially independent of each other. Thus a strong emotion, like
+fear, may cause a profuse sweat to break out, with cold, pallid skin.
+During a fever the skin may be hot, and its vessels full of blood, and
+yet there may be no perspiration.
+
+Illustration: Fig. 103.—Papillæ of the Skin of the Palm of the Hand.
+In each papilla are seen vascular loops (dark lines) running up from
+the vascular network below, the tactile corpuscles with their nerve
+branches (white lines) which supply the papillæ.
+
+The skin may have important uses with which we are not yet acquainted.
+Death ensues when the heat of the body has been reduced to about 70°
+F., and suppression of the action of the skin always produces a
+lowering of the temperature. Warm-blooded animals usually die when more
+than half of the general surface has been varnished. Superficial burns
+which involve a large part of the surface of the body, generally have a
+fatal result due to shock.
+
+If the skin be covered with some air-tight substance like a coating of
+varnish, its functions are completely arrested. The bodily heat falls
+very rapidly. Symptoms of blood-poisoning arise, and death soon ensues.
+The reason is not clearly known, unless it be from the sudden retention
+of poisonous exhalations.
+
+243. The Skin and the Kidneys. There is a close relationship between
+the skin and the kidneys, as both excrete organic and saline matter. In
+hot weather, or in conditions producing great activity of the skin, the
+amount of water excreted by the kidneys is diminished. This is shown in
+the case of firemen, stokers, bakers, and others who are exposed to
+great heat, and drink heavily and sweat profusely, but do not have a
+relative increase in the functions of the kidneys. In cool weather,
+when the skin is less active, a large amount of water is excreted by
+the kidneys, as is shown by the experience of those who drive a long
+distance in severe weather, or who have caught a sudden cold.
+
+Illustration: Fig. 104.—Magnified View of a Sweat Gland with its Duct.
+
+The convoluted gland is seen surrounded with big fat-cells, and may be
+traced through the dermis to its outlet in the horny layers of the
+epidermis.
+
+244. Absorbent Powers of the Skin. The skin serves to some extent as an
+organ for absorption. It is capable of absorbing certain substances to
+which it is freely exposed. Ointments rubbed in, are absorbed by the
+lymphatics in those parts where the skin is thin, as in the bend of the
+elbow or knee, and in the armpits. Physicians use medicated ointments
+in this way, when they wish to secure prompt and efficient results.
+Feeble infants often grow more vigorous by having their skin rubbed
+vigorously daily with olive oil.
+
+A slight amount of water is absorbed in bathing. Sailors deprived of
+fresh water have been able to allay partially their intense thirst by
+soaking their clothing in salt water. The extent to which absorption
+occurs through the healthy skin is, however, quite limited. If the
+outer skin be removed from parts of the body, the exposed surface
+absorbs rapidly. Various substances may thus be absorbed, and rapidly
+passed into the blood. When the physician wishes remedies to act
+through the skin, he sometimes raises a small blister, and dusts over
+the surface some drug, a fine powder, like morphine.
+
+The part played by the skin as an organ of touch will be considered in
+sections 314 and 315.
+
+Experiment 125. _To illustrate the sense of temperature_. Ask the
+person to close his eyes. Use two test tubes, one filled with cold and
+the other with hot water, or two spoons, one hot and one cold. Apply
+each to different parts of the surface, and ask the person whether the
+touching body is hot or cold. Test roughly the sensibility of different
+parts of the body with cold and warm metallic-pointed rods.
+
+Experiment 126. Touch fur, wood, and metal. The metal feels coldest,
+although all the objects are at the same temperature. Why?
+
+Experiment 127. Plunge the hand into water at about 97°F. One
+experiences a feeling of heat. Then plunge it into water at about
+86°F.; at first it feels cold, because heat is abstracted from the
+hand. Plunge the other hand direct into water at 86°F. without
+previously placing it in water at 97°F.,—it will feel pleasantly warm.
+
+Experiment 128. _To illustrate warm and cold spots_. With a blunt
+metallic point, touch different parts of the skin. Certain points
+excite the sensation of warmth, others of cold, although the
+temperatures of the skin and of the instrument remain constant.
+
+245. Necessity for Personal Cleanliness. It is evident that the skin,
+with its myriads of blood-vessels, nerves, and sweat and oil glands, is
+an exceedingly complicated and important structure. The surface is
+continually casting off perspiration, oily material, and dead scales.
+By friction and regular bathing we get rid of these waste materials. If
+this be not thoroughly done, the oily secretion holds the particles of
+waste substances to the surface of the body, while dust and dirt
+collect, and form a layer upon the skin. When we remember that this
+dirt consists of a great variety of dust particles, poisonous matters,
+and sometimes germs of disease, we may well be impressed with the
+necessity of personal cleanliness.
+
+This layer of foreign matter on the skin is in several ways injurious
+to health. It clogs the pores and retards perspiration, thus checking
+the proper action of the skin as one of the chief means of getting rid
+of the waste matters of the body. Hence additional work is thrown upon
+other organs, chiefly the lungs and the kidneys, which already have
+enough to do. This extra work they can do for only a short time. Sooner
+or later they become disordered, and illness follows. Moreover, as this
+unwholesome layer is a fertile soil in which bacteria may develop, many
+skin diseases may result from this neglect. It is also highly probable
+that germs of disease thus adherent to the skin may then be absorbed
+into the system. Parasitic skin diseases are thus greatly favored by
+the presence of an unclean skin. It is also a fact that uncleanly
+people are more liable to take cold than those who bathe often.
+
+The importance of cleanliness would thus seem too apparent to need
+special mention, were it not that the habit is so much neglected. The
+old and excellent definition that dirt is suitable matter, but in the
+wrong place, suggests that the place should be changed. This can be
+done only by regular habits of personal cleanliness, not only of the
+skin, the hair, the teeth, the nails, and the clothing, but also by the
+rigid observance of a proper system in daily living.
+
+246. Baths and Bathing. In bathing we have two distinct objects in
+view,—to keep the skin clean and to impart vigor. These are closely
+related, for to remove from the body worn-out material, which tends to
+injure it, is a direct means of giving vigor to all the tissues. Thus a
+cold bath acts upon the nervous system, and calls out, in response to
+the temporary abstraction of heat, a freer play of the general vital
+powers. Bathing is so useful, both locally and constitutionally, that
+it should be practiced to such an extent as experience proves to be
+beneficial. For the general surface, the use of hot water once a week
+fulfills the demands of cleanliness, unless in special occupations.
+Whether we should bathe in hot or cold water depends upon
+circumstances. Most persons, especially the young and vigorous, soon
+become accustomed to cool, and even cold water baths, at all seasons of
+the year.
+
+The hot bath should be taken at night before going to bed, as in the
+morning there is usually more risk of taking cold. The body is readily
+chilled, if exposed to cold when the blood-vessels of the skin have
+been relaxed by heat. Hot baths, besides their use for the purposes of
+cleanliness, have a sedative influence upon the nervous system, tending
+to allay restlessness and weariness. They are excellent after severe
+physical or mental work, and give a feeling of restful comfort like
+that of sleep.
+
+Illustration: Fig. 105.—Epithelial Cells from the Sweat Glands. The
+cells are very distinct, with nuclei enclosing pigmentary granulations
+(Magnified 350 times)
+
+Cold baths are less cleansing than hot, but serve as an excellent tonic
+and stimulant to the bodily functions. The best and most convenient
+time for a cold bath is in the morning, immediately after rising. To
+the healthy and vigorous, it is, if taken at this time, with proper
+precautions, a most agreeable and healthful luxury. The sensation of
+chilliness first felt is caused by the contraction of the skin and its
+blood-vessels, so that the blood is forced back, as it were, into the
+deeper parts of the body. This stimulates the nervous system, the
+breathing becomes quicker and deeper, the heart beats more vigorously,
+and, as a consequence, the warm blood is sent back to the skin with
+increased force. This is known as the stage of reaction, which is best
+increased by friction with a rough towel. This should produce the
+pleasant feeling of a warm glow all over the body.
+
+A cold bath which is not followed by reaction is likely to do more harm
+than good. The lack of this reaction may be due to the water being too
+cold, the bath too prolonged, or to the bather being in a low condition
+of health. In brief, the ruddy glow which follows a cold bath is the
+main secret of its favorable influence.
+
+The temperature of the water should be adapted to the age and strength
+of the bather. The young and robust can safely endure cold baths, that
+would be of no benefit but indeed an injury to those of greater age or
+of less vigorous conditions of health. After taking a bath the skin
+should be rapidly and vigorously rubbed dry with a rough towel, and the
+clothing at once put on.
+
+247. Rules and Precautions in Bathing. Bathing in cold water should not
+be indulged in after severe exercise or great fatigue, whether we are
+heated or not. Serious results have ensued from cold baths when the
+body is in a state of exhaustion or of profuse perspiration. A daily
+cold bath when the body is comfortably warm, is a safe tonic for almost
+all persons during the summer months, and tends especially to restore
+the appetite. Cold baths, taken regularly, render persons who are
+susceptible to colds much less liable to them, and less likely to be
+disturbed by sudden changes of temperature. Persons suffering from
+heart disease or from chronic disease of an important organ should not
+indulge in frequent cold bathing except by medical advice. Owing to the
+relaxing nature of hot baths, persons with weak hearts or suffering
+from debility may faint while taking them.
+
+Outdoor bathing should not be taken for at least an hour after a full
+meal, and except for the robust it is not prudent to bathe with the
+stomach empty, especially before breakfast. It is a wise rule, in
+outdoor or sea bathing, to come out of the water as soon as the glow of
+reaction is felt. It is often advisable not to apply cold water very
+freely to the head. Tepid or even hot water is preferable, especially
+by those subject to severe mental strain. But it is often a source of
+great relief during mental strain to bathe the face, neck, and chest
+freely at bedtime with cold water. It often proves efficient at night
+in calming the sleeplessness which results from mental labor.
+
+Hot baths, if taken at bedtime, are often serviceable in preventing a
+threatened cold or cutting it short, the patient going immediately to
+bed, with extra clothing and hot drinks. The free perspiration induced
+helps to break up the cold.
+
+Salt water acts more as a stimulant to the skin than fresh water.
+Salt-water bathing is refreshing and invigorating for those who are
+healthy, but the bather should come out of the water the moment there
+is the slightest feeling of chilliness. The practice of bathing in salt
+water more than once a day is unhealthful, and even dangerous. Only the
+strongest can sustain so severe a tax on their power of endurance. Sea
+bathing is beneficial in many ways for children, as their skin reacts
+well after it. In all cases, brisk rubbing with a rough towel should be
+had afterwards.
+
+Illustration: Fig. 106.—Magnified Section of the Lower Portion of a
+Hair and Hair-Follicle.
+
+
+A,  membrane of the hair-follicle, cells with nuclei and pigmentary
+granules;
+  B, external lining of the root sheath;
+  C, internal lining of the root sheath;
+  D, cortical or fibrous portion of the hair shaft;
+  E, medullary portion (pith) of shaft;
+  F, hair-bulb, showing its development from cells from A.
+
+The golden rule of all bathing is that it must never be followed by a
+chill. If even a chilliness occur after bathing, it must immediately be
+broken up by some appropriate methods, as lively exercise, brisk
+friction, hot drinks, and the application of heat.
+
+Swimming is a most valuable accomplishment, combining bathing and
+exercise. Bathing of the feet should never be neglected. Cleanliness of
+the hair is also another matter requiring strict attention, especially
+in children.
+
+248. Care of the Hair and Nails. The hair brush should not be too
+stiff, as this increases the tendency towards scurfiness of the head.
+If, however, the hair is brushed too long or too hard, the scalp is
+greatly stimulated, and an increased production of scurf may result. If
+the head be washed too often with soap its natural secretion is
+checked, and the scalp becomes dry and scaly. The various hair pomades
+are as a rule undesirable and unnecessary.
+
+The nails should be kept in proper condition, else they are not only
+unsightly, but may serve as carriers of germs of disease. The nails are
+often injured by too much interference, and should never be trimmed to
+the quick. The upper surfaces should on no account be scraped. The
+nail-brush is sufficient to cleanse them without impairing their smooth
+and polished surfaces.
+
+Illustration: Fig. 107.—Longitudinal Section of a Finger-Nail.
+
+
+A,  last phalanx of the fingers;
+  B, true skin on the dorsal surface of the finger;
+  C, epidermis;
+  D, true skin;
+  E, bed of the nail;
+  F, superficial layer of the nail;
+  H, true skin of the pulp of the finger.
+
+
+249. Use of Clothing. The chief use of clothing, from a hygienic point
+of view, is to assist in keeping the body at a uniform temperature. It
+also serves for protection against injury, and for personal adornment.
+The heat of the body, as we have learned, is normally about 98½° F.
+This varies but slightly in health. A rise of temperature of more than
+one degree is a symptom of disturbance. The normal temperature does not
+vary with the season. In summer it is kept down by the perspiration and
+its rapid evaporation. In winter it is maintained by more active
+oxidation, by extra clothing, and by artificial heat.
+
+The whole matter of clothing is modified to a great extent by climatic
+conditions and local environments,—topics which do not come within the
+scope of this book.
+
+250. Material Used for Clothing. It is evident that if clothing is to
+do double duty in preventing the loss of heat by radiation, and in
+protecting us from the hot rays of the sun, some material must be used
+that will allow the passage of heat in either direction. The ideal
+clothing should be both a bad conductor and a radiator of heat. At the
+same time it must not interfere with the free evaporation of the
+perspiration, otherwise chills may result from the accumulation of
+moisture on the surface of the body.
+
+Wool is a bad conductor, and should be worn next the skin, both in
+summer and winter, especially in variable climates. It prevents, better
+than any other material, the loss of heat from the body, and allows
+free ventilation and evaporation. Its fibers are so lightly woven that
+they make innumerable meshes enclosing air, which is one of the best of
+non-conductors.
+
+Silk ranks next to wool in warmth and porosity. It is much softer and
+less irritating than flannel or merino, and is very useful for summer
+wear. The practical objection to its general use is the expense. Fur
+ranks with wool as a bad conductor of heat. It does not, however, like
+wool, allow of free evaporation. Its use in cold countries is
+universal, but in milder climates it is not much worn.
+
+Cotton and linen are good conductors of heat, but are not absorbents of
+moisture, and should not be worn next the skin. They are, however, very
+durable and easily cleansed. As an intermediate clothing they may be
+worn at all seasons, especially over wool or silk. Waterproof clothing
+is also useful as a protection, but should not be worn a longer time
+than necessary, as it shuts in the perspiration, and causes a sense of
+great heat and discomfort.
+
+The color of clothing is of some importance, especially if exposed
+directly to the sun’s rays. The best reflectors, such as white and
+light gray clothing, absorb comparatively little heat and are the
+coolest, while black or dark-colored materials, being poor reflectors
+and good absorbents, become very warm.
+
+251. Suggestions for the Use of Clothing. Prudence and good sense
+should guide us in the spring, in changing winter flannels or clothing
+for fabrics of lighter weight. With the fickle climate in most sections
+of this country, there are great risks of severe colds, pneumonia, and
+other pulmonary diseases from carelessness or neglect in this matter. A
+change from heavy to lighter clothing should be made first in the outer
+garments, the underclothing being changed very cautiously.
+
+The two essentials of healthful clothing are cleanliness and dryness.
+To wear garments that are daily being soiled by perspiration and other
+cutaneous excretions, is a most uncleanly and unhealthful practice.
+Clothing, especially woolen underclothing, should be frequently
+changed. One of the objections to the use of this clothing is that it
+does not show soiling to the same extent as do cotton and linen.
+
+Infectious and contagious diseases may be conveyed by the clothing.
+Hence, special care must be taken that all clothing in contact with
+sick people is burned or properly disinfected. Children especially are
+susceptible to scarlet fever, diphtheria, and measles, and the greatest
+care must be exercised to prevent their exposure to infection through
+the clothing.
+
+We should never sleep in a damp bed, or between damp sheets. The vital
+powers are enfeebled during sleep, and there is always risk of
+pneumonia or rheumatism. The practice of sitting with wet feet and damp
+clothing is highly injurious to health. The surface of the body thus
+chilled may be small, yet there is a grave risk of serious, if not of
+fatal, disease. No harm may be done, even with clothing wet with water
+or damp with perspiration, so long as exercise is maintained, but the
+failure or inability to change into dry garments as soon as the body is
+at rest is fraught with danger.
+
+Woolen comforters, scarfs, and fur mufflers, so commonly worn around
+the neck, are more likely to produce throat troubles and local chill
+than to have any useful effect. Harm ensues from the fact that the
+extra covering induces local perspiration, which enfeebles the natural
+defensive power of the parts; and when the warmer covering is removed,
+the perspiring surface is readily chilled. Those who never bundle their
+throats are least liable to suffer from throat ailments.
+
+252. Ill Effects of Wearing Tightly Fitting Clothing. The injury to
+health caused by tight lacing, when carried to an extreme, is due to
+the compression and displacement of various organs by the pressure
+exerted on them. Thus the lungs and the heart may be compressed,
+causing short breath on exertion, palpitation of the heart, and other
+painful and dangerous symptoms. The stomach, the liver, and other
+abdominal organs are often displaced, causing dyspepsia and all its
+attendant evils. The improper use of corsets, especially by young
+women, is injurious, as they interfere with the proper development of
+the chest and abdominal organs. The use of tight elastics below the
+knee is often injurious. They obstruct the local venous circulation and
+are a fruitful source of cold feet and of enlarged or varicose veins.
+
+Tightly fitting boots and shoes often cause corns, bunions, and
+ingrowing nails; on the other hand, if too loosely worn, they cause
+corns from friction. Boots too narrow in front crowd the toes together,
+make them overlap, and render walking difficult and painful.
+High-heeled boots throw the weight of the body forwards, so that the
+body rests too much on the toes instead of on the heels, as it should,
+thus placing an undue strain upon certain groups of muscles of the leg,
+in order to maintain the balance, while other groups are not
+sufficiently exercised. Locomotion is never easy and graceful, and a
+firm, even tread cannot be expected.
+
+The compression of the scalp by a tight-fitting hat interferes with the
+local circulation, and may cause headaches, neuralgia, or baldness, the
+nutrition of the hair-follicles being diminished by the impaired
+circulation. The compression of the chest and abdomen by a tight belt
+and various binders interferes with the action of the diaphragm,—the
+most important muscle of respiration.
+
+253. Miscellaneous Hints on the Use of Clothing. Children and old
+people are less able to resist the extreme changes of temperature than
+are adults of an average age. Special care should be taken to provide
+children with woolen underclothing, and to keep them warm and in
+well-ventilated rooms. Neither the chest nor limbs of young children
+should be unduly exposed, as is often done, to the cold blasts of
+winter or the fickle weather of early spring. Very young children
+should not be taken out in extremely cold weather, unless quite warmly
+clad and able to run about. The absurd notion is often entertained that
+children should be hardened by exposure to the cold. Judicious
+“hardening” means ample exposure of well-fed and well-clothed children.
+Exposure of children not thus cared for is simple cruelty. The many
+sicknesses of children, especially diseases of the throat and lungs,
+may often be traced directly to gross carelessness, ignorance, or
+neglect with reference to undue exposure. The delicate feet of children
+should not be injured by wearing ill-fitting or clumsy boots or shoes.
+Many deformities of the feet, which cause much vexation and trouble in
+after years, are acquired in early life.
+
+No one should sleep in any of the clothes worn during the day, not even
+in the same underclothing. All bed clothing should be properly aired,
+by free exposure to the light and air every morning. Never wear wet or
+damp clothing one moment longer than necessary. After it is removed rub
+the body thoroughly, put on at once dry, warm clothing, and then
+exercise vigorously for a few minutes, until a genial glow is felt.
+Neglect of these precautions often results in rheumatism, neuralgia,
+and diseases of the chest, especially among delicate people and young
+women.
+
+Pupils should not be allowed to sit in the schoolroom with any outer
+garments on. A person who has become heated in a warm room should not
+expose himself to cold without extra clothing. We must not be in a
+hurry to put on heavy clothes for winter, but having once worn them,
+they must not be left off until milder weather renders the change safe.
+The cheaper articles of clothing are often dyed with lead or arsenic.
+Hence such garments, like stockings and colored underclothing, worn
+next the skin have been known to produce severe symptoms of poisoning.
+As a precaution, all such articles should be carefully washed and
+thoroughly rinsed before they are worn.
+
+The Kidneys.
+
+254. The Kidneys. The kidneys are two important organs in the abdomen,
+one on each side of the spine. They are of a reddish-brown color, and
+are enveloped by a transparent capsule made up of a fold of the
+peritoneum. Embedded in fat, the kidneys lie between the upper lumbar
+vertebræ, and the crest of the hip bone. The liver is above the right
+kidney, and the spleen above the left, while both lie close against the
+rear wall of the abdomen, with the intestines in front of them. The
+human kidneys, though somewhat larger, are exactly of the same shape,
+color, and general appearance as those of the sheep, so commonly seen
+in the markets.
+
+The kidneys are about four inches long, two inches across, one inch
+thick, and weigh from 41/2 to 51/2 ounces each. The hollow or concave
+side of the kidneys is turned inwards, and the deep fissure of this
+side, known as the hilus, widens out to form the pelvis. Through the
+hilus the renal artery passes into each kidney, and from each hilus
+passes outwards the renal vein, a branch of the inferior vena cava.
+
+A tube, called the ureter, passes out from the concave border of each
+kidney, turns downwards, and enters the bladder in the basin of the
+pelvis. This tube is from 12 to 14 inches long, about as large as a
+goose quill, and conveys the secretion of the kidneys to the bladder.
+
+255. Structure of the Kidneys. The pelvis is surrounded by reddish
+cones, about twelve in number, projecting into it, called the pyramids
+of Malpighi. The apices of these cones, known as the _papillæ_, are
+crowded with minute openings, the mouths of the uriniferous tubules,
+which form the substance of the kidney. These lie parallel in the
+medullary or central structure, but On reaching the cortical or outer
+layer, they wind about and interlace, ending, at last, in dilated
+closed sacs called Malpighian capsules.
+
+Illustration: Fig. 108.—Vertical Section of the Kidney.
+
+
+A,  pyramids of Malpighi;
+  B, apices, or papillæ, of the pyramids, surrounded by subdivisions of
+  the pelvis known as cups or calices;
+  C, pelvis of the kidney;
+  D, upper end of ureter.
+
+
+256. Function of the Kidneys. The Malpighian capsules are really the
+beginning of the tubules, for here the work of excretion begins. The
+thin wall of the capillaries within each capsule separates the blood
+from the cavity of the tubule. The blood-pressure on the delicate
+capillary walls causes the exudation of the watery portions of the
+blood through the cell walls into the capsule. The epithelial cell
+membrane allows the water of the blood with certain salts in solution
+to pass, but rejects the albumen. From the capsules, the excretion
+passes through the tubules into the pelvis, and on through the ureters
+to the bladder. But the delicate epithelial walls of the tubules
+through which it passes permit the inflow of urea and other waste
+products from the surrounding capillaries. By this twofold process are
+separated from the blood the fluid portions of the renal secretion with
+soluble salts, and the urea with other waste material.
+
+257. How the Action of the Kidneys may be Modified. The action of the
+kidneys is subject to very marked and sudden modifications, especially
+those operating through the nervous system. Thus whatever raises the
+blood-pressure in the capillaries of the capsules, will increase the
+quantity of fluid filtering through them. That is, the watery portion
+of the secretion will be increased without necessarily adding to its
+solids. So anything which lowers the blood-pressure will diminish the
+watery portion of the secretion, that is, the secretion will be scanty,
+but concentrated.
+
+The Renal Secretion.—The function of the kidneys is to secrete a fluid
+commonly known as the urine. The average quantity passed in 24 hours by
+an adult varies from 40 to 60 fluid ounces. Normal urine consists of
+about 96 per cent of water and 4 per cent of solids. The latter consist
+chiefly of certain nitrogenous substances known as urea and uric acid,
+a considerable quantity of mineral salts, and some coloring matter.
+Urea, the most important and most abundant constituent of urine,
+contains the four elements, but nitrogen forms one-half its weight.
+While, therefore, the lungs expel carbon dioxid chiefly, the kidneys
+expel nitrogen. Both of these substances express the result of
+oxidations going on in the body. The urea and uric acids represent the
+final result of the breaking down in the body of nitrogenous
+substances, of which albumen is the type.
+
+Unusual constituents of the urine are _albumen, sugar_, and _bile_.
+When albumen is present in urine, it often indicates some disease of
+the kidneys, to which the term _albuminuria_ or Bright’s Disease is
+applied. The presence of grape sugar or glucose indicates the disease
+known as diabetes. Bile is another unusual constituent of the urine,
+appearing in _jaundice_.
+
+The bladder is situated in the pelvic cavity or in the lowest part of
+the abdomen. When full, the bladder is pear-shaped; when empty, it is
+collapsed and lies low in the pelvis. The functions of the bladder are
+to collect and retain the urine, which has reached it drop by drop from
+the kidneys through the ureters, until a certain quantity accumulates,
+and then to expel it from the body.
+
+Illustration: Fig. 109.—Vertical Section of the Back. (Showing kidneys
+_in situ_ and the relative position of adjacent organs and vessels.)
+[Posterior view.]
+
+
+A,  12th dorsal vertebra;
+  B, diaphragm;
+  C, receptaculum chyli;
+  D, small intestines
+
+In the kidneys, as elsewhere, the vaso-motor nerves are distributed to
+the walls of the blood-vessels, and modify the quantity and the
+pressure of blood in these organs. Thus, some strong emotion, like fear
+or undue anxiety, increases the blood-pressure, drives more blood to
+the kidneys, and causes a larger flow of watery secretion. When the
+atmosphere is hot, there is a relaxation of the vessels of the skin,
+with a more than ordinary flow of blood, which is thus withdrawn from
+the deeper organs. The blood-pressure in the kidneys is not only
+diminished, but the total quantity passing through them in a given time
+is much lessened. As a result, the secretion of the kidneys is scanty,
+but it contains an unusual percentage of solids.
+
+When the atmosphere is cold, the reverse is true. The cutaneous vessels
+contract, the blood is driven to the deeper organs with increased
+pressure, and there is a less amount of sweat, but an increased renal
+secretion, containing a smaller proportion of solids. Certain drugs
+have the power of increasing or diminishing the renal secretion. As the
+waste matters eliminated by the kidneys are being constantly produced
+in the tissues, the action of the renal organs is continuous, in marked
+contrast with the intermittent flow of most of the secretions proper,
+as distinguished from the excretions.
+
+258. Effects of Alcoholic Drinks upon the Kidneys. The kidneys differ
+from some of the other organs in this: those can rest a while without
+any harm to themselves, or to the body. We can keep the eyes closed for
+a few days, if necessary, without injury, and in fact often with
+benefit; or, we can abstain from food for some days, if need be, and
+let the stomach rest. But the kidneys cannot, with safety, cease their
+work. Their duty in ridding the blood of waste products, and of any
+foreign or poisonous material introduced, must be done not only
+faithfully, but continually, or the whole body at once suffers from the
+evil effects of the retained waste matters.
+This vital fact is the key to the injurious results developed in the
+kidneys by the use of alcoholic drinks. These two organs have large
+blood-vessels conveying full amounts of blood to and from their
+structures, and they feel very quickly the presence of alcohol.
+Alcoholic liquors excite and irritate the delicate renal membranes, and
+speedily disturb and eventually destroy their capacity to excrete the
+proper materials from the blood.
+
+The continued congestion of the minute structure of the kidney cuts off
+the needed nutrition of the organ, and forms the primary step in the
+series of disasters. Sometimes from this continued irritation, with the
+resulting inflammation, and sometimes from change of structure of the
+kidney by fatty degeneration, comes the failure to perform its proper
+function. Then, with this two-edged sword of disaster, the urea, which
+becomes a poisonous element, and should be removed, is retained in the
+system, while the albumen, which is essential to healthy blood, is
+filtered away through the diseased kidney.
+
+259. Alcoholic Liquors as a Cause of Bright’s Disease. The unfortunate
+presence of albumen in the urine is often a symptom of that insidious
+and fatal malady known as _albuminuria_ or Bright’s disease, often
+accompanied with dropsy and convulsions. One of the most constant
+causes of this disease is the use of intoxicants. It is not at all
+necessary to this fatal result that a person be a heavy drinker.
+Steady, moderate drinking will often accomplish the work. Kidney
+diseases produced by alcoholic drinks, are less responsive to medical
+treatment and more fatal than those arising from any other known
+cause.[39]
+
+Experiment 129. Obtain a sheep’s kidney in good order. Observe that its
+shape is something like that of a bean, and note that the concave part
+(hilus), when in its normal position, is turned towards the backbone.
+Notice that all the vessels leave and enter the kidney at the hilus.
+Observe a small thick-walled vessel with open mouth from which may be
+pressed a few drops of blood. This is the renal artery. Pass a bristle
+down it. With the forceps, or even with a penknife, lift from the
+kidney the fine membrane enclosing it. This is the kidney capsule.
+Divide the kidney in halves by a section from its outer to near its
+inner border. Do not cut directly through the hilus. Note on the cut
+surfaces, on the outer side, the darker cortical portion, and on the
+inner side, the smooth, pale, medullary portion. Note also the pyramids
+of Malpighi.
+
+
+
+
+Chapter X.
+The Nervous System.
+
+
+260. General View of the Nervous System. Thus far we have learned
+something of the various organs and the manner in which they do their
+work. Regarding our bodily structure as a kind of living machine, we
+have studied its various parts, and found that each is designed to
+perform some special work essential to the well-being of the whole. As
+yet we have learned of no means by which these organs are enabled to
+adjust their activities to the needs of other tissues and other organs.
+We are now prepared to study a higher, a more wonderful and complex
+agency,—the nervous system, the master tissue, which controls,
+regulates, and directs every other tissue of the human body.
+
+The nervous system, in its properties and mode of action, is distinct
+from all the other systems and organs, and it shares with no other
+organ or tissue the power to do its special work. It is the medium
+through which all impressions are received. It connects all the parts
+of the body into an organism in which each acts in harmony with every
+other part for the good of the whole. It animates and governs all
+movements, voluntary or involuntary,—secretion, excretion, nutrition;
+in fact all the processes of organic life are subject to its regulating
+power. The different organs of the body are united by a common sympathy
+which regulates their action: this harmonious result is secured by
+means of the nervous system.
+
+This system, in certain of its parts, receives impressions, and
+generates a force peculiar to itself. We shall learn that there can be
+no physical communication between or coördination of the various parts
+of organs, or harmonious acts for a desire result, without the nerves.
+General impressions, as in ordinary sensation, or special impressions,
+as in sight, smell, taste, or hearing,—every instinct, every act of the
+will, and every thought are possible only through the action of the
+nerve centers.
+
+261. Nerve Cells. However complicated the structure of nerve tissue in
+man seems to be, it is found to consist of only two different elements,
+nerve cells and nerve fibers. These are associated and combined in many
+ways. They are arranged in distinct masses called nerve centers, or in
+the form of cords known as nerves. The former are made up of nerve
+fibers; the latter of both cells and fibers.
+
+Illustration: Fig. 110.—Nerve Cells from the Spinal Cord.
+
+Nerve cells, which may be regarded as the central organs of the nerve
+fibers, consist of masses of cell protoplasm, with a large _nucleus_
+and _nucleolus_. They bear a general resemblance to other cells, but
+vary much in size and shape. Nerve cells grow, become active, and die,
+as do other cells. A number of processes branch off from them, some
+cells giving one or two, others many. The various kinds of nerve cells
+differ much in the shape and number of processes. One of the processes
+is a strand which becomes continuous with the axis cylinder of the
+nerve fibers; that is, the axis cylinders of all nerve fibers are
+joined in one place or another with at least one cell.
+
+Each part of this system has its own characteristic cell. Thus we have
+in the spinal cord the large, irregular cells with many processes, and
+in the brain proper the three-sided cells with a process jutting out
+from each corner. So characteristic are these forms of cells, that any
+particular part of nerve structure may be identified by the kind of
+cells seen under the microscope. Nerve cells and nerve fibers are often
+arranged in groups, the various cells of the groups communicating with
+one another. This clustered arrangement is called a nerve center.
+
+262. Nerve Fibers. The nerve fibers, the essential elements of the
+nerves, somewhat resemble tubes filled with a clear, jelly-like
+substance. They consist of a rod, or central core, continuous
+throughout the whole length of the nerve, called the axis cylinder.
+This core is surrounded by the white substance of Schwann, or medullary
+sheath, which gives the nerve its characteristic ivory-white
+appearance. The whole is enclosed in a thin, delicate sheath, known as
+neurilemma.
+
+Illustration: Fig. 111.—Nerve Cells from the Gray Matter of the Brain.
+
+
+The axis cylinder generally passes without any break from the nerve
+centers to the end of the fibers.[40] The outer sheath (neurilemma) is
+also continuous throughout the length of the fibers. The medullary
+sheath, on the other hand, is broken at intervals of about 1/25 of an
+inch, and at the same intervals nuclei are found along the fiber,
+around each of which is a minute protoplasmic mass. Between each pair
+of nuclei the sheath is interrupted. This point is known as the _node
+of Ranvier_.
+
+Some nerve fibers have no inner sheath (medullary), the outer alone
+protecting the axis cylinder. These are known as the non-medullary
+fibers. They are gray, while the ordinary medullary fibers are white in
+appearance. The white nerve fibers form the white part of the brain and
+of the spinal cord, and the greater part of the cerebro-spinal nerves.
+The gray fibers occur chiefly in branches from the sympathetic ganglia,
+though found to some extent in the nerves of the cerebro-spinal system.
+
+In a general way, the nerve fibers resemble an electric cable wire with
+its central rod of copper, and its outer non-conducting layer of silk
+or gutta percha. Like the copper rod, the axis cylinder along which the
+nerve impulse travels is the essential part of a nerve fiber. In a cut
+nerve this cylinder projects like the wick of a candle. It is really
+the continuation of a process of a nerve cell. Thus the nerve cells and
+nerve fibers are related, in that the process of one is the axis
+cylinder and essential part of the other.
+
+The separate microscopic threads or fibers, bound together in cords of
+variable size, form the nerves. Each strand or cord is surrounded and
+protected by its own sheath of connective tissue, made up of nerves.
+According to its size a nerve may have one or many of these strands.
+The whole nerve, not unlike a minute tendon in appearance, is covered
+by a dense sheath of fibrous tissue, in which the blood-vessels and
+lymphatics are distributed to the nerve fibers.
+
+Illustration: Fig. 112.—Medullated Nerve Fibers.
+
+
+A,  a medullated nerve fiber, showing the subdivision of the medullary
+sheath into cylindrical sections imbricated with their ends, a nerve
+corpuscle with an oval nucleus is seen between the neurilemma and the
+medullary sheath;
+  B, a medullated nerve fiber at a node or constriction of Ranvier, the
+  axis cylinder passes uninterruptedly from one segment into the other,
+  but the medullary sheath is interrupted.
+
+
+263. The Functions of the Nerve Cells and Nerve Fibers. The nerve cells
+are a highly active mass of living material. They find their
+nourishment in the blood, which is supplied to them in abundance. The
+blood not only serves as nourishment, but also supplies new material,
+as it were, for the cells to work over for their own force or energy.
+Thus we may think of the nerve cells as a sort of a miniature
+manufactory, deriving their material from the blood, and developing
+from it nervous energy.
+
+The nerve fibers, on the other hand, are conductors of nervous energy.
+They furnish a pathway along which the nerve energy generated by the
+cells may travel. Made up as they are of living nerve substance, the
+fibers can also generate energy, yet it is their special function to
+conduct influences to and from the cells.
+
+Illustration: Fig. 113.—Non-Medullated Fibers.
+Two nerve fibers, showing the nodes or constrictions of Ranvier and the
+axis cylinder. The medullary sheath has been dissolved away. The deeply
+stained oblong nuclei indicate the nerve corpuscles within the
+neurilemma.
+
+
+264. The Nervous System Compared to a Telegraphic System. In men and
+other highly organized animals, nerves are found in nearly every tissue
+and organ of the body. They penetrate the most minute muscular fibers;
+they are closely connected with the cells of the glands, and are found
+in the coats of even the smallest blood-vessels. They are among the
+chief factors of the structure of the sense organs, and ramify through
+the skin. Thus the nervous system is the system of organs through the
+functions of which we are brought into relation with the world around
+us. When we hear, our ears are bringing us into relation with the outer
+world. So sight opens up to us another gateway of knowledge.
+
+It will help us the better to understand the complicated functions of
+the nervous system, if we compare it to a telegraph line. The brain is
+the main office, and the multitudes of nerve fibers branching off to
+all parts of the body are the wires. By means of these, nerve messages
+are constantly being sent to the brain to inform it of what is going on
+in various parts of the body, and asking what is to be done in each
+case. The brain, on receiving the intelligence, at once sends back the
+required instructions. Countless messages are sent to and fro with
+unerring accuracy and marvelous rapidity.
+
+Thus, when we accidentally pick up something hot, it is instantly
+dropped. A nerve impulse passes from the nerves of touch in the fingers
+to the brain, which at once hurries off its order along another set of
+nerves for the hand to drop the burning object. These examples, so
+common in daily life, may be multiplied to any extent. Almost every
+voluntary act we perform is executed under the direction of the nervous
+system, although the time occupied is so small that it is beyond our
+power to estimate it. The very frequency with which the nerves act
+tends to make us forget their beneficent work.
+
+265. Divisions of the Nervous System. This system in man consists of
+two great divisions. The first is the great nerve center of the body,
+the cerebro-spinal system, which rules the organs of animal life. This
+includes the brain, the spinal cord, and the cerebro-spinal nerves.
+Nerves are given off from the brain and the cord, and form the mediums
+of communication between the external parts of the body, the muscles or
+the sense organs, and the brain.
+
+The second part is the sympathetic system, which regulates the organic
+life. This consists of numerous small nerve centers arranged in oval
+masses varying greatly in size, called ganglia or knots. These are
+either scattered irregularly through the body, or arranged in a double
+chain of knots lying on the front of the spine, within the chest and
+abdomen. From this chain large numbers of nerves are given off, which
+end chiefly in the organs of digestion, circulation, and respiration.
+The sympathetic system serves to bring all portions of the animal
+economy into direct sympathy with one another.
+
+266. The Brain as a Whole. The brain is the seat of the intellect, the
+will, the affections, the emotions, the memory, and sensation. It has
+also many other and complex functions. In it are established many
+reflex, automatic, and coordinating centers, which are as independent
+of consciousness as are those of the spinal cord.
+
+The brain is the largest and most complex mass of nerve tissue in the
+body, made up of an enormous collection of gray cells and nerve fibers.
+This organ consists of a vast number of distinct ganglia, or separate
+masses of nerve matter, each capable of performing separate functions,
+but united through the cerebral action into a harmonious whole.
+
+Illustration: Fig. 114.—The Upper Surface of the Cerebrum. (Showing its
+division into two hemispheres, and also the convolutions)
+
+The average weight of the adult human brain is about 50 ounces for men
+and 45 ounces for women. Other things being equal, the size and weight
+of the brain bear a general relation to the mental power of the
+individual. As a rule, a large, healthy brain stands for a vigorous and
+superior intellect. The brains of many eminent men have been found to
+be 8 to 12 ounces above the average weight, but there are notable
+exceptions. The brains of idiots are small; indeed, any weight under a
+certain size, about 30 ounces, seems to be invariably associated with
+an imbecile mind.
+
+The human brain is absolutely heavier than that of any other animal,
+except the whale and elephant. Comparing the size of these animals with
+that of man, it is instructive to notice how much larger in proportion
+to the body is man’s brain. The average proportion of the weight of the
+brain to the weight of the body is greater in man than in most animals,
+being about 1 to 36. In some small birds, in the smaller monkeys, and
+in some rodents, the proportional weight of the brain to that of the
+body is even greater than in man.
+
+267. The Cerebrum. The three principal masses which make up the brain
+when viewed as a whole are:
+
+The cerebrum, or brain proper.
+
+The cerebellum, or lesser brain.
+
+The medulla oblongata.
+
+The cerebrum comprises nearly seven-eighths of the entire mass, and
+fills the upper part of the skull. It consists of two halves, the right
+and left cerebral hemispheres. These are almost separated from each
+other by a deep median fissure. The hemispheres are united at the
+bottom of the fissure by a mass of white fibers passing from side to
+side. Each of these hemispheres is subdivided into three lobes, so that
+the entire cerebrum is made up of six distinct lobes.
+
+The cerebrum has a peculiar convoluted appearance, its deep folds being
+separated by fissures, some of them nearly an inch in depth.
+
+It is composed of both white and gray matter. The former comprises the
+greater part of the mass, while the latter is spread over the surface
+in a layer of about ⅛ of an inch thick. The gray matter is the portion
+having the highest functions, and its apparent quantity is largely
+increased by being formed in convolutions.
+
+The convolutions of the cerebrum are without doubt associated with all
+those higher actions which distinguish man’s life; but all the
+convolutions are not of equal importance. Thus it is probable that only
+the frontal part of the brain is the intellectual region, while certain
+convolutions are devoted to the service of the senses.
+
+The cerebrum is the chief seat of the sensations, the intellect, the
+will, and the emotions. A study of cerebral injuries and diseases, and
+experiments upon the lower animals, prove that the hemispheres, and
+more especially the gray matter, are connected with mental states. The
+convolutions in the human brain are more prominent than in that of the
+higher animals, most nearly allied to man, although some species of
+animals, not especially intelligent, have marked cerebral convolutions.
+The higher races of men have more marked convolutions than those less
+civilized.
+
+A view of the under surface of the brain, which rests on the floor of
+the skull, shows the origin of important nerves, called the cranial
+nerves, the cerebellum, the structure connecting the optic nerves
+(optic commissure), the bridge of nervous matter (pons Varolii)
+connecting the two hemispheres of the cerebellum, and lastly numerous
+and well-marked convolutions.
+
+268. The Cerebellum. The cerebellum, or lesser brain, lies in the back
+of the cranium, and is covered over in man by the posterior lobe of the
+cerebrum. It is, at it were, astride of the back of the cerebro-spinal
+axis, and consists of two hemispheres joined by a central mass. On its
+under surface is a depression which receives the medulla oblongata. The
+cerebellum is separated from the cerebrum by a horizontal partition of
+membrane, a portion of the dura mater. In some animals, as in the cat,
+this partition is partly bone.
+
+The cerebellum is connected with other parts of the nervous system by
+strands of white matter on each side, radiating from the center and
+divided into numerous branches. Around these branches the gray matter
+is arranged in a beautiful manner, suggesting the leaves of a tree:
+hence its name, arbor vitæ, or the tree of life.
+
+The functions of the cerebellum are not certainly known. It appears to
+influence the muscles of the body so as to regulate their movements;
+that is, it serves to bring the various muscular movements into
+harmonious action. The mechanism by which it does this has not yet been
+clearly explained. In an animal from which the cerebellum has been
+removed, the functions of life do not appear to be destroyed, but all
+power of either walking or flying straight is lost.
+
+Illustration: Fig. 115.—A Vertical Section of the Brain.
+
+
+A,  frontal lobe of the cerebrum;
+  B, parietal lobe;
+  C, parieto occipital lobe with fissure between this lobe and
+  D, the occipital lobe;
+  E, cerebellum;
+  F, arbor vitæ;
+  H, pons Varolu;
+  K, medulla oblongata;
+  L, portion of lobe on the opposite side of brain.
+
+The white curved band above H represents the corpus callosum.
+
+Disease or injury of the cerebellum usually produces blindness,
+giddiness, a tendency to move backwards, a staggering, irregular gait,
+and a feeling of insecurity in maintaining various positions. There is
+no loss of consciousness, or other disturbance of the mental functions.
+
+269. The Membranes of the Brain. The brain and spinal cord are
+protected by three important membranes, known as the meninges,—the dura
+mater, the arachnoid, and the pia mater.
+
+The outer membrane, the dura mater, is much thicker and stronger than
+the others, and is composed of white fibrous and elastic connective
+tissue. It closely lines the inner surface of the skull, and forms a
+protective covering for the brain. Folds of it pass between the several
+divisions of the brain and serve to protect them.
+
+The arachnoid is a thin membrane which lies beneath the dura mater. It
+secretes a serous fluid which keeps the inner surfaces moist.
+
+The pia mater is a very delicate, vascular membrane which covers the
+convolutions, dips into all the fissures, and even penetrates into the
+interior of the brain. It is crowded with blood-vessels, which divide
+and subdivide very minutely before they penetrate the brain. The
+membranes of the brain are sometimes the seat of inflammation, a
+serious and painful disease, commonly known as brain fever.
+
+270. The Medulla Oblongata. This is the thick upper part of the spinal
+cord, lying within the cavity of the skull. It is immediately under the
+cerebellum, and forms the connecting link between the brain and the
+spinal cord. It is about an inch and a quarter long, and from one-half
+to three-fourths of an inch wide at its upper part. The medulla
+oblongata consists, like the spinal cord, of columns of white fibers
+and masses of gray matter, but differently arranged. The gray matter is
+broken up into masses which serve as centers of origin for various
+nerves. The functions of the medulla oblongata are closely connected
+with the vital processes. It is a great nerve tract for transmitting
+sensory and motor impressions, and also the seat of a number of centers
+for reflex actions of the highest importance to life. Through the
+posterior part of the medulla the sensory impressions pass, that is,
+impressions from below upwards to the brain resulting in sensation or
+feeling. In the anterior part of the medulla, pass the nerves for motor
+transmission, that is, nerve influences from above downwards that shall
+result in muscular contractions in some part of the body.
+
+The medulla is also the seat of a number of reflex centers connected
+with the influence of the nervous system on the blood-vessels, the
+movements of the heart, of respiration, and of swallowing, and on the
+secretion of saliva. This spot has been called the “vital knot.” In the
+medulla also are centers for coughing, vomiting, swallowing, and the
+dilatation of the pupil of the eye. It is also in part the deep origin
+of many of the important cranial nerves.
+
+Illustration: Fig. 116.—Illustrating the General Arrangement of the
+Nervous System. (Posterior view.)
+
+
+271. The Cranial Nerves. The cranial or cerebral nerves consist of
+twelve pairs of nerves which pass from the brain through different
+openings in the base of the skull, and are distributed over the head
+and face, also to some parts of the trunk and certain internal organs.
+These nerves proceed in pairs from the corresponding parts of each side
+of the brain, chiefly to the organs of smell, taste, hearing, and
+sight.
+
+The cranial nerves are of three kinds: sensory, motor, and both
+combined, _viz_., mixed.
+
+Distribution and Functions of the Cranial Nerves. The cranial nerves
+are thus arranged in pairs:
+
+The first pair are the olfactory nerves, which pass down through the
+ethmoid bone into the nasal cavities, and are spread over the inner
+surface of the nose. They are sensory, and are the special nerves of
+smell.
+
+The second pair are the optic nerves, which, under the name of the
+_optic tracts_, run down to the base of the brain, from which an optic
+nerve passes to each eyeball. These are sensory nerves, and are devoted
+to sight.
+
+The third, fourth, and sixth pairs proceed to the muscles of the eyes
+and control their movements. These are motor nerves, the movers of the
+eye.
+
+Each of the fifth pair of nerves is in three branches, and proceeds
+mainly to the face. They are called tri-facial, and are mixed nerves,
+partly sensory and partly motor. The first branch is purely sensory,
+and gives sensibility to the eyeball. The second gives sensibility to
+the nose, gums, and cheeks. The third (mixed) gives the special
+sensation of taste on the front part of the tongue, and ordinary
+sensation on the inner side of the cheek, on the teeth, and also on the
+scalp in front of the ear. The motor branches supply the chewing
+muscles.
+
+The seventh pair, the facial, proceed to the face, where they spread
+over the facial muscles and control their movements. The eighth pair
+are the auditory, or nerves of hearing, and are distributed to the
+special organs of hearing.
+
+The next three pairs of nerves all arise from the medulla, and escape
+from the cavity of the skull through the same foramen. They are
+sometimes described as one pair, namely, the eighth, but it is more
+convenient to consider them separately.
+
+The ninth pair, the glosso-pharyngeal, are partly sensory and partly
+motor. Each nerve contains two roots: one a nerve of taste, which
+spreads over the back part of the tongue; the other a motor nerve,
+which controls the muscles engaged in swallowing.
+
+The tenth pair, the pneumogastric, also known as the vagus or wandering
+nerves, are the longest and most complex of all the cranial nerves.
+They are both motor and sensory, and are some of the most important
+nerves in the body. Passing from the medulla they descend near the
+œsophagus to the stomach, sending off, on their way, branches to the
+throat, the larynx, the lungs, and the heart. Some of their branches
+restrain the movements of the heart, others convey impressions to the
+brain, which result in quickening or slowing the movements of
+breathing. Other branches pass to the stomach, and convey to the brain
+impressions which inform us of the condition of that organ. These are
+the nerves by which we experience the feelings of pain in the stomach,
+hunger, nausea, and many other vague impressions which we often
+associate with that organ.
+
+Illustration: Fig. 117.—Anterior View of the Medulla Oblongata.
+
+
+A,  chiasm of the optic nerves;
+  B, optic tracts;
+  C, motor oculi communis;
+  D, fifth nerve;
+  E, motor oculi externus;
+  F, facial nerve;
+  H, auditory nerve;
+  I, glosso-pharyngeal nerve;
+  K, pneumogastric;
+  L, spinal accessory;
+  M, cervical nerves;
+  N, upper extremity of spinal cord;
+  O, decussation of the anterior pyramids;
+  R, anterior pyramids of the medulla oblongata;
+  S, pons Varolii.
+
+The eleventh pair, the spinal accessory, are strictly motor, and supply
+the muscles of the neck and the back.
+
+The twelfth pair, the hypoglossal, are also motor, pass to the muscles
+of the tongue, and help control the delicate movements in the act of
+speech.
+
+272. The Spinal Cord. This is a long, rod-like mass of white nerve
+fibers, surrounding a central mass of gray matter. It is a continuation
+of the medulla oblongata, and is lodged in the canal of the spinal
+column. It extends from the base of the skull to the lower border of
+the first lumbar vertebra, where it narrows off to a slender filament
+of gray substance.
+
+The spinal cord is from 16 to 18 inches long, and has about the
+thickness of one’s little finger, weighing about 1½ ounces. Like the
+brain, it is enclosed in three membranes, which in fact are the
+continuation of those within the skull. They protect the delicate cord,
+and convey vessels for its nourishment. The space between the two inner
+membranes contains a small quantity of fluid, supporting the cord, as
+it were in a water-bath. It is thus guarded against shocks.
+
+The cord is suspended and kept in position in the canal by delicate
+ligaments at regular intervals between the inner and outer membranes.
+Finally, between the canal, enclosed by its three membranes, and the
+bony walls of the spinal canal, there is considerable fatty tissue, a
+sort of packing material, imbedded in which are some large
+blood-vessels.
+
+273. Structure of the Spinal Cord. The arrangement of the parts of the
+spinal cord is best understood by a transverse section. Two fissures,
+one behind, the other in front, penetrate deeply into the cord, very
+nearly dividing it into lateral halves. In the middle of the isthmus
+which joins the two halves, is a very minute opening, the _central
+canal_ of the cord. This tiny channel, just visible to the naked eye,
+is connected with one of the openings of the medulla oblongata, and
+extends, as do the anterior and posterior fissures, the entire length
+of the cord.
+
+The spinal cord, like the brain, consists of gray and white matter, but
+the arrangement differs. In the brain the white matter is within, and
+the gray matter is on the surface. In the cord the gray matter is
+arranged in two half-moon-shaped masses, the backs of which are
+connected at the central part. The white matter, consisting mainly of
+fibers, running for the most part in the direction of the length of the
+cord, is outside of and surrounds the gray crescents. Thus each half or
+side of the cord has its own gray crescent, the horns of which point
+one forwards and the other backwards, called respectively the anterior
+and posterior cornua or horns.
+
+It will also be seen that the white substance itself, in each half of
+the cord, is divided by the horns of the gray matter and by fibers
+passing from them into three parts, which are known as the anterior,
+posterior, and lateral columns.
+
+Experiment 130. Procure at the market an uninjured piece of the spinal
+cord from the loin of mutton or the sirloin or the rib of beef. After
+noting its general character while fresh, put it to soak in dilute
+alcohol, until it is sufficiently hard to be cut in sections.
+
+274. The Spinal Nerves. From the gray matter on each side of the spinal
+cord 31 spinal nerves are given off and distributed chiefly to the
+muscles and the skin. They pass out at regular intervals on each side
+of the canal, by small openings between the vertebræ. Having escaped
+from the spine, they pass backwards and forwards, ramifying in the soft
+parts of the body. The first pair pass out between the skull and the
+atlas, the next between the atlas and the axis, and so on down the
+canal. The eighth pair, called _cervical_, pass out in the region of
+the neck; twelve, called _dorsal_, in the region of the ribs; five are
+_lumbar_, and five _sacral_, while the last pair leave the cord near
+the coccyx.
+
+Each spinal nerve has two roots, one from the anterior, the other from
+the posterior portion of the cord. These unite and run side by side,
+forming as they pass between the vertebræ one silvery thread, or nerve
+trunk. Although bound up in one bundle, the nerve fibers of the two
+roots remain quite distinct, and perform two entirely different
+functions.
+
+After leaving the spinal cord, each nerve divides again and again into
+finer and finer threads. These minute branches are distributed through
+the muscles, and terminate on the surface of the body. The anterior
+roots become motor nerves, their branches being distributed to certain
+muscles of the body, to control their movements. The posterior roots
+develop into sensory nerves, their branches being distributed through
+the skin and over the surface of the body to become nerves of touch. In
+brief, the spinal nerves divide and subdivide, to reach with their
+twigs all parts of the body, and provide every tissue with a nerve
+center, a station from which messages may be sent to the brain.
+
+Illustration: Fig. 118.—Side View of the Spinal Cord. (Showing the
+fissures and columns.)
+
+
+A,  anterior median fissure;
+  B, posterior median fissure;
+  C, anterior lateral fissure;
+  D, posterior lateral fissure;
+  E, lateral column;
+  F, anterior column;
+  G, posterior column;
+  H, posterior median column;
+  K, anterior root;
+  L, posterior root;
+  M, ganglion of
+  N, a spinal nerve.
+
+
+275. The Functions of the Spinal Nerves. The messages which pass along
+the spinal nerves to and from the brain are transmitted mostly through
+the gray matter of the cord, but some pass along the white matter on
+the outer part. As in the brain, however, all the active powers of the
+cord are confined to the gray matter. The spinal nerves themselves have
+nothing to do with sensation or will. They are merely conductors to
+carry messages to and fro. They neither issue commands nor feel a
+sensation. Hence, they consist entirely of white matter.
+
+276. Functions of the Spinal Cord. The spinal cord is the principal
+channel through which all impulses from the trunk and extremities pass
+to the brain, and all impulses to the trunk and extremities pass from
+the brain. That is, the spinal cord receives from various parts of the
+body by means of its sensory nerves certain impressions, and conveys
+them to the brain, where they are interpreted.
+
+The cord also transmits by means of its motor nerves the commands of
+the brain to the voluntary muscles, and so causes movement. Thus, when
+the cord is divided at any point, compressed, as by a tumor or broken
+bone, or disorganized by disease, the result is a complete loss of
+sensation and voluntary movement below the point of injury. If by
+accident a man has his spinal cord injured at some point, he finds he
+has lost all sensation and power of motion below that spot. The impulse
+to movement started in his brain by the will does not reach the muscles
+he wishes to move, because traveling _down_ the spinal cord, it cannot
+pass the seat of injury.
+
+So the impression produced by pricking the leg with a pin, which,
+before pain can be felt, must travel up the spinal cord to the brain,
+cannot reach the brain because the injury obstructs the path. The
+telegraph wire has been cut, and the current can no longer pass.
+
+277. The Spinal Cord as a Conductor of Impulses. The identity in
+structure of the spinal nerves, whether motor or sensory, and the vast
+number of nerves in the cord make it impossible to trace for any
+distance with the eye, even aided by the microscope and the most
+skillful dissection, the course of nerve fibers. The paths by which the
+motor impulses travel down the cord are fairly well known. These
+impulses originate in the brain, and passing down keep to the same side
+of the cord, and go out by nerves to the same side of the body.
+
+The sensory impulses, however, soon after they enter the cord by the
+nerve of one side, cross in the cord to the opposite side, up which
+they travel to the brain. Thus the destruction of one lateral half of
+the cord causes paralysis of motion on the _same side_ as the injury,
+but loss of sensation on the _opposite side_, because the posterior
+portion destroyed consists of fibers which have crossed from the
+opposite side.
+
+Experiment proves that if both roots of a spinal nerve be cut, all
+those parts of the body to which they send branches become paralyzed,
+and have neither sense of pain nor power of voluntary movement. The
+parts might even be cut or burned without pain. It is precisely like
+cutting a telegraph wire and stopping the current.
+
+Illustration: Fig. 119.—The Base of the Brain.
+
+
+A,  anterior lobe of the cerebrum;
+  B, olfactory nerve;
+  C, sphenoid portion of the posterior lobe;
+  D, optic chiasm;
+  E, optic tract;
+  F, abducens;
+  H, M, hemispheres of the cerebellum;
+  K, occipital portion of the occipital lobe;
+  L, fissure separating the hemispheres;
+  N, medulla oblongata;
+  O, olivary body;
+  P, antenor pyramids;
+  R, pons Valoru;
+  S, section of olfactory nerve, with the trunk removed to show sulcus
+  in which it is lodged;
+  T, anterior extremity of median fissure
+
+Experiment also proves that if only the posterior root of a spinal
+nerve be cut, all sensation is lost in the parts to which the nerve
+passes, but the power of moving these parts is retained. But if the
+anterior root alone be divided, all power of motion in the parts
+supplied by that nerve is lost, but sensation remains. From these and
+many other experiments, it is evident that those fibers of a nerve
+which are derived from the anterior root are motor, and those from the
+posterior root sensory, fibers. Impulses sent _from_ the brain and
+spinal cord to muscles will, therefore, pass along the anterior roots
+through those fibers of the nerves which are derived from these (motor)
+roots. On the other hand, impressions or sensations passing _to_ the
+brain will enter the spinal cord and reach the brain through the
+posterior or sensory roots.
+
+278. The Spinal Cord as a Reflex Center. Besides this function of the
+spinal cord as a great nerve conductor to carry sensations to the
+brain, and bring back its orders, it is also an independent center for
+what is called reflex action. By means of its sensory nerves it
+receives impressions from certain parts of the body, and on its own
+authority sends back instructions to the muscles by its motor nerves,
+without consulting the brain. This constitutes reflex action, so called
+because the impulse sent to the spinal cord by certain sensory nerves
+is at once reflected or sent back as a motor impulse to the muscles.
+
+This reflex action is a most important function of the spinal cord.
+This power is possessed only by the gray matter of the cord, the white
+substance being simply a conductor.
+
+The cells of gray matter are found all along the cord, but are grouped
+together in certain parts, notably in the cervical and lumbar regions.
+The cells of the anterior horns are in relation with the muscles by
+means of nerve fibers, and are also brought into connection with the
+skin and other sensory surfaces, by means of nerve fibers running in
+the posterior part of the cord. Thus there is established in the spinal
+cord, without reference to the brain at all, a reflex mechanism.
+
+279. Reflex Centers. For the purpose of illustration, we might consider
+the body as made up of so many segments piled one on another, each
+segment presided over by a similar segment of spinal cord. Each bodily
+segment would have sensory and motor nerves corresponding to its
+connection with the spinal cord. The group of cells in each spinal
+segment is intimately connected with the cells of the segments above
+and below. Thus an impression reaching the cells of one spinal segment
+might be so strong as to overflow into the cells of other segments, and
+thus cause other parts of the body to be affected.
+
+Take as an example the case of a child who has eaten improper food,
+which irritates its bowels. Sensory nerves of the bowels are disturbed,
+and powerful impressions are carried up to a center in the spinal cord.
+These impressions may now overflow into other centers, from which
+spasmodic discharges of nerve energy may be liberated, which passing to
+the muscles, throw them into violent and spasmodic contraction. In
+other words, the child has a fit, or convulsion. All this disturbance
+being the result of reflex action (the spasmodic motions being quite
+involuntary, as the brain takes no part in them), the child meanwhile
+is, of course, entirely unconscious and, however it may seem to be
+distressed, really suffers no pain.
+
+Scattered along the entire length of the spinal cord, especially in the
+upper part, are groups of nerve cells which preside over certain
+specific functions of animal life; that is, definite collections of
+cells which control definite functions. Thus there are certain centers
+for maintaining the action of the heart, and the movements of
+breathing; and low down in the cord, in the lumbar regions, are centers
+for the control of the various abdominal organs.
+
+Numerous other reflex centers are described by physiologists, but
+enough has been said to emphasize the great importance of the spinal
+cord as an independent nerve center, besides its function as a
+conductor of nervous impulses to and from the brain.
+
+280. The Brain as a Reflex Center. The brain, as we have just stated,
+is the seat of consciousness and intelligence. It is also the seat of
+many reflex, automatic, and coordinating centers. These give rise to
+certain reflex actions which are as entirely independent of
+consciousness as are those of the spinal cord. These acts take place
+independently of the will, and often without the consciousness of the
+individual. Thus, a sudden flash of light causes the eyes to blink, as
+the result of reflex action. The optic nerves serve as the sensory, and
+the facial nerves as the motor, conductors. The sudden start of the
+whole body at some loud noise, the instinctive dodging a threatened
+blow, and the springing back from sudden danger, are the results of
+reflex action. The result ensues in these and in many other instances,
+without the consciousness of the individual, and indeed beyond his
+power of control.
+
+281. The Importance of Reflex Action. Reflex action is thus a marvelous
+provision of nature for our comfort, health, and safety. Its vast
+influence is not realized, as its numberless acts are so continually
+going on without our knowledge. In fact, the greater part of nerve
+power is expended to produce reflex action. The brain is thus relieved
+of a vast amount of work. It would be impossible for the brain to serve
+as a “thinking center” to control every act of our daily life. If we
+had to plan and to will every heart-beat or every respiration, the
+struggle for life would soon be given up.
+
+The fact that the gray cells of the spinal cord can originate a
+countless number of reflex and automatic activities is not only of
+great importance in protecting the body from injury, but increases
+vastly the range of the activities of our daily life.
+
+Even walking, riding the bicycle, playing on a piano, and numberless
+other such acts may be reflex movements. To learn how, requires, of
+course, the action of the brain, but with frequent repetition the
+muscles become so accustomed to certain successive movements, that they
+are continued by the cord without the control of the brain. Thus we may
+acquire a sort of artificial reflex action, which in time becomes in a
+way a part of our organization, and is carried on without will power or
+even consciousness.
+
+So, while the hands are busily doing one thing, the brain can be
+intently thinking of another. In fact, any attempt to control reflex
+action is more apt to hinder than to help. In coming rapidly down
+stairs, the descent will be made with ease and safety if the spinal
+cord is allowed entire charge of the act, but the chances of stumbling
+or of tripping are very much increased if each step be taken as the
+result of the will power. The reflex action of the cord may be
+diminished, or inhibited as it is called, but this power is limited.
+Thus, we can by an effort of the will stop breathing for a certain
+time, but beyond that the reflex mechanism overcomes our will and we
+could not, if we would, commit suicide by holding our breath. When we
+are asleep, if the palm of the hand be tickled, it closes; when we are
+awake we can prevent it.
+
+Illustration: Fig. 120.—Dr. Waller’s Diagrammatic Illustration of the
+Reflex Process.
+
+From the sentient surface (1) an afferent impulse passes along (2) to
+the posterior root of the spinal cord, the nerve fibers of the
+posterior root ending in minute filaments among the small cells of this
+part of the cord (3). In some unknown way this impulse passes across
+the gray part of the cord to the large cells of the anterior root (5),
+the cells of this part being connected by their axis-cylinder with the
+efferent fibers (6). These convey the stimulus to the fibers of the
+muscle (7), which accordingly contract. Where the brain is concerned in
+the action the circuit is longer through S and M.
+
+Experiment 131. _To illustrate reflex action by what is called
+knee-jerk._ Sit on a chair, and cross the right leg over the left one.
+With the tips of the fingers or the back of a book, strike the right
+ligamentum patellæ. The right leg will be raised and thrown forward
+with a jerk, owing to the contraction of the quadriceps muscles. An
+appreciable time elapses between the striking of the tendon and the
+jerk. The presence or absence of the knee-jerk may be a most
+significant symptom to the physician.
+
+282. The Sympathetic System. Running along each side of the spine, from
+the base of the skull to the coccyx, is a chain of nerve knots, or
+ganglia. These ganglia, twenty-four on each side, and their branches
+form the sympathetic system, as distinguished from the cerebro-spinal
+system consisting of the brain and spinal cord and the nerves springing
+from them. The ganglia of the sympathetic system are connected with
+each other and with the sensory roots of the spinal nerves by a network
+of gray nerve fibers.
+
+At the upper end the chain of each side passes up into the cranium and
+is closely connected with the cranial nerves. In the neck, branches
+pass to the lungs and the heart. From the ganglia in the chest three
+nerves form a complicated network of fibers, from which branches pass
+to the stomach, the liver, the intestines, the kidneys, and other
+abdominal organs. A similar network of fibers is situated lower down in
+the pelvis, from which branches are distributed to the pelvic organs.
+At the coccyx the two chains unite into a single ganglion.
+
+Thus, in general, the sympathetic system, while intimately connected
+with the cerebro-spinal, forms a close network of nerves which
+specially accompany the minute blood-vessels, and are distributed to
+the muscles of the heart, the lungs, the stomach, the liver, the
+intestines, and the kidneys—that is, the hollow organs of the body.
+
+283. The Functions of the Sympathetic System. This system exercises a
+superintending influence over the greater part of the internal organs
+of the body, controlling to a certain extent the functions of
+digestion, nutrition, circulation, and respiration. The influence thus
+especially connected with the processes of organic life is generally
+different from, or even opposed to, that conveyed to the same organs by
+fibers running in the spinal or cranial nerves. These impulses are
+beyond the control of the will.
+
+Illustration: Fig. 121.—The Cervical and Thoracic Portion of the
+Sympathetic Nerve and its Main Branches.
+
+
+A,  right pneumogastric;
+  B, spinal accessory;
+  C, glosso-pharyngeal;
+  D, right bronchus;
+  E, right branch of pulmonary artery;
+  F, one of the intercostal nerves;
+  H, great splanchnic nerve;
+  K, solar plexus;
+  L, left pneumogastric;
+  M, stomach branches of right pneumogastric;
+  N, right ventricle;
+  O, right auricle;
+  P, trunk of pulmonary artery;
+  R, aorta; S, cardiac nerves;
+  T, recurrent laryngeal nerve;
+  U, superior laryngeal nerve;
+  V, submaxillary ganglion;
+  W, lingual branch of the 5th nerve;
+  X, ophthalmic ganglion;
+  Y, motor oculi externus.
+
+Hence, all these actions of the internal organs just mentioned that are
+necessary to the maintenance of the animal life, and of the harmony
+which must exist between them, are controlled by the sympathetic
+system. But for this control, the heart would stop beating during
+sleep, digestion would cease, and breathing would be suspended. Gentle
+irritation of these nerves, induced by contact of food in the stomach,
+causes that organ to begin the churning motion needed for digestion.
+Various mental emotions also have a reflex action upon the sympathetic
+system. Thus, terror dilates the pupils, fear acts upon the nerves of
+the small blood-vessels of the face to produce pallor, and the sight of
+an accident, or even the emotions produced by hearing of one, may
+excite nausea and vomiting.
+
+The control of the blood-vessels, as has been stated (sec. 195), is one
+of the special functions of the sympathetic system. Through the nerves
+distributed to the muscular coats of the arteries, the caliber of these
+vessels can be varied, so that at one moment they permit a large
+quantity of blood to pass, and at another will contract so as to
+diminish the supply. This, too, is beyond the control of the will, and
+is brought about by the vaso-motor nerves of the sympathetic system
+through a reflex arrangement, the center for which is the medulla
+oblongata.
+
+284. Need of Rest. The life of the body, as has been emphasized in the
+preceding chapters, is subject to constant waste going on every moment,
+from the first breath of infancy to the last hour of old age. We should
+speedily exhaust our life from this continual loss, but for its
+constant renewal with fresh material. This exhaustion of life is
+increased by exertion, and the process of repair is vastly promoted by
+rest. Thus, while exercise is a duty, rest is equally imperative.
+
+The eye, when exactingly used in fine work, should have frequent
+intervals of rest in a few moments of darkness by closing the lids. The
+brain, when urged by strenuous study, should have occasional seasons of
+rest by a dash of cold water upon the forehead, and a brief walk with
+slow and deep inspirations of fresh air. The muscles, long cramped in a
+painful attitude, should be rested as often as may be, by change of
+posture or by a few steps around the room.
+
+It is not entirely the amount of work done, but the continuity of
+strain that wears upon the body. Even a brief rest interrupts this
+strain; it unclogs the wheels of action. Our bodies are not designed
+for continuous toil. An alternation of labor and rest diminishes the
+waste of life. The benign process of repair cannot go on, to any
+extent, during strenuous labor, but by interposing frequent though
+brief periods of rest, we lessen the amount of exhaustion, refresh the
+jaded nerves, and the remaining labor is more easily endured.
+
+285. Benefits of Rest. There is too little repose in our American
+nature and in our modes of life. A sense of fatigue is the mute appeal
+of the body for a brief respite from labor, and the appeal should, if
+possible, be heeded. If this appeal be not met, the future exertion
+exhausts far more than if the body had been even slightly refreshed. If
+the appeal be met, the brief mid-labor rest eases the friction of toil,
+and the remaining labor is more easily borne. The feeling that a
+five-minute rest is so much time lost is quite an error. It is a gain
+of physical strength, of mental vigor, and of the total amount of work
+done.
+
+The merchant burdened with the cares of business life, the soldier on
+the long march, the ambitious student over-anxious to win success in
+his studies, the housewife wearied with her many hours of exacting
+toil, each would make the task lighter, and would get through it with
+less loss of vital force, by occasionally devoting a few minutes to
+absolute rest in entire relaxation of the strained muscles and
+overtaxed nerves.
+
+286. The Sabbath as a Day of Physiological Rest. The divine institution
+of a Sabbath of rest, one day in seven, is based upon the highest needs
+of our nature. Rest, to be most effective, should alternate in brief
+periods with labor.
+
+It is sound physiology, as well as good morals and manners, to cease
+from the usual routine of six days of mental or physical work, and rest
+both the mind and the body on the seventh. Those who have succeeded
+best in what they have undertaken, and who have enjoyed sound health
+during a long and useful life, have studiously lived up to the mandates
+of this great physiological law. It is by no means certain that the
+tendency nowadays to devote the Sabbath to long trips on the bicycle,
+tiresome excursions by land and sea, and sight-seeing generally,
+affords that real rest from a physiological point of view which nature
+demands after six days of well-directed manual or mental labor.
+
+287. The Significance of Sleep as a Periodical Rest. Of the chief
+characteristics of all living beings none is so significant as their
+periodicity. Plants as well as animals exhibit this periodic character.
+Thus plants have their annual as well as daily periods of activity and
+inactivity. Hibernating animals pass the winter in a condition of
+unconsciousness only to have their functions of activity restored in
+early spring. Human beings also present many instances of a periodic
+character, many of which have been mentioned in the preceding pages.
+Thus we have learned that the heart has its regular alternating periods
+of work and rest. After every expiration from the lungs there is a
+pause before the next inspiration begins.
+
+Now sleep is just another manifestation of this periodic and
+physiological rest by which Nature refreshes us. It is during the
+periods of sleep that the energy expended in the activities of the
+waking hours is mainly renewed. In our waking moments the mind is kept
+incessantly active by the demands made on it through the senses. There
+is a never-ceasing expenditure of energy and a consequent waste which
+must be repaired. A time soon comes when the brain cells fail to
+respond to the demand, and sleep must supervene. However resolutely we
+may resist this demand, Nature, in her relentless way, puts us to
+sleep, no matter what objects are brought before the mind with a view
+to retain its attention.[41]
+
+288. Effect of Sleep upon the Bodily Functions. In all the higher
+animals, the central nervous system enters once at least in the
+twenty-four hours into the condition of rest which we call sleep.
+Inasmuch as the most important modifications of this function are
+observed in connection with the cerebro-spinal system, a brief
+consideration of the subject is properly studied in this chapter. In
+Chapter IV. we learned that repose was as necessary as exercise to
+maintain muscular vigor. So after prolonged mental exertion, or in fact
+any effort which involves an expenditure of what is often called
+nerve-force, sleep becomes a necessity. The need of such a rest is
+self-evident, and the loss of it is a common cause of the impairment of
+health. While we are awake and active, the waste of the body exceeds
+the repair; but when asleep, the waste is diminished, and the cells are
+more actively rebuilding the structure for to-morrow’s labor. The
+organic functions, such as are under the direct control of the
+sympathetic nervous system,—circulation, respiration, and
+digestion,—are diminished in activity during sleep. The pulsations of
+the heart and the respiratory movements are less frequent, and the
+circulation is slower. The bodily temperature is reduced, and the
+cerebral circulation is diminished. The eyes are turned upward and
+inward, and the pupils are contracted.
+
+The senses do not all fall to sleep at once, but drop off successively:
+first the sight, then the smell, the taste, the hearing and lastly the
+touch. The sleep ended, they awake in an inverse order, touch, hearing,
+taste, smell, and sight.
+
+289. The Amount of Sleep Required. No precise rule can be laid down
+concerning the amount of sleep required. It varies with age,
+occupation, temperament, and climate to a certain extent. An infant
+whose main business it is to grow spends the greater part of its time
+in sound sleep. Adults of average age who work hard with their hands or
+brain, under perfectly normal physiological conditions, usually require
+at least eight hours of sleep. Some need less, but few require more.
+Personal peculiarities, and perhaps habit to a great extent, exert a
+marked influence. Some of the greatest men, as Napoleon I., have been
+very sparing sleepers. Throughout his long and active life, Frederick
+the Great never slept more than five or six hours in the twenty-four.
+On the other hand, some of the busiest brain-workers who lived to old
+age, as William Cullen Bryant and Henry Ward Beecher, required and took
+care to secure at least eight or nine hours of sound sleep every night.
+
+In old age, less sleep is usually required than in adult life, while
+the aged may pass much of their time in sleep. In fact, each person
+learns by experience how much sleep is necessary. There is no one thing
+which more unfits one for prolonged mental or physical effort than the
+loss of natural rest.
+
+290. Practical Rules about Sleep. Children should not be played with
+boisterously just before the bedtime hour, nor their minds excited with
+weird goblin stories, or a long time may pass before the wide-open eyes
+and agitated nerves become composed to slumber. Disturbed or
+insufficient sleep is a potent factor towards producing a fretful,
+irritable child.
+
+At all ages the last hour before sleep should, if possible, be spent
+quietly, to smooth the way towards sound and refreshing rest. The sleep
+induced by medicine is very often troubled and unsatisfactory.
+Medicines of this sort should not be taken except on the advice of a
+physician.
+
+While a hearty meal should not usually be taken just before bedtime, it
+is not well to go to bed with a sense of positive faintness and hunger.
+Rather, one should take a very light lunch of quite simple food as a
+support for the next eight hours.
+
+Illustration: Fig. 122.—Trunk of the Left Pneumogastric.
+(Showing its distribution by its branches and ganglia to the larynx,
+pharynx, heart, lungs, and other parts.)
+
+It is better, as a rule, not to engage in severe study during the hours
+just before bedtime. Neither body nor mind being at its best after the
+fatigues of the day, study at that time wears upon the system more, and
+the progress is less than at earlier hours. One hour of morning or day
+study is worth a much longer time late at night. It is, therefore, an
+economy both of time and of nerve force to use the day hours and the
+early evening for study.
+
+The so-called “cat naps” should never be made to serve as a substitute
+for a full night’s sleep. They are largely a matter of habit, and are
+detrimental to some as well as beneficial to others. Late hours are
+usually associated with exposure, excitement, and various other drains
+upon the nerve force, and hence are injurious.
+
+It is better to sleep on one or other side than on the back. The head
+should be somewhat raised, and a mattress is better than a feather bed.
+The bedclothes should be sufficient, but not too heavy. Light tends to
+prevent sleep, as do loud or abrupt sounds, but monotonous sounds aid
+it.
+
+291. Alcohol and the Brain. The unfortunate effects which alcoholic
+drinks produce upon the brain and nervous system differ from the
+destructive results upon other parts of the body in this respect, that
+elsewhere the consequences are usually both less speedy and less
+obvious. The stomach, the liver, and even the heart may endure for a
+while the trespass of the narcotic poison, and not betray the invasion.
+But the nervous system cannot, like them, suffer in silence.
+
+In the other parts of the body the victim may (to a certain extent)
+conceal from others the suffering of which he himself is painfully
+conscious. But the tortured brain instantly reveals the calamity and
+the shame, while the only one who may not fully realize it is the
+victim himself. Besides this, the injuries inflicted upon other organs
+affect only the body, but here they drag down the mind, ruin the
+morals, and destroy the character.
+
+The brain is indeed the most important organ of the body, as it
+presides over all the others. It is the lofty seat of power and
+authority. Here the king is on his throne. But if, by this malignant
+adversary, the king himself be dethroned, his whole empire falls to
+ruins.
+
+292. How Alcohol Injures the Brain. The brain, the nerve centers, and
+the nerves are all made up of nerve pulp, the softest and most delicate
+tissue in the whole bodily structure. Wherever this fragile material
+occurs in our bodies,—in the skull, the spine, the trunk, or the
+limbs,—the all-wise Architect has carefully protected it from violence,
+for a rough touch would injure it, or even tender pressure would
+disturb its function.
+
+It is a further indication of the supreme importance of the brain, that
+about one-fifth of the entire blood of the body is furnished to it.
+Manifestly, then, this vital organ must be tenderly cared for. It must
+indeed be well nourished, and therefore the blood sent to it must be
+highly nutrient, capable of supplying oxygen freely. This condition is
+essential to successful brain action. But intoxicants bring to it blood
+surcharged with a poisonous liquid, and bearing only a limited supply
+of oxygen.
+
+Another condition of a healthy brain is that the supply of blood to it
+shall be equable and uniform. But under the influence of strong drink,
+the blood pours into the paralyzed arteries a surging tide that floods
+the head, and hinders and may destroy the use of the brain and the
+senses. Still another requirement is that whatever is introduced into
+the cerebral tissues, having first passed through the stomach walls and
+thence into the blood, shall be bland, not irritating. But in the brain
+of the inebriate are found not only the distinct odor but the actual
+presence of alcohol. Thus we plainly see how all these three vital
+conditions of a healthy brain are grossly violated by the use of
+intoxicants.
+
+“I think there is a great deal of injury being done by the use of
+alcohol in what is supposed by the consumer to be a most moderate
+quantity, to persons who are not in the least intemperate, and to
+people supposed to be fairly well. It leads to degeneration of the
+tissues; it damages the health; it injures the intellect. Short of
+drunkenness, that is, in those effects of it which stop short of
+drunkenness, I should say from my experience that alcohol is the most
+destructive agent we are aware of in this country.”—Sir William Gull,
+the most eminent English physician of our time.
+
+
+293. Why the Brain Suffers from the Alcoholic Habit. We do not find
+that the alcoholic habit has produced in the brain the same coarse
+injuries that we see in other organs, as in the stomach, the liver, or
+the heart. Nor should we expect to find them; for so delicate and so
+sensitive is the structure of this organ, that a very slight injury
+here goes a great way,—a disturbance may be overwhelming to the brain
+that would be only a trifle to some of the less delicate organs.
+
+Alcohol has different degrees of affinity for different organs of the
+body, but much the strongest for the cerebral tissues. Therefore the
+brain feels more keenly the presence of alcohol than does any other
+organ. Almost the moment that the poison is brought into the stomach,
+the nerves send up the alarm that an invading foe has come. At once
+there follows a shock to the brain, and very soon its paralyzed
+blood-vessels are distended with the rush of blood. This first effect
+is, in a certain sense, exhilarating, and from this arousing influence
+alcohol has been erroneously considered a stimulant; but the falsity of
+this view is pointed out elsewhere in this book.
+
+294. Alcohol, the Enemy of Brain Work. The healthy brain contains a
+larger proportion of water than does any other organ. Now alcohol, with
+its intense affinity for water, absorbs it from the brain, and thus
+condenses and hardens its structure. One of the important elements of
+the brain is its albumen; this also is contracted by alcohol. The nerve
+cells and fibers gradually become shriveled and their activity is
+lowered, the elasticity of the arteries is diminished, the membranes
+enveloping the brain are thickened, and thus all proper brain nutrition
+is impaired. The entire organ is slowly hardened, and becomes unfitted
+for the proper performance of its delicate duties. In brief, alcohol in
+any and every form is the enemy of successful and long-continued brain
+work.
+
+Illustration: Fig. 123.—Nerve Trunks of the Right Arm.
+
+
+295. Other Physical Results of Intoxicants. What are some of the
+physical results observed? First, we note the failure of the vaso-motor
+nerves to maintain the proper tone of the blood-vessels, as in the
+turgid face and the congested cornea of the eye. Again, we observe the
+loss of muscular control, as is shown by the drop of the lower lip, the
+thickened speech, and the wandering eye. The spinal cord, too, is often
+affected and becomes unable to respond to the demand for reflex action,
+as appears from the trembling hands, the staggering legs, the swaying
+body, and the general muscular uncertainty. All these are varied
+results of the temporary paralysis of the great nerve centers.
+
+Besides, the sensibility of the nerves is deadened. The inebriate may
+seize a hot iron and hardly know it, or wound his hand painfully and
+never feel the injury. The numbness is not of the skin, but of the
+brain, for the drunken man may be frozen or burned to death without
+pain. The senses, too, are invaded and dulled. Double vision is
+produced, the eyes not being so controlled as to bring the image upon
+corresponding points of the retina.
+
+296. Diseases Produced by Alcohol. The diseases that follow in the
+train of the alcoholic habit are numerous and fatal. It lays its
+paralyzing hand upon the brain itself, and soon permanently destroys
+the integrity of its functions. In some the paralysis is local only,
+perhaps in one of the limbs, or on one side of the body; in others
+there is a general muscular failure. The vitality of the nerve centers
+is so thoroughly impaired that general paralysis often ensues. A
+condition of insomnia, or sleeplessness, often follows, or when sleep
+does come, it is in fragments, and is far from refreshing to the jaded
+body.
+
+In time follows another and a terrible disease known as _delirium
+tremens_; and this may occur in those who claim to be only moderate
+drinkers, rarely if ever intoxicated. It accompanies an utter breakdown
+of the nervous system. Here reason is for the time dethroned, while at
+some times wild and frantic, or at others a low, mumbling delirium
+occurs, with a marked trembling from terror and exhaustion.
+
+There is still another depth of ruin in this downward course, and that
+is _insanity_. In fact, every instance of complete intoxication is a
+case of temporary insanity, that is, of mental unsoundness with loss of
+self-control. Permanent insanity may be one of the last results of
+intemperance. Alcoholism sends to our insane asylums a large proportion
+of their inmates, as ample records testify.
+
+297. Mental and Moral Ruin Caused by Alcoholism. Alcoholism, the evil
+prince of destroyers, also hastens to lay waste man’s mental and moral
+nature. Just as the inebriate’s senses, sight, hearing, and touch, fail
+to report correctly of the outer world, so the mind fails to preside
+properly over the inner realm. Mental perceptions are dulled. The
+stupefied faculties can hardly be aroused by any appeal. Memory fails.
+Thus the man is disqualified for any responsible labor. No railroad
+company, no mercantile house, will employ any one addicted to drinking.
+The mind of the drunkard is unable to retain a single chain of thought,
+but gropes about with idle questionings. The intellect is debased.
+Judgment is impossible, for the unstable mind cannot think, compare, or
+decide.
+
+The once active power of the will is prostrate, and the victim can no
+longer resist the feeblest impulse of temptation. The grand faculty of
+self-control is lost; and as a result, the baser instincts of our lower
+nature are now uppermost; greed and appetite rule unrestrained.
+
+But the moral power is also dragged down to the lowest depths. All the
+finer sensibilities of character are deadened; all pride of personal
+appearance, all nice self-respect and proper regard for the good
+opinion of others, every sense of decorum, and at last every pretence
+of decency. Dignity of behavior yields to clownish silliness, and the
+person lately respected is now an object of pity and loathing. The
+great central convictions of right and wrong now find no place in his
+nature; conscience is quenched, dishonesty prevails. This is true both
+as to the solemn promises, which prove mere idle tales, and also as to
+property, for he resorts to any form of fraud or theft to feed the
+consuming craving for more drink.
+
+298. Evil Results of Alcoholism Inherited. But the calamity does not
+end with the offender. It may follow down the family line, and fasten
+itself upon the unoffending children. These often inherit the craving
+for drink, with the enfeebled nature that cannot resist the craving,
+and so are almost inevitably doomed to follow the appalling career of
+their parents before them.
+
+Nor does this cruel taint stop with the children. Even their
+descendants are often prone to become perverse. As one example, careful
+statistics of a large number of families, more than two hundred
+descended from drunkards, show that a very large portion of them gave
+undoubted proof of well-marked degeneration. This was plain in the
+unusual prevalence of infant mortality, convulsions, epilepsy,
+hysteria, fatal brain diseases, and actual imbecility.[42]
+
+It is found that the long-continued habitual user of alcoholic drinks,
+the man who is never intoxicated, but who will tell you that he has
+drunk whiskey all his life without being harmed by it, is more likely
+to transmit the evil effects to his children than the man who has
+occasional drunken outbreaks with intervals of perfect sobriety
+between. By his frequently repeated small drams he keeps his tissues
+constantly “alcoholized” to such an extent that they are seldom free
+from some of the more or less serious consequences. His children are
+born with organisms which have received a certain bias from which they
+cannot escape; they are freighted with some heredity, or predisposition
+to particular forms of degeneration, to some morbid tendency, to an
+enfeebled constitution, to various defective conditions of mind and
+body. Let the children of such a man attempt to imitate the drinking
+habits of the father and they quickly show the effects. Moderate
+drinking brings them down.
+
+Among other consequences of an alcoholic inheritance which have been
+traced by careful observers are: Morbid changes in the nerve centers,
+consisting of inflammatory lesions, which vary according to the age in
+which they occur; alcoholic insanity; congenital malformations; and a
+much higher infant death rate, owing to lack of vitality, than among
+the children of normal parents.
+
+Where the alcoholic inheritance does not manifest itself in some
+definite disease or disorder, it can still be traced in the limitations
+to be found in the drinking man’s descendants. They seem to reach a
+level from which they cannot ascend, and where from slight causes they
+deteriorate. The parents, by alcoholic poisoning, have lowered the race
+stock of vitality beyond the power of ascent or possibility to rise
+above or overcome the downward tendency.
+
+Of course these effects of alcoholics differ widely according to the
+degree of intoxication. Yet, we must not forget that the real nature of
+inebriety is always the same. The end differs from the beginning only
+in degree. He who would avoid a life of sorrow, disgrace, and shame
+must carefully shun the very first glass of intoxicants.
+
+299. Opium. Opium is a gum-like substance, the dried juice of the
+unripe capsule of the poppy. The head of the plant is slit with fine
+incisions, and the exuding white juice is collected. When it thickens
+and is moulded in mass, it becomes dark with exposure. _Morphine_, a
+white powder, is a very condensed form of opiate; _laudanum_, an
+alcoholic solution of marked strength; and _paregoric_, a diluted and
+flavored form of alcoholic tincture.
+
+300. Poisonous Effects of Opium. Some persons are drawn into the use of
+opium, solely for its narcotic and intoxicating influence. Every early
+consent to its use involves a lurking pledge to repeat the poison, till
+soon strong cords of the intoxicant appetite bind the now yielding
+victim.
+
+Opium thus used lays its benumbing hand upon the brain, the mind is
+befogged, thought and reasoning are impossible. The secretions of the
+stomach are suspended, digestion is notably impaired, and the gastric
+nerves are so deadened that the body is rendered unconscious of its
+needs.
+
+The moral sense is extinguished, persons once honest resort to fraud
+and theft, if need be, to obtain the drug, till at last health,
+character, and life itself all become a pitiful wreck.
+
+301. The Use of Opium in Patent Medicines. Some forms of this drug are
+found in nearly all the various patent medicines so freely sold as a
+cure-all for every mortal disease. Opiates are an ingredient in
+different forms and proportions in almost all the soothing-syrups,
+cough medicines, cholera mixtures, pain cures, and consumption
+remedies, so widely and unwisely used. Many deaths occur from the use
+of these opiates, which at first seem indeed to bring relief, but
+really only smother the prominent symptoms, while the disease goes on
+unchecked, and at last proves fatal.
+
+These patent medicines may appear to help one person and be fraught
+with danger to the next, so widely different are the effects of opiates
+upon different ages and temperaments. But it is upon children that
+these fatal results oftenest fall. Beyond doubt, thousands of children
+have been soothed and soothed out of existence.[43]
+
+302. The Victim of the Opium Habit. Occasionally persons convalescing
+from serious sickness where anodynes were taken, unwisely cling to them
+long after recovery. Other persons, jaded with business or with worry,
+and unable to sleep, unwisely resort to some narcotic mixture to
+procure rest. In these and other similar cases, the use of opiates is
+always most pernicious. The amount must be steadily increased to obtain
+the elusive repose, and at best the phantom too often escapes.
+
+Even if the desired sleep is procured, it is hardly the coveted rest,
+but a troubled and dreamy slumber, leaving in the morning the body
+quite unrefreshed, the head aching, the mouth dry, and the stomach
+utterly devoid of appetite. But far worse than even this condition is
+the slavish yielding to the habit, which soon becomes a bondage in
+which life is shorn of its wholesome pleasures, and existence becomes a
+burden.
+
+303. Chloral. There are other preparations which have become
+instruments of direful and often fatal injury. Chloral is a powerful
+drug that has been much resorted to by unthinking persons to produce
+sleep. Others, yielding to a morbid reluctance to face the problems of
+life, have timidly sought shelter in artificial forgetfulness. To all
+such it is a false friend. Its promises are treason. It degrades the
+mind, tramples upon the morals, overpowers the will, and destroys life
+itself.
+
+304. Cocaine, Ether, Chloroform, and Other Powerful Drugs. Another
+dangerous drug is Cocaine. Ether and chloroform, those priceless
+blessings to the human race if properly controlled, become instruments
+of death when carelessly trifled with. Persons who have been accustomed
+to inhale the vapor in slight whiffs for neuralgia or similar troubles
+do so at imminent hazard, especially if lying down. They are liable to
+become slowly unconscious, and so to continue the inhalation till life
+is ended.
+
+There is still another class of drugs often carelessly used, whose
+effect, while less directly serious than those mentioned, is yet far
+from harmless. These drugs, which have sprung into popular use since
+the disease _la grippe_ began its dreaded career, include
+_phenacetine_, _antipyrine_, _antifebrine_, and other similar
+preparations. These drugs have been seized by the public and taken
+freely and carelessly for all sorts and conditions of trouble. The
+random arrow may yet do serious harm. These drugs, products of coal-oil
+distillation, are powerful depressants. They lower the action of the
+heart and the tone of the nervous centers. Thus the effect of their
+continued use is to so diminish the vigor of the system as to aggravate
+the very disorder they are taken to relieve.
+
+305. Effect of Tobacco on the Nervous System. That the use of tobacco
+produces a pernicious effect upon the nervous system is obvious from
+the indignant protest of the entire body against it when it is first
+used. Its poisonous character is amply shown by the distressing
+prostration and pallor, the dizziness and faintness, with extreme
+nausea and vomiting, which follow its employment by a novice.
+
+The morbid effects of tobacco upon the nervous system of those who
+habitually use it are shown in the irregular and enfeebled action of
+the heart, with dizziness and muscular tremor. The character of the
+pulse shows plainly the unsteady heart action, caused by partial
+paralysis of the nerves controlling this organ. Old, habitual smokers
+often show an irritable and nervous condition, with sleeplessness, due
+doubtless to lack of proper brain nutrition.
+
+All these results tend to prove that tobacco is really a nerve poison,
+and there is reason to suspect that the nervous breakdown of many men
+in mature life is often due to the continued use of this depressing
+agent. This is shown more especially in men of sedentary life and
+habits, as men of active habits and out-door life, experience less of
+the ill effects of tobacco.
+
+Few, if any, habitual users of tobacco ever themselves approve of it.
+They all regret the habit, and many lament they are so enslaved to it
+that they cannot throw it off. They very rarely advise any one to
+follow their example.
+
+306. Effects of Tobacco on the Mind. With this continuously depressing
+effect of tobacco upon the brain, it is little wonder that the mind may
+become enfeebled and lose its capacity for study or successful effort.
+This is especially true of the young. The growth and development of the
+brain having been once retarded, the youthful user of tobacco
+(especially the foolish cigarette-smoker) has established a permanent
+drawback which may hamper him all his life.
+
+The young man addicted to the use of tobacco is often through its use
+retarded in his career by mental languor or weakening will power, and
+by mental incapacity. The keenness of mental perception is dulled, and
+the ability to seize and hold an abstract thought is impaired. True,
+these effects are not sharply obvious, as it would be impossible to
+contrast the present condition of any one person with what it might
+have been. But the comparison of large numbers conveys an instructive
+lesson. Scholars who start well and give promise of a good future fail
+by the way. The honors of the great schools, academies, and colleges
+are very largely taken by the tobacco abstainers. This is proved by the
+result of repeated and extensive comparisons of the advanced classes in
+a great number of institutions in this country and in Europe. So true
+is this that any young man who aspires to a noble career should bid
+farewell either to his honorable ambition or to his tobacco, for the
+two very rarely travel together. Consequently our military and naval
+academies and very many seminaries and colleges prohibit the use of
+tobacco by their students. For the same reasons the laws of many states
+very properly forbid the sale to boys of tobacco, and especially of
+cigarettes.
+
+307. Effect of Tobacco upon Character. Nor does tobacco spare the
+morals. The tobacco-user is apt to manifest a selfish disregard of the
+courtesies due to others. He brings to the presence of others a
+repulsive breath, and clothing tainted with offensive odors. He poisons
+the atmosphere that others must inhale, and disputes their rights to
+breathe a pure, untainted air. The free use of tobacco by young people
+dulls the acuteness of the moral senses, often leads to prevarication
+and deceit in the indulgence, and is apt to draw one downward to bad
+associates. It is not the speed but the direction that tells on the
+future character and destiny of young men.
+
+Additional Experiments.
+
+Experiment 132. _To illustrate the cooperation of certain parts of the
+body._ Tickle the inside of the nose with a feather. This does not
+interfere with the muscles of breathing, but they come to the help of
+the irritated part, and provoke sneezing to clear and protect the nose.
+
+Experiment 133. Pretend to aim a blow at a person’s eye. Even if he is
+warned beforehand, the lids will close in spite of his effort to
+prevent them.
+
+Experiment 134. _To illustrate how sensations are referred to the ends
+of the nerves_. Strike the elbow end of the ulna against anything hard
+(commonly called “hitting the crazy bone”) where the ulna nerve is
+exposed, and the little finger and the ring finger will tingle and
+become numb.
+
+Experiment 135. _To show that every nerve is independent of any other._
+Press two fingers closely together. Let the point of the finest needle
+be carried ever so lightly across from one finger to another, and we
+can easily tell just when the needle leaves one finger and touches the
+other.
+
+Experiment 136. _To paralyze a nerve temporarily_. Throw one arm over
+the sharp edge of a chair-back, bringing the inner edge of the biceps
+directly over the edge of the chair. Press deep and hard for a few
+minutes. The deep pressure on the nerve of the arm will put the arm
+“asleep,” causing numbness and tingling. The leg and foot often “get
+asleep” by deep pressure on the nerves of the thigh.
+
+Experiment 137. Press the ulnar nerve at the elbow, the prickling
+sensation is referred to the skin on the ulnar side of the hand.
+
+Experiment 138. Dip the elbow in ice-cold water; at first one feels the
+sensation of cold, owing to the effect on the cutaneous nerve-endings.
+Afterwards, when the trunk of the ulnar nerve is affected, pain is felt
+in the skin of the ulnar side of the hand, where the nerve terminates.
+
+
+
+
+Chapter XI.
+The Special Senses.
+
+
+308. The Special Senses. In man certain special organs are set apart
+the particular duty of which is to give information of the nature of
+the relations which he sustains to the great world of things, and of
+which he is but a mere speck. The special senses are the avenues by
+which we obtain this information as to our bodily condition, the world
+around us, and the manner in which it affects us.
+
+Animals high in the scale are affected in so many different ways, and
+by so many agencies, that a subdivision of labor becomes necessary that
+the sense avenues may be rigidly guarded. One person alone may be a
+sufficient watch on the deck of a sloop, but an ocean steamer needs a
+score or more on guard, each with his special duty and at his own post.
+Or the senses are like a series of disciplined picket-guards, along the
+outposts of the mind, to take note of events, and to report to
+headquarters any information which may be within the range of their
+duty.
+
+Thus it is that we are provided with a number of special senses, by
+means of which information is supplied regarding outward forces and
+objects. These are touch, taste, smell, seeing, and hearing, to which
+may be added the muscular sense and a sense of temperature.
+
+309. General Sensations. The body, as we have learned, is made up of a
+great number of complicated organs, each doing its own part of the
+general work required for the life and vigor of the human organism.
+These organs should all work in harmony for the good of the whole. We
+must have some means of knowing whether this harmony is maintained, and
+of receiving timely warning if any organ fails to do its particular
+duty.
+
+Such information is supplied by the common or general sensations. Thus
+we have a feeling of hunger or thirst indicating the need of food, and
+a feeling of discomfort when imperfectly clad, informing us of the need
+of more clothing.
+
+To these may be added the sensation of pain, tickling, itching, and so
+on, the needs of which arise from the complicated structure of the
+human body. The great majority of sensations result from some stimulus
+or outward agency; and yet some sensations, such as those of faintness,
+restlessness, and fatigue seem to spring up within us in some
+mysterious way, without any obvious cause.
+
+310. Essentials of a Sense Organ. Certain essentials are necessary for
+a sensation. First, there is a special structure adapted to a
+particular kind of influence. Thus the ear is formed specially for
+being stimulated by the waves of sound, while the eye is not influenced
+by sound, but responds to the action of light. These special structures
+are called terminal organs.
+
+Again, a nerve proceeds from the special structure, which is in direct
+communication with nerve cells in the brain at the region of
+consciousness. This last point is important to remember, for if on some
+account the impression is arrested in the connecting nerve, no
+sensation will result. Thus a man whose spine has been injured may not
+feel a severe pinch on either leg. The impression may be quite
+sufficient to stimulate a nerve center in a healthy cord, so as to
+produce a marked reflex act, but he has no sensation, because the
+injury has prevented the impression from being carried up the cord to
+the higher centers in the brain.
+
+311. The Condition of Sensation. It is thus evident that while an
+impression may be made upon a terminal organ, it cannot strictly be
+called a sensation until the person becomes conscious of it. The
+consciousness of an impression is, therefore, the essential element of
+a sensation.
+
+It follows that sensation may be prevented in various ways. In the
+sense of sight, for example, one person may be blind because the
+terminal organ, or eye, is defective or diseased. Another may have
+perfect eyes and yet have no sight, because a tumor presses on the
+nerve between the eye and the brain. In this case, the impression fails
+because of the break in the communication. Once more, the eye may be
+perfect and the nerve connection unbroken, and yet the person cannot
+see, because the center in the brain itself is injured from disease or
+accident, and cannot receive the impression.
+
+312. The Functions of the Brain Center in the Perception of an
+Impression. Sensation is really the result of a change which occurs in
+a nerve center in the brain, and yet we refer impressions to the
+various terminal organs. Thus, when the skin is pinched, the sensation
+is referred to the skin, although the perception is in the brain. We
+may think it is the eyes that see objects; in reality, it is only the
+brain that takes note of them.
+
+This is largely the result of education and habit. From a blow on the
+head one sees flashes of light as vividly as if torches actually dance
+before the eyes. Impressions have reached the seeing-center in the
+brain from irritation of the optic nerve, producing the same effect as
+real lights would cause. In this case, however, knowing the cause of
+the colors, the person is able to correct the erroneous conclusion.
+
+As a result of a depraved condition of blood, the seeing-center itself
+may be unduly stimulated, and a person may see objects which appear
+real. Thus in an attack of delirium tremens, the victim of alcoholic
+poisoning sees horrible and fantastic creatures. The diseased brain
+refers them as usual to the external world; hence they appear real. As
+the sufferer’s judgment is warped by the alcoholic liquor, he cannot
+correct the impressions, and is therefore deceived by them.
+
+313. Organs of Special Sense. The organs of special sense, the means by
+which we are brought into relation with surrounding objects, are
+usually classed as five in number. They are sometimes fancifully called
+“the five gateways of knowledge”—the skin, the organ of touch; the
+tongue, of taste; the nose, of smell; the eye, of sight; and the ear,
+of hearing.
+
+Illustration: Fig. 124.—Magnified View of a Papilla of the Skin, with a
+Touch Corpuscle.
+
+
+314. The Organ of Touch. The organ of touch, or tactile sensibility, is
+the most widely extended of all the special senses, and perhaps the
+simplest. It is certainly the most precise and certain in its results.
+It is this sense to which we instinctively appeal to escape from the
+illusions into which the other senses may mislead us. It has its seat
+in the skin all over the body, and in the mucous membrane of the
+nostrils. All parts of the body, however, do not have this sense in an
+equal degree.
+
+In Chapter IX. we learned that the superficial layers of the skin
+covers and dips in between the papillæ. We also learned that these
+papillæ are richly provided with blood-vessels and sensory nerve fibers
+(sec. 234). Now these nerve fibers terminate in a peculiar way in those
+parts of the body which are endowed with a very delicate sense of
+touch. In every papilla are oval-shaped bodies about 1/300 of an inch
+long, around which the nerve fibers wind, and which they finally enter.
+These are called touch-bodies, or tactile corpuscles, and are found in
+great numbers on the feet and toes, and more scantily in other places,
+as on the edges of the eyelids.
+
+Again, many of the nerve fibers terminate in corpuscles, the largest
+about 1/20 of an inch long, called Pacinian corpuscles. These are most
+numerous in the palm of the hand and the sole of the foot. In the
+papillæ of the red border of the lips the nerves end in capsules which
+enclose one or more fibers, and are called end-bulbs.
+
+The great majority of the nerve fibers which supply the skin do not end
+in such well-defined organs. They oftener divide into exceedingly
+delicate filaments, the terminations of which are traced with the
+greatest difficulty.
+
+315. The Sense of Touch. Touch is a sensation of contact referred to
+the surface of the body. It includes three things,—the sense of
+contact, the sense of pressure, and the sense of heat and cold.
+
+The sense of contact is the most important element in touch. By it we
+learn of the form, size, and other properties of objects, as their
+smoothness and hardness. As we all know, the sense of touch varies in
+different parts of the skin. It is most acute where the outer skin is
+thinnest. The tips of the fingers, the edges of the lips, and the tip
+of the tongue are the most sensitive parts.
+
+Even the nails, the teeth, and the hair have the sense of touch in a
+slight degree. When the scarf skin is removed, the part is not more
+sensitive to sense of contact. In fact, direct contact with the
+unprotected true skin occasions pain, which effectually masks the
+feeling of touch. The sense of touch is capable of education, and is
+generally developed to an extraordinary degree in persons who are
+deprived of some other special sense, as sight or hearing. We read of
+the famous blind sculptor who was said to model excellent likenesses,
+guided entirely by the sense of touch. An eminent authority on botany
+was a blind man, able to distinguish rare plants by the fingers, and by
+the tip of the tongue. The blind learn to read with facility by passing
+their fingers over raised letters of a coarse type. It is impossible to
+contemplate, even for a moment, the prominence assigned to the sense of
+touch in the physical organism, without being impressed with the
+manifestations of design—the work of an all-wise Creator.
+
+316. Muscular Sense; Sense of Temperature; Pain. When a heavy object is
+laid upon certain parts of the body, it produces a sensation of
+pressure. By it we are enabled to estimate differences of weight. If an
+attempt be made to raise this object, it offers resistance which the
+muscles must overcome. This is known as the muscular sense. It depends
+on sensory nerves originating in the muscles and carrying impressions
+from them to the nerve centers.
+
+The skin also judges, to a certain extent, of heat and cold. These
+sensations can be felt only by the skin. Direct irritation of a nerve
+does not give rise to them. Thus, the exposed pulp of a diseased tooth,
+when irritated by cold fluids, gives rise to pain, and not to a
+sensation of temperature. Various portions of the body have different
+degrees of sensibility in this respect. The hand will bear a degree of
+heat which would cause pain to some other parts of the body. Then,
+again, the sensibility of the outer skin seems to affect the
+sensibility to heat, for parts with a thin skin can bear less heat than
+portions with a thick cuticle.
+
+Experiment 139. _To illustrate how the sense of touch is a matter of
+habit or education_. Shut both eyes, and let a friend run the tips of
+your fingers first lightly over a hard plane surface; then press hard,
+then lightly again, and the surface will seem to be concave.
+
+Experiment 140. Cross the middle over the index finger, roll a small
+marble between the fingers; one has a distinct impression of two
+marbles. Cross the fingers in the same way, and rub them against the
+point of the nose. A similar illusion is experienced.
+
+Experiment 141. _To test the sense of locality_. Ask a person to shut
+his eyes, touch some part of his body lightly with the point of a pin,
+and ask him to indicate the part touched.
+    As to the general temperature, this sense is relative and is much
+    modified by habit, for what is cold to an inhabitant of the torrid
+    zone would be warm to one accustomed to a very cold climate.
+    Pain is an excessive stimulation of the sensory nerves, and in it
+    all finer sensations are lost. Thus, when a piece of hot iron burns
+    the hand, the sensation is the same as when the iron is very cold,
+    and extreme cold feels like intense heat.
+
+317. The Organ of Taste. The sense of taste is located chiefly in the
+tongue, but may also be referred even to the regions of the fauces.
+Taste, like touch, consists in a particular mode of nerve termination.
+
+The tongue is a muscular organ covered with mucous membrane, and is
+richly supplied with blood-vessels and nerves. By its complicated
+movements it is an important factor in chewing, in swallowing, and in
+articulate speech. The surface of the tongue is covered with irregular
+projections, called papillæ,—fine hair-like processes, about 1/12 of an
+inch high. Interspersed with these are the fungiform papillæ. These are
+shaped something like a mushroom, and may often be detected by their
+bright red points when the rest of the tongue is coated.
+
+Towards the root of the tongue is another kind of papillæ, the
+circumvallate, eight to fifteen in number, arranged in the form of the
+letter V, with the apex directed backwards. These are so called because
+they consist of a fungiform papilla surrounded by a fold of mucous
+membrane, presenting the appearance of being walled around.
+
+In many of the fungiform and most of the circumvallate papillæ are
+peculiar structures called taste buds or taste goblets. These exist in
+great numbers, and are believed to be connected with nerve fibers.
+These taste buds are readily excited by savory substances, and transmit
+the impression along the connected nerve.
+
+The tongue is supplied with sensory fibers by branches from the fifth
+and eighth pairs of cranial nerves. The former confers taste on the
+front part of the tongue, and the latter on the back part. Branches of
+the latter also pass to the soft palate and neighboring parts and
+confer taste on them. The motor nerve of the tongue is the ninth pair,
+the hypoglossal.
+
+Illustration: Fig. 125.—The Tongue.
+
+
+A,  epiglottis;
+  B, glands at the base of tongue;
+  C, tonsil;
+  D, median circumvallate papilla,
+  E, circumvallate papillæ;
+  F, filiform papillæ;
+  H, furrows on border of the tongue;
+  K, fungiform papillæ.
+
+
+318. The Sense of Taste. The sense of taste is excited by stimulation
+of the mucous membrane of the tongue and of the palate, affecting the
+ends of the nerve fibers. Taste is most acute in or near the
+circumvallate papillæ. The middle of the tongue is scarcely sensitive
+to taste, while the edges and the tip are, as a rule, highly sensitive.
+
+Certain conditions are necessary that the sense of taste may be
+exercised. First, the substance to be tasted must be in _solution_, or
+be soluble in the fluids of the mouth. Insoluble substances are
+tasteless. If we touch our tongue to a piece of rock crystal, there is
+a sensation of contact or cold, but no sense of taste. On the other
+hand, when we bring the tongue in contact with a piece of rock salt, we
+experience the sensations of contact, coolness, and saline taste.
+
+Again, the mucous membrane of the mouth must be _moist_. When the mouth
+is dry, and receives substances not already in solution, there is no
+saliva ready to dissolve them; hence, they are tasteless. This absence
+of taste is common with the parched mouth during a fever.
+
+The tongue assists in bringing the food in contact with the nerves, by
+pressing it against the roof of the mouth and the soft palate, and thus
+is produced the fullest sense of taste.
+
+319. Physiological Conditions of Taste. The tongue is the seat of
+sensations which are quite unlike each other. Thus, besides the sense
+of taste, there is the sensation of touch, pressure, heat and cold,
+burning or acrid feelings, and those produced by the application of the
+tongue to an interrupted electric current. These are distinct
+sensations, due to some chemical action excited probably in the touch
+cells, although the true tastes may be excited by causes not strictly
+chemical. Thus a smart tap on the tongue may excite the sensation of
+taste.
+
+In the majority of persons the back of the tongue is most sensitive to
+bitters, and the tip to sweets. Saline matters are perceived most
+distinctly at the tip, and acid substances at the sides. The nerves of
+taste are sensitive in an extraordinary degree to some articles of food
+and certain drugs. For example, the taste of the various preparations
+of quinine, peppermint, and wild cherry is got rid of with difficulty.
+
+Like the other special senses, that of taste may become fatigued. The
+repeated tasting of one substance rapidly deadens the sensibility,
+probably by over-stimulation. Some savors so impress the nerves of
+taste that others fail to make any impression. This principle is used
+to make disagreeable medicine somewhat tasteless. Thus a few cloves, or
+grains of coffee, or a bit of pepper, eaten before a dose of castor
+oil, renders it less nauseous.
+
+Flavor is something more than taste. It is in reality a mixed
+sensation, in which smell and taste are both concerned, as is shown by
+the common observation that one suffering from a cold in the head,
+which blunts his sense of smell, loses the proper flavor of his food.
+So if a person be blindfolded, and the nose pinched, he will be unable
+to distinguish between an apple and an onion, if one be rubbed on the
+tongue after the other. As soon as the nostrils are opened the
+difference is at once perceived.
+
+Experiment 142. Put a drop of vinegar on a friend’s tongue, or on your
+own. Notice how the papillæ of the tongue start up.
+
+Experiment 143. Rub different parts of the tongue with the pointed end
+of a piece of salt or gum-aloes, to show that the _back_ of the tongue
+is most sensitive to salt and bitter substances.
+
+Experiment 144. Repeat the same with some sweet or sour substances, to
+show that the _edges_ of the tongue are the most sensitive to these
+substances.
+
+Experiment 145. We often fail to distinguish between the sense of taste
+and that of smell. Chew some pure, roasted coffee, and it seems to have
+a distinct taste. Pinch the nose hard, and there is little taste.
+Coffee has a powerful odor, but only a feeble taste. The same is true
+of garlic, onions, and various spices.
+
+Experiment 146. Light helps the sense of taste. Shut the eyes, and
+palatable foods taste insipid. Pinch the nose, close the eyes, and see
+how palatable one half of a teaspoonful of cod-liver oil becomes.
+
+Experiment 147. Close the nostrils, shut the eyes, and attempt to
+distinguish by taste alone between a slice of an apple and one of a
+potato.
+
+320. Modifications of the Sense of Taste. Taste is modified to a great
+extent by habit, education, and other circumstances. Articles of food
+that are unpleasant in early life often become agreeable in later
+years. There is occasionally a craving, especially with people of a
+peculiar nervous organization, for certain unnatural articles (as chalk
+and laundry starch) which are eaten without the least repugnance.
+Again, the most savory dishes may excite disgust, while the simplest
+articles may have a delicious flavor to one long deprived of them. The
+taste for certain articles is certainly acquired. This is often true of
+raw tomatoes, olives, and especially of tobacco.
+
+The organs of taste and smell may be regarded as necessary accessories
+of the general apparatus of nutrition, and are, therefore, more or less
+essential to the maintenance of animal life. While taste and smell are
+generally maintained until the close of life, sight and hearing are
+often impaired by time, and may be altogether destroyed, the other
+vital functions remaining unimpaired.
+
+321. Effect of Tobacco and Alcohol upon Taste. It would be remarkable
+if tobacco should fail to injure the sense of taste. The effect
+produced upon the tender papillæ of the tongue by the nicotine-loaded
+juices and the acrid smoke tends to impair the delicate sensibility of
+the entire surface. The keen appreciation of fine flavors is destroyed.
+The once clear and enjoyable tastes of simple objects become dull and
+vapid; thus highly spiced and seasoned articles of food are in demand,
+and then follows continued indigestion, with all its suffering.
+
+Again, the burning, almost caustic effect of the stronger alcoholic
+drinks, and the acrid pungency of tobacco smoke, are disastrous to the
+finer perceptions of both taste and odors.
+
+322. Smell. The sense of smell is lodged in the delicate membrane which
+lines the nasal cavities. The floor, sides, and roof of these cavities
+are formed by certain bones of the cranium and the face. Man, in common
+with all air-breathing animals, has two nasal cavities. They
+communicate with the outer air by two nostrils opening in front, while
+two other passages open into the pharynx behind.
+
+To increase the area of the air passages, the two light, spongy
+turbinated bones, one on each side, form narrow, winding channels. The
+mucous membrane, with the branches of the olfactory nerve, lines the
+dividing wall and the inner surfaces of these winding passages. Below
+all these bones the lower turbinated bones may be said to divide the
+olfactory chamber above from the ordinary air passages.
+
+Illustration: Fig. 126.—Distribution of Nerves over the Interior of the
+Nostrils. (Outer wall.)
+
+
+A,  branches of the nerves of smell—olfactory nerve, or ganglion;
+  B, nerves of common sensation to the nostril;
+  E, F, G, nerves to the, palate springing from a ganglion at C;
+  H, vidian nerve, from which branches
+  D, I, and J spring to be distributed to the nostrils.
+
+The nerves which supply the nasal mucous membrane are derived from the
+branches of the fifth and the first pair of cranial nerves,—the
+olfactory. The latter, however, are the nerves of smell proper, and are
+spread out in a kind of thick brush of minute nerve filaments. It is in
+the mucous membrane of the uppermost part of the cavity of the nostril
+that the nerve endings of smell proper reside. The other nerves which
+supply the nostrils are those of common sensation (sec. 271).
+
+323. The Sense of Smell. The sense of smell is excited by the contact
+of odorous particles contained in the air, with the fibers of the
+olfactory nerves, which are distributed over the delicate surface of
+the upper parts of the nasal cavities. In the lower parts are the
+endings of nerves of ordinary sensation. These latter nerves may be
+irritated by some substance like ammonia, resulting in a powerfully
+pungent sensation. This is not a true sensation of smell, but merely an
+irritation of a nerve of general sensation.
+
+In ordinary quiet breathing, the air simply flows along the lower nasal
+passages into the pharynx, scarcely entering the olfactory chamber at
+all. This is the reason why, when we wish to perceive a faint odor, we
+sniff up the air sharply. By so doing, the air which is forcibly drawn
+into the nostrils passes up even into the higher olfactory chamber,
+where some of the floating particles of the odorous material come into
+contact with the nerves of smell.
+
+One of the most essential conditions of the sense of smell is that the
+nasal passages be kept well bathed in the fluid secreted by the lining
+membrane. At the beginning of a cold in the head, this membrane becomes
+dry and swollen, thus preventing the entrance of air into the upper
+chamber, deadening the sensibility of the nerves, and thus the sense of
+smell is greatly diminished.
+
+The delicacy of the sense of smell varies greatly in different
+individuals and in different animals. It is generally more acute in
+savage races. It is highly developed in both the carnivora and the
+herbivora. Many animals are more highly endowed with this sense than is
+man. The dog, for example, appears to depend on the sense of smell
+almost as much as on sight. It is well known, also, that fishes have a
+sense of smell. Fragments of bait thrown into the water soon attract
+them to a fishing ground, and at depths which little or no light can
+penetrate. Deer, wild horses, and antelopes probably surpass all other
+animals in having a vivid sense of smell.
+
+Smell has been defined as “taste at a distance,” and it is obvious that
+these two senses not only form a natural group, but are clearly
+associated in their physical action, especially in connection with the
+perception of the flavor of food. The sense of odor gives us
+information as to the quality of food and drink, and more especially as
+to the quality of the air we breathe. Taste is at the gateway of the
+alimentary canal, while smell acts as the sentinel of the respiratory
+tract. Just as taste and flavor influence nutrition by affecting the
+digestive process, so the agreeable odors about us, even those of the
+perfumes, play an important part in the economy of life.
+
+324. The Sense of Sight. The sight is well regarded as the highest and
+the most perfect of all our senses. It plays so common and so
+beneficent a part in the animal economy that we scarcely appreciate
+this marvelous gift. Sight is essential not only to the simplest
+matters of daily comfort and necessity, but is also of prime importance
+in the culture of the mind and in the higher forms of pleasure. It
+opens to us the widest and the most varied range of observation and
+enjoyment. The pleasures and advantages it affords, directly and
+indirectly, have neither cessation nor bounds.
+
+Apart from its uses, the eye itself is an interesting and instructive
+object of study. It presents beyond comparison the most beautiful
+example of design and artistic workmanship to be found in the bodily
+structure. It is the watchful sentinel and investigator of the external
+world. Unlike the senses of taste and smell we seem, by the sense of
+vision, to become aware of the existence of objects which are entirely
+apart from us, and which have no direct or material link connecting
+them with our bodies. And yet we are told that in vision the eye is
+affected by something which is as material as any substance we taste or
+smell.
+
+Note. “The higher intelligence of man is intimately associated with the
+perfection of the eye. Crystalline in its transparency, sensitive in
+receptivity, delicate in its adjustments, quick in its motions, the eye
+is a fitting servant for the eager soul, and, at times, the truest
+interpreter between man and man of the spirit’s inmost workings. The
+rainbow’s vivid hues and the pallor of the lily, the fair creations of
+art and the glance of mutual affection, all are pictured in its
+translucent depths, and transformed and glorified by the mind within.
+Banish vision, and the material universe shrinks for us to that which
+we may touch; sight alone sets us free to pierce the limitless abyss of
+space.”—M’Kendrick and Snodgrass’s _Physiology of the Senses_.
+
+Physicists tell us that this material, known as the _luminiferous
+ether_, permeates the universe, and by its vibrations transmits
+movements which affect the eye, giving rise to the sensation of light,
+and the perception of even the most distant objects. Our eyes are so
+constructed as to respond to the vibrations of this medium for the
+transmission of light.
+
+325. The Eye. The eye, the outer instrument of vision, is a most
+beautiful and ingenious machine. All its parts are arranged with such a
+delicate adjustment to one another, and such an exquisite adaptation of
+every part to the great object of the whole, that the eye is properly
+regarded as one of the wonders of nature.
+
+The eyeball is nearly spherical in shape, but is slightly elongated
+from before backwards. The front part is clear and transparent, and
+bulges somewhat prominently to allow the entrance of the rays of light.
+The eye rests in a bowl-shaped socket, called the orbit, formed by
+parts of various bones of the head and face. The margins of this cavity
+are formed of strong bone which can withstand heavy blows. The socket
+is padded with loose, fatty tissue, and certain membranes, which serve
+as a soft and yielding bed in which the eyeball can rest and move
+without injury. In a severe sickness this fatty tissue is absorbed, and
+this fact explains the sunken appearance of the eyes.
+
+The orbit is pierced through its posterior surface by an opening
+through which the nerve of sight, the optic, passes to the eyeball. We
+may think of the optic nerve holding the eyeball much as the stem holds
+the apple. It is the function of this most important nerve to transmit
+retinal impressions to the seat of consciousness in the brain, where
+they are interpreted.
+
+The eye is bathed with a watery fluid, and protected by the eyelids and
+the eyebrows; it is moved in various directions, by muscles, all of
+which will soon be described.
+
+Illustration: Fig. 127.—Section of the Human Eye.
+
+
+326. The Coats of the Eyeball. The eyeball proper is elastic but firm,
+and is composed of three coats, or layers, each of which performs
+important functions. These coats are the sclerotic, the choroid, and
+the retina.
+
+The sclerotic coat is the outside layer and enclosing membrane of the
+eyeball. It is a tough, fibrous coat for the protection and maintenance
+of the shape of the eye. It is white and glistening in appearance, and
+is in part visible, to which the phrase, “the white of the eye,” is
+applied. To this coat, which serves as a kind of framework for the eye,
+are attached the muscles which move the eyeball. In front of the globe,
+the sclerotic passes into a transparent circular portion forming a
+window through which one can see into the interior. This is the cornea.
+
+The cornea, a clear, transparent, circular disk, fits into the
+sclerotic, somewhat as the crystal fits into the metallic case of a
+watch, forming a covering for its dial. It projects from the general
+contour of the eyeball, not unlike a rounded bay-window, and is often
+spoken of as the “window of the eye.”
+
+Lining the inner surface of the sclerotic is the second coat, the
+choroid. It is dark in color and fragile in structure, and is made up
+almost entirely of blood-vessels and nerves. As the choroid approaches
+the front part of the eyeball, its parts become folded upon themselves
+into a series of ridges, called ciliary processes. These folds
+gradually become larger, and at last merge into the ciliary or
+accommodation muscle of the eye. The circular space thus left in front
+by the termination of the choroid is occupied by the iris, a thin,
+circular curtain, suspended in the aqueous humor behind the cornea and
+in front of the crystalline lens. In its center is a round opening for
+the admission of light.
+
+This is the pupil, which appears as if it were a black spot. The back
+of the iris is lined with dark pigment, and as the coloring matter is
+more or less abundant, we may have a variety of colors. This pigment
+layer and that of the choroid and retina absorb the light entering the
+eye, so that little is reflected.
+
+The pupil appears black, just as the open doorway to a dark closet
+seems black. The margin of the iris is firmly connected with the
+eyeball all round, at the junction of the sclerotic and the cornea.
+
+327. The Retina. The third and innermost coat of the eyeball is the
+retina. This is the perceptive coat, without which it would be
+impossible to see, and upon which the images of external objects are
+received. It lines nearly the whole of the inner surface of the
+posterior chamber, resting on the inner surface of the choroid. It is
+with the retina, therefore, that the vitreous humor is in contact.
+
+The retina is a very thin, delicate membrane. Although very thin, it is
+made up of ten distinct layers, and is so complicated in structure that
+not even a general description will be attempted in this book. It does
+not extend quite to the front limits of the posterior chamber, but
+stops short in a scalloped border, a little behind the ciliary
+processes. This is the nerve coat of the eye, and forms the terminal
+organ of vision. It is really an expansion of the ultimate fibers of
+the optic nerve, by means of which impressions are sent to the brain.
+
+The retina contains curious structures which can be seen only with the
+aid of the microscope. For instance, a layer near the choroid is made
+up of nerve cells arranged in innumerable cylinders called “rods and
+cones,” and packed together not unlike the seeds of a sunflower. These
+rods and cones are to be regarded as the peculiar modes of termination
+of the nerve filaments of the eye, just as the taste buds are the modes
+of termination of the nerve of taste in the tongue, and just as the
+touch corpuscles are the terminations of the nerves in the skin.
+
+Experiment 148. Close one eye and look steadily at the small a in the
+figure below. The other letters will also be visible at the same time.
+If now the page be brought slowly nearer to the eye while the eye is
+kept steadily looking at the small a, the large A will disappear at a
+certain point, reappearing when the book is brought still nearer.
+
+Illustration:
+
+On the reappearance of the A it will be noted that it comes into view
+from the inner side, the x being seen before it. If now we move the
+book towards its original place, the A will again disappear, coming
+again into view from the outer side when the o is seen before it.
+
+328. Inner Structure of the Eye. Let us imagine an eyeball divided
+through the middle from above downwards. Let us now start in front and
+observe its parts (Fig. 127). We come first to the cornea, which has
+just been described. The iris forms a sort of vertical partition,
+dividing the cavity of the eyeball into two chambers.
+
+Illustration: Fig. 128.—Diagram illustrating the Manner in which the
+Image of an Object is brought to a Focus on the Retina.
+
+The anterior chamber occupies the space between the cornea and the
+iris, and is filled with a thin, watery fluid called the aqueous humor.
+
+The portion behind the iris forms the posterior chamber, and contains
+the crystalline lens and a transparent, jelly-like fluid, the vitreous
+humor. This fluid is never renewed, and its loss is popularly described
+by the phrase, “when the eye runs out.”
+
+Experiment 149. The retina is not sensitive where the optic nerve
+enters the eyeball. This is called the “blind spot.” Put two
+ink-bottles about two feet apart, on a table covered with white paper.
+Close the left eye, and fix the right steadily on the left-hand
+inkstand, gradually varying the distance from the eye to the
+ink-bottle. At a certain distance the right-hand bottle will disappear;
+but nearer or farther than that, it will be plainly seen.
+
+The vitreous humor fills about four-fifths of the eyeball and prevents
+it from falling into a shapeless mass. It also serves to hold the
+choroid and the retina in position, and to maintain the proper
+relations of the inner structures of the eye.
+
+The iris consists of a framework of connective tissue, the surface of
+which is lined by cells containing pigment, which gives color to the
+eye.
+
+Bundles of involuntary muscular fibers are found in the substance of
+the iris. Some are arranged in a ring round the margin of the pupil;
+others radiate from it like the spokes of a wheel. When the circular
+fibers contract, the pupil is made smaller, but if these fibers relax,
+the radiating fibers cause the pupil to dilate more or less widely.
+
+329. The Crystalline Lens. Just behind the pupil and close to the iris
+is a semi-solid, double-convex body, called the crystalline lens. It is
+shaped like a magnifying glass, convex
+
+Illustration: Fig. 129.—Diagram showing the Change in the Lens during
+Accommodation.
+
+On the right the lens is arranged for distant vision, the ciliary
+muscle is relaxed and the ligament D is tense, so flattening by its
+compression the front of the lens C; on the left the muscle A is
+acting, and this relaxes the ligament and allows the lens B to become
+more convex, and so fitted for the vision of near objects]
+
+on each side, but with the posterior surface more convex than the
+anterior. In health it is perfectly clear and transparent, and highly
+elastic. When the lens becomes opaque, from change in old age, or from
+ulcers or wounds, we have the disease known as _cataract_.
+
+The lens is not placed loosely in the eyeball, but is enclosed in a
+transparent and elastic capsule suspended throughout its circumference
+by a ligament called the suspensory ligament. This ligament not only
+retains the lens in place, but is capable of altering its shape. In
+ordinary conditions of the eye, this ligament is kept tense so that the
+front part of the lens is flattened somewhat by the pressure on it.
+
+All around the edge, where the cornea, sclerotic, and choroid meet, is
+a ring of involuntary muscular fibers, forming the ciliary muscle. When
+these fibers contract, they draw forwards the attachment of the
+suspensory ligament of the lens, the pressure of which on the lens is
+consequently diminished. The elasticity of the lens causes it at once
+to bulge forwards, and it becomes more convex.
+
+The ciliary muscle is thus known as the muscle of accommodation,
+because it has the power to accommodate the eye to near and distant
+objects. In this respect it corresponds in its use to the adjusting
+screw in the opera-glass and the microscope.
+
+330. The Eye Compared to the Photographic Camera. As an optical
+instrument, the eye may be aptly compared, in many particulars, to the
+photographic camera. The latter, of course, is much simpler in
+structure. The eyelid forms the cap, which being removed, the light
+from the object streams through the eye and passes across the dark
+chamber to the retina behind, which corresponds to the sensitive plate
+of the camera. The transparent structures through which the rays of
+light pass represent the lenses. To prevent any reflected light from
+striking the plate and interfering with the sharpness of the picture,
+the interior of the photographic camera box is darkened. The pigmented
+layer of the choroid coat represents this blackened lining.
+
+In the camera, the artist uses a thumb-screw to bring to a focus on the
+sensitive plate the rays of light coming from objects at different
+distances. Thus the lens of the camera may be moved nearer to or
+farther from the object. In order to obtain clear images, the same
+result must be accomplished by the eye. When the eye is focused for
+near objects, those at a distance are blurred, and when focused for
+distant objects, those near at hand are indistinct. Now, in the eye
+there is no arrangement to alter the position of the lenses, as in the
+camera, but the same result is obtained by what is called
+“accommodation.”
+
+Again, every camera has an arrangement of diaphragms regulating the
+amount of light. This is a rude contrivance compared with the iris,
+which by means of its muscular fibers can in a moment alter the size of
+the pupil, thus serving a similar purpose.
+
+Illustration: Fig. 130.—Illustrating the manner in which the Image of
+an Object is brought to a Focus in a Photographer’s Camera.
+
+
+331. The Refractive Media of the Eye. The eye is a closed chamber into
+which no light can pass but through the cornea. All the rays that enter
+the eye must also pass through the crystalline lens, which brings them
+to a focus, as any ordinary lens would do.
+
+Now, if the media through which the light from an object passes to
+reach the retina were all of the same density as the air, and were also
+plane surfaces, an impression would be produced, but the image would
+not be distinct. The action of the lens is aided by several refractive
+media in the eye. These media are the cornea, the aqueous humor, and
+the vitreous humor. By reason of their shape and density these media
+refract the rays of light, and bring them to a focus upon the retina,
+thus aiding in producing a sharp and distinct image of the object. Each
+point of the image being the focus or meeting-place of a vast number of
+rays coming from the corresponding point of the object is sufficiently
+bright to stimulate the retina to action.[44]
+
+Thus, the moment rays of light enter the eye they are bent out of their
+course. By the action of the crystalline lens, aided by the refractive
+media, the rays of light that are parallel when they fall upon the
+normal eye are brought to a focus on the retina.
+
+If the entire optical apparatus of the eye were rigid and immovable,
+one of three things would be necessary, in order to obtain a clear
+image of an object; for only parallel rays (that is, rays coming from
+objects distant about thirty feet or more), are brought to a focus in
+the average normal eye, unless some change is brought about in the
+refractive media. First, the posterior wall of the eye must be moved
+further back, or the lens would have to be capable of movement, or
+there must be some way of increasing the focusing power of the lens. In
+the eye it is the convexity of the lens that is altered so that the eye
+is capable of adjusting itself to different distances.[45]
+
+Illustration: Fig. 131.—The Actual Size of the Test-Type, which should
+be seen by the Normal Eye at a Distance of Twenty Feet.
+
+
+332. The More Common Defects of Vision. The eye may be free from
+disease and perfectly sound, and yet vision be indistinct, because the
+rays of light are not accurately brought to a focus on the retina. “Old
+sight,” known as presbyopia, is a common defect of vision in advancing
+years. This is a partial loss of the power to accommodate the eye to
+different distances. This defect is caused by an increase in the
+density of the crystalline lens, and an accompanying diminution in the
+ability to change its form. The far point of vision is not changed, but
+the near point is removed so far from the eye, that small objects are
+no longer visible.
+
+Illustration: Fig. 132.—Diagram illustrating the Hypermetropic
+(far-sighted) Eye.
+
+The image P′ of a point P falls behind the retina in the unaccommodated
+eye. By means of a convex lens it may be focused on the retina without
+accommodation (dotted lines). (To save space P is placed much too near
+the eye.)
+
+Hence, when a person about forty-five years of age complains of dim
+light, poor print, and tired eyes, the time has come to seek the advice
+of an optician. A convex lens may be needed to aid the failing power to
+increase the convexity of the lens, and to assist it in bringing the
+divergent rays of light to a focus.
+
+In “long sight,” or hypermetropia both the near and far point of vision
+are concerned, and there is no distinct vision at any distance without
+a strain. It is a defect in the focus, dependent upon the form of the
+eyes, and exists in childhood. The axis of the eyeball is too short,
+and the focus falls beyond the retina, which is too near the cornea. In
+childhood this strain may pass unnoticed, but, sooner or later it
+manifests itself by a sense of fatigue, dizziness, and a blurred and
+indistinct vision. The remedy is in the use of convex glasses to
+converge parallel rays of light before they enter the eye. The muscles
+of accommodation are thus relieved of their extra work.
+
+“Short sight,” known as myopia, is one of the commonest defects of
+vision. In this defect the axis of the eye, or the distance between the
+cornea and the retina, is too long and the rays of light are brought to
+a focus in front of the retina. The tendency to short-sightedness
+exists in many cases at birth, and is largely hereditary. It is
+alarmingly common with those who make a severe demand upon the eyes.
+During childhood there is a marked increase of near-sightedness. The
+results of imprudence and abuse, in matters of eyesight, are so
+disastrous, especially during school life, that the question of short
+sight becomes one of paramount importance.
+
+Experiment 150. With a hand-mirror reflect the sunlight on a white
+wall. Look steadily at the spot for a full minute, and then let the
+mirror suddenly be removed. The “complementary” color—a dark spot—will
+appear.
+
+Experiment 151. _To show that impressions made upon the retina do not
+disappear at once_. Look steadily at a bright light for a moment or
+two, and then turn away suddenly, or shut the eyes. A gleam of light
+will be seen for a second or two.
+    Look steadily at a well-lighted window for a few seconds, and then
+    turn the eyes suddenly to a darkened wall. The window frame may be
+    plainly seen for a moment.
+    Glance at the sun for a moment, close the eyes and the image of the
+    sun may be seen for a few seconds.
+
+Experiment 152. Take a round piece of white cardboard the size of a
+saucer, and paint it in alternate rings of red and yellow,—two primary
+colors. Thrust a pin through the center and rotate it rapidly. The eye
+perceives neither color, but orange,—the secondary color.
+
+Experiment 153. To note the shadows cast upon the retina by opaque
+matters in the vitreous humor (popularly known as floating specks, or
+gossamer threads), look through a small pin-hole in a card at a bright
+light covered by a ground-glass shade.
+
+Experiment 154. _To illustrate accommodation_. Standing near a source
+of light, close one eye, hold up both forefingers not quite in a line,
+keeping one finger about six or seven inches from the other eye, and
+the other forefinger about sixteen to eighteen inches from the eye.
+Look at the _near_ finger; a distinct image is obtained of it, while
+the far one is blurred or indistinct. Look at the far image; it becomes
+distinct, while the near one becomes blurred. Observe that in
+accommodating for the near object, one is conscious of a distinct
+effort.
+
+In many cases near-sightedness becomes a serious matter and demands
+skillful advice and careful treatment. To remedy this defect, something
+must be done to throw farther back the rays proceeding from an object
+so that they will come to a focus exactly on the retina. This is done
+by means of concave glasses, properly adjusted to meet the conditions
+of the eyes. The selection of suitable glasses calls for great care, as
+much harm may be done by using glasses not properly fitted to the eye.
+
+Illustration: Fig. 133.—Diagram illustrating the Myopic (near-sighted)
+Eye.
+
+The image P′ of a distant object P falls in front of the retina even
+without accommodation. By means of a concave lens (L) the image may be
+made to fall on the retina (dotted lines). (To save space P is placed
+much too near the eye).
+
+There is an optical condition of the eye known as astigmatism, in which
+the cornea is usually at fault. In this defect of vision the curvature
+of the cornea is greater in one meridian than in another. As a result
+the rays from an object are not all brought to the same focus. Objects
+appear distorted or are seen with unequal clearness. Glasses of a
+peculiar shape are required to counteract this defect.
+
+333. The Movements of the Eyes. In order that our eyes may be efficient
+instruments of vision, it is necessary that they have the power of
+moving independently of the head. The mechanical arrangement by which
+the eyeballs are moved in different directions is quite simple. It is
+done by six little muscles, arranged in three pairs, which, with one
+exception, originate in the back of the cavity in which the eye rests.
+Four of these muscles run a straight course and are called the _recti_.
+The remaining two muscles bend in their course and are called
+_oblique_. The coördination of these tiny muscles is marvellous in its
+delicacy, accuracy, and rapidity of action.
+
+When, for any cause, the coördination is faulty, “cross eye,”
+technically called strabismus, is produced. Thus, if the internal
+rectus is shortened, the eye turns in; if the external rectus, the eye
+turns out, producing what is known as “wall eye.” It is thus evident
+that the beauty of the internal mechanism of the eye has its fitting
+complement in the precision, delicacy, and range of movement conferred
+upon it by its muscles.
+
+334. The Eyelids and Eyebrows. The eye is adorned and protected by the
+eyelids, eyelashes, and eyebrows.
+
+Illustration: Fig. 134.—Muscles of the Eyeball.
+
+
+A,  attachment of tendon connected with the three recti muscles;
+  B, external rectus, divided and turned downward, to expose the
+  internus rectus;
+  C, inferior rectus;
+  D, internal rectus;
+  E, superior rectus;
+  F, superior oblique;
+  H, pulley and reflected portion of the superior oblique;
+  K, inferior oblique; L, levator palpebri superioris;
+  M, middle portion of the same muscle (L);
+  N, optic nerve.
+
+The eyelids, two in number, move over the front of the eyeball and
+protect it from injury. They consist of folds of skin lined with mucous
+membrane, kept in shape by a layer of fibrous material. Near the inner
+surface of the lids is a row of twenty or thirty glands, known as the
+_Meibomian glands_, which open on the free edges of each lid. When one
+of these glands is blocked by its own secretion, the inflammation which
+results is called a “sty.”
+
+The inner lining membrane of the eyelids is known as the conjunctiva;
+it is richly supplied with blood-vessels and nerves. After lining the
+lids it is reflected on to the eyeballs. It is this membrane which is
+occasionally inflamed from taking cold.
+
+The free edges of the lids are bordered with two or more rows of hairs
+called the eyelashes, which serve both for ornament and for use. They
+help to protect the eyes from dust, and to a certain extent to shade
+them. Their loss gives a peculiar, unsightly look to the face.
+
+The upper border of the orbit is provided with a fringe of short, stiff
+hairs, the eyebrows. They help to shade the eyes from excessive light,
+and to protect the eyelids from perspiration, which would otherwise
+cause serious discomfort.
+
+335. The Lacrymal Apparatus. Nature provides a special secretion, the
+tears, to moisten and protect the eye. The apparatus producing this
+secretion consists of the lacrymal or tear gland and lacrymal canals or
+tear passages (Fig. 136).
+
+Outside of the eyeball, in the loose, fatty tissue of the orbit, in the
+upper and outer corner is the lacrymal or tear gland. It is about the
+size of a small almond and from it lead several little canals which
+open on the inner surface of the upper lid. The fluid from the gland
+flows out by these openings over the eyeball, and is collected at the
+inner or nasal corner. Here in each lid is a little reddish elevation,
+or _lacrymal caruncle_, in which is an opening, communicating with a
+small canal in the lid which joins the lacrymal sac, lodged between the
+orbit and the bridge of the nose (Fig. 137).
+
+From this sac there passes a channel, the nasal duct, about one-half of
+an inch long, leading into the lower portion of the nostril. The fluid
+which has flowed over the eye is drained off by these canals into the
+nose. During sleep this secretion is much diminished. When the eyes are
+open the quantity is sufficient to moisten the eyeball, the excess
+being carried into the nose so gradually that the attention is not
+attracted to it.
+
+The lacrymal canals are at times blocked by inflammation of the nasal
+duct, and the fluid collects in the corners of the eyelids and
+overflows down the cheeks, producing much inconvenience. The lining
+membrane of the eyelids through these canals is continuous with that of
+the nostrils. Hence, when the lining membrane of the eye is red and
+swollen, as during a cold, the nasal passages are also irritated, and
+when the nasal membrane is inflamed, the irritation is apt to pass
+upwards and affect the eyelids.
+
+336. The Tears. The lacrymal or tear gland is under the control of the
+nervous system. Thus, if anything irritates the eyelids, the sensory
+nerves are stimulated and the impression is carried to the brain.
+Thence the nerve impulses travel to the lacrymal glands, leading to an
+increased flow of their secretion. The irritation of the sensory nerves
+in the nasal passages by smelling such substances as onions, or pungent
+salts, often causes a copious flow of tears.
+
+Illustration: Fig. 135.—Lacrymal Gland and Ducts.
+
+
+A lachrymal gland, the size of a small almond lodged in a shallow
+depression in the bones of the orbit;
+
+B, lachrymal ducts (usually seven), which form a row of openings into
+the conjunctival fold.
+
+Various mental emotions, as joy and grief, may produce similar results.
+In these cases the glands secrete the fluid in such quantities that it
+cannot escape by the lacrymal canals, and the excess rolls over the
+cheeks as tears. Excessive grief sometimes acts on the nerve centers in
+exactly the opposite manner, so that the activity of the glands is
+arrested and less fluid is secreted. This explains why some people do
+not shed tears in times of deep grief.
+
+Experiment 155. Gently turn the inner part of your lower eyelid down.
+Look in a mirror, and the small lacrymal point, or opening into the
+nasal duct, may be observed.
+
+337. Color-blindness. There is an abnormal condition of vision called
+color-blindness, in which the power of discrimination between different
+colors is impaired. Experiment shows that ninety-six out of every one
+hundred men agree as to the identity or the difference of color, while
+the remaining four show a defective perception of color.
+
+The first may be said to have _normal vision_; the second are called
+_color-blind_. It is a curious fact that ten times more men than women
+are color-blind.
+
+In its true sense, color-blindness is always congenital, often
+hereditary. This condition of abnormal vision is totally incurable. A
+person may be color-blind and not know it until the defect is
+accidentally revealed. The common form of defective color-vision is the
+inability to distinguish between _red_ and _green_. As green lights
+mean safety, and red lights danger, on railroads, on shipboard, and
+elsewhere, it becomes of paramount importance that no one who is
+color-blind should be employed in such service. Various tests are now
+required by statute law in many states to be used for the detection of
+such defects of vision among employees in certain occupations.
+
+338. School Life and the Eyesight. The eyes of children need more care
+than those of adults, because their eyes are still in the course of
+development. The eyes, like any other organ which is yet to attain its
+full growth, require more care in their use than one which has already
+reached its full size. They are peculiarly liable to be affected by
+improper or defective light. Hence the care of the eyes during school
+life is a matter of the most practical importance.
+
+In no matter of health can the teacher do a more distinct service than
+in looking after the eyesight of the pupils. Children suffering from
+defective vision are sometimes punished by teachers for supposed
+stupidity. Such pupils, as well as the deaf, are peculiarly sensitive
+to their defects. Every schoolroom should have plenty of light; it
+should come from either side or the rear, and should be regulated with
+suitable shades and curtains.
+
+Pupils should not be allowed to form the bad habit of reading with the
+book held close to the eyes. The long search on maps for obscure names
+printed in letters of bad and trying type should be discouraged.
+Straining the eyes in trying to read from slates and blackboards, in
+the last hour of the afternoon session, or in cloudy weather, may do a
+lifelong injury to the eyesight. Avoid the use, so far as possible,
+especially in a defective light, of text-books which are printed on
+battered type and worn plates.
+
+The seat and desk of each scholar should be carefully arranged to suit
+the eyesight, as well as the bones and muscles. Special pains should be
+taken with the near-sighted pupils, and those who return to school
+after an attack of scarlet fever, measles, or diphtheria.
+
+Experiment 156. _To test color-blindness._ On no account is the person
+being tested to be asked to name a color. In a large class of students
+one is pretty sure to find some who are more or less color-blind. The
+common defects are for red and green.
+
+Place worsteds on a white background in a good light. Select, as a test
+color, a skein of light green color, such as would be obtained by
+mixing a pure green with white. Ask the examinee to select and pick out
+from the heap all those skeins which appear to him to be of the same
+color, whether of lighter or darker shades. A color-blind person will
+select amongst others some of the confusion-colors, _e.g._, pink,
+yellow. A colored plate showing these should be hung up in the room.
+Any one who selects all the greens and no confusion-colors has normal
+color vision. If, however, one or more confusion-colors be selected,
+proceed as follows: select as a test color a skein of pale rose. If the
+person be red-blind, he will choose blue and violet; if green-blind,
+gray and green.
+
+Select a bright red skein. The red-blind will select green and brown;
+the green-blind picks out reds or lighter brown.
+
+339. Practical Hints on the Care of the Eyes. The eye is an exceedingly
+delicate and sensitive organ. While it is long-suffering, its endurance
+has a limit. Like all the other organs of the body, the eyes are better
+for moderate and rational use. More than any other organ they require
+attention to the general health, as the condition of the skin, exercise
+in the open air, good food, and proper habits of daily living.
+
+The tissues of the eyes are peculiarly sensitive to any general
+influence. Certain constitutional diseases, like rheumatism,
+lead-poisoning, diphtheria, and measles often affect the eyes. Special
+care should be taken with children’s eyes during and after an attack of
+measles and scarlet fever. The eyes of young infants should not be
+exposed to glaring lights or to the direct rays of the sun, as when
+taken out in baby carriages.
+
+Illustration: Fig. 136.—Showing the Relative Position of the Lacrymal
+Apparatus, the Eyeball, and the Eyelids.
+
+
+A,  lacrymal canals, with the minute orifices represented as two black
+dots (puncta lacrymalia) to the right;
+  B, tendon of the orbicularis palpebrarum muscle; apparently under B
+  is seen the lacrymal sac. The minute openings of the Meibomian glands
+  are seen on the free margins of the eyelids.
+
+Below A is seen a small conical elevation, with black dots (the
+lacrymal papilla or caruncle).
+
+Glasses should be worn when they are needed. A failure to do this
+ususally causes much unnecessary suffering. It is far from wise to
+postpone as long as possible the first use of glasses. The selection
+and proper fitting of glasses call for the combined skill of both the
+physician and the optician. Obstinate headaches are often caused by
+defective vision, and may disappear after discontinuing improper
+glasses.
+
+The habit of reading, in the cars or elsewhere, the daily paper and
+poorly printed books, with their blurred and indistinct type, is a
+severe strain on the accommodation apparatus of the eyes. It is a
+dangerous practice to read in bed at night, or while lying down in a
+darkened or shaded room. This is especially true during recovery from
+illness. The muscles of the eyes undergo excessive strain in
+accommodating themselves to the unnatural position. The battered type,
+wood-pulp paper, and poor presswork, now so commonly used in the cheap
+editions of books and periodicals, are often injurious to the eyesight.
+
+Reading-matter should not be held nearer to the eyes than is necessary
+to make the print appear perfectly sharp and distinct. No print should
+be read continuously that cannot be seen clearly at about eighteen
+inches. Those who read music are especially liable to strain the eyes,
+because exact vision is required to follow the notes. Persons who wear
+glasses for reading should be careful to use them while reading music,
+and good light is necessary to avoid any undue strain.
+
+After reading steadily for some time, the eyes should be rested by
+closing them a short period or by looking at some distant object, even
+if only for a few moments. The book, the sewing, and work generally,
+should be held as far from the eyes as is compatible with good vision.
+The natural tendency is to reverse this rule. We should never read,
+write, sew, stitch, or otherwise use the eyes when they smart or
+tingle, or when the sight is dim or blurred. The eyes are then tired
+and need a rest. Much injury may be done by reading in twilight, or by
+artificial light in the early morning, and by reading and working in
+badly lighted and ill-ventilated rooms.
+
+Good artificial light is much to be preferred to insufficient sunlight.
+The artificial light should be sufficiently bright and steady; a
+fickering light is always bad. Riding against a strong wind, especially
+on a bicycle, may prove hurtful, at least for eyes that are inclined to
+any kind of inflammation. The light reflected from snow is a common
+source of injury to the eyes. It is a wise caution in passing from a
+dark room to avoid looking immediately at the sun, an incandescent
+light, the glistening snow, or other bright objects.
+
+The eyes should never be rubbed, or the fingers thrust into them,[46]
+and much less when they are irritated by any foreign substance. The
+sooner the offending substance is removed the better.
+
+Illustration: Fig. 137.—Lacrymal Canals, Lacrymal Sac, and Nasal ducts,
+opened by their Anterior Portion.
+
+
+340. Effect of Alcohol upon the Eye. The earlier and slighter forms of
+injury done to the eye by the use of intoxicants are quite familiar:
+the watery condition of the eye and of the lids, and the red and
+bleared aspect of the organ. Both are the result of chronic
+inflammation, which crowds the blood into the vessels of the cornea,
+making them bloodshot and visible. The nerves controlling the
+circulation of the eye are partially paralyzed, and thus the relaxed
+vessels become distended.
+
+But more serious results ensue. Long use of intoxicants produces
+diseases of the retina, involving in many cases marked diminution of
+acuteness as well as quickness of vision, and at times distorted images
+upon the surface of the retina. In other instances, the congestion of
+the optic nerve is so serious as to involve a progressive wasting of
+that organ, producing at first a hazy dimness of vision which gradually
+becomes worse and worse, till total blindness may ensue.
+
+It is beyond question that a wide comparison of cases by careful
+observers proves that a large fraction of those who indulge in strong
+drink suffer from some form of disease of the eye.
+
+341. Effect of Tobacco upon Vision. Tobacco, in its distribution of
+evil effects, does not neglect the senses and especially the eye. A
+variety of vicious results is produced. The pungent smoke inflames the
+lids. The narcotic dilates the pupil, causing dimness and confusion of
+vision. A diseased condition occurs with severe pain in the eye
+followed by impaired vision.
+
+Oculists speak impressively of the ill effects of tobacco, and
+especially of cigarettes, upon the eyes of the young. They mention a
+well-known disease, tobacco blindness, usually beginning with
+color-blindness, and progressing occasionally with increasing dimness
+of vision to entire loss of sight.[47]
+
+342. The Sense of Hearing. The structure of the human ear is much more
+complicated than is generally supposed. It is an apparatus constructed
+to respond to the waves of sound. As a whole, it may be considered a
+peculiar form of nerve-ending.
+
+The external ear forms only a part of a most elaborate apparatus
+whereby sound waves may be transmitted inwards to the real organ of
+hearing. The really sensitive part of the ear, in which the auditory
+nerve ends, is buried for protection deep out of sight in the bones of
+the head; so deep that sounds cannot directly affect it. Some
+arrangement, therefore, is required for conducting the sounds inwards
+to this true organ.
+
+Illustration: Fig. 138.—The Pinna, or Auricle.
+
+In studying the structure of the ear, and how it is fitted to respond
+to sonorous vibrations, we may divide it into three parts: the
+sound-conducting part, known as the external ear, the middle ear, and
+the deeply placed nerve portion, the inner ear.
+
+343. The External Ear. The external ear consists of an expanded portion
+known as the pinna or _auricle_, and of a passage, the auditory canal
+or _meatus_, leading inwards from it. The surface of the auricle is
+convoluted to collect and transmit the vibrations of air by which sound
+is produced the auditory canal conducts these vibrations to the
+tympanic membrane. Many animals move the auricle in the direction of
+the sound. Thus the horse pricks up its ears when it hears a noise, the
+better to judge of the direction of sounds.[48]
+
+The external auditory meatus, the passage to the middle ear, is curved
+and is about an inch and a quarter long. Near its outer portion are a
+number of fine hairs slanting outwards to prevent the entrance of
+insects. Embedded in the deeper parts of the canal are glands which
+secrete the _cerumen_, or ear-wax, which keeps the canal moist, and
+helps to protect it against foreign bodies and insects. As the result
+of a cold, this wax may collect in sufficient quantities to block the
+passage, and to diminish to a considerable extent the power of hearing.
+
+344. The Middle Ear. At the inner end of the outer ear passage is the
+tympanum, known as “the drum of the ear.” It is a thin, oval membrane,
+stretched at an angle across the deep end of the passage, which it
+completely closes. The tympanum is thus a partition between the passage
+of the outer ear and the cavity of the middle ear. On its inner side is
+a small air chamber in the petrous portion of the temporal bone, called
+the cavity of the tympanum. Its bony walls are lined with mucous
+membrane similar to that lining the nose, mouth, and throat. On the
+inner wall of the tympanum are two openings, the round window, or
+_foramen rotundum_, and the oval window, or _foramen ovale_.
+
+The tympanic cavity communicates with the back part of the throat, by
+the Eustachian tube. This tube is about one and a half inches long and
+lined with mucous membrane similar to that of the tympanic chamber and
+the throat. This passage is usually closed, but is opened in the act of
+swallowing. In health there is no communication between the chamber of
+the middle ear and the outside, except by the Eustachian tube. Thus a
+throat cold, with redness and swelling of the mucous membrane, is
+usually accompanied with some degree of deafness, because the swelling
+may block the lumen of the tube, and thus prevent the free passage of
+air to and fro.
+
+Illustration: Fig. 139.—General View of the Organ of Hearing.
+
+
+A,  pinna;
+  B, cavity of the concha, showing the orifices of a great number of
+  sebaceous glands;
+  C, external auditory meatus;
+  D, membrana tympani;
+  F, incus;
+  H, malleus;
+  K, handle of malleus applied to the internal surface of the membrana
+  tympani;
+  L, tensor tympani muscle;
+  between M and K is the tympanic cavity;
+  N, Eustachian tube;
+  O, P, semicircular canals;
+  R, internal auditory canal;
+  S, large nerve given off from the facial ganglion;
+  T, facial and auditory nerves.
+
+A most curious feature of the ear is the chain of tiny movable bones
+which stretch across the cavity of the middle ear. They connect the
+tympanic membrane with the labyrinth, and serve to convey the
+vibrations communicated to the membrane across the cavity of the
+tympanum to the internal ear. These bones are three in number, and from
+their shape are called the malleus, or _hammer_, incus, or _anvil_; and
+stapes, or _stirrup_.
+
+The hammer is attached by its long handle to the inner surface of the
+drum of the ear. The round head is connected with the anvil by a
+movable joint, while the long projection of the anvil is similarly
+connected with the stirrup bone. The plate of the stirrup is fixed by a
+membrane into the oval window of the inner wall of the tympanic
+chamber.
+
+These little bones are connected with each other and the tympanum by
+ligaments and moved by three tiny muscles. Two are attached to the
+hammer, and tighten and relax the drum; the other is attached to the
+stirrup, and prevents it from being pushed too deeply into the oval
+window.
+
+Illustration: Fig. 140.—Ear-Bones. (Anterior View.)
+
+
+1, malleus, or hammer;
+  2, incus, or anvil;
+  3, stapes, or stirrup.
+
+
+345. The Internal Ear. This forms one of the most delicate and complex
+pieces of mechanism in the whole body. It is that portion of the organ
+which receives the impression of sound, and carries it directly to the
+seat of consciousness in the brain. We are then able to say that we
+hear.
+
+The internal ear, or bony labyrinth, consists of three distinct parts,
+or variously shaped chambers, hollowed out in the temporal bone,—the
+vestibule, the semicircular canals, and the cochlea, or snail’s shell.
+
+Illustration: Fig. 141.—A Cast of the External Auditory Canal.
+(Posterior view)
+
+The vestibule is the common cavity with which all the other portions of
+the labyrinth connect. It is an oval-shaped chamber, about ⅓ of an inch
+in diameter, occupying the middle part of the internal ear. It is on
+the inner side of the oval window, which was closed, as we have seen,
+by the stirrup bone. From one side of this vestibule, or central hall,
+the three semicircular canals pass off, and from the other side, the
+cochlea.
+
+The three semicircular canals, so called from their shape, are simply
+bony tubes about 1/20 of an inch in width, making a curve of about 1/4
+of an inch in diameter. They pass out from the vestibule, and after
+bending around somewhat like a hoop, they return again to the
+vestibule. Each bony canal contains within it a membranous canal, at
+the end of which it is dilated to form an _ampulla_.
+
+Experiment 157. _To vibrate the tympanic membrane and the little
+ear-bones._ Shut the mouth, and pinch the nose tightly. Try to force
+air through the nose. The air dilates the Eustachian tube, and is
+forced into the ear-drum. The distinct crackle, or clicking sound, is
+due to the movement of the ear-bones and the tympanic membrane.
+
+The cochlea, or snail’s shell, is another chamber hollowed out in the
+solid bone. It is coiled on itself somewhat like a snail’s shell. There
+is a central pillar, around which winds a long spiral canal. One
+passage from the cochlea opens directly into the vestibule; the other
+leads to the chamber of the middle ear, and is separated from it by the
+little round window already described.
+
+The cochlea contains thousands of the most minute cords, known as the
+fibers or _organ of Corti_.[49] Under the microscope they present the
+appearance of the keyboard of a piano. These fibers appear to vibrate
+in sympathy with the countless shades of sounds which daily penetrate
+the ear. From the hair-like processes on these tightly stretched
+fibers, auditory impulses appear to be transmitted to the brain.
+
+The tubes and chambers of the inner ear enclose and protect a delicate
+membranous sac of exactly the same shape as themselves. Between the
+bony walls of the passages and the membranous bag inside is a thin,
+clear fluid, the _perilymph_. The membranous bag itself contains a
+similar fluid, the _endolymph_. In this fluid are found some minute
+crystals of lime like tiny particles of sand, called _otoliths_, or
+ear-stones. Every movement of the fluid itself throws these grains from
+side to side.
+
+Illustration: Fig. 142.—Bony internal Ear of Right Side. (Magnified;
+the upper figure of the natural size.)
+
+
+A,  oval window (foramen ovale);
+  B, C, D, semicircular canals;
+  * represents the bulging part (ampulla) of each canal;
+  E, F, G cochlea, H, round window (foramen rotundum).
+
+The auditory nerve, or nerve of hearing, passes to the inner ear,
+through a passage in the solid bone of the skull. Its minute filaments
+spread at last over the inner walls of the membranous labyrinth in two
+branches,—one going to the vestibule and the ampullæ at the ends of the
+semicircular canals, the other leading to the cochlea.
+
+346. Mechanism of Hearing. Waves of sound reach the ear, and are
+directed by the concha to the external passage, at the end of which
+they reach the tympanic membrane. When the sound-waves beat upon this
+thin membrane, it is thrown into vibration, reproducing in its
+movements the character of the air-vibrations that have fallen upon it.
+
+Now the vibrations of the tympanic membrane are passed along the chain
+of bones attached to its inner surface and reach the stirrup bone. The
+stirrup now performs a to-and-fro movement at the oval window, passing
+the auditory impulse inwards to the internal ear.
+
+Every time the stirrup bone is pushed in and drawn out of the oval
+window, the watery fluid (the perilymph) in the vestibule and inner ear
+is set in motion more or less violently, according to the intensity of
+the sound. The membranous labyrinth occupies the central portion of the
+vestibule and the passages leading from it. When, therefore, the
+perilymph is shaken it communicates the impulse to the fluid
+(endolymph) contained in the inner membranous bag. The endolymph and
+the tiny grains of ear-sand now perform their part in this marvelous
+and complex mechanism. They are driven against the sides of the
+membranous bag, and so strike the ends of the nerves of hearing, which
+transmit the auditory impulses to the seat of sensation in the brain.
+
+It is in the seat of sensation in the brain called the _sensorium_ that
+the various auditory impulses received from different parts of the
+inner ear are fused into one, and interpreted as sounds. It is the
+extent of the vibrations that determines the loudness of the sound; the
+number of them that determines the pitch.
+
+Experiment 158. Hold a ticking watch between the teeth, or touch the
+upper incisors with a vibrating tuning-fork; close both ears, and
+observe that the ticking or vibration is heard louder. Unstop one ear,
+and observe that the ticking or vibration is heard loudest in the
+stopped ear.
+
+Experiment 159. Hold a vibrating tuning-fork on the incisor teeth until
+you cannot hear it sounding. Close one or both ears, and you will hear
+it.
+
+Experiment 160. Listen to a ticking watch or a tuning-fork kept
+vibrating electrically. Close the mouth and nostrils, and take either a
+deep inspiration or deep expiration, so as to alter the tension of the
+air in the tympanum; in both cases the sound is diminished.
+
+Experiment 161. With a blindfolded person test his sense of the
+direction of sound, _e.g._, by clicking two coins together. It is very
+imperfect. Let a person press both auricles against the side of the
+head, and hold both hands vertically in front of each meatus. On a
+person making a sound in front, the observed person will refer it to a
+position behind him.
+
+347. Practical Hints on the Care of the Ear. This very delicate and
+complicated organ is often neglected when skilled treatment is urgently
+needed, and it is often ignorantly and carelessly tampered with when it
+should be let alone.
+
+Never insert into the ear canal the corners of towels, ear spoons, the
+ends of toothpicks, hairpins, or any other pointed instruments. It is a
+needless and dangerous practice, usually causing, in time, some form of
+inflammation. The abrasion of the skin in the canal thus produced
+affords a favorable soil for the growth of vegetable parasites.
+
+Illustration: Fig. 143.—Diagram of the Middle and Internal Ear.
+
+This, in turn, may lead to a chronic inflammation of the canal and of
+the tympanic membrane. Again, there is always risk that the elbow may
+be jogged and the instrument pushed through the drum-head. There is, of
+course, a natural impulse to relieve the itching of the ear. This
+should be done with the tips of the fingers or not at all.
+
+The popular notion that something should be put into the ear to cure
+toothache is erroneous. This treatment does not cure a toothache, and
+may lead to an injury to the delicate parts of the ear. A piece of
+absorbent cotton, carefully inserted into the ear, may be worn out of
+doors, when the cold air causes pain, but should be removed on coming
+into the house.
+
+Frequent bathing in the cold water of ponds and rivers is liable to
+injure both the ears and the general health. In salt-water bathing, the
+force of the waves striking against the ears often leads to earache,
+long-continued inflammation, or defective hearing; to diminish this
+risk, insert into the ears a small plug of absorbent cotton.
+
+The ears are often carelessly exposed to cold water and inclement
+weather. Very cold water should never be used to bathe the ears and
+nostrils. Bathe moderately and gently in lukewarm water, using a
+wash-rag in preference to a sponge; dry gently and thoroughly.
+Children’s ears are often rudely washed, especially in the auditory
+canal. This is not at all necessary to cleanliness, and may result in a
+local inflammation.
+
+Never shout suddenly in a person’s ear. The ear is not prepared for the
+shock, and deafness has occasionally resulted. A sudden explosion, the
+noise of a cannon, may burst the drum-head, especially if the
+Eustachian tube be closed at the time. During heavy cannonading,
+soldiers are taught to keep the mouth open to allow an equal tension of
+air.
+
+Illustration: Fig. 144.—Section of Cochlea.
+
+From A straight downwards is the direction of the central column, to
+which E points. B points to the projecting ridge, almost dividing the
+canal of the tube into an upper compartment (D), and a lower (C).]
+
+Insects may gain entrance to the ears and occasion annoyance, pain, and
+fright, perhaps leading to vomiting, even to convulsions, with nervous
+children. A lighted lamp held at the entrance of the ear will often
+induce the offending insect to crawl out towards the light. A few drops
+of warm water, sweet oil, or molasses, dropped into the ear, will help
+remove the intruder.
+
+When a discharge occurs from the ears, it is not best to plug them with
+cotton wads. It only keeps in what should be got rid of. Do not go to
+sleep with the head on a window sill or in any position, with the ears
+exposed to draughts of cold or damp air.
+
+No effort should be made to remove the ear wax unless it accumulates
+unduly. The skin of the canal grows outward, and the extra wax and dust
+will be naturally carried out, if let alone. Never employ any of the
+many articles or “drops,” advertised to cure deafness. Neuralgic pain
+in the canal, usually classed as earache, may be due to decayed or
+improperly filled teeth.
+
+Quinine, so generally used in its many preparations for malaria, causes
+a peculiar ringing or buzzing in the ears. This is a warning that it
+should be taken in smaller doses, or perhaps stopped for a time. In
+some cases quinine may produce temporary deafness.
+
+The practice of snuffing up cold water into the nostrils is
+occasionally followed by an acute inflammation of the middle ear, some
+of the water finding its way through the Eustachian tube into this part
+of the organ of hearing. The nasal douche, so often advised as a home
+remedy for nasal catarrh, should be used only with great caution, and
+always in accordance with detailed directions from a physician.
+
+348. Effect of Tobacco upon the Hearing. The sense of hearing is often
+injured by the use of tobacco. The irritating smoke filling all the
+inner cavity of the mouth and throat, readily finds its way up the
+Eustachian tube, dries the membrane, and irritates or inflames the
+delicate mechanism of the inner ear. Thus may be produced a variety of
+serious aural disturbances, such as unnatural noises, whistling, and
+roaring, followed oftentimes by a partial loss of hearing.
+
+Hearing may be impaired by the use of alcoholic beverages. Alcohol
+inflames the mucous membrane of the throat, then by its nearness the
+lining of the Eustachian tube, and finally may injure the delicate
+apparatus of the internal ear.
+
+Additional Experiments.
+
+Experiment 162. Use a small pair of wooden compasses, or an ordinary
+pair of dividers with their points guarded by a small piece of cork.
+Apply the points of the compasses lightly and simultaneously to
+different parts of the body, and ascertain at what distance apart the
+points are felt as two. The following is the order of sensibility: tip
+of tongue, tip of the middle finger, palm, forehead, and back of hand.
+
+Experiment 163. Test as in preceding experiment the skin of the arm,
+beginning at the shoulder and passing downwards. Observe that the
+sensibility is greater as one tests towards the fingers, and also in
+the transverse than in the long axis of the limb. In all cases compare
+the results obtained on both sides of the body.
+
+Experiment 164. By means of a spray-producer, spray the back of the
+hand with ether, and observe how the sensibility is abolished.
+
+Experiment 165. Touch your forehead with your forefinger; the finger
+appears to feel the contact, but on rubbing the forefinger rapidly over
+the forehead, it is the latter which is interpreted as “feeling” the
+finger.
+
+Experiment 166. Generally speaking, the sensation of touch is referred
+to the cutaneous surfaces. In certain cases, however, it is referred
+even beyond this. Holding firmly in one hand a cane or a pencil, touch
+an object therewith; the sensation is referred to the extremity of the
+cane or pencil.
+    If, however, the cane or pencil be held loosely in one’s hand, one
+    experiences two sensations: one corresponding to the object
+    touched, and the other due to the contact of the rod with the skin.
+    The process of mastication affords a good example of the reference
+    of sensations to and beyond the periphery of the body.
+
+Experiment 167. Prepare a strong solution of sulphate of quinine with
+the aid of a little sulphuric acid to dissolve it (_bitter_), a
+five-per-cent solution of sugar (_sweet_), a ten-per-cent solution of
+common salt (_saline_), and a one-per-cent solution of acetic acid
+(_acid_). Wipe the tongue dry, and lay on its tip a crystal of sugar.
+It is not tasted until it is dissolved.
+
+Experiment 168. Apply a crystal of sugar to the tip, and another to the
+back of the tongue. The sweet taste is more pronounced at the tip.
+
+Experiment 169. Repeat the process with sulphate of quinine in
+solution. It is scarcely tasted on the tip, but is tasted immediately
+on the back part of the tongue. Test where salines and acids are tasted
+most acutely.
+
+Experiment 170. _To illustrate the muscular sense_. Take two equal iron
+or lead weights; heat one and leave the other cold. The cold weight
+will feel the heavier.
+
+Experiment 171. Place a thin disk of _cold_ lead, the size of a silver
+dollar, on the forehead of a person whose eyes are closed; remove the
+disk, and on the same spot place two warm disks of equal size. The
+person will judge the latter to be about the same weight, or lighter,
+than the single cold disk.
+
+Experiment 172. Compare two similar wooden disks, and let the diameter
+of one be slightly greater than that of the other. Heat the smaller one
+to over 120° F., and it will be judged heavier than the larger cold
+one.
+
+Experiment 173. _To illustrate the influence of excitation of one sense
+organ on the other sense organs_. Small colored patches the shape and
+color of which are not distinctly visible may become so when a
+tuning-fork is kept vibrating near the ears. In other individuals the
+visual impressions are diminished by the same process.
+    On listening to the ticking of a watch, the ticking sounds feebler
+    or louder on looking at a source of light through glasses of
+    different colors.
+    If the finger be placed in cold or warm water the temperature
+    appears to rise when a red glass is held in front of the eyes.
+
+Experiment 174. _Formation of an inverted image on the retina_. Take a
+freshly removed ox-eye; dissect the sclerotic from that part of its
+posterior segment near the optic nerve. Roll up a piece of blackened
+paper in the form of a tube, black surface innermost, and place the eye
+in it with the cornea directed forward. Look at an object—_e.g._, a
+candle-flame—and observe the inverted image of the flame shining
+through the retina and choroid, and notice how the image moves when the
+candle is moved.
+
+Experiment 175. Focus a candle-flame or other object on the
+ground-glass plate of an ordinary photographic camera, and observe the
+small inverted image.
+
+Experiment 176. _To illustrate spherical aberration_. Make a pin-hole
+in a blackened piece of cardboard; look at a light placed at a greater
+distance than the normal distance of accommodation. One will see a
+radiate figure with four to eight radii. The figures obtained from
+opposite eyes will probably differ in shape.
+
+Experiment 177. Hold a thin wooden rod or pencil about a foot from the
+eyes and look at a distant object. Note that the object appears double.
+Close the right eye; the left image disappears, and _vice versa_.
+
+Experiment 178. _To show the movements of the iris_. It is an extremely
+beautiful experiment, and one that can easily be made. Look through a
+pin-hole in a card at a uniform white surface as the white shade of an
+ordinary reading-lamp. With the right eye look through the pin-hole,
+the left eye being closed. Note the size of the (slightly dull)
+circular visual field. Open the left eye, the field becomes brighter
+and smaller (contraction of pupil); close the left eye, after an
+appreciable time, the field (now slightly dull) is seen gradually to
+expand. One can thus see and observe the rate of movements of his own
+iris.
+
+Illustration: Fig. 145.
+
+
+Experiment 179. _To show the blind spot_. The left eye being shut, let
+the right eye be fixed upon the cross as in Fig. 145. When the book is
+held at arm’s length, both cross and round spot will be visible; but if
+the book be brought to about 8 inches from the eye, the gaze being kept
+steadily upon the cross, the round spot will at first disappear, but as
+the book, is brought still nearer both cross and round spot will again
+be seen.
+
+Experiment 180. _To illustrate the duration of retinal impressions_. On
+a circular white disk, about halfway between the center and
+circumference, fix a small, black, oblong disk, and rapidly rotate it
+by means of a rotating wheel. There appears a ring of gray on the
+black, showing that the impression on the retina lasts a certain time.
+
+Illustration: Fig. 146.—Optic Disks.
+The disk A, having black and white sectors, when rotated rapidly gives
+an even gray tint as in B.
+
+
+Experiment 181. Mark off a round piece of cardboard into black and
+white sectors as in A (Fig. 146). Attach it so as to rotate it rapidly,
+as on a sewing machine. An even gray tint will be produced as in B.
+
+Experiment 182._To illustrate imperfect visual judgments_. Make three
+round black dots, A, B, C, of the same size, in the same line, and let
+A and C be equidistant from B. Between A and B make several more dots
+of the same size. A and B will then appear to be farther apart than B
+and C.
+
+Illustration:
+
+For the same reason, of two squares absolutely identical in size, one
+marked with alternately clear and dark cross-bands, and the other with
+alternately clear and dark upright markings, the former will appear
+broader and the latter higher than the other.
+
+Experiment 183. Make on a white card two squares of equal size. Across
+the one draw _horizontal_ lines at equal distances, and in the other
+make similar _vertical_ lines. Hold them at some distance. The one with
+horizontal lines appears higher than it really is, while the one with
+vertical lines appears broader, _i.e._, both appear oblong.
+
+Experiment 184. Look at the row of letters (S) and figures (8). To some
+the upper halves of the letters and figures may appear to be of the
+same size as the lower halves, to others the lower halves may appear
+larger. Hold the figure upside down, and observe that there is a
+considerable difference between the two, the lower halves being
+considerably larger.
+
+S S S S S S S S                    8 8 8 8 8 8 8 8
+
+
+Experiment 185. _To illustrate imperfect visual judgment_. The length
+of a line appears to vary according to the angle and direction of
+certain other lines in relation to it (Fig. 147). The length of the two
+vertical lines is the same, yet B appears much longer than A.
+
+Illustration: Fig. 147.—To show False Estimate of Size.
+
+
+Experiment 186. In indirect vision the appreciation of direction is
+still more imperfect. While leaning on a large table, fix a point on
+the table, and then try to arrange three small pieces of colored paper
+in a straight line. Invariably, the papers, being at a distance from
+the fixation-point, and being seen by indirect vision, are arranged,
+not in a straight line, but in the arc of a circle with a long radius.
+
+
+
+
+Chapter XII.
+The Throat and the Voice.
+
+
+349. The Throat. The throat is a double highway, as it were, through
+which the air we breathe traverses the larynx on its way to the lungs,
+and through which the food we swallow reaches the œsophagus on its
+passage to the stomach. It is, therefore, a very important region of
+the body, being concerned in the great acts of respiration and
+digestion.
+
+The throat is enclosed and protected by various muscles and bony
+structures, along which run the great blood-vessels that supply the
+head, and the great nerve trunks that pass from the brain to the parts
+below.
+
+We have already described the food passages (Chapter VI.) and the air
+passages (Chapter VIII.).
+
+To get a correct idea of the throat we should look into the wide-open
+mouth of some friend. Depressing the tongue we can readily see the back
+wall of the pharynx, which is common to the two main avenues leading to
+the lungs and the stomach. Above, we notice the air passages, which
+lead to the posterior cavities of the nose. We have already described
+the hard palate, the soft palate, the uvula, and the tonsils (Fig. 46).
+
+On looking directly beyond these organs, we see the beginning of the
+downward passage,—the pharynx. If now the tongue be forcibly drawn
+forward, a curved ridge may be seen behind it. This is the epiglottis,
+which, as we have already learned shuts down, like the lid of a box,
+over the top of the larynx (secs. 137 and 203).
+
+The throat is lined with mucous membrane covered with ciliated
+epithelium, which secretes a lubricating fluid which keeps the parts
+moist and pliable. An excess of this secretion forms a thick, tenacious
+mass of mucus, which irritates the passages and gives rise to efforts
+of hawking and coughing to get rid of it.
+
+350. The Larynx. The larynx, the essential organ of voice, forms the
+box-like top of the windpipe. It is built of variously shaped
+cartilages, connected by ligaments. It is clothed on the outside with
+muscles; on the inside it is lined with mucous membrane, continuous
+with that of the other air passages.
+
+Illustration: Fig. 148.—View of the Cartilages in front project and
+form the lages and Ligaments of the “Adam’s apple,” plainly seen and
+Larynx. (Anterior view.)
+
+
+A,  hyoid bone;
+  B, thyro-hyoid membrane;
+  C, thyroid cartilage;
+  D, erico-thyroid membrane;
+  E, cricoid cartilage, lateral ligaments seen on each side;
+  F, upper ring of the trachea.
+  (“Adam’s apple” is in the V-shaped groove on a line with B and C.)
+
+The larynx has for a framework two cartilages, the thyroid and the
+cricoid, one above the other. The larger of these, called the thyroid,
+from a supposed resemblance to a shield, consists of two extended wings
+which join in front, but are separated by a wide interval behind. The
+united edges in front project and form the “Adam’s apple” plainly seen
+and easily felt on most people, especially on very lean men.
+
+Above and from the sides rise two horns connected by bands to the hyoid
+bone from which the larynx is suspended. This bone is attached by
+muscles and ligaments to the skull. It lies at the base of the tongue,
+and can be readily felt by the finger behind the chin at the angle of
+the jaw and the neck (sec. 41 and Fig. 46). From the under side of the
+thyroid two horns project downwards to become jointed to the cricoid.
+The thyroid thus rests upon, and is movable on, the cricoid cartilage.
+
+The cricoid cartilage, so called from its fancied resemblance to a
+signet-ring, is smaller but thicker and stronger than the thyroid, and
+forms the lower and back part of the cavity of the larynx. This
+cartilage is quite sensitive to pressure from the fingers, and is the
+cause of the sharp pain felt when we try to swallow a large and hard
+piece of food not properly chewed.
+
+Illustration: Fig. 149.—Diagram of a Sectional of Nasal and Throat
+Passages.
+
+  C, nasal cavities;
+  T, tongue;
+  L, lower jaw;
+  M, mouth;
+  U, uvula;
+  E, epiglottis;
+  G, larynx;
+  O, œsophagus.
+
+On the upper edge of the cricoid cartilage are perched a pair of very
+singular cartilages, pyramidal in shape, called the arytenoid, which
+are of great importance in the production of the voice. These
+cartilages are capped with little horn-like projections, and give
+attachment at their anterior angles to the true vocal cords, and at
+their posterior angles to the muscles which open and close the glottis,
+or upper opening of the windpipe. When in their natural position the
+arytenoid cartilages resemble somewhat the mouth of a pitcher, hence
+their name.
+
+351. The Vocal Cords. The mucous membrane which lines the various
+cartilages of the larynx is thrown into several folds. Thus, one fold,
+the free edge of which is formed of a band of elastic fibers, passes
+horizontally outwards from each side towards the middle line, at the
+level of the base of the arytenoid cartilages. These folds are called
+the true vocal cords, by the movements of which the voice is produced.
+
+Above them are other folds of mucous membrane called the false vocal
+cords, which take no part in the production of the voice. The
+arrangement of the true vocal cords, projecting as they do towards the
+middle line, reduces to a mere chink the space between the part of the
+larynx above them and the part below them. This constriction of the
+larynx is called the glottis.
+
+Illustration: Fig. 150.—View of the Cartilages and Ligaments of Larynx.
+(Posterior view.)
+
+
+A,  epiglottis;
+  B, thyroid cartilage;
+  C, arytenoid cartilage;
+  D, ligament connecting lower cornu of the thyroid with the back of
+  the cricoid cartilage;
+  E, cricoid cartilage;
+  F, upper ring of the trachea.
+
+
+352. The Mechanism of the Voice. The mechanism of the voice may be more
+easily understood by a study of Fig. 150. We have here the larynx,
+viewed from behind, with all the soft parts in connection with it. On
+looking down, the folds forming the true vocal cords are seen enclosing
+a V-shaped aperture (the glottis), the narrow part being in front.
+
+The form of this aperture may be changed by the delicately coordinate
+activities of the muscles of the larynx. For instance, the vocal cords
+may be brought so closely together that the space becomes a mere slit.
+Air forced through the slit will throw the edges of the folds into
+vibration and a sound will be produced.
+
+The Variations in the form of the opening will determine the variations
+in the sound. Now, if the various muscles of the larynx be relaxed, the
+opening of the glottis is wider. Thus the air enters and leaves the
+larynx during breathing, without throwing the cords into vibration
+enough to produce any sound.
+
+We may say that the production of the voice is effected by an
+arrangement like that of some musical instruments, the sounds produced
+by the vibrations of the vocal cords being modified by the tubes above
+and below. All musical sounds are due to movements or vibrations
+occurring with a certain regularity, and they differ in loudness,
+pitch, and quality. Loudness of the sound depends upon the extent of
+the vibrations, pitch on the rapidity of the vibrations, and quality on
+the admixture of tones produced by vibrations of varying rates of
+rapidity, related to one another.
+
+Illustration: Fig. 151.—Longitudinal Section of the Larynx. (Showing
+the vocal cords.)
+
+
+A,  epiglottis;
+  B, section of hyoid bone;
+  C, superior vocal cord;
+  D, ventricle of the larynx;
+  E, inferior vocal cord;
+  F, section of the thyroid cartilage;
+  H, section of anterior portion of the cricoid cartilage;
+  K, trachea;
+  L, section of the posterior portion of the cricoid cartilage;
+  M, arytenoid cartilage;
+  N, section of the arytenoid muscle.
+
+
+353. Factors in the Production of the Voice. Muscles which pass from
+the cricoid cartilage to the outer angle of the arytenoids act to bring
+the vocal cords close together, and parallel to one another, so that
+the space between them is narrowed to a slit. A strong expiration now
+drives the air from the lungs through the slit, between the cords, and
+throws them into vibration. The vibration is small in amount, but very
+rapid. Other muscles are connected with the arytenoid cartilages which
+serve to seperate the vocal cords and to widely open the glottis. The
+force of the outgoing current of air determines the extent of the
+movement of the cords, and thus the loudness of the sound will increase
+with greater force of expiration.
+
+We have just learned that the pitch of sound depends on the rapidity of
+the vibrations. This depends on the length of cords and their tightness
+for the shorter and tighter a string is, the higher is the note which
+its vibration produces. The vocal cords of women are about one-third
+shorter than those of men, hence the higher pitch of the notes they
+produce. In children the vocal cords are shorter than in adults.[50]
+The cords of tenor singers are also shorter than those of basses and
+baritones. The muscles within the larynx, of course, play a very
+important part in altering the tension of the vocal cords. Those
+qualities of the voice which we speak of as sweet, harsh, and
+sympathetic depend to a great extent upon the peculiar structure of the
+vocal cords of the individual.
+
+Besides the physical condition of the vocal cords, as their degree of
+smoothness, elasticity, thickness, and so on, other factors determine
+the quality of an individual’s voice. Thus, the general shape and
+structure of the trachea, the larynx, the throat, and mouth all
+influence the quality of voice. In fact, the air passages, both below
+and above the vibrating cords, act as resonators, or resounding
+chambers, and intensify and modify the sounds produced by the cords. It
+is this fact that prompts skillful teachers of music and elocution to
+urge upon their pupils the necessity of the mouth being properly opened
+during speech, and especially during singing.
+
+Experiment 187. _To show the anatomy of the throat_. Study the general
+construction of the throat by the help of a hand mirror. Repeat the
+same on the throat of some friend.
+
+Experiment 188. _To show the construction of the vocal organs_. Get a
+butcher to furnish two windpipes from a sheep or a calf. They differ
+somewhat from the vocal organs of the human body, but will enable us to
+recognize the different parts which have been described, and thus to
+get a good idea of the gross anatomy.
+
+  One specimen should be cut open lengthwise in the middle line in
+  front, and the other cut in the same way from behind.
+
+354. Speech. Speech is to be distinguished from voice. It may exist
+without voice, as in a whisper. Speech consists of articulated sounds,
+produced by the action of various parts of the mouth, throat, and nose.
+Voice is common to most animals, but speech is the peculiar privilege
+of man.
+
+Illustration: Fig. 152.—Diagramatic Horizontal Section of Larynx to
+show the Direction of Pull of the Posterior Crico-Arytenoid Muscles,
+which abduct the Vocal Cords. (Dotted lines show position in
+abduction.)]
+
+The organ of speech is perhaps the most delicate and perfect _motor_
+apparatus in the whole body. It has been calculated that upwards of 900
+movements per minute can be made by the movable organs of speech during
+reading, speaking, and singing. It is said that no less than a hundred
+different muscles are called into action in talking. Each part of this
+delicate apparatus is so admirably adjusted to every other that all
+parts of this most complex machinery act in perfect harmony.
+
+There are certain articulate sounds called vowel or vocal, from the
+fact that they are produced by the vocal cords, and are but slightly
+modified as they pass out of the mouth. The true vowels, _a, e, i, o,
+u_, can all be sounded alone, and may be prolonged in expiration. These
+are the sounds chiefly used in singing. The differences in their
+characters are produced by changes in the position of the tongue,
+mouth, and lips.
+
+Consonants are sounds produced by interruptions of the outgoing current
+of air, but in some cases have no sound in themselves, and serve merely
+to modify vowel sounds. Thus, when the interruption to the outgoing
+current takes place by movements of the lips, we have the _labial_
+consonants, _p_, _b_, _f_, and _v_. When the tongue, in relation with
+the teeth or hard palate, obstructs the air, the _dental_ consonants,
+_d_, _t_, _l_, and _s_ are produced. _Gutturals_, such as _k_, _g_,
+_ch_, _gh_, and _r_, are due to the movements of the root of the tongue
+in connection with the soft palate or pharynx.
+
+To secure an easy and proper production of articulate sounds, the
+mouth, teeth, lips, tongue, and palate should be in perfect order. The
+modifications in articulation occasioned by a defect in the palate, or
+in the uvula, by the loss of teeth, from disease, and from congenital
+defects, are sufficiently familiar. We have seen that speech consists
+essentially in a modification of the vocal sounds by the accessory
+organs, or by parts above the larynx, the latter being the essential
+vocal instrument.
+
+Many animals have the power of making articulated sounds; a few have
+risen, like man, to the dignity of sentences, but these are only by
+imitation of the human voice. Both vowels and consonants can be
+distinguished in the notes of birds, the vocal powers of which are
+generally higher than those of mammals. The latter, as a rule, produce
+only vowels, though some are also able to form consonants.
+
+Persons idiotic from birth are incapable of producing any other vocal
+sounds than inarticulate cries, although supplied with all the internal
+means of articulation. Persons deaf and dumb are in the same situation,
+though from a different cause; the one being incapable of imitating,
+and the other being deprived of hearing the sounds to be imitated.
+
+Illustration: Fig. 153.—Direction of Pull of the Lateral
+Crico-Arytenoids, which adduct the Vocal Cords. (Dotted lines show
+position in adduction.)
+
+In _whispering_, the larynx takes scarcely any part in the production
+of the sounds; the vocal cords remain apart and comparatively slack,
+and the expiratory blast rushes through without setting them in
+vibration.
+
+In _stammering_, spasmodic contraction of the diaphragm interrupts the
+effort of expiration. The stammerer has full control of the mechanism
+of articulation, but not of the expiratory blast. His larynx and his
+lips are at his command, but not his diaphragm. To conquer this defect
+he must train his muscles of respiration to calm and steady action
+during speech. The _stutterer_, on the other hand, has full control of
+the muscles of expiration. His diaphragm is well drilled, but his lips
+and tongue are insubordinate.
+
+355. The Care of the Throat and Voice. The throat, exposed as it is to
+unwholesome and overheated air, irritating dust of the street,
+factories, and workshops, is often inflamed, resulting in that common
+ailment, _sore throat_. The parts are red, swollen, and quite painful
+on swallowing. Speech is often indistinct, but there is no hoarseness
+or cough unless the uvula is lengthened and tickles the back part of
+the tongue. Slight sore throat rarely requires any special treatment,
+aside from simple nursing.
+
+The most frequent cause of throat trouble is the action of cold upon
+the heated body, especially during active perspiration. For this reason
+a cold bath should not be taken while a person is perspiring freely.
+The muscles of the throat are frequently overstrained by loud talking,
+screaming, shouting, or by reading aloud too much. People who strain or
+misuse the voice often suffer from what is called “clergyman’s sore
+throat.” Attacks of sore throat due to improper methods of breathing
+and of using the voice should be treated by judicious elocutionary
+exercises and a system of vocal gymnastics, under the direction of
+proper teachers.
+
+Persons subject to throat disease should take special care to wear
+suitable underclothing, adapted to the changes of the seasons. Frequent
+baths are excellent tonics to the skin, and serve indirectly to protect
+one liable to throat ailments from changes in the weather. It is not
+prudent to muffle the neck in scarfs, furs, and wraps, unless perhaps
+during an unusual exposure to cold. Such a dress for the neck only
+makes the parts tender, and increases the liability to a sore throat.
+
+Every teacher of elocution or of vocal music, entrusted with the
+training of a voice of some value to its possessor, should have a good,
+practical knowledge of the mechanism of the voice. Good voices are
+often injured by injudicious management on the part of some incompetent
+instructor. It is always prudent to cease speaking or singing in public
+the moment there is any hoarseness or sore throat.
+
+The voice should not be exercised just after a full meal, for a full
+stomach interferes with the free play of the diaphragm. A sip of water
+taken at convenient intervals, and held in the mouth for a moment or
+two, will relieve the dryness of the throat during the use of the
+voice.
+
+356. Effect of Alcohol upon the Throat and Voice. Alcoholic beverages
+seriously injure the throat, and consequently the voice, by causing a
+chronic inflammation of the membrane lining the larynx and the vocal
+cords. The color is changed from the healthful pink to red, and the
+natural smooth surface becomes roughened and swollen, and secretes a
+tough phlegm.
+
+The vocal cords usually suffer from this condition. They are thickened,
+roughened, and enfeebled, the delicate vibration of the cords is
+impaired, the clearness and purity of the vocal tones are gone, and
+instead the voice has become rough and husky. So well known is this
+result that vocalists, whose fortune is the purity and compass of their
+tones, are scrupulously careful not to impair these fine qualities by
+convivial indulgences.
+
+357. Effect of Tobacco upon the Throat and Voice. The effect of tobacco
+is often specially serious upon the throat, producing a disease well
+known to physicians as “the smoker’s sore throat.” Still further, it
+produces inflammation of the larynx, and thus entails disorders of the
+vocal cords, involving rough voice and harsh tones. For this reason
+vocalists rarely allow themselves to come under the narcotic influence
+of tobacco smoke. It is stated that habitual smokers rarely have a
+normal condition of the throat.
+
+Additional Experiments.
+
+Experiment 189. _To illustrate the importance of the resonating cavity
+of the nose in articulation_. Pinch the nostrils, and try to pronounce
+slowly the words “Lincoln,” “something,” or any other words which
+require the sound of _m_, _ln_, or _ng_.
+
+Illustration: Fig. 154.
+
+
+Experiment 190. _To illustrate the passage of air through the glottis._
+Take two strips of India rubber, and stretch them over the open end of
+a boy’s “bean-blower,” or any kind of a tube. Tie them tightly with
+thread, so that a chink will be left between them, as shown in Fig.
+154. Force the air through such a tube by blowing hard, and if the
+strips are not too far apart a sound will be produced. The sound will
+vary in character, just as the bands are made tight or loose.
+
+Experiment 191. “A very good illustration of the action of the vocal
+bands in the production of the voice may be given by means of a piece
+of bamboo or any hollow wooden tube, and a strip of rubber, about an
+inch or an inch and a half wide, cut from the pure sheet rubber used by
+dentists.
+    “One end of the tube is to be cut sloping in two directions, and
+    the strip of sheet rubber is then to be wrapped round the tube, so
+    as to leave a narrow slit terminating at the upper corners of the
+    tube.
+    “By blowing into the other end of the tube the edges of the rubber
+    bands will be set in vibration, and by touching the vibrating
+    membrane at different points so as to check its movements it may be
+    shown that the pitch of the note emitted depends upon the length
+    and breadth of the vibrating portion of the vocal bands.”[51]—Dr.
+    H. P. Bowditch.
+
+Note. The limitations of a text-book on physiology for schools do not
+permit so full a description of the voice as the subject deserves. For
+additional details, the student is referred to Cohen’s _The Throat and
+the Voice_, a volume in the “American Health Primer Series.” Price 40
+cents.
+
+
+
+
+Chapter XIII.
+Accidents and Emergencies.
+
+
+358. Prompt Aid to the Injured. A large proportion of the accidents,
+emergencies, and sudden sicknesses that happen do not call for medical
+or surgical attention. For those that do require the services of a
+physician or surgeon, much can be often done before the arrival of
+professional help. Many a life has been saved and much suffering and
+anxiety prevented by the prompt and efficient help of some person with
+a cool head, a steady hand, and a practical knowledge of what to do
+first. Many of us can recall with mingled admiration and gratitude the
+prompt services rendered our families by some neighbor or friend in the
+presence of an emergency or sudden illness.
+
+In fact, what we have studied in the preceding chapters becomes tenfold
+more interesting, instructive, and of value to us, if we are able to
+supplement such study with its practical application to the treatment
+of the more common and less serious accidents and emergencies.
+
+While no book can teach one to have presence of mind, a cool head, or
+to restrain a more or less excitable temperament in the midst of sudden
+danger, yet assuredly with proper knowledge for a foundation, a certain
+self-confidence may be acquired which will do much to prevent hasty
+action, and to maintain a useful amount of self-control.
+
+Space allows us to describe briefly in this chapter only a few of the
+simplest helps in the more common accidents and emergencies which are
+met with in everyday life.[52]
+
+ 359. Hints as to what to Do First. Retain so far as possible your
+ presence of mind, or, in other words, keep cool. This is an
+ all-important direction. Act promptly and quietly, but not with haste.
+ Whatever you do, do in earnest; and never act in a half-hearted manner
+ in the presence of danger. Of course, a knowledge of what to-do and
+ how to do it will contribute much towards that self-control and
+ confidence that command success. Be sure and send for a doctor at once
+ if the emergency calls for skilled service. All that is expected of
+ you under such circumstances is to tide over matters until the doctor
+ comes.
+
+Illustration: Fig. 155.—Showing how Digital Compression should be
+applied to the Brachial Artery.
+
+Do not presume upon any smattering of knowledge you have, to assume any
+risk that might lead to serious results. Make the sufferer comfortable
+by giving him an abundance of fresh air and placing him in a restful
+position. Do all that is possible to keep back the crowd of curious
+lookers-on, whom a morbid curiosity has gathered about the injured
+person. Loosen all tight articles of clothing, as belts, collars,
+corsets, and elastics. Avoid the use of alcoholic liquors. They are
+rarely of any real service, and in many instances, as in bleeding, may
+do much harm.
+
+360. Incised and Lacerated Wounds. An incised or cut wound is one made
+by a sharp instrument, as when the finger is cut with a knife. Such a
+wound bleeds freely because the clean-cut edges do not favor the
+clotting of blood. In slight cuts the bleeding readily ceases, and the
+wound heals by primary union, or by “first intention,” as surgeons call
+it.
+
+Lacerated and contused wounds are made by a tearing or bruising
+instrument, for example, catching the finger on a nail. Such wounds
+bleed but little, and the edges and surfaces are rough and ragged.
+
+If the incised wound is deep or extensive, a physician is necessary to
+bring the cut edges together by stitches in order to get primary union.
+Oftentimes, in severe cuts, and generally in lacerations, there is a
+loss of tissue, so that the wound heals by “second intention”; that is,
+the wound heals from the bottom by a deposit of new cells called
+_granulations_, which gradually fill it up. The skin begins to grow
+from the edges to the center, covering the new tissue and leaving a
+cicatrix or scar with which every one is familiar.
+
+361. Contusion and Bruises. An injury to the soft tissues, caused by a
+blow from some blunt instrument, or a fall, is a contusion, or bruise.
+It is more or less painful, followed by discoloration due to the escape
+of blood under the skin, which often may not be torn through. A black
+eye, a knee injured by a fall from a bicycle, and a finger hurt by a
+baseball, are familiar examples of this sort of injury. Such injuries
+ordinarily require very simple treatment.
+
+The blood which has escaped from the capillaries is slowly absorbed,
+changing color in the process, from blue black to green, and fading
+into a light yellow. Wring out old towels or pieces of flannel in hot
+water, and apply to the parts, changing as they become cool. For cold
+applications, cloths wet with equal parts of water and alcohol,
+vinegar, and witch-hazel may be used. Even if the injury is apparently
+slight it is always safe to rest the parts for a few days.
+
+When wounds are made with ragged edges, such as those made by broken
+glass and splinters, more skill is called for. Remove every bit of
+foreign substance. Wash the parts clean with one of the many antiseptic
+solutions, bring the torn edges together, and hold them in place with
+strips of plaster. Do not cover such an injury all over with plaster,
+but leave room for the escape of the wound discharges. For an outside
+dressing, use compresses made of clean cheese-cloth or strips of any
+clean linen cloth. The antiseptic _corrosive-sublimate gauze_ on sale
+at any drug store should be used if it can be had.
+
+Wounds made by toy pistols, percussion-caps, and rusty nails and tools,
+if neglected, often lead to serious results from blood-poisoning. A hot
+flaxseed poultice may be needed for several days. Keep such wounds
+clean by washing or syringing them twice a day with hot _antiseptics_,
+which are poisons to _bacteria_ and kill them or prevent their growth.
+Bacteria are widely distributed, and hence the utmost care should be
+taken to have everything which is to come in contact with a wounded
+surface free from the germs of inflammation. In brief, such injuries
+must be kept _scrupulously neat_ and _surgically clean_.
+
+Illustration: Fig. 156.—Dotted Line showing the Course of the Brachial
+Artery.
+
+The injured parts should be kept at rest. Movement and disturbance
+hinder the healing process.
+
+362. Bites of Mad Dogs. Remove the clothing at once, if only from the
+bitten part, and apply a temporary ligature _above_ the wound. This
+interrupts the activity of the circulation of the part, and to that
+extent delays the absorption of the poisonous saliva by the
+blood-vessels of the wound. A dog bite is really a lacerated and
+contused wound, and lying in the little roughnesses, and between the
+shreds, is the poisonous saliva. If by any means these projections and
+depressions affording the lodgment can be removed, the poison cannot do
+much harm. If done with a knife, the wound would be converted,
+practically, into an incised wound, and would require treatment for
+such.
+
+If a surgeon is at hand he would probably cut out the injured portion,
+or cauterize it thoroughly. Professional aid is not always at our
+command, and in such a case it would be well to take a poker, or other
+suitable piece of iron, heat it _red_ hot in the fire, wipe off and
+destroy the entire surface of the wound. As fast as destroyed, the
+tissue becomes white. An iron, even at a white heat, gives less pain
+and at once destroys the vitality of the part with which it comes in
+contact.
+
+If the wound is at once well wiped out, and a stick of solid nitrate of
+silver (lunar caustic) rapidly applied to the entire surface of the
+wound, little danger is to be apprehended. Poultices and warm
+fomentations should be applied to the injury to hasten the sloughing
+away of the part whose vitality has been intentionally destroyed.
+
+Any dog, after having bitten a person, is apt, under a mistaken belief,
+to be at once killed. This should not be done. There is no more danger
+from a dog-bite, unless the dog is suffering from the disease called
+_rabies_ or is “mad,” than from any other lacerated wound. The
+suspected animal should be at once placed in confinement and watched,
+under proper safeguards, for the appearance of any symptoms that
+indicate rabies.
+
+Should no pronounced symptoms indicate this disease in the dog, a great
+deal of unnecessary mental distress and worry can be saved both on the
+part of the person bitten and his friends.
+
+363. Injuries to the Blood-vessels. It is very important to know the
+difference between the bleeding from an artery and that from a vein.
+
+If an artery bleeds, the blood leaps in spurts, and is of a bright
+scarlet color.
+
+If a vein bleeds, the blood flows in a steady stream, and is of a dark
+purple color.
+
+If the capillaries are injured the blood merely oozes.
+
+Bleeding from an artery is a dangerous matter in proportion to the size
+of the vessel, and life itself may be speedily lost. Hemorrhage from a
+vein or from the capillaries is rarely troublesome, and is ordinarily
+easily checked, aided, if need be, by hot water, deep pressure, the
+application of some form of iron styptic, or even powdered alum. When
+an artery is bleeding, always remember to make deep pressure between
+the wound and the heart. In all such cases send at once for the doctor.
+
+Illustration: Fig. 157.—Showing how Digital Compression should be
+applied to the Femoral Artery.
+
+
+Do not be afraid to act at once. A resolute grip in the right place
+with firm fingers will do well enough, until a twisted handkerchief,
+stout cord, shoestring, suspender, or an improvised tourniquet[53] is
+ready to take its place. If the flow of blood does not stop, change the
+pressure until the right spot is found.
+
+Sometimes it will do to seize a handful of dry earth and crowd it down
+into the bleeding wound, with a firm pressure. Strips of an old
+handkerchief, underclothing, or cotton wadding may also be used as a
+compress, provided pressure is not neglected.
+
+In the after-treatment it is of great importance that the wound and the
+dressing should be kept free from bacteria by keeping everything
+surgically clean.
+
+364. Where and how to Apply Pressure. The principal places in which to
+apply pressure when arteries are injured and bleeding should always be
+kept in mind.
+
+Experiment 192. _How to tie a square knot_. If the student would render
+efficient help in accidents and emergencies, to say nothing of service
+on scores of other occasions, he must learn how to tie a square or
+“reef” knot. This knot is secure and does not slip as does the “granny”
+knot. The square knot is the one used by surgeons in ligating vessels
+and securing bandages. Unless one knew the difference, the insecure
+“granny” knot might be substituted.
+    A square knot is tied by holding an end of a bandage or cord in
+    each hand, and then passing the end in the _right_ hand over the
+    one in the left and tying; the end now in the _left_ hand is passed
+    over the one in the right and again tied.
+
+Illustration: Fig. 158.—Showing how a Square Knot may be tied with a
+Cord and a Handkerchief.
+
+If in the finger, grasp it with the thumb and forefinger, and pinch it
+firmly on each side; if in the hand, press on the bleeding spot, or
+press with the thumb just above and in front of the wrist.
+
+For injuries below the elbow, grasp the upper part of the arm with the
+hands, and squeeze hard. The main artery runs in the middle line of the
+bend of the elbow. Tie the knotted cord here, and bend the forearm so
+as to press hard against the knot.
+
+For the upper arm, press with the fingers against the bone on the inner
+side, and just on the edge of the swell of the biceps muscle. Now we
+are ready for the knotted cord. Take a stout stick of wood, about a
+foot long, and twist the cord hard with it, bringing the knot firmly
+over the artery.
+
+For the foot or leg, pressure as before, in the hollow behind the knee,
+just above the calf of the leg. Bend the thigh towards the abdomen and
+bring the leg up against the thigh, with the knot in the bend of the
+knee.
+
+365. Bleeding from the Stomach and Lungs. Blood that comes from the
+lungs is bright red, frothy, or “soapy.” There is rarely much; it
+usually follows coughing, feels warm, and has a salty taste. This is a
+grave symptom. Perfect rest on the back in bed and quiet must be
+insisted upon. Bits of ice should be eaten freely. Loosen the clothing,
+keep the shoulders well raised, and the body in a reclining position
+and absolutely at rest. Do not give alcoholic drinks.
+
+Blood from the stomach is not frothy, has a sour taste, and is usually
+dark colored, looking somewhat like coffee grounds. It is more in
+quantity than from the lungs, and is apt to be mixed with food. Employ
+the same treatment, except that the person should be kept flat on the
+back.
+
+366. Bleeding from the Nose. This is the most frequent and the least
+dangerous of the various forms of bleeding. Let the patient sit
+upright; leaning forward with the head low only increases the
+hemorrhage. Raise the arm on the bleeding side; do not blow the nose.
+Wring two towels out of cold water; wrap one around the neck and the
+other properly folded over the forehead and upper part of the nose.
+
+Add a teaspoonful of powdered _alum_ to a cup of water, and snuff it up
+from the hand. If necessary, soak in alum water a piece of absorbent
+cotton, which has been wound around the pointed end of a pencil or
+penholder; plug the nostril by pushing it up with a twisting motion
+until firmly lodged.
+
+367. Burns or Scalds. Burns or scalds are dangerous in proportion to
+their extent and depth. A child may have one of his fingers burned off
+with less danger to life than an extensive scald of his back and legs.
+A deep or extensive burn or scald should always have prompt medical
+attendance.
+
+In burns by acids, bathe the parts with an alkaline fluid, as diluted
+ammonia, or strong soda in solution, and afterwards dress the burn.
+
+In burns caused by lime, caustic potash, and other alkalies, soak the
+parts with vinegar diluted with water; lemon juice, or any other
+diluted acid.
+
+Remove the clothing with the greatest care. Do not pull, but carefully
+cut and coax the clothes away from the burned places. Save the skin
+unbroken if possible, taking care not to break the blisters. The secret
+of treatment is to prevent friction, and to keep out the air. If the
+burn is slight, put on strips of soft linen soaked in a strong solution
+of baking-soda and water, one heaping table spoonful to a cupful of
+water. This is especially good for scalds.
+
+Illustration: Fig. 159.—Dotted Line showing the Course of the Femoral
+Artery.
+
+_Carron oil_ is one of the best applications. It is simply half
+linseed-oil and half lime-water shaken together. A few tablespoonfuls
+of carbolic acid solution to one pint may be added to this mixture to
+help deaden the pain. Soak strips of old linen or absorbent cotton in
+this time-honored remedy, and gently apply.
+
+If carbolized or even plain _vaseline_ is at hand, spread it freely on
+strips of old linen, and cover well the burnt parts, keeping out the
+air with other strips carefully laid on. Simple cold water is better
+than flour, starch, toilet powder, cotton batting, and other things
+which are apt to stick, and make an after-examination very painful.
+
+Illustration: Fig. 160.—Showing how Hemorrhage from the Femoral Artery
+may be arrested by the Use of an Improvised Apparatus (technically
+called a _Tourniquet_).
+
+
+368. Frost Bites. The ears, toes, nose, and fingers are occasionally
+frozen, or frost-bitten. No warm air, warm water, or fire should be
+allowed near the frozen parts until the natural temperature is nearly
+restored. Rub the frozen part vigorously with snow or snow-water in a
+cold room. Continue this until a burning, tingling pain is felt, when
+all active treatment should cease.
+
+Pain shows that warmth and circulation are beginning to return. The
+after effects of a frost bite are precisely like those of a burn, and
+require similar treatment. Poultices made from scraped raw potatoes
+afford much comfort for an after treatment.
+
+369. Catching the Clothing on Fire. When the clothing catches fire,
+throw the person down on the ground or floor, as the flames will tend
+less to rise toward the mouth and nostrils. Then without a moment’s
+delay, roll the person in a carpet or hearth-rug, so as to stifle the
+flames, leaving only the head out for breathing.
+
+If no carpet or rug can be had, then take off your coat, shawl, or
+cloak and use it instead. Keep the flame as much as possible from the
+face, so as to prevent the entrance of the hot air into the lungs. This
+can be done by beginning at the neck and shoulders with the wrapping.
+
+370. Foreign Bodies in the Throat. Bits of food or other small objects
+sometimes get lodged in the throat, and are easily extracted by the
+forefinger, by sharp slaps on the back, or expelled by vomiting. If it
+is a sliver from a toothpick, match, or fishbone, it is no easy matter
+to remove it; for it generally sticks into the lining of the passage.
+If the object has actually passed into the windpipe, and is followed by
+sudden fits of spasmodic coughing, with a dusky hue to the face and
+fingers, surgical help must be called without delay.
+
+If a foreign body, like coins, pencils, keys, fruit-stones, etc., is
+swallowed, it is not wise to give a physic. Give plenty of hard-boiled
+eggs, cheese, and crackers, so that the intruding substance maybe
+enfolded in a mass of solid food and allowed to pass off in the natural
+way.
+
+371. Foreign Bodies in the Nose. Children are apt to push beans, peas,
+fruit-stones, buttons, and other small objects, into the nose.
+Sometimes we can get the child to help by blowing the nose hard. At
+other times, a sharp blow between the shoulders will cause the
+substance to fall out. If it is a pea or bean, which is apt to swell
+with the warmth and moisture, call in medical help at once.
+
+372. Foreign Bodies in the Ear. It is a much more difficult matter to
+get foreign bodies out of the ear than from the nose. Syringe in a
+little warm water, which will often wash out the substance. If live
+insects get into the ear, drop in a little sweet oil, melted vaseline,
+salt and water, or even warm molasses.
+
+If the tip of the ear is pulled up gently, the liquid will flow in more
+readily. If a light is held close to the outside ear, the insect may be
+coaxed to crawl out towards the outer opening of the ear, being
+attracted by the bright flame.
+
+373. Foreign Bodies in the Eye. Cinders, particles of dust, and other
+small substances, often get into the eye, and cause much pain. It will
+only make bad matters worse to rub the eye. Often the copious flow of
+tears will wash the substance away. It is sometimes seen, and removed
+simply by the twisted corner of a handkerchief carefully used. If it is
+not removed, or even found, in this way, the upper lid must be turned
+back.
+
+Illustration: Fig. 161.—Showing how the Upper Eyelid may be everted
+with a Pencil or Penholder.
+
+This is done usually as follows: Seize the lashes between the thumb and
+forefinger, and draw the edge of the lid away from the eyeball. Now,
+telling the patient to look down, press a slender lead-pencil or
+penholder against the lid, parallel to and above the edge, and then
+pull the edge up, and turn it over the pencil by means of the lashes.
+
+The eye is now readily examined, and usually the foreign body is easily
+seen and removed. Do not increase the trouble by rubbing the eye after
+you fail, but get at once skilled help. After the substance has been
+removed, bathe the eye for a time with hot water.
+
+If lime gets into the eye, it may do a great amount of mischief, and
+generally requires medical advice, or permanent injury will result.
+Until such advice can be had, bathe the injured parts freely with a
+weak solution of vinegar and hot water.
+
+374. Broken Bones. Loss of power, pain, and swelling are symptoms of a
+broken bone that may be easily recognized. Broken limbs should always
+be handled with great care and tenderness. If the accident happens in
+the woods, the limb should be bound with handkerchiefs, suspenders, or
+strips of clothing, to a piece of board, pasteboard, or bark, padded
+with moss or grass, which will do well enough for a temporary splint.
+Always put a broken arm into a sling after the splints are on.
+
+Illustration: Fig. 162.—Showing how an Umbrella may be used as a
+Temporary Splint in Fracture of the Leg.
+
+
+Never move the injured person until the limb is made safe from further
+injuries by putting on temporary splints. If you do not need to move
+the person, keep the limb in a natural, easy position, until the doctor
+comes.
+
+Remember that this treatment for broken bones is only to enable the
+patient to be moved without further injury. A surgeon is needed at once
+to set the broken bone.
+
+Illustration: Fig. 163.—Showing how a Pillow may be used as a Temporary
+Splint in Fracture of the Leg.
+
+
+375. Fainting. A fainting person should be laid flat at once. Give
+plenty of fresh air, and dash cold water, if necessary, on the head and
+neck. Loosen all tight clothing. Smelling-salts may be held to the
+nose, to excite the nerves of sensation.
+
+376. Epileptic and Hysterical Fits, Convulsions of Children. Sufferers
+from “fits” are more or less common. In _epilepsy_, the sufferer falls
+with a peculiar cry; a loss of consciousness, a moment of rigidity, and
+violent convulsions follow. There is foaming at the mouth, the eyes are
+rolled up, and the tongue or lips are often bitten. When the fit is
+over the patient remains in a dazed, stupid state for some time. It is
+a mistake to struggle with such patients, or to hold them down and keep
+them quiet. It does more harm than good.
+
+See that the person does not injure himself; crowd a pad made from a
+folded handkerchief or towel between the teeth, to prevent biting of
+the lips or tongue. Do not try to make the sufferer swallow any drink.
+Unfasten the clothes, especially about the neck and chest. Persons who
+are subject to such fits should rarely go out alone, and never into
+crowded or excited gatherings of any kind.
+
+_Hysterical fits_ almost always occur in young women. Such patients
+never bite their tongue nor hurt themselves. Placing a towel wrung out
+in cold water across the face, or dashing a little cold water on the
+face or neck, will usually cut short the fit, speaking firmly to the
+patient at the same time. Never sympathize too much with such patients;
+it will only make them a great deal worse.
+
+377. Asphyxia. Asphyxia is from the Greek, and means an “absence of
+pulse.” This states a fact, but not the cause. The word is now commonly
+used to mean _suspended animation_. When for any reason the proper
+supply of oxygen is cut off, the tissues rapidly load up with carbon
+dioxid. The blood turns dark, and does not circulate. The healthy red
+or pink look of the lips and finger-nails becomes a dusky purple. The
+person is suffering from a lack of oxygen; that is, from asphyxia, or
+suffocation. It is evident there can be several varieties of asphyxia,
+as in apparent drowning, strangulation and hanging, inhalation of
+gases, etc.
+
+The first and essential thing to do is to give fresh air. Remove the
+person to the open air and place him on his back. Remove tight clothing
+about the throat and waist, dash on cold water, give a few drops of
+ammonia in hot water or hot ginger tea. Friction applied to the limbs
+should be kept up. If necessary, use artificial respiration by the
+Sylvester method (sec. 380).
+
+The chief dangers from poisoning by noxious gases come from the fumes
+of burning coal in the furnace, stove, or range; from “blowing out”
+gas, turning it down, and having it blown out by a draught; from the
+foul air often found in old wells; from the fumes of charcoal and the
+foul air of mines.
+
+378. Apparent Drowning. Remove all tight clothing from the neck, chest,
+and waist. Sweep the forefinger, covered with a handkerchief or towel,
+round the mouth, to free it from froth and mucus. Turn the body on the
+face, raising it a little, with the hands under the hips, to allow any
+water to run out from the air passages. Take only a moment for this.
+
+Lay the person flat upon the back, with a folded coat, or pad of any
+kind, to keep the shoulders raised a little. Remove all the wet,
+clinging clothing that is convenient. If in a room or sheltered place,
+strip the body, and wrap it in blankets, overcoats, etc. If at hand,
+use bottles of hot water, hot flats, or bags of hot sand round the
+limbs and feet. Watch the tongue: it generally tends to slip back, and
+to shut off the air from the glottis. Wrap a coarse towel round the tip
+of the tongue, and keep it well pulled forward.
+
+The main thing to do is to keep up artificial respiration until the
+natural breathing comes, or all hope is lost. This is the simplest way
+to do it: The person lies on the back; let some one kneel behind the
+head. Grasp both arms near the elbows, and sweep them upward above the
+head until they nearly touch. Make a firm pull for a moment. This tends
+to fill the lungs with air by drawing the ribs up, and making the chest
+cavity larger. Now return the arms to the sides of the body until they
+press hard against the ribs. This tends to force out the air. This
+makes artificially a complete act of respiration. Repeat this act about
+fifteen times every minute.
+
+Illustration: Fig. 164.—The Sylvester Method. (First
+movement—inspiration.)
+
+All this may be kept up for several hours. The first sign of recovery
+is often seen in the slight pinkish tinge of the lips or finger-nails.
+That the pulse cannot be felt at the wrist is of little value in itself
+as a sign of death. Life may be present when only the most experienced
+ear can detect the faintest heart-beat.
+
+When a person can breathe, even a little, he can swallow. Hold
+smelling-salts or hartshorn to the nose. Put one teaspoonful of the
+aromatic spirits of ammonia, or even of ammonia water, into a
+half-glass of hot water, and give a few teaspoonfuls of this mixture
+every few minutes. Meanwhile do not fail to keep up artificial warmth
+in the most vigorous manner.
+
+379. Methods of Artificial Respiration. There are several
+well-established methods of artificial respiration. The two known as
+the Sylvester and the Marshall Hall methods are generally accepted as
+efficient and practical.
+
+Illustration: Fig. 165.—The Sylvester Method. (Second
+movement—expiration.)
+
+
+380. The Sylvester Method. The water and mucus are supposed to have
+been removed from the interior of the body by the means above described
+(sec. 378).
+
+The patient is to be placed on his back, with a roll made of a coat or
+a shawl under the shoulders; the tongue should then be drawn forward
+and retained by a handkerchief which is placed across the extended
+organ and carried under the chin, then crossed and tied at the back of
+the neck. An elastic band or small rubber tube or a suspender may be
+used for the same purpose.
+
+The attendant should kneel at the head and grasp the elbows of the
+patient and draw them upward until the hands are carried above the head
+and kept in this position until one, two, three, can be slowly counted.
+This movement elevates the ribs, expands the chest, and creates a
+vacuum in the lungs into which the air rushes, or in other words, the
+movement produces _inspiration_. The elbows are then slowly carried
+downward, placed by the side, and pressed inward against the chest,
+thereby diminishing the size of the latter and producing _expiration_.
+
+These movements should be repeated about fifteen times each minute for
+at least two hours, provided no signs of animation show themselves.
+
+381. The Marshall Hall Method. The patient should be placed face
+downwards, the head resting on the forearm with a roll or pillow placed
+under the chest; he should then be turned on his side, an assistant
+supporting the head and keeping the mouth open; after an interval of
+two or three seconds, the patient should again be placed face downward
+and allowed to remain in this position the same length of time. This
+operation should be repeated fifteen or sixteen times each minute, and
+continued (unless the patient recovers) for at least two hours.
+
+Illustration: Fig. 166.—The Marshall Hall Method. (First position.)
+
+
+If, after using one of the above methods, evidence of recovery appears,
+such as an occasional gasp or muscular movement, the efforts to produce
+artificial respiration must not be discontinued, but kept up until
+respiration is fully established. All wet clothing should then be
+removed, the patient rubbed dry, and if possible placed in bed, where
+warmth and warm drinks can be properly administered. A small amount of
+nourishment, in the form of hot milk or beef tea, should be given, and
+the patient kept quiet for two or three days.
+
+Illustration: Fig. 167.—The Marshall Hall Method. (Second position.)
+
+
+382. Sunstroke or Heatstroke. This serious accident, so far-reaching
+oftentimes in its result, is due to an unnatural elevation of the
+bodily temperature by exposure to the direct rays of the sun, or from
+the extreme heat of close and confined rooms, as in the cook-rooms and
+laundries of hotel basements, from overheated workshops, etc.
+
+There is sudden loss of consciousness, with deep, labored breathing, an
+intense burning heat of the skin, and a marked absence of sweat. The
+main thing is to lower the temperature. Strip off the clothing; apply
+chopped ice, wrapped in flannel to the head. Rub ice over the chest,
+and place pieces under the armpits and at the sides. If there is no
+ice, use sheets or cloths wet with cold water. The body may be
+stripped, and sprinkled with ice-water from a common watering-pot.
+
+If the skin is cold, moist, or clammy, the trouble is due to heat
+exhaustion. Give plenty of fresh air, but apply no cold to the body.
+Apply heat, and give hot drinks, like hot ginger tea. Sunstroke or
+heatstroke is a dangerous affliction. It is often followed by serious
+and permanent results. Persons who have once suffered in this way
+should carefully avoid any risk in the future.
+
+
+
+
+Chapter XIV.
+In Sickness and in Health.
+
+
+383. Arrangement of the Sick-room. This room, if possible, should be on
+the quiet and sunny side of the house. Pure, fresh air, sunshine, and
+freedom from noise and odor are almost indispensable. A fireplace as a
+means of ventilation is invaluable. The bed should be so placed that
+the air may get to it on all sides and the nurse move easily around it.
+Screens should be placed, if necessary, so as to exclude superfluous
+light and draughts.
+
+The sick-room should be kept free from all odors which affect the sick
+unpleasantly, as perfumery, highly scented soaps, and certain flowers.
+Remove all useless ornaments and articles likely to collect dust, as
+unnecessary pieces of furniture and heavy draperies. A clean floor,
+with a few rugs to deaden the footsteps, is much better than a woolen
+carpet. Rocking-chairs should be banished from the sick-room, as they
+are almost sure to disturb the sick.
+
+A daily supply of fresh flowers tends to brighten the room. Keep the
+medicines close at hand, but all poisonous drugs should be kept
+carefully by themselves and ordinarily under lock and key. A small
+table should be placed at the bedside, and on it the bell, food tray,
+flowers and other small things which promote the comfort of the
+patient.
+
+The nurse should not sleep with the patient. Sofas and couches are not
+commonly comfortable enough to secure needed rest. A cot bed is at once
+convenient and inexpensive, and can be readily folded and put out of
+sight in the daytime. It can also be used by the patient occasionally,
+especially during convalescence.
+
+384. Ventilation of the Sick-room. Proper ventilation is most essential
+to the sick-room, but little provision is ordinarily made for so
+important a matter. It is seldom that one of the windows cannot be let
+down an inch or more at the top, a screen being arranged to avoid any
+draught on the patient. Remove all odors by ventilation and not by
+spraying perfumery, or burning pastilles, which merely conceal
+offensive odors without purifying the air. During cold weather and in
+certain diseases, the patient may be covered entirely with blankets and
+the windows opened wide for a few minutes.
+
+Avoid ventilation by means of doors, for the stale air of the house,
+kitchen smells, and noises made by the occupants of the house, are apt
+to reach the sick-room. The entire air of the room should be changed at
+least two or three times a day, in addition to the introduction of a
+constant supply of fresh air in small quantities.
+
+385. Hints for the Sick-room. Always strive to look cheerful and
+pleasant before the patient. Whatever may happen, do not appear to be
+annoyed, discouraged, or despondent. Do your best to keep up the
+courage of sick persons under all circumstances. In all things keep in
+constant mind the comfort and ease of the patient.
+
+Do not worry the sick with unnecessary questions, idle talk, or silly
+gossip. It is cruel to whisper in the sick-room, for patients are
+always annoyed by it. They are usually suspicious that something is
+wrong and generally imagine that their condition has changed for the
+worse.
+
+Symptoms of the disease should never be discussed before the patient,
+especially if he is thought to be asleep. He may be only dozing, and
+any such talk would then be gross cruelty. Loud talking must, of
+course, be avoided. The directions of the physician must be rigidly
+carried out in regard to visitors in the sick-room. This is always a
+matter of foremost importance, for an hour or even a night of needed
+sleep and rest may be lost from the untimely call of some thoughtless
+visitor. A competent nurse, who has good sense and tact, should be able
+to relieve the family of any embarrassment under such circumstances.
+
+Do not ever allow a kerosene light with the flame turned down to remain
+in the sick-room. Use the lamp with the flame carefully shaded, or in
+an adjoining room, or better still, use a sperm candle for a night
+light.
+
+Keep, so far as possible, the various bottles of medicine, spoons,
+glasses, and so on in an adjoining room, rather than to make a
+formidable array of them on a bureau or table near the sick-bed. A few
+simple things, as an orange, a tiny bouquet, one or two playthings, or
+even a pretty book, may well take their place.
+
+The ideal bed is single, made of iron or brass, and provided with woven
+wire springs and a hair mattress. Feather-beds are always objectionable
+in the sick-room for many and obvious reasons. The proper making of a
+sick-bed, with the forethought and skill demanded in certain diseases,
+is of great importance and an art learned only after long experience.
+The same principle obtains in all that concerns the lifting and the
+moving of the sick.
+
+Sick people take great comfort in the use of fresh linen and fresh
+pillows. Two sets should be used, letting one be aired while the other
+is in use. In making changes the fresh linen should be thoroughly aired
+and warmed and everything in readiness before the patient is disturbed.
+
+386. Rules for Sick-room. Do not deceive sick people. Tell what is
+proper or safe to be told, promptly and plainly. If a physician is
+employed, carry out his orders to the very letter, as long as he visits
+you. Make on a slip of paper a note of his directions. Make a brief
+record of exactly what to do, the precise time of giving medicines,
+etc. This should always be done in serious cases, and by night
+watchers. Then there is no guesswork. You have the record before you
+for easy reference. All such things are valuable helps to the doctor.
+
+Whatever must be said in the sick-room, say it openly and aloud. How
+often a sudden turn in bed, or a quick glance of inquiry, shows that
+whispering is doing harm! If the patient is in his right mind, answer
+his questions plainly and squarely. It may not be best to tell all the
+truth, but nothing is gained in trying to avoid a straightforward
+reply.
+
+Noises that are liable to disturb the patient, in other parts of the
+house than the sick-room, should be avoided. Sounds of a startling
+character, especially those not easily explained, as the rattling or
+slamming of distant blinds and doors, are always irritating to the
+sick.
+
+Always attract the attention of a patient before addressing him,
+otherwise he may be startled and a nervous spell be induced. The same
+hint applies equally to leaning or sitting upon the sick-bed, or
+running against furniture in moving about the sick-room.
+
+387. Rest of Mind and Body. The great importance of rest for the sick
+is not so generally recognized as its value warrants. If it is worry
+and not work that breaks down the mental and physical health of the
+well, how much more important is it that the minds and bodies of the
+sick should be kept at rest, free from worry and excitement! Hence the
+skilled nurse does her best to aid in restoring the sick to a condition
+of health by securing for her patient complete rest both of mind and
+body. To this end, she skillfully removes all minor causes of alarm,
+irritation, or worry. There are numberless ways in which this may be
+done of which space does not allow even mention. Details apparently
+trifling, as noiseless shoes, quietness, wearing garments that do not
+rustle, use of small pillows of different sizes, and countless other
+small things that make up the refinement of modern nursing, play an
+important part in building up the impaired tissues of the sick.
+
+388. Care of Infectious and Contagious Diseases. There are certain
+diseases which are known to be infectious and can be communicated from
+one person to another, either by direct contact, through the medium of
+the atmosphere, or otherwise.
+
+Of the more prevalent infectious and contagious diseases are _scarlet
+fever, diphtheria, erysipelas, measles_, and _typhoid fever_.
+
+Considerations of health demand that a person suffering from any one of
+these diseases should be thoroughly isolated from all other members of
+the family. All that has been stated in regard to general nursing in
+previous sections of this chapter, applies, of course, to nursing
+infectious and contagious diseases. In addition to these certain
+special directions must be always kept in mind.
+
+Upon the nurse, or the person having the immediate charge of the
+patient, rests the responsibility of preventing the spread of
+infectious diseases. The importance must be fully understood of
+carrying out in every detail the measures calculated to check the
+spread or compass the destruction of the germs of disease.
+
+389. Hints on Nursing Infectious and Contagious Diseases. Strip the
+room of superfluous rugs, carpets, furniture, etc. Isolate two rooms,
+if possible, and have these, if convenient, at the top of the house.
+Tack sheets, wet in some proper disinfectant, to the outer frame of the
+sick-room door. Boil these sheets every third day. In case of diseases
+to which young folks are very susceptible, send the children away, if
+possible, to other houses where there are no children.
+
+Most scrupulous care should be taken in regard to cleanliness and
+neatness in every detail. Old pieces of linen, cheese-cloth, paper
+napkins, should be used wherever convenient or necessary and then at
+once burnt. All soiled clothing that cannot well be burnt should be put
+to soak at once in disinfectants, and afterward boiled apart from the
+family wash. Dishes and all utensils should be kept scrupulously clean
+by frequent boiling. For the bed and person old and worn articles of
+clothing that can be destroyed should be worn so far as possible.
+
+During convalescence, or when ready to leave isolation, the patient
+should be thoroughly bathed in water properly disinfected, the hair and
+nails especially being carefully treated.
+
+Many details of the after treatment depend upon the special disease, as
+the rubbing of the body with carbolized vaseline after scarlet fever,
+the care of the eyes after measles, and other particulars of which
+space does not admit mention here.
+
+Poisons and Their Antidotes.
+
+390. Poisons. A poison is a substance which, if taken into the system
+in sufficient amounts, will cause serious trouble or death. For
+convenience poisons may be divided into two classes, irritants and
+narcotics.
+
+The effects of irritant poisons are evident immediately after being
+taken. They burn and corrode the skin or membrane or other parts with
+which they come in contact. There are burning pains in the mouth,
+throat, stomach, and abdomen, with nausea and vomiting. A certain
+amount of faintness and shock is also present.
+
+With narcotic poisoning, the symptoms come on more slowly. After a time
+there is drowsiness, which gradually increases until there is a
+profound sleep or stupor, from which the patient can be aroused only
+with great difficulty. There are some substances which possess both the
+irritant and narcotic properties and in which the symptoms are of a
+mixed character.
+
+391. Treatment of Poisoning. An antidote is a substance which will
+either combine with a poison to render it harmless, or which will have
+a directly opposite effect upon the body, thus neutralizing the effect
+of the poison. Hence in treatment of poisoning the first thing to do,
+if you know the special poison, is to give its antidote at once.
+
+If the poison is unknown, and there is any delay in obtaining the
+antidote, the first thing to do is to remove the poison from the
+stomach. Therefore cause vomiting as quickly as possible. This may be
+done by an emetic given as follows: Stir a tablespoonful of mustard or
+of common salt in a glass of warm water and make the patient swallow
+the whole. It will usually be vomited in a few moments. If mustard or
+salt is not at hand, compel the patient to drink lukewarm water very
+freely until vomiting occurs.
+
+Vomiting may be hastened by thrusting the forefinger down the throat.
+Two teaspoonfuls of the syrup of ipecac, or a heaping teaspoonful of
+powdered ipecac taken in a cup of warm water, make an efficient emetic,
+especially if followed with large amounts of warm water.
+
+It is to be remembered that in some poisons, as certain acids and
+alkalies, no emetic should be given. Again, for certain poisons (except
+in case of arsenic) causing local irritation, but which also affect the
+system at large, no emetic should be given.
+
+392. Reference Table of Common Poisons; Prominent Symptoms; Antidotes
+and Treatment. The common poisons with their leading symptoms,
+treatment, and antidotes, may be conveniently arranged for easy
+reference in the form of a table.
+
+It is to be remembered, of course, that a complete mastery of the table
+of poisons, as set forth on the two following pages, is really a
+physician’s business. At the same time, no one of fair education should
+neglect to learn a few of the essential things to do in accidental or
+intentional poisoning.
+
+                  A Table of the More Common Poisons,
+
+       With their prominent symptoms, antidotes, and treatment.
+       Poison Prominent Symptoms Antidotes and Treatment _Strong
+       Acids:_
+
+Muriatic,
+
+Nitric,
+
+Sulphuric (vitriol),
+
+Oxalic.
+Burning sensation in mouth, throat, and stomach; blisters about mouth;
+vomiting; great weakness _No emetic_ Saleratus; chalk; soap; plaster
+from the wall; lime; magnesia; baking soda (3 or 4 teaspoonfuls in a
+glass of water). _Alkalies_:
+
+Caustic potash and soda,
+
+Ammonia,
+
+Lye,
+
+Pearlash,
+
+Saltpeter.
+Burning sensation in the parts; severe pain in stomach; vomiting;
+difficulty in swallowing; cold skin; weak pulse. _No emetic_ Olive
+oil freely; lemon juice, vinegar; melted butter and vaseline; thick
+cream. _Arsenic:_
+
+Paris green,
+Rough on rats,
+White arsenic,
+Fowler’s solution,
+Scheele’s green. Intense pains in stomach and bowels; thirst; vomiting,
+perhaps with blood; cold and clammy skin. Vomit patient repeatedly,
+give hydrated oxide of iron with magnesia, usually kept by druggists
+for emergencies; follow with strong solution of common salt and water.
+_Other Metallic Poisons_:
+Blue vitriol,
+Copperas,
+Green vitriol,
+Sugar of lead,
+Corrosive sublimate,
+Bedbug poison. Symptoms in general, same as in arsenical poisoning. 
+With lead and mercury there may be a metallic taste in the
+mouth. Emetic with lead; none with copper and iron; white of eggs in
+abundance with copper; with iron and lead give epsom salts freely;
+afterwards, oils, flour, and water. _No emetic with mercury;_ raw eggs;
+milk, or flour, and water. _Phosphorus from_
+Matches, rat poisons, etc. Pain in the stomach; vomiting; purging;
+general collapse. _Cause vomiting_. Strong soapsuds; magnesia in
+water. Never give oils. _Opium:_
+
+Morphine,
+Laudanum,
+Paregoric,
+Dover’s powder,
+Soothing syrups,
+Cholera and diarrhœa mixtures Sleepiness; dullness; stupor; “pin-hole”
+pupils; slow breathing; profuse sweat. _Cause vomiting_. Keep
+patient awake by any means, especially by vigorous walking; give strong
+coffee freely; dash cold water on face and chest. _Carbolic Acid:_
+Creasote. Severe pain in abdomen; odor of carbolic acid, mucous
+membrane in around mouth white and benumbed; cold and clammy
+skin. _No emetic._ Milk or flour and water; white of  eggs.
+_Aconite:_
+Wolfsbane Monkshood Numbness everywhere, great weakness; cold
+sweat. _Vomit patient freely._ Stimulating drinks. _Belladonna_
+Deadly Nightshade Atropia Eyes bright, with pupil enlarged; dry mouth
+and throat. _Vomit patient freely._ _Various Vegetable Poisons_
+
+Wild parsley,
+Indian tobacco,
+Toadstools,
+Tobacco plant,
+Hemlock,
+Berries of the Mountain Ash,
+Bitter sweet, etc. Stupor, nausea, great weakness and other symptoms
+according to the poison. _Cause brisk vomiting_. Stimulating drinks.
+
+393. Practical Points about Poisons. Poisons should never be kept in
+the same place with medicines or other preparations used in the
+household. They should always be put in some secure place under lock
+and key. Never use internally or externally any part of the contents of
+any package or bottle unless its exact nature is known. If there is the
+least doubt about the substance, do not assume the least risk, but
+destroy it at once. Many times the unknown contents of some bottle or
+package has been carelessly taken and found to be poison.
+
+Careless and stupid people often take, by mistake, with serious, and
+often fatal, results, poisonous doses of carbolic acid, bed-bug poison,
+horse-liniment, oxalic acid, and other poisons. A safe rule is to keep
+all bottles and boxes containing poisonous substances securely bottled
+or packed, and carefully labeled with the word POISON plainly written
+in large letters across the label. Fasten the cork of a bottle
+containing poison to the bottle itself with copper or iron wire twisted
+into a knot at the top. This is an effective means of preventing any
+mistakes, especially in the night.
+
+This subject of poisons assumes nowadays great importance, as it is a
+common custom to keep about stables, workshops, bathrooms, and living
+rooms generally a more or less formidable array of germicides,
+disinfectants, horse-liniments, insect-poisons, and other preparations
+of a similar character. For the most part they contain poisonous
+ingredients.
+
+Bacteria.
+
+394. Nature Of Bacteria. The word bacteria is the name applied to very
+low forms of plant life of microscopic size. Thus, if hay be soaked in
+water for some time, and a few drops of the liquid are examined under a
+high power of the microscope, the water is found to be swarming with
+various forms of living vegetable organisms, or bacteria. These
+microscopic plants belong to the great fungus division, and consist of
+many varieties, which may be roughly divided into groups, according as
+they are spherical, rod-like, spiral, or otherwise in shape.
+
+Each plant consists of a mass of protoplasm surrounded by an
+ill-defined cell wall. The bacteria vary considerably in size. Some of
+the rod-shaped varieties are from 1/12,000 to 1/8,000 of an inch in
+length, and average about 1/50,000 of an inch in diameter. It has been
+calculated that a space of one cubic millimeter would contain
+250,000,000 of these minute organisms, and that they would not weigh
+more than a milligram.
+
+Illustration: Fig. 168.—Examples of Micro-Organisms called Bacteria.
+(Drawn from photographs.)
+
+
+A,  spheroidal bacteria (called _cocci_) in pairs;
+  B, same kind of bacteria in chains;
+  C, bacteria found in pus (grouped in masses like a bunch of grapes).
+     [Bacteria in A, B, and C magnified about 1000 diameters].
+  D, bacteria found in pus (tendency to grow in the form of chains).
+     [Magnified about 500 diameters.]
+
+Bacteria are propagated in a very simple manner. The parent cell
+divides into two; these two into two others, and so on. The rapidity
+with which these organisms multiply under favorable conditions, makes
+them, in some cases, most dangerous enemies. It has been calculated
+that if all of the organisms survived, one bacterium would lead to the
+production of several billions of others in twenty-four hours.
+
+395. The Struggle of Bacteria for Existence. Like all kinds of living
+things, many species of bacteria are destroyed if exposed to boiling
+water or steam, but seem able to endure prolonged cold, far below the
+freezing-point. Thus ice from ponds and rivers may contain numerous
+germs which resume their activity when the ice is melted. Typhoid fever
+germs have been known to take an active and vigorous growth after they
+have been kept for weeks exposed in ice to a temperature below zero.
+
+The bacteria of consumption (bacillus tuberculosis) may retain their
+vitality for months, and then the dried expectoration of the invalids
+may become a source of danger to those who inhale air laden with such
+impurities (sec. 220 and Fig. 94).
+
+Like other living organisms, bacteria need warmth, moisture, and some
+chemical compound which answers for food, in order to maintain the
+phenomena of life. Some species grow only in contact with air, others
+need no more oxygen than they can obtain in the fluid or semi-fluid
+which they inhabit.
+
+396. Importance of Bacteria in Nature. We might well ask why the
+myriads of bacteria do not devastate the earth with their marvelous
+rapidity of propagation. So indeed they might, were it not for the
+winds, rains, melting snow and ice which scatter them far and wide, and
+destroy them.
+
+Again, as in countless other species of living organisms, bacteria are
+subject to the relentless law which allows only the fittest to survive.
+The bacteria of higher and more complex types devour those of a lower
+type. Myriads perish in the digestive tract of man and other animals.
+The excreta of some species of bacteria act as poison to destroy other
+species.
+
+It is true from the strictest scientific point of view that all living
+things literally return to the dust whence they came. While living they
+borrow a few elementary substances and arrange them in new
+combinations, by aid of the energy given them by the sun, and after a
+time die and leave behind all they had borrowed both of energy and
+matter.
+
+Countless myriads of bacteria are silently at work changing dead animal
+and vegetable matter into useful substances. In brief, bacteria prepare
+food for all the rest of the world. Were they all destroyed, life upon
+the earth would be impossible, for the elements necessary to maintain
+it would be embalmed in the bodies of the dead.
+
+397. Action of Bacteria. In certain well-known processes bacteria have
+the power of bringing about decomposition of various kinds. Thus a
+highly organized fungus, like the yeast plant, growing in the presence
+of sugar, has the power of breaking down this complex body into simpler
+ones, _viz._, alcohol and carbon dioxid.
+
+In the same way, various forms of bacteria have the power of breaking
+down complex bodies in their immediate neighborhood, the products
+depending upon the substance, the kind of bacteria, and the conditions
+under which they act. Thus the _bacteria lactis_ act upon the milk
+sugar present in milk, and convert it into lactic acid, thus bringing
+about the souring of milk.
+
+Illustration: Fig. 169.—Examples of Pathogenic Bacteria. (Drawn from
+photographs.)
+
+
+A,  spiral form of bacteria found in cholera (Magnified about 1000
+diameters)
+  B, rod-shaped bacteria (called _bacilli_) from a culture obtained in
+  _anthrax_ or malignant fustule of the face. Diseased hides carry this
+  micro-organism, and thus may occasion disease among those who handle
+  hides and wool. (Magnified about 1000 diameters)
+
+Now, while most species of bacteria are harmless, some are the cause of
+sickness and death when they gain admittance to the body under certain
+conditions. These disease-producing bacteria (known as _pathogenic_),
+when established in the blood and tissues of the body, bring about
+important chemical changes, depending upon the species of bacteria, and
+also produce a particular form of disease. The production of certain
+diseases by the agency of bacteria has now been proved beyond all
+doubt. In yellow fever, erysipelas, diphtheria, typhoid fever,
+consumption and other diseases, the connection has been definitely
+established.
+
+The evil results these germs of disease produce vary greatly in kind
+and severity. Thus the bacteria of Asiatic cholera and diphtheria may
+destroy life in a few hours, while those of consumption may take years
+to produce a fatal result. Again, the bacteria may attack some
+particular organ, or group of organs, and produce mostly local
+symptoms. Thus in a boil there is painful swelling due to the local
+effect of the bacteria, with slight general disturbance.
+
+398. The Battle against Bacteria. When we reflect upon the terrible
+ravages made by infectious diseases, and all their attendant evils for
+these many years, we can the better appreciate the work done of late
+years by tireless scientists in their efforts to modify the activity of
+disease-producing bacteria. It is now possible to cultivate certain
+pathogenic bacteria, and by modifying the conditions under which they
+are grown, to destroy their violence.
+
+In brief, science has taught us, within certain limitations, how to
+change the virulent germs of a few diseases into harmless microbes.
+
+399. Alcoholic Fermentation and Bacteria. Men of the lowest, as well as
+of the highest, type of civilization have always known that when the
+sugary juice of any fruit is left to itself for a time, at a moderately
+warm temperature, a change takes place under certain conditions, and
+the result is a liquid which, when drank, produces a pronounced effect
+upon the body. In brief, man has long known how to make for himself
+alcoholic beverages, by means of which he may become intoxicated with
+their poisonous ingredients.
+
+Whether it is a degraded South Sea Islander making a crude intoxicant
+from a sugary plant, a Japanese preparing his favorite alcoholic
+beverage from the fermentation of rice by means of a fungus plant grown
+for the purpose, a farmer of this country making cider from fermenting
+apple juice, or a French expert manufacturing costly champagne by a
+complicated process, the outcome and the intent are one and the same.
+The essential thing is to produce an alcoholic beverage which will have
+a marked physiological effect. This effect is poisonous, and is due
+solely to the alcoholic ingredient, without which man would have little
+or no use for the otherwise harmless liquid.
+
+While the practical process of making some form of alcoholic beverage
+has been understood for these many centuries, the real reason of this
+remarkable change in a wholesome fruit juice was not known until
+revealed by recent progress in chemistry, and by the use of the
+microscope. We know now that the change is due to fermentation, brought
+about from the influence, and by the action, of bacteria (sec. 125).
+
+In other words, fermentation is the result of the growth of low form of
+vegetable life known as an organised ferment. The ferment, whether it
+be the commonly used brewer’s yeast, or any other species of alcoholic
+ferment, has the power to decompose or break down a large part of the
+sugar present in the liquid into alcohol, which remains as a poison,
+and _carbon dioxid_, which escapes more or less completely.
+
+Thus man, ever prone to do evil, was once obliged, in his ignorance, to
+make his alcoholic drinks in the crudest manner; but now he has forced
+into his service the latest discoveries in science, more especially in
+bacteriology, that he may manufacture more scientifically and more
+economically alcoholic beverages of all sorts and kinds, and distribute
+them broadcast all over God’s earth for the physical and moral ruin of
+the people.
+
+Disinfectants.
+
+400. Disinfectants, Antiseptics, and Deodorants. The word disinfectant
+is synonymous with the term _bactericide_ or _germicide_. A
+disinfectant is a substance which destroys infectious material. An
+antiseptic is an agent which may hinder the growth, but does not
+destroy the vitality, of bacteria. A deodorant is not necessarily a
+disinfectant, or even an antiseptic, but refers to a substance that
+destroys or masks offensive odors.
+
+401. Air and Water as Disinfectants. Nature has provided for our
+protection two most efficient means of disinfection,—pure air (sec.
+218) and pure water (sec. 119). The air of crowded rooms contains large
+quantities of bacteria, whereas in pure air there are comparatively
+few, especially after rain, which carries them to the earth. Living
+micro-organisms have never been detected in breezes coming from the
+sea, but in those blowing out from the shore large numbers may be
+found.
+
+In water tainted with organic matter putrefactive bacteria will
+flourish, whereas pure water is fatal to their existence. Surface
+water, because it comes from that part of the soil where bacteria are
+most active, and where there is most organic matter, generally contains
+great quantities of these organisms. In the deeper strata of the soil
+there is practically no decomposition of organic matter going on,
+hence, water taken from deep sources is comparatively free from
+bacteria. For this reason, deep well water is greatly to be preferred
+for drinking purposes to that from surface wells.
+
+402. Disinfectants. It is evident that air and water are not always
+sufficient to secure disinfection, and this must be accomplished by
+other means. The destruction of infected material by fire is, of
+course, a sure but costly means of disinfection. Dry heat, steam, and
+boiling water are valuable disinfectants and do not injure most
+fabrics. These agents are generally used in combination with various
+chemical disinfectants.
+
+Certain chemical agents that are capable of destroying micro-organisms
+and their spores have come, of late years, into general use. A form of
+mercury, called _corrosive sublimate_, is a most efficacious and
+powerful germicide, but is exceedingly poisonous and can be bought only
+under restrictions.[54] _Carbolic acid, chloride of lime, permanganate
+of potash_, and various other preparations made from zinc, iron, and
+petroleum, are the chemical disinfectants most commonly and
+successfully used at the present time. There are also numerous
+varieties of commercial disinfectants now in popular use, such as
+Platt’s chlorides, bromo-chloral, sanitas, etc., which have proved
+efficient germicides.
+
+Instructions for the Management of Contagious Diseases.
+
+The following instructions for the management of contagious diseases
+were prepared for the National Board of Health by an able corps of
+scientists and experienced physicians.
+
+403. Instructions for Disinfection. Disinfection is the destruction of
+the poisons of infectious and contagious diseases. Deodorizers, or
+substances which destroy smells, are not necessarily disinfectants, and
+disinfectants do not necessarily have an odor. Disinfection cannot
+compensate for want of cleanliness nor of ventilation.
+
+404. Disinfectants to be Employed. 1. Roll sulphur (brimstone); for
+fumigation.
+
+2. Sulphate of iron (copperas) dissolved in water in the proportion of
+one and a half pounds to the gallon; for soil, sewers, etc.
+
+Note. A most useful little manual to consult in connection with this
+chapter is the _Hand-Book of Sanitary Information_, written by Roger S.
+Tracy, Sanitary Inspector of the New York City Health Department.
+Price, 50 cents.]
+
+3. Sulphate of zinc and common salt, dissolved together in water in the
+proportion of four ounces sulphate and two ounces salt to the gallon;
+for clothing, bed-linen, etc.
+
+405. How to Use Disinfectants. 1. _In the sick-room._ The most
+available agents are fresh air and cleanliness. The clothing, towels,
+bed-linen, etc., should, on removal from the patient, and before they
+are taken from the room, be placed in a pail or tub of the zinc
+solution, boiling-hot, if possible.
+
+All discharges should either be received in vessels containing copperas
+solution, or, when this is impracticable, should be immediately covered
+with copperas solution. All vessels used about the patient should be
+cleansed with the same solution.
+
+Unnecessary furniture, especially that which is stuffed, carpets, and
+hangings, should, when possible, be removed from the room at the
+outset; otherwise they should remain for subsequent fumigation and
+treatment.
+
+2. _Fumigation_. Fumigation with sulphur is the only practicable method
+for disinfecting the house. For this purpose, the rooms to be
+disinfected must be vacated. Heavy clothing, blankets, bedding, and
+other articles which cannot be treated with zinc solution, should be
+opened and exposed during fumigation, as directed below. Close the
+rooms as tightly as possible, place the sulphur in iron pans supported
+upon bricks placed in washtubs containing a little water, set it on
+fire by hot coals or with the aid of a spoonful of alcohol, and allow
+the room to remain closed for twenty-four hours. For a room about ten
+feet square, at least two pounds of sulphur should be used; for larger
+rooms, proportionally increased quantities.[55]
+
+3. _Premises_. Cellars, yards, stables, gutters, privies, cesspools,
+water-closets, drains, sewers, etc., should be frequently and liberally
+treated with copperas solution. The copperas solution is easily
+prepared by hanging a basket containing about sixty pounds of copperas
+in a barrel of water.[56]
+
+4. _Body and bed clothing, etc_. It is best to burn all articles which
+have been in contact with persons sick with contagious or infectious
+diseases. Articles too valuable to be destroyed should be treated as
+follows:
+
+_(a)_ Cotton, linen, flannels, blankets, etc., should be treated with
+the boiling-hot zinc solution; introduce piece by piece, secure
+thorough wetting, and boil for at least half an hour.
+
+_(b)_ Heavy woolen clothing, silks, furs, stuffed bed-covers, beds, and
+other articles which cannot be treated with the zinc solution, should
+be hung in the room during fumigation, their surfaces thoroughly
+exposed and pockets turned inside out. Afterward they should be hung in
+the open air, beaten, and shaken. Pillows, beds, stuffed mattresses,
+upholstered furniture, etc., should be cut open, the contents spread
+out and thoroughly fumigated. Carpets are best fumigated on the floor,
+but should afterward be removed to the open air and thoroughly beaten.
+
+Books for Collateral Study. Among the many works which may be consulted
+with profit, the following are recommended as among those most useful:
+Parkes _Elements of Health_; Canfield’s _Hygiene of the Sick-Room;_
+Coplin & Bevan’s _Practical Hygiene;_ Lincoln’s _School Hygiene_;
+Edward Smith’s _Health_; McSherrys _Health; American Health Primers_
+(12 little volumes, edited by Dr. Keen of Philadelphia); Reynold’s
+_Primer of Health_; Corfield’s _Health_; Appleton’s _Health Primers;_
+Clara S. Weeks’ _Nursing_; Church’s _Food_; Yeo’s _Food in Health and
+Disease;_ Hampton’s _Nursing, its Principles and Practice_; Price’s
+_Nurses and Nursing;_ Cullinworth’s _Manual of Nursing_; Wise’s
+_Text-Book of Nursing_ (2 vols.); and Humphrey’s _Manual of Nursing_.
+
+
+
+
+Chapter XV.
+Experimental Work in Physiology.
+
+
+406. The Limitations of Experimental Work in Physiology in Schools.
+Unlike other branches of science taught in the schools from the
+experimental point of view, the study of physiology has its
+limitations. The scope and range of such experiments is necessarily
+extremely limited compared with what may be done with the costly and
+elaborate apparatus of the medical laboratory. Again, the foundation of
+physiology rests upon systematic and painstaking dissection of the dead
+human body and the lower animals, which mode of study very properly is
+not permitted in ordinary school work. Experiments upon the living
+human body and the lower animals, now so generally depended upon in our
+medical and more advanced scientific schools, for obvious reasons can
+be performed only in a crude and quite superficial manner in secondary
+schools.
+
+Hence in the study of physiology in schools many things must be taken
+for granted. The observation and experience of medical men, and the
+experiments of the physiologist in his laboratory must be depended upon
+for data which cannot be well obtained at first hand by young students.
+
+407. Value of Experiments in Physiology in Secondary Schools. While
+circumstances and regard for certain proprieties of social life forbid
+the use of a range of experiments, in anatomy and physiology, such as
+are permitted in other branches of science in secondary schools, it by
+no means follows that we are shut out altogether from this most
+important and interesting part of the study. However simple and crude
+the apparatus, the skillful and enthusiastic teacher has at his command
+a wide series of materials which can be profitably utilized for
+experimental instruction. As every experienced teacher knows, pupils
+gain a far better knowledge, and keep up a livelier interest in any
+branch of science, if they see with their own eyes and do with their
+own hands that which serves to illuminate and illustrate the
+subject-matter.
+
+Note. For additional suggestions and practical helps on the subject of
+experimental work in physiology the reader is referred to Blaisdell’s
+_How to Teach Physiology_, a handbook for teachers. A copy of this
+pamphlet will be sent postpaid to any address by the publishers of this
+book on receipt of ten cents.
+
+
+The experimental method of instruction rivets the attention and arouses
+and keeps alive the interest of the young student; in fact, it is the
+only true method of cultivating a scientific habit of study[57]. The
+subject-matter as set forth on the printed pages of this book should be
+mastered, of course, but at the same time the topics discussed should
+be illuminated and made more interesting and practical by a
+well-arranged series of experiments, a goodly show of specimens, and a
+certain amount of microscopical work.
+
+408. The Question of Apparatus. The author well understands from
+personal experience the many practical difficulties in the way of
+providing a suitable amount of apparatus for classroom use. If there
+are ample funds for this purpose, there need be no excuse or delay in
+providing all that is necessary from dealers in apparatus in the larger
+towns, from the drug store, markets, and elsewhere. In schools where
+both the funds and the time for such purposes are limited, the zeal and
+ingenuity of teachers and students are often put to a severe test.
+Fortunately a very little money and a great deal of ingenuity and
+patience will do apparent wonders towards providing a working supply of
+apparatus.
+
+It will be noticed that many of the experiments in the preceding
+chapters of this book can be performed with very simple, and often a
+crude and home-made sort of apparatus. This plan has been rigidly
+followed by the author, first, because he fully realizes the
+limitations and restrictions of the subject; and secondly, because he
+wishes to emphasize the fact that expensive and complicated apparatus
+is by no means necessary to illustrate the great principles of anatomy
+and physiology.
+
+409. Use of the Microscope. To do thorough and satisfactory work in
+physiology in our higher schools a compound microscope is almost
+indispensable. Inasmuch as many of our best secondary schools are
+equipped with one or more microscopes for use in other studies, notably
+botany, it is much less difficult than it was a few years ago to obtain
+this important help for the classes in physiology.
+
+Illustration: Fig. 170.—A Compound Microscope
+
+For elementary class work a moderate-priced, but well-made and strong,
+instrument should be provided. If the school does not own a microscope,
+the loan of an instrument should be obtained for at least a few weeks
+from some person in the neighborhood.
+
+The appearance of the various structures and tissues of the human body
+as revealed by the microscope possesses a curious fascination for every
+observer, especially for young people. No one ever forgets the first
+look at a drop of blood, or the circulation of blood in a frog’s foot
+as shown by the microscope.
+
+Note. For detailed suggestions in regard to the manipulation and use of
+the microscope the student is referred to any of the standard works on
+the subject. The catalogues of scientific-instrument makers of our
+larger cities generally furnish a list of the requisite materials or
+handbooks which describe the use of the various microscopes of standard
+make.
+    The author is indebted to Bergen’s _Elements of Botany_ for the
+    following information concerning the different firms which deal in
+    microscopes. “Several of the German makers furnish excellent
+    instruments for use in such a course as that here outlined. The
+    author is most familar with the Leitz microscopes, which are
+    furnished by Wm. Krafft, 411 West 59th St., New York city, or by
+    the Franklin Educational Co., 15 and 17 Harcourt St., Boston. The
+    Leitz Stand, No. IV., can be furnished duty free (for schools
+    only), with objectives 1, 3, and 5, eye-pieces I. and III., for
+    $24.50. If several instruments are being provided, it would be well
+    to have part of them equipped with objectives 3 and 7, and
+    eye-pieces I. and III.
+    “The American manufacturers, Bausch & Lomb Optical Company,
+    Rochester, N.Y., and No. 130 Fulton St., New York city, have this
+    year produced a microscope of the Continental type which is
+    especially designed to meet the requirements of the secondary
+    schools for an instrument with rack and pinion coarse adjustment
+    and serviceable fine adjustment, at a low price. They furnish this
+    new stand, ‘AAB,’ to schools and teachers at ‘duty-free’ rates, the
+    prices being for the stand with two eye-pieces (any desired power),
+    ⅔-inch and ¼-inch objectives, $25.60, or with 2-inch, ⅔-inch, and
+    ¼-inch objectives, and two eye-pieces, $29.20. Stand ‘A,’ the same
+    stand as the ‘AAB,’ without joint and with sliding tube coarse
+    adjustment (as in the Leitz Stand IV.), and with three eye-pieces
+    and ⅔-inch and ¼-inch objectives, is furnished for $20.40. Stand
+    ‘A,’ with two eye-pieces, ⅔-inch and ⅙-inch objectives, $20.40.”
+
+
+410. The Use of the Skeleton and Manikin. The study of the bones by the
+help of a skeleton is almost a necessity. To this intent, schools of a
+higher grade should be provided both with a skeleton and a manikin. If
+the former is not owned by the school, oftentimes a loan of one can be
+secured of some medical man in the vicinity. Separate bones will also
+prove useful. In fact, there is no other way to study properly the
+structure and use of the bones and joints than by the bones themselves.
+A good manikin is also equally serviceable, although not so commonly
+provided for schools on account of its cost.
+
+411. The Question of Vivisection and Dissection. There should be no
+question at all concerning vivisection. _In no shape or form should it
+be allowed in any grade of our schools._ Nor is there any need of much
+dissection in the grammar-school grades. A few simple dissections to be
+performed with fresh beef-joints, tendons of turkey legs, and so on,
+will never engender cruel or brutal feelings toward living things. In
+the lower grades a discreet teacher will rarely advise his pupils to
+dissect a dead cat, dog, frog, or any other animal. Instead of actual
+dissection, the pupils should examine specimens or certain parts
+previously dissected by the teacher,—as the muscles and tendons of a
+sheep, the heart of an ox, the eye of a codfish, and so on. Even under
+these restrictions the teacher should not use the knife or scissors
+before the class to open up any part of the specimen. In brief, avoid
+everything that can possibly arouse any cruel or brutal feeling on the
+part of young students.
+
+In the higher schools, in normal and other training schools, different
+conditions prevail. Never allow vivisection in any form whatever,
+either in school or at home. Under the most exact restrictions students
+in these schools may be taught to make a few simple dissections.
+
+Most teachers will find, however, even in schools of a higher grade,
+that the whole subject is fraught with many difficulties. It will not
+require much oftentimes to provoke in a community a deal of unjust
+criticism. A teacher’s good sense and discretion are often put to a
+severe test.
+
+Additional Experiments.
+
+To the somewhat extended list of experiments as described in the
+preceding chapters a few more are herewith presented which may be used
+as opportunity allows to supplement those already given.
+
+Experiment 193. _To examine white fibrous tissue._ Snip off a very
+minute portion from the muscle of a rabbit, or any small animal
+recently dead. Tease the specimen with needles, mount in salt solution
+and examine under a high power. Note the course and characters of the
+fibers.
+
+Experiment 194. _To examine elastic tissue._ Tease out a small piece of
+ligament from a rabbit’s leg in salt solution; mount in the same, and
+examine as before. Note the curled elastic fibers.
+
+Experiment 195. _To examine areolar tissue._ Gently tease apart some
+muscular fibers, noting that they are attached to each other by
+connective tissue. Remove a little of this tissue to a slide and
+examine as before. Examine the matrix with curled elastic fiber mixed
+with straight white fibers.
+
+Experiment 196. _To examine adipose tissue._ Take a bit of fat from the
+mesentery of a rabbit. Tease the specimen in salt solution and mount in
+the same. Note the fat cells lying in a vascular meshwork.
+
+Experiment 197. _To examine connective tissues._ Take a very small
+portion from one of the tendons of a rabbit, or any animal recently
+dead; place upon a glass slide with a drop of salt solution; tease it
+apart with needles, cover with thin glass and examine with microscope.
+The fine wavy filaments will be seen. Allow a drop of dilute acetic
+acid to run under the cover glass; the filaments will swell and become
+transparent.
+
+Experiment 198. Tease out a small piece of ligament from the rabbit’s
+leg in salt solution; mount in the same, and examine under a high
+power. Note the curled elastic fibers.
+
+Experiment 199. _A crude experiment to represent the way in which a
+person’s neck is broken._ Bring the ends of the left thumb and the left
+second finger together in the form of a ring. Place a piece of a wooden
+toothpick across it from the middle of the finger to the middle of the
+thumb. Put the right forefinger of the other hand up through the front
+part to represent the odontoid process of the axis, and place some
+absorbent cotton through the other part to represent the spinal cord.
+Push backwards with the forefinger with just enough force to break the
+toothpick and drive its fragments on to the cotton.
+
+Experiment 200. _To illustrate how the pulse-wave is transmitted along
+an artery._ Use the same apparatus as in Experiment 106, p. 201. Take
+several thin, narrow strips of pine wood. Make little flags by
+fastening a small piece of tissue paper on one end of a wooden
+toothpick. Wedge the other end of the toothpick into one end of the
+strips of pine wood. Use these strips like levers by placing them
+across the long rubber tube at different points. Let each lever
+compress the tube a little by weighting one end of it with a blackboard
+eraser or book of convenient size.
+    As the pulse-wave passes along under the levers they will be
+    successively raised, causing a slight movement of the tissue-paper
+    flags.
+
+Experiment 201. _The dissection of a sheep’s heart._ Get a sheep’s
+heart with the lungs attached, as the position of the heart will be
+better understood. Let the lungs be laid upon a dish so that the heart
+is uppermost, with its apex turned toward the observer.
+    The line of fat which extends from the upper and left side of the
+    heart downwards and across towards the right side, indicates the
+    division between the right and left ventricles.
+    Examine the large vessels, and, by reference to the text and
+    illustrations, make quite certain which are the _aorta_, the
+    _pulmonary artery_, the _superior_ and _inferior venæ cavæ_, and
+    the _pulmonary veins_.
+    Tie variously colored yarns to the vessels, so that they may be
+    distinguished when separated from the surrounding parts.
+    Having separated the heart from the lungs, cut out a portion of the
+    wall of the _right ventricle_ towards its lower part, so as to lay
+    the cavity open. Gradually enlarge the opening until the _chordæ
+    tendineæ_ and the flaps of the _tricuspid valve_ are seen. Continue
+    to lay open the ventricle towards the pulmonary artery until the
+    _semilunar valves_ come into view.
+    The pulmonary artery may now be opened from above so as to display
+    the upper surfaces of the semilunar valves. Remove part of the wall
+    of the right auricle, and examine the right auriculo-ventricular
+    opening.
+    The heart may now be turned over, and the _left ventricle_ laid
+    open in a similar manner. Notice that the mitral valve has only two
+    flaps. The form of the valves is better seen if they are placed
+    under water, and allowed to float out. Observe that the walls of
+    the _left_ ventricle are much thicker than those of the _right_.
+    Open the left auricle, and notice the entrance of the _pulmonary
+    veins_, and the passage into the ventricle.
+    The ventricular cavity should now be opened up as far as the aorta,
+    and the semilunar valves examined. Cut open the aorta, and notice
+    the form of the _semilunar valves_.
+
+Experiment 202. _To show the circulation in a frog’s foot_ (see Fig.
+78, p. 192). In order to see the blood circulating in the membrane of a
+frog’s foot it is necessary to firmly hold the frog. For this purpose
+obtain a piece of soft wood, about six inches long and three wide, and
+half an inch thick. At about two inches from one end of this, cut a
+hole three-quarters of an inch in diameter and cover it with a piece of
+glass, which should be let into the wood, so as to be level with the
+surface. Then tie up the frog in a wet cloth, leaving one of the hind
+legs outside. Next, fasten a piece of cotton to each of the two longest
+toes, but not too tightly, or the circulation will be stopped and you
+may hurt the frog.
+    Tie the frog upon the board in such a way that the foot will just
+    come over the glass in the aperture. Pull carefully the pieces of
+    cotton tied to the toes, so as to spread out the membrane between
+    them over the glass. Fasten the threads by drawing them into
+    notches cut in the sides of the board. The board should now be
+    fixed by elastic bands, or by any other convenient means, upon the
+    stage of the microscope, so as to bring the membrane of the foot
+    under the object glass.
+    The flow of blood thus shown is indeed a wonderful sight, and never
+    to be forgotten. The membrane should be occasionally moistened with
+    water.
+    Care should be taken not to occasion any pain to the frog.
+
+Experiment 203. _To illustrate the mechanics of respiration_[58] (see
+Experiment 122, p. 234). “In a large lamp-chimney, the top of which is
+closed by a tightly fitting perforated cork (A), is arranged a pair of
+rubber bags (C) which are attached to a Y connecting tube (B), to be
+had of any dealer in chemical apparatus or which can be made by a
+teacher having a bunsen burner and a little practice in the
+manipulation of glass (Fig. 171). From the center of the cork is
+attached a rubber band by means of a staple driven through the cork,
+the other end of which (D) is attached to the center of a disk of
+rubber (E) such as dentists use. This disk is held to the edge of the
+chimney by a wide elastic band (F). There is a string (G) also attached
+to the center of the rubber disk by means of which the diaphragm may be
+lowered. Such is a description of the essentials of the model. The
+difficulties encountered in its construction are few and easily
+overcome. In the first place, the cork must be air-tight, and it is
+best made so by pouring a little melted paraffin over it, care being
+taken not to close the tube. The rubber bags were taken from toy
+balloon-whistles. In the construction of the diaphragm, it is to be
+remembered that it also must be air-tight, and in order to resemble the
+human diaphragm, it must have a conical appearance when at rest. In
+order to avoid making any holes in the rubber, the two attachments (one
+of the rubber band, and the other of the string) were made in this
+wise: the rubber was stretched over a button having an eye, then under
+the button was placed a smaller ring from an old umbrella; to this ring
+was attached the rubber band, and to the eye of the button was fastened
+the operating string. When not in use the diaphragm should be taken off
+to relieve the strain on the rubber band.”
+
+Illustration: Fig. 171.
+
+
+Experiment 204. _To illustrate the action of the intercostal muscles_
+(see sec. 210). The action of the intercostal muscles is not at first
+easy to understand; but it will be readily comprehended by reference to
+a model such as that represented in Fig. 172. This maybe easily made by
+the student himself with four laths of wood, fastened together at the
+corners, A, B, C, D, with pins or small screws, so as to be movable. At
+the points E, F, G, H, pins are placed, to which elastic bands may be
+attached (A). B D represents the vertebral column; A C, the sternum;
+and A B and C D, the ribs. The elastic band F G represents the
+_external_ intercostal muscles, and E H, the _internal_ intercostals.
+    If now the elastic band E H be removed, the remaining band, F G,
+    will tend to bring the two points to which it is attached, nearer
+    together, and the result will be that the bars A B and C D will be
+    drawn upwards (B), that is, in the same direction as the ribs in
+    the act of _inspiration_. When the elastic band E H is allowed to
+    exert its force, the opposite effect will be produced (C); in this
+    case representing the position of the ribs in an act of
+    _expiration_.
+
+Illustration: Fig. 172.
+
+
+Experiment 205. Pin a round piece of bright red paper (large as a
+dinner-plate) to a white wall, with a single pin. Fasten a long piece
+of thread to it, so it can be pulled down in a moment. Gaze steadily at
+the red paper. Have it removed while looking at it intently, and a
+greenish spot takes its place.
+
+Experiment 206. Lay on different parts of the skin a small, square
+piece of paper with a small central hole in it. Let the person close
+his eyes, while another person gently touches the uncovered piece of
+skin with cotton wool, or brings near it a hot body. In each case ask
+the observed person to distinguish between them. He will always succeed
+on the volar side of the hand, but occasionally fail on the dorsal
+surface of the hand, the extensor surface of the arm, and very
+frequently on the skin of the back.
+
+Experiment 207. _Wheatstone’s fluttering hearts_. Make a drawing of a
+red heart on a bright blue ground. In a dark room lighted by a candle
+hold the picture below the level of the eyes and give it a gentle
+to-and-fro motion. On continuing to look at the heart it will appear to
+move or flutter over the blue background.
+
+Experiment 208. At a distance of six inches from the eyes hold a veil
+or thin gauze in front of some printed matter placed at a distance of
+about two feet. Close one eye, and with the other we soon see either
+the letters distinctly or the fine threads of the veil, but we cannot
+see both equally distinct at the same time. The eye, therefore, can
+form a distinct image of a near or distant object, but not of both at
+the same time; hence the necessity for accommodation.
+
+Experiment 209. Place a person in front of a bright light opposite a
+window, and let him look at the light; or place one’s self opposite a
+well-illuminated mirror. Close one eye with the hand and observe the
+diameter of the other pupil. Then suddenly remove the hand from the
+closed eye: light falls upon it; at the same time the pupil of the
+other eye contracts.
+
+Experiment 210. _To illustrate the blind spot. Marriott’s experiment_.
+On a white card make a cross and a large dot, either black or colored.
+Hold the card vertically about ten inches from the right eye, the left
+being closed. Look steadily at the cross with the right eye, when both
+the cross and the circle will be seen. Gradually approach the card
+toward the eye, keeping the axis of vision fixed on the cross. At a
+certain distance the circle will disappear, _i.e._, when its image
+falls on the entrance of the optic nerve. On bringing the card nearer,
+the circle reappears, the cross, of course, being visible all the time
+(see Experiment 180, p. 355).
+
+Experiment 211. _To map out the field of vision_. A crude method is to
+place the person with his back to a window, ask him to close one eye,
+stand in front of him about two feet distant, hold up the forefingers
+of both hands in front of and in the plane of your own face. Ask the
+person to look steadily at your nose, and as he does so observe to what
+extent the fingers can be separated horizontally, vertically, and in
+oblique directions before they disappear from his field of vision.
+
+Experiment 212. _To illustrate imperfect judgment of distance_. Close
+one eye and hold the left forefinger vertically in front of the other
+eye, at arm’s length, and try to strike it with the right forefinger.
+    On the first trial one will probably fall short of the mark, and
+    fail to touch it. Close one eye, and rapidly try to dip a pen into
+    an inkstand, or put a finger into the mouth of a bottle placed at a
+    convenient distance. In both cases one will not succeed at first.
+    In these cases one loses the impressions produced by the
+    convergence of the optic axes, which are important factors in
+    judging of distance.
+
+Experiment 213. Hold a pencil vertically about twelve inches from the
+nose, fix it with both eyes, close the left eye, and then hold the
+right index finger vertically, so as to cover the lower part of the
+pencil. With a sudden move, try to strike the pencil with the finger.
+In every case one misses the pencil and sweeps to the right of it.
+
+Experiment 214. _To illustrate imperfect judgment of direction_. As the
+retina is spherical, a line beyond a certain length when looked at
+always shows an appreciable curvature.
+    Hold a straight edge just below the level of the eyes. Its upper
+    margin shows a slight concavity.
+
+Surface Anatomy and Landmarks.
+
+In all of our leading medical colleges the students are carefully and
+thoroughly drilled on a study of certain persons selected as models.
+The object is to master by observation and manipulation the details of
+what is known as surface anatomy and landmarks. Now while detailed work
+of this kind is not necessary in secondary schools, yet a limited
+amount of study along these lines is deeply interesting and profitable.
+The habit of looking at the living body with anatomical eyes and with
+eyes at our fingers’ ends, during the course in physiology, cannot be
+too highly estimated.
+
+In elementary work it is only fair to state that many points of surface
+anatomy and many of the landmarks cannot always be defined or located
+with precision. A great deal in this direction can, however, be done in
+higher schools with ingenuity, patience, and a due regard for the
+feelings of all concerned. Students should be taught to examine their
+own bodies for this purpose. Two friends may thus work together, each
+serving as a “model” to the other.
+
+To the following syllabus may be added such other similar exercises as
+ingenuity may suggest or time permit.
+
+Syllabus.
+
+I. Bony Landmarks.
+
+1. The _occipital protuberance_ can be distinctly felt at the back of
+the head. This is always the thickest part (often three-quarters of an
+inch or more) of the skull-cap, and is more prominent in some than in
+others. The thinnest part is over the temples, where it may be almost
+as thin as parchment.
+
+2. The working of the _condyle of the lower jaw_ vertically and from
+side to side can be distinctly felt and seen in front of the ear. When
+the mouth is opened wide, the condyle advances out of the glenoid
+cavity, and returns to its socket when the mouth is shut. In front of
+the ear, lies the zygoma, one of the most marked and important
+landmarks to the touch, and in lean persons to the eye.
+
+3. The sliding movement of the _scapula_ on the chest can be properly
+understood only on the living subject. It can move not only upwards and
+downwards, as in shrugging the shoulders, backwards and forwards, as in
+throwing back the shoulders, but it has a rotary movement round a
+movable center. This rotation is seen while the arm is being raised
+from the horizontal to the vertical position, and is effected by the
+cooperation of the trapezius with the serratus magnus muscles.
+
+4. The _patella_, or knee-pan, the _two condyles of the tibia_, the
+_tubercle on the tibia_ for the attachment of the ligament of the
+patella, and the _head of the fibula_ are the chief bony landmarks of
+the knee. The head of the fibula lies at the outer and back part of the
+tibia. In extension of the knee, the patella is nearly all above the
+condyles. The inner border of the patella is thicker and more prominent
+than the outer, which slopes down toward its condyle.
+
+5. The short, front edge of the _tibia_, called the “shin,” and the
+broad, flat, subcutaneous surface of the bone can be felt all the way
+down. The inner edge can be felt, but not so plainly.
+
+6. The head of the _fibula_ is a good landmark on the outer side of the
+leg, about one inch below the top of the tibia. Note that it is placed
+well back, and that it forms no part of the knee joint, and takes no
+share in supporting the weight. The shaft of the fibula arches
+backwards and is buried deep among the muscles, except at the lower
+fourth, which can be distinctly felt.
+
+7. The _malleoli_ form the great landmarks of the ankle. The outer
+malleolus descends lower than the inner. The inner malleolus advances
+more to the front and does not descend so low as the outer.
+
+8. The line of the _clavicle_, or collar bone, and the projection of
+the joint at either end of it can always be felt. Its direction is not
+perfectly horizontal, but slightly inclined downwards. We can
+distinctly feel the _spine_ of the scapula and its highest point, the
+_acromion_.
+
+9. Projecting beyond the acromion (the arm hanging by the side), we can
+feel, through the fibers of the _deltoid_, the upper part of the
+humerus. It distinctly moves under the hand when the arm is rotated. It
+is not the head of the bone which is felt, but its prominences (the
+tuberosities). The greater, externally; the lesser in front.
+
+10. The _tuberosities of the humerus_ form the convexity of the
+shoulder. When the arm is raised, the convexity disappears,—there is a
+slight depression in its place. The head of the bone can be felt by
+pressing the fingers high up in the axilla.
+
+11. The _humerus_ ends at the elbow in two bony prominences (internal
+and external condyles). The internal is more prominent. We can always
+feel the _olecranon_. Between this bony projection of the ulna and the
+internal condyle is a deep depression along which runs the ulna nerve
+(commonly called the “funny” or “crazy” bone).
+
+12. Turn the hand over with the palm upwards, and the edge of the
+_ulna_ can be felt from the olecranon to the prominent knob (styloid
+process) at the wrist. Turn the forearm over with the palm down, and
+the head of the ulna can be plainly felt and seen projecting at the
+back of the wrist.
+
+13. The upper half of the _radius_ cannot be felt because it is so
+covered by muscles; the lower half is more accessible to the touch.
+
+14. The three rows of projections called the “knuckles” are formed by
+the proximal bones of the several joints. Thus the first row is formed
+by the ends of the metacarpals, the second by the ends of the first
+phalanges, and the third by the ends of the second phalanges. That is,
+in all cases the line of the joints is a little in advance of the
+knuckles and nearer the ends of the fingers.
+
+II. Muscular Landmarks.
+
+1. The position of the _sterno-mastoid_ muscle as an important and
+interesting landmark of the neck has already been described (p. 70).
+
+2. If the left arm be raised to a vertical position and dropped to a
+horizontal, somewhat vigorously, the tapering ends of the _pectoralis
+major_ and the tendons of the _biceps_ and _deltoid_ may be felt by
+pressing the parts in the axilla between the fingers and thumb of the
+right hand.
+
+3. The appearance of the _biceps_ as a landmark of the arm has already
+been described (p. 70). The action of its antagonist, the _triceps_,
+may be studied in the same manner.
+
+4. The _sartorius_ is one of the fleshy landmarks of the thigh, as the
+biceps is of the arm, and the sterno-cleido-mastoid of the neck. Its
+direction and borders may be easily traced by raising the leg,—a
+movement which puts the muscle in action.
+
+5. If the model be directed to stand on tiptoe, both of the large
+muscles of the calf, the _gastrocnemius_ and _soleus_, can be
+distinguished.
+
+6. Direct the model, while sitting upright, to cross one leg over the
+other, using his utmost strength. The great muscles of the inner thigh
+are fully contracted. Note the force required to pull the legs to the
+ordinary position.
+
+7. With the model lying in a horizontal position with both legs firmly
+held together, note the force required to pull the feet apart while the
+great muscles of the thigh are fully contracted.
+
+8. In forcible and resisted flexion of the wrist two tendons come up in
+relief. On the outer side of one we feel the pulse at the wrist, the
+radial artery here lying close to the radius.
+
+9. On the outer side of the wrist we can distinctly see and feel when
+in action, the three extensor tendons of the thumbs. Between two of
+them is a deep depression at the base of the thumb, which the French
+call the “anatomical tobacco box.”
+
+10. The relative position of the several extensor tendons on the back
+of the wrist and fingers as they play in their grooves over the back of
+the radius and ulna can be distinctly traced when the several muscles
+are put in action.
+
+11. There are several strong tendons to be seen and felt about the
+ankle. Behind is the _tendo Achillis_. It forms a high relief with a
+shallow depression on each side of it. Behind both the inner and outer
+ankle several tendons can be felt. Over the front of the ankle, when
+the muscles are in action, we can see and feel several tendons. They
+start up like cords when the action is resisted. They are kept in their
+proper relative position by strong pulleys formed by the annular
+ligament. Most of these tendons can be best seen by stand a model on
+one foot, _i.e._ in unstable equilibrium.
+
+III. Landmarks of the Heart.
+
+To have a general idea of the form and position of the _heart_, map its
+outline with colored pencils or crayon on the chest wall itself, or on
+some piece of clean, white cloth, tightly pinned over the clothing. A
+pattern of the heart may be cut out of pasteboard, painted red, or
+papered with red paper, and pinned in position outside the clothing.
+The apex of the heart is at a point about two inches below the left
+nipple and one inch to its sternal side. This point will be between the
+fifth and sixth ribs, and can generally be determined by feeling the
+apex beat.
+
+IV. Landmarks of a Few Arteries.
+
+The pulsation of the _temporal_ artery can be felt in front of the ear,
+between the zygoma and the ear. The _facial_ artery can be distinctly
+felt as it passes over the upper jaw at the front edge of the masseter
+muscle. The pulse of a sleeping child can often be counted at the
+anterior fontanelle by the eye alone.
+
+About one inch above the clavicle, near the outer border of the
+sterno-mastoid, we can feel the pulsation of the great _subclavian_
+artery. At the back of the knee the _popliteal_ artery can be felt
+beating. The _dorsal_ artery of the foot can be felt beating on a line
+from the middle of the ankle to the interval between the first and
+second metatarsal bones.
+
+When the arm is raised to a right angle with the body, the _axillary_
+artery can be plainly felt beating in the axilla. Extend the arm with
+palm upwards and the _brachial_ artery can be felt close to the inner
+side of the biceps. The position of the _radial_ artery is described in
+Experiment 102.
+
+
+
+
+Glossary.
+
+
+Abdomen (Lat. _abdo_, _abdere_, to conceal). The largest cavity of the
+body, containing the liver, stomach, intestines, and other organs.
+
+Abductor (Lat. _abduco_, to draw from). A muscle which draws a limb
+from the middle line of the body, or a finger or toe from the middle
+line of the foot or hand.
+
+Absorbents (Lat. _absorbere_, to suck up). The vessels which take part
+in the process of absorption.
+
+Absorption. The process of sucking up nutritive or waste matters by the
+blood-vessels or lymphatics.
+
+Accommodation of the Eye. The alteration in the shape of the
+crystalline lens, which accommodates, or adjusts, the eye for near or
+remote vision.
+
+Acetabulum (Lat. _acetabulum_, a small vinegar-cup). The cup-shaped
+cavity of the innominate bone for receiving the head of the femur.
+
+Acid (Lat. _acidus_, from _acere_, to be sour). A substance usually
+sour, sharp, or biting to the taste.
+
+Acromion (Gr. ἀκρον the tip, and ᾧμος, the shoulder). The part of the
+scapula forming the tip of the shoulder.
+
+Adam’s Apple. An angular projection of cartilage in the front of the
+neck. It may be particularly prominent in men.
+
+Adductor (Lat. _adduco_, to draw to). A muscle which draws towards the
+middle line of the body, or of the hand or foot.
+
+Adenoid (Gr. ἀδήν, a gland). Tissue resembling gland tissue.
+
+Afferent (Lat. _ad_, to, and _fero_, to convey). Vessels or nerves
+carrying the contents or impulses from the periphery to the center.
+
+Albumen, or Albumin (Lat. _albus_, white). An animal substance
+resembling the white of an egg.
+
+Albuminuria. A combination of the words “albumin” and “urine.” Presence
+of _albumen_ in the _urine_.
+
+Aliment (Lat. _alo_, to nourish). That which affords nourishment; food.
+
+Alimentary (Lat. _alimentum_, food). Pertaining to _aliment_, or food.
+
+Alimentary Canal (Lat. _alimentum_). The tube in which the food is
+digested or prepared for reception into the blood.
+
+Alkali (Arabic _al kali_, the soda plant). A name given to certain
+substances, such as soda, potash, and the like, which have the power of
+combining with acids.
+
+Alveolar (Lat. _alveolus_, a little hollow). Pertaining to the alveoli,
+the _cavities_ for the reception of the teeth.
+
+Amœba (Gr. ἀμείβω, to change). A single-celled, protoplasmic organism,
+which is constantly changing its form by protrusions and withdrawals of
+its substance.
+
+Amœboid. Like an _amœba_.
+
+Ampulla (Lat. _ampulla_, a wine-flask). The dilated part of the
+semicircular canals of the internal ear.
+
+Anabolism (Gr. ἀναβάλλω, to throw or build up). The process by means of
+which simpler elements are _built up_ into more complex.
+
+Anæsthetics (Gr. ἀν, without, and αἰσθησία, feeling). Those medicinal
+agents which prevent the feeling of pain, such as chloroform, ether,
+laughing-gas, etc.
+
+Anastomosis (Gr. ἀνά, by, and στόμα, a mouth). The intercommunication
+of vessels.
+
+Anatomy (Gr. ἀνατέμνω, to cut up). The science which describes the
+structure of living things. The word literally means dissection.
+
+Antiseptic (Lat. _anti_, against, and _sepsis_, poison). Opposing or
+counter-acting putrefaction.
+
+Antrum (Lat. _antrum_, a cave). The cavity in the upper jaw.
+
+Aorta (Gr. ἀορτή, from ἀείρο, to raise up). The great artery that
+_rises up_ from the left ventricle of the heart.
+
+Aponeurosis (Gr. ἀπό, from, and νεῦρον, a nerve). A fibrous membranous
+expansion of a tendon; the nerves and tendons were formerly thought to
+be identical structures, both appearing as white cords.
+
+Apoplexy (Gr. ἀποπληξία, a sudden stroke). The escape of blood from a
+ruptured blood-vessel into the substance of the brain.
+
+Apparatus. A number of organs of various sizes and structures working
+together for some special object.
+
+Appendages (Lat. _ad_ and _pendeo_, to hang from). Something connected
+with a part.
+
+Aqueous Humor (Lat. _aqua_, water). The watery fluid occupying the
+space between the cornea and crystalline lens of the eye.
+
+Arachnoid Membrane (Gr. ἀράχνη, a spider, and εἰδώς, like). The thin
+covering of the brain and spinal cord, between the dura mater and the
+pia mater.
+
+Arbor Vitæ. Literally, “the tree of life”; a name given to the peculiar
+appearance presented by a section of the cerebellum.
+
+Areolar (Lat. _areola_, a small space, dim. of _area_). A term applied
+to a connective tissue containing _small spaces_.
+
+Artery (Gr. ἀήρ, air, and τερέω, to contain). A vessel by which blood
+is carried away from the heart. It was supposed by the ancients to
+contain only air, hence the name.
+
+Articulation (Lat. _articulo_, to form a joint). The more or less
+movable union of bones, etc.; a joint.
+
+Arytenoid Cartilages (Gr. ἀρύταινα, a ladle). Two small cartilages of
+the larynx, resembling the mouth of a pitcher.
+
+Asphyxia (Gr. ἀ, without, and σφίξις, the pulse). Literally, “without
+pulse.” Condition caused by non-oxygenation of the blood.
+
+Assimilation (Lat. _ad_, to, and _similis_, like). The conversion of
+food into living tissue.
+
+Asthma (Gr. ἆσθμα, a gasping). Spasmodic affection of the bronchial
+tubes in which free respiration is interfered with, owing to their
+diminished caliber.
+
+Astigmatism (Gr. ἀ, without, and στίγμα, a point). Irregular refraction
+of the eye, producing a blurred image.
+
+Atrophy (Gr. ἀ, without, and τροφή, nourishment). Wasting of a part
+from lack of nutrition.
+
+Auditory Nerve (Lat. _audio_, to hear). The special nerve of hearing.
+
+Auricle (Lat. _auricula_, a little ear). A cavity of the heart.
+
+Azygos (Gr. ἀ, without, and ζυγός, a yoke). Without fellow; not paired.
+
+Bacteria (βακτήριον, a staff). A microscopic, vegetable organism;
+certain species are active agents in fermentation, while others appear
+to be the cause of infectious diseases.
+
+Bactericide (_Bacterium_ and Lat. _caedere_, to kill). Same as
+_germicide_.
+
+Bile. The gall, or peculiar secretion of the liver; a viscid, yellowish
+fluid, and very bitter to the taste.
+
+Biology (Gr. βίος, life, and λόγος, discourse). The science which
+treats of living bodies.
+
+Bladder (Saxon _bleddra_, a bladder, a goblet). A bag, or sac, serving
+as a receptacle of some secreted fluid, as the _gall bladder_, etc. The
+receptacle of the urine in man and other animals.
+
+Bright’s Disease. A group of diseases of the kidney, first described by
+Dr. Bright, an English physician.
+
+Bronchi (Gr. βρόγχος, windpipe). The first two divisions, or branches,
+of the trachea; one enters each lung.
+
+Bronchial Tubes. The smaller branches of the trachea within the
+substance of the lungs terminating in the air cells.
+
+Bronchitis. Inflammation of the larger bronchial tubes; a “cold”
+affecting the air passages.
+
+Bunion. An enlargement and inflammation of the first joint of the great
+toe.
+
+Bursa. A pouch; a membranous sac interposed between parts which are
+subject to movement, one on the other, to allow them to glide smoothly.
+
+Callus (Lat. _calleo_, to be thick-skinned). Any excessive hardness of
+the skin caused by friction or pressure.
+
+Canal (Lat. _canalis_, a canal). A tube or passage.
+
+Capillary (Lat. _capillus_, hair). The smallest blood-vessels, so
+called because they are so minute.
+
+Capsule (Lat. _capsula_, a little chest). A membranous bag enclosing a
+part.
+
+Carbon Dioxid, often called _carbonic acid_. The gas which is present
+in the air breathed out from the lungs; a waste product of the animal
+kingdom and a food of the vegetable kingdom.
+
+Cardiac (Gr. καρδία, the heart). The cardiac orifice of the stomach is
+the upper one, and is near the heart; hence its name.
+
+Carnivorous (Lat. _caro_, flesh, and _voro_, to devour). Subsisting
+upon flesh.
+
+Carron Oil. A mixture of equal parts of linseed oil and lime-water, so
+called because first used at the Carron Iron Works in Scotland.
+
+Cartilage. A tough but flexible material forming a part of the joints,
+air passages, nostrils, ear; gristle, etc.
+
+Caruncle (Lat. _caro_, flesh). The small, red, conical-shaped body at
+the inner angle of the eye, consisting of a cluster of follicles.
+
+Casein (Lat. _caseus_, cheese). The albuminoid substance of milk; it
+forms the basis of cheese.
+
+Catarrh. An inflammation of a mucous membrane, usually attended with an
+increased secretion of mucus. The word is often limited to _nasal_
+catarrh.
+
+Cauda Equina (Lat., horse’s tail). The collection of large nerves
+descending from the lower end of the spinal cord.
+
+Cell (Lat. _cella_, a storeroom). The name of the tiny miscroscopic
+elements, which, with slender threads or fibers, make up most of the
+body; they were once believed to be little hollow chambers; hence the
+name.
+
+Cement. The substance which forms the outer part of the fang of a
+tooth.
+
+Cerebellum (dim. for _cerebrum_, the brain). The little brain, situated
+beneath the posterior third of the cerebrum.
+
+Cerebrum. The brain proper, occupying the upper portion of the skull.
+
+Ceruminous (Lat. _cerumen_, ear wax). A term applied to the glands
+secreting cerumen, or _ear wax_.
+
+Chloral. A powerful drug and narcotic poison used to produce sleep.
+
+Chloroform. A narcotic poison generally used by inhalation; of
+extensive use in surgical operations. It produces anæsthesia.
+
+Chondrin (Gr. χονδρός, cartilage). A kind of gelatine obtained by
+boiling _cartilage_.
+
+Chordæ Tendineæ. Tendinous cords.
+
+Choroid (Gr. χορίον, skin, and εἶδος, form). The middle coat of the
+eyeball.
+
+Chyle (Gr. χυλός, juice). The milk-like fluid formed by the digestion
+of fatty articles of food in the intestines.
+
+Chyme (Gr. χυμός, juice). The pulpy liquid formed by digestion in the
+stomach.
+
+Cilia (pl. of _cilium_, an eyelash). Minute hair-like processes found
+upon the cells of the air passages and other parts.
+
+Ciliary Muscle. A small muscle of the eye which assists in
+accommodation.
+
+Circumvallate (Lat. _circum_, around, and _vallum_, a rampart).
+Surrounded by a rampart, as are certain papillæ of the tongue.
+
+Coagulation (Lat. _coagulo_, to curdle). Applied to the process by
+which the blood clots or solidifies.
+
+Cochlea (Lat. _cochlea_, a snail shell). The spiral cavity of the
+internal ear.
+
+Columnæ Carneæ. Fleshy projections in the ventricles of the heart.
+
+Commissure (Lat. _con_, together, and _mitto_, _missum_, to put). A
+joining or uniting together.
+
+Compress. A pad or bandage applied directly to an injury to compress
+it.
+
+Concha (Gr. κόγχη, a mussel shell). The shell-shaped portion of the
+external ear.
+
+Congestion (Lat. _con_, together, and _gero_, to bring). Abnormal
+gathering of blood in any part of the body.
+
+Conjunctiva (Lat. _con_, together, and _jungo_, to join). A thin layer
+of mucous membrane which lines the eyelids and covers the front of the
+eyeball, thus joining the latter to the lids.
+
+Connective Tissue. The network which connects the minute parts of most
+of the structures of the body.
+
+Constipation (Lat. _con_, together, and _stipo_, to crowd close).
+Costiveness.
+
+Consumption (Lat. _consumo_, to consume). A disease of the lungs,
+attended with fever and cough, and causing a decay of the bodily
+powers. The medical name is _phthisis_.
+
+Contagion (Lat. _con_, with, and _tango_ or _tago_, to touch). The
+communication of disease by contact, or by the inhalation of the
+effluvia of a sick person.
+
+Contractility (Lat. _con_, together, and _traho_, to draw). The
+property of a muscle which enables it to contract, or draw its
+extremities closer together.
+
+Convolutions (Lat. _con_, together, and _volvo_, to roll). The tortuous
+foldings of the external surface of the brain.
+
+Convulsion (Lat. _convello_, to pull together). A more or less violent
+agitation of the limbs or body.
+
+Coördination. The manner in which several different organs of the body
+are brought into such relations with one another that their functions
+are performed in harmony.
+
+Coracoid (Gr. κόραξ, a crow, εἶδος, form). Shaped like a crow’s beak.
+
+Cornea (Lat. _cornu_, a horn). The transparent horn-like substance
+which covers a part of the front of the eyeball.
+
+Coronary (Lat. _corona_, a crown). A term applied to vessels and nerves
+which encircle parts, as the _coronary_ arteries of the heart.
+
+Coronoid (Gr. κορώνη, a crow). Like a crow’s beak; thus the _coronoid_
+process of the ulna.
+
+Cricoid (Gr. κρίκος, a ring, and εἶδος, form). A cartilage of the
+larynx resembling a seal ring in shape.
+
+Crystalline Lens (Lat. _crystallum_, a crystal). One of the humors of
+the eye; a double-convex body situated in the front part of the
+eyeball.
+
+Cumulative. A term applied to the violent action from drugs which
+supervenes after the taking of several doses with little or no effect.
+
+Cuticle (Lat. dim. of _cutis_, the skin). Scarf skin; the epidermis.
+
+Cutis (Gr. σκῦτος, a skin or hide). The true skin, also called the
+_dermis_.
+
+Decussation (Lat. _decusso_, _decussatum_, to cross). The _crossing_ or
+running of one portion athwart another.
+
+Degeneration (Lat. _degenerare_, to grow worse, to deteriorate). A
+change in the structure of any organ which makes it less fit to perform
+its duty.
+
+Deglutition (Lat. _deglutire_, to swallow). The process of swallowing.
+
+Deltoid. Having a triangular shape; resembling the Greek letter Δ
+(_delta_).
+
+Dentine (Lat. _dens_, _dentis_, a tooth). The hard substance which
+forms the greater part of a tooth; ivory.
+
+Deodorizer. An agent which corrects any foul or unwholesome odor.
+
+Dextrin. A soluble substance obtained from starch.
+
+Diabetes Mellitus (Gr. διά, through, βαίνω, to go, and μέλι, honey).
+Excessive flow of sugar-containing urine.
+
+Diaphragm (Gr. διαφράσσω, to divide by a partition). A large, thin
+muscle which separates the cavity of the chest from the abdomen.
+
+Diastole (Gr. διαστέλλω, to dilate). The _dilatation_ of the heart.
+
+Dietetics. That part of medicine which relates to diet, or food.
+
+Diffusion of Gases. The power of gases to become intimately mingled.
+
+Diplöe (Gr. διπλόω, to double, to fold). The osseous tissue between the
+tables of the skull.
+
+Dipsomania (Gr. δίψα, thirst, and μανία, madness). An insatiable desire
+for intoxicants.
+
+Disinfectants. Agents used to destroy the germs or particles of living
+matter that are believed to be the causes of infection.
+
+Dislocation (Lat. _dislocare_, to put out of place). An injury to a
+joint in which the bones are displaced or forced out of their sockets.
+
+Dissection (Lat. _dis_, apart, and _seco_, to cut). The cutting up of
+an animal in order to learn its structure.
+
+Distal (Lat. _dis_, apart, and _sto_, to stand). Away from the center.
+
+Duct (Lat. _duco_, to lead). A narrow tube.
+
+Duodenum (Lat. _duodeni_, twelve). The first division of the small
+intestines, about twelve fingers’ breadth long.
+
+Dyspepsia (Gr. -δύς, ill, and πέπτειν, to digest). A condition of the
+alimentary canal in which it digests imperfectly. Indigestion.
+
+Dyspnœa (Gr. δύς, difficult, and πνέω, to breathe). Difficult
+breathing.
+
+Efferent (Lat. _effero_, to carry out). _Bearing_ or _carrying
+outwards_, as from the center to the periphery.
+
+Effluvia (Lat. _effluo_, to flow out). Exhalations or vapors coming
+from the body, and from decaying animal or vegetable substances.
+
+Element. One of the simplest parts of which anything consists.
+
+Elimination (Lat. _e_, out of, and _limen, liminis_, a threshold). The
+act of _expelling_ waste matters. Signifies, literally, “to throw out
+of doors.”
+
+Emetic (Gr. ἐμέω, to vomit). A medicine which causes vomiting.
+
+Emulsion (Lat. _emulgere_, to milk). Oil in a finely divided state,
+suspended in water.
+
+Enamel (Fr. _émail_). Dense material covering the crown of a tooth.
+
+Endolymph (Gr. ἔνδον, within, and Lat. _lympha_, water). The fluid in
+the membranous labyrinth of the ear.
+
+Endosmosis (Gr. ἔνδον, within, and ὠθέω, to push). The current from
+without _inwards_ when diffusion of fluids takes place through a
+membrane.
+
+Epidemic (Gr. ἐπί, upon, and δέμος, the people). An extensively
+prevalent disease.
+
+Epiglottis (Gr. ἐπί, upon, and γλόττις, the entrance to the windpipe).
+A leaf-shaped piece of cartilage which covers the top of the larynx
+during the act of swallowing.
+
+Epilepsy (Gr. ἐπίληψις, a seizure). A nervous disease accompanied by
+fits in which consciousness is lost; the falling sickness.
+
+Ether (Gr. αἰθήρ, the pure, upper air). A narcotic poison. Used as an
+anæsthetic in surgical operations.
+
+Eustachian (from an Italian anatomist named Eustachi). The tube which
+leads from the throat to the middle ear, or tympanum.
+
+Excretion (Lat. _excerno_, to separate). The separation from the blood
+of the waste matters of the body; also the materials excreted.
+
+Exosmosis (Gr. ἔξω, without, and ᾀθέω, to push). The current from
+within _outwards_ when diffusion of fluids takes place through a
+membrane.
+
+Expiration (Lat. _expiro_, to breathe out). The act of forcing air out
+of the lungs.
+
+Extension (Lat. _ex_, out, and _tendo_, to stretch). The act of
+restoring a limb, etc., to its natural position after it has been
+flexed or bent; the opposite of _flexion_.
+
+Fauces. The part of the mouth which opens into the pharynx.
+
+Fenestra (Lat.). Literally, “a window.” Fenestra ovalis and fenestra
+rotunda, the oval and the round window; two apertures in the bone
+between the tympanic cavity and the labyrinth of the ear.
+
+Ferment. That which causes fermentation, as yeast.
+
+Fermentation (Lat. _fermentum_, boiling). The process of undergoing an
+effervescent change, as by the action of yeast; in a wider sense, the
+change of organized substances into new compounds by the action of a
+ferment. It differs in kind according to the nature of the ferment.
+
+Fiber (Lat. _fibra_, a filament). One of the tiny threads of which many
+parts of the body are composed.
+
+Fibrilla. A little fiber; one of the longitudinal threads into which a
+striped muscular fiber can be divided.
+
+Fibrin (Lat. _fibra_, a fiber). An albuminoid substance contained in
+the flesh of animals, and also produced by the coagulation of blood.
+
+Flexion (Lat. _flecto_, to bend). The act of bending a limb, etc.
+
+Follicle (Lat. dim. of _follis_, a money bag). A little pouch or
+depression.
+
+Fomentation (Lat. _foveo_, to keep warm). The application of any warm,
+medicinal substance to the body, by which the vessels are relaxed.
+
+Foramen. A hole, or aperture.
+
+Frontal Sinus. A blind or closed cavity in the bones of the skull just
+over the eyebrows.
+
+Fumigation (Lat. _fumigo_, to perfume a place). The use of certain
+fumes to counteract contagious effluvia.
+
+Function (Lat. _functio_, a doing). The special duty of any organ.
+
+Ganglion (Gr. γάγγλιν, a knot). A knot-like swelling in a nerve; a
+smaller nerve center.
+
+Gastric (Gr. γαστήρ, stomach). Pertaining to the stomach.
+
+Gelatine (Lat. _gelo_, to congeal). An animal substance which dissolves
+in hot water and forms a jelly on cooling.
+
+Germ (Lat. _germen_, a sprout, bud). Disease germ; a name applied to
+certain tiny bacterial organisms which have been demonstrated to be the
+cause of disease.
+
+Germicide (_Germ_, and Lat. _caedere_, to kill). Any agent which has a
+destructive action upon living germs, especially _bacteria_.
+
+Gland (Lat. _glans_, an acorn). An organ consisting of follicles and
+ducts, with numerous blood-vessels interwoven.
+
+Glottis (Gr. γλόττα, the tongue). The narrow opening between the vocal
+cords.
+
+Glucose. A kind of sugar found in fruits, also known as grape sugar.
+
+Gluten. The glutinous albuminoid ingredient of cereals.
+
+Glycogen. Literally, “producing glucose.” Animal starch found in liver,
+which may be changed into glucose.
+
+Gram. Unit of metric system, 15.43 grains troy.
+
+Groin. The lower part of the abdomen, just above each thigh.
+
+Gustatory (Lat. _gusto_, _gustatum_, to taste). Belonging to the sense
+of _taste_.
+
+Gymnastics (Gr. γυμνάξω, to exercise). The practice of athletic
+exercises.
+
+Hæmoglobin (Gr. αἷμα, blood, and Lat. _globus_, a globe or globule). A
+complex substance which forms the principal coloring constituent of the
+red corpuscles of the blood.
+
+Hemispheres (Gr. ἡμί, half, and σφαῖρα, a sphere). Half a sphere, the
+lateral halves of the cerebrum, or brain proper.
+
+Hemorrhage (Gr. αἷμα, blood, and ῥήγνυμι, to burst). Bleeding, or the
+loss of blood.
+
+Hepatic (Gr. ἧπαρ, the liver). Pertaining to the liver.
+
+Herbivorous (Lat. _herba_, an herb, and _voro_, to devour). Applied to
+animals that subsist upon vegetable food.
+
+Heredity. The predisposition or tendency derived from one’s ancestors
+to definite physiological actions.
+
+Hiccough. A convulsive motion of some of the muscles used in breathing,
+accompanied by a shutting of the glottis.
+
+Hilum, sometimes written Hilus. A small fissure, notch, or depression.
+A term applied to the concave part of the kidney.
+
+Homogeneous (Gr. ὁμός, the same, and γένος, kind). Of the _same kind_
+or quality throughout; uniform in nature,—the reverse of heterogeneous.
+
+Humor. The transparent contents of the eyeball.
+
+Hyaline (Gr. ὕαλος, glass). Glass-like, resembling glass in
+transparency.
+
+Hydrogen. An elementary gaseous substance, which, in combination with
+oxygen, produces water.
+
+Hydrophobia (Gr. ὕδωρ, water, and φοβέομαι, to fear). A disease caused
+by the bite of a rabid dog or other animal.
+
+Hygiene (Gr. ὑγἰεια health). The art of preserving health and
+preventing disease.
+
+Hyoid (Gr. letter υ, and εἰδος, form, resemblance). The bone at the
+root of the tongue, shaped like the Greek letter υ.
+
+Hypermetropia (Gr. ὑπέρ over, beyond, μέτρον, measure, and ώ̓ψ, the
+eye). Far-sightedness.
+
+Hypertrophy (Gr. ὑπέρ, over, and τροφή, nourishment). Excessive growth;
+thickening or enlargement of any part or organ.
+
+Incisor (Lat. _incido_, to cut). Applied to the four front teeth of
+both jaws, which have sharp, cutting edges.
+
+Incus. An anvil; the name of one of the bones of the middle ear.
+
+Indian Hemp. The common name of _Cannabis Indica_, an intoxicating drug
+known as _hasheesh_ and by other names in Eastern countries.
+
+Inferior Vena Cava. The chief vein of the lower part of the body.
+
+Inflammation (Lat. prefix _in_ and _flammo_, to flame). A redness or
+swelling of any part of the body with heat and pain.
+
+Insalivation (Lat. _in_ and _saliva_, the fluid of the mouth). The
+mingling of the saliva with the food during the act of chewing.
+
+Inspiration (Lat. _inspiro, spiratum_, to breathe in). The act of
+drawing in the breath.
+
+Intestine (Lat. _intus_, within). The part of the alimentary canal
+which is continuous with the lower end of the stomach; also called the
+bowels.
+
+Iris (Lat. _iris_, the rainbow). The thin, muscular ring which lies
+between the cornea and crystalline lens, giving the eye its special
+color.
+
+Jaundice (Fr. _jaunisse_, yellow). A disorder in which the skin and
+eyes assume a yellowish tint.
+
+Katabolism (Gr. καταβάλλω, to throw down). The process by means of
+which the more complex elements are rendered more simple and less
+complex. The opposite of _anabolism_.
+
+Labyrinth. The internal ear, so named from its many windings.
+
+Lacrymal Apparatus (Lat. _lacryma_, a tear). The organs for forming and
+carrying away the tears.
+
+Lacteals (Lat. _lac, lactis_, milk). The absorbent vessels of the small
+intestines.
+
+Laryngoscope (Gr. λάρυγξ, larynx, and σκοπέω, to behold). An instrument
+consisting of a mirror held in the throat, and a reflector to throw
+light on it, by which the interior of the larynx is brought into view.
+
+Larynx. The cartilaginous tube situated at the top of the windpipe.
+
+Lens. Literally, a lentil; a piece of transparent glass or other
+substance so shaped as either to converge or disperse the rays of
+light.
+
+Ligament (Lat. _ligo_, to bind). A strong, fibrous material binding
+bones or other solid parts together.
+
+Ligature (Lat. _ligo_, to bind). A thread of some material used in
+tying a cut or injured artery.
+
+Lobe. A round, projecting part of an organ, as of the liver, lungs, or
+brain.
+
+Lymph (Lat. _lympha_, pure water). The watery fluid conveyed by the
+lymphatic vessels.
+
+Lymphatic Vessels. A system of absorbent vessels.
+
+Malleus. Literally, the mallet; one of the small bones of the middle
+ear.
+
+Marrow. The soft, fatty substance contained in the cavities of bones.
+
+Mastication (Lat. _mastico_, to chew). The act of cutting and grinding
+the food to pieces by means of the teeth.
+
+Meatus (Lat. _meo_, _meatum_, to pass). A _passage_ or canal.
+
+Medulla Oblongata. The “oblong marrow”; that portion of the brain which
+lies upon the basilar process of the occipital bone.
+
+Meibomian. A term applied to the small glands between the conjunctiva
+and tarsal cartilages, discovered by _Meibomius_.
+
+Membrana Tympani. Literally, the membrane of the drum; a delicate
+partition separating the outer from the middle ear; it is sometimes
+popularly called “the drum of the ear.”
+
+Membrane. A thin layer of tissue serving to cover some part of the
+body.
+
+Mesentery (Gr. μέσος, middle, and ἔντερον, the intestine). A
+duplicature of the peritoneum covering the small _intestine_, which
+occupies the _middle_ or center of the abdominal cavity.
+
+Metabolism (Gr. μεταβολή, change). The _changes_ taking place in cells,
+whereby they become more complex and contain more force, or less
+complex and contain less force. The former is constructive metabolism,
+or _anabolism_; the latter, destructive metabolism, or _katabolism_.
+
+Microbe (Gr. μικρός, little, and βίος, life). A microscopic organism,
+particularly applied to bacteria.
+
+Microscope (Gr. μικρός, small, and σκοπέω, to look at). An optical
+instrument which assists in the examination of minute objects.
+
+Molar (Lat. _mola_, a mill). The name applied to the three back teeth
+at each side of the jaw; the grinders, or mill-like teeth.
+
+Molecule (dim. of Lat. _moles_, a mass). The smallest quantity into
+which the mass of any substance can physically be divided. A molecule
+may be chemically separated into two or more atoms.
+
+Morphology (Gr. μόρφη, form, and λόγος, discourse). The study of the
+laws of form or structure in living beings.
+
+Motor (Lat. _moveo_, _motum_, to move). The name of the nerves which
+conduct to the muscles the stimulus which causes them to contract.
+
+Mucous Membrane. The thin layer of tissue which covers those internal
+cavities or passages which communicate with the external air.
+
+Mucus. The glairy fluid secreted by mucous membranes.
+
+Myopia (Gr. μύω, to shut, and ὤψ, the eye). A defect of vision
+dependent upon an eyeball that is too long, rendering distant objects
+indistinct; _near sight_.
+
+Myosin (Gr. μῶς, muscle). Chief proteid substance of muscle.
+
+Narcotic (Gr. ναρκάω, to benumb). A medicine which, in poisonous doses,
+produces stupor, convulsions, and sometimes death.
+
+Nerve Cell. A minute round and ashen-gray cell found in the brain and
+other nervous centers.
+
+Nerve Fiber. An exceedingly slender thread of nervous tissue.
+
+Nicotine. The poisonous and stupefying oil extracted from tobacco.
+
+Nostril (Anglo-Saxon _nosu_, nose, and _thyrl_, a hole). One of the two
+outer openings of the nose.
+
+Nucleolus (dim. of _nucleus_). A little nucleus.
+
+Nucleus (Lat. _nux_, a nut). A central part of any body, or that about
+which matter is collected. In anatomy, a cell within a cell.
+
+Nutrition (Lat. _nutrio_, to nourish). The processes by which the
+nourishment of the body is accomplished.
+
+Odontoid (Gr. ὀδούς, a tooth, εἶδσ, shape). The name of the bony peg of
+the second vertebra, around which the first turns.
+
+Œsophagus. Literally, that which carries food. The tube leading from
+the throat to the stomach; the gullet.
+
+Olecranon (Gr. ὠλένη, the elbow, and κρανίον, the top of the head). A
+curved eminence at the upper and back part of the ulna.
+
+Olfactory (Lat. _olfacio_, to smell). Pertaining to the sense of smell.
+
+Optic (Gr. ὀπτεύω, to see). Pertaining to the sense of sight.
+
+Orbit (Lat. _orbis_, a circle). The bony socket or cavity in which the
+eyeball is situated.
+
+Organ (Lat. _organum_, an instrument or implement). A portion of the
+body having some special function or duty.
+
+Osmosis (Gr. ὠσμός, impulsion). Diffusion of liquids through membranes.
+
+Ossa Innominata, pl. of Os Innominatum (Lat.). “Unnamed bones.” The
+irregular bones of the pelvis, unnamed on account of their
+non-resemblance to any known object.
+
+Otoconia (Gr. οὖς, an ear, and κονία, dust). Minute crystals of lime in
+the vestibule of the ear; also known as _otoliths_.
+
+Palate (Lat. _palatum_, the palate). The roof of the mouth, consisting
+of the hard and soft palate.
+
+Palpitation (Lat. _palpitatio_, a frequent or throbbing motion). A
+violent and irregular beating of the heart.
+
+Papilla. The small elevations found on the skin and mucous membranes.
+
+Paralysis (Gr. παραλύω, to loosen; also, to disable). Loss of function,
+especially of motion or feeling. Palsy.
+
+Parasite. A plant or animal that grows or lives on another.
+
+Pelvis. Literally, a basin. The bony cavity at the lower part of the
+trunk.
+
+Pepsin (Gr. πέπτω, to digest). The active principle of the gastric
+juice.
+
+Pericardium (Gr. περί, about, and καρδία, heart). The sac enclosing the
+heart.
+
+Periosteum (Gr. περί, around, ὀστέον, a bone). A delicate fibrous
+membrane which invests the bones.
+
+Peristaltic Movements (Gr. περί, round, and στέλλω, to send). The slow,
+wave-like movements of the stomach and intestines.
+
+Peritoneum (Gr. περιτείνω, to stretch around). The investing membrane
+of the stomach, intestines, and other abdominal organs.
+
+Perspiration (Lat. _perspiro_, to breathe through). The sweat.
+
+Petrous (Gr. πέτρα, a rock). The name of the hard portion of the
+temporal bone, in which are situated the drum of the ear and labyrinth.
+
+Phalanges (Gr. φάλαγξ, a body of soldiers closely arranged in ranks and
+files). The bones of the fingers and toes.
+
+Pharynx (Gr. φάρμγξ, the throat). The cavity between the back of the
+mouth and the gullet.
+
+Physiology (Gr. φύσις, nature, and λόγος, a discourse). The science of
+the functions of living, organized beings.
+
+Pia Mater (Lat.). Literally, the tender mother; the innermost of the
+three coverings of the brain. It is thin and delicate; hence the name.
+
+Pinna (Lat. a feather or wing). External cartilaginous flap of the ear.
+
+Plasma (Gr. πλάσσω, to mould). Anything formed or moulded. The liquid
+part of the blood.
+
+Pleura (Gr. πλευρά, the side, also a rib). A membrane covering the
+lung, and lining the chest.
+
+Pleurisy. An inflammation affecting the pleura.
+
+Pneumogastric (Gr. πνεύμων, the lungs, and γαστήρ, the stomach). The
+chief nerve of respiration; also called the _vagus_, or wandering
+nerve.
+
+Pneumonia. An inflammation affecting the air cells of the lungs.
+
+Poison (Fr. _poison_). Any substance, which, when applied externally,
+or taken into the stomach or the blood, works such a change in the
+animal economy as to produce disease or death.
+
+Pons Varolii. Bridge of Varolius. The white fibers which form a
+_bridge_ connecting the different parts of the brain, first described
+by _Varolius_.
+
+Popliteal (Lat. _poples_, _poplitis_, the ham, the back part of the
+knee). The space _behind the knee joint_ is called the _popliteal_
+space.
+
+Portal Vein (Lat. _porta_, a gate). The venous trunk formed by the
+veins coming from the intestines. It carries the blood to the liver.
+
+Presbyopia (Gr. πρέσβυς, old, and ὤψ, the eye). A defect of the
+accommodation of the eye, caused by the hardening of the crystalline
+lens; the “far sight” of adults and aged persons.
+
+Process (Lat. _procedo_, _processus_, to proceed, to go forth). Any
+projection from a surface; also, a method of performance; a procedure.
+
+Pronation (Lat. _pronus_, inclined forwards). The turning of the hand
+with the palm downwards.
+
+Pronator. The group of muscles which turn the hand palm downwards.
+
+Proteids (Gr. πρῶτος, first, and εἶδος, form). A general term for the
+albuminoid constitutents of the body.
+
+Protoplasm (Gr. πρῶτος, first, and πλάσσω, to form). A _first-formed_
+organized substance; primitive organic cell matter.
+
+Pterygoid (Gr. πτέρων, a wing, and εἶδος, form, resemblance).
+Wing-like.
+
+Ptomaine (Gr. πτῶμα, a dead body). One of a class of animal bases or
+alkaloids formed in the putrefaction of various kinds of albuminous
+matter.
+
+Ptyalin (Gr. σίαλον, saliva). A ferment principle in _saliva_, having
+power to convert starch into sugar.
+
+Pulse (Lat. _pello, pulsum_, to beat). The throbbing of an artery
+against the finger, occasioned by the contraction of the heart.
+Commonly felt at the _wrist_.
+
+Pupil (Lat. _pupilla_). The central, round opening in the iris, through
+which light passes into the interior of the eye.
+
+Pylorus (Gr. πυλουρός, a gatekeeper). The lower opening of the stomach,
+at the beginning of the small intestine.
+
+Reflex (Lat. _reflexus_, turned back). The name given to involuntary
+movements produced by an excitation traveling along a sensory nerve to
+a center, where it is turned back or reflected along motor nerves.
+
+Renal (Lat. _ren_, _renis_, the kidney). Pertaining to the _kidneys_.
+
+Respiration (Lat. _respiro_, to breathe frequently). The function of
+breathing, comprising two acts,—_inspiration_, or breathing in, and
+_expiration_, or breathing out.
+
+Retina (Lat. _rete_, a net). The innermost of the three tunics, or
+coats, of the eyeball, being an expansion of the optic nerve.
+
+Rima Glottidis (Lat. _rima_, a chink or cleft). The _opening_ of the
+glottis.
+
+Saccharine (Lat. _saccharum_, sugar). The group of food substances
+which embraces the different varieties of sugar, starch, and gum.
+
+Saliva. The moisture, or fluids, of the mouth, secreted by the salivary
+glands; the spittle.
+
+Sarcolemma (Gr. σάρξ, flesh, and λέμμα, a husk). The membrane which
+surrounds the contractile substance of a striped muscular fiber.
+
+Sclerotic (Gr. σκληρός, hard). The tough, fibrous, outer coat of the
+eyeball.
+
+Scurvy. Scorbutus,—a disease of the general system, having prominent
+skin symptoms.
+
+Sebaceous (Lat. _sebum_, fat). Resembling fat; the name of the oily
+secretion by which the skin is kept flexible and soft.
+
+Secretion (Lat. _secerno_, _secretum_, to separate). The process of
+separating from the blood some essential, important fluid; which fluid
+is also called a _secretion_.
+
+Semicircular Canals. Three canals in the internal ear.
+
+Sensation. The perception of an external impression by the nervous
+system.
+
+Serum. The clear, watery fluid which separates from the clot of the
+blood.
+
+Spasm (Gr. σπασμός, convulsion). A sudden, violent, and involuntary
+contraction of one or more muscles.
+
+Special Sense. A sense by which we receive particular sensations, such
+as those of sight, hearing, taste, and smell.
+
+Sputum, pi. Sputa (Lat. _spuo_, _sputum_, to _spit_). The matter which
+is coughed up from the air passages.
+
+Stapes. Literally, a stirrup; one of the small bones of the middle ear.
+
+Stimulant (Lat. _stimulo_, to prick or goad on). An agent which causes
+an increase of vital activity in the body or in any of its parts.
+
+Striated (Lat. _strio_, to furnish with channels). Marked with fine
+lines.
+
+Styptics (Gr. στυπτικός astringent). Substances used to produce a
+contraction or shrinking of living tissues.
+
+Subclavian Vein (Lat. _sub_, under, and _clavis_, a key). The great
+vein bringing back the blood from the arm and side of the head; so
+called because it is situated underneath the _clavicle_, or collar
+bone.
+
+Superior Vena Cava (Lat., upper hollow vein). The great vein of the
+upper part of the body.
+
+Suture (Lat. _sutura_, a seam). The union of certain bones of the skull
+by the interlocking of jagged edges.
+
+Sympathetic System of Nerves. A double chain of nervous ganglia,
+situated chiefly in front of, and on each side of, the spinal column.
+
+Symptom (Gr. σύν, with, and πίπτω, to fall). A sign or token of
+disease.
+
+Synovial (Gr. σύν, with, and ὠόν, an egg). The liquid which lubricates
+the joints; joint-oil. It resembles the white of a raw egg.
+
+System. A number of different organs, of similar structures,
+distributed throughout the body and performing similar functions.
+
+Systemic. Belonging to the system, or body, as a whole.
+
+Systole (Gr. συστέλλω, to contract). The contraction of the heart, by
+which the blood is expelled from that organ.
+
+Tactile (Lat. _tactus_, touch). Relating to the sense of touch.
+
+Tartar. A hard crust which forms on the teeth, and is composed of
+salivary mucus, animal matter, and a compound of lime.
+
+Temporal (Lat. _tempus_, time, and _tempora_, the temples). Pertaining
+to the temples; so called because the hair begins to turn white with
+age in that portion of the scalp.
+
+Tendon (Lat. _tendo_, to stretch). The white, fibrous cord, or band, by
+which a muscle is attached to a bone; a sinew.
+
+Tetanus (Gr. τείνω, to stretch). A disease marked by persistent
+contractions of all or some of the voluntary muscles; those of the jaw
+are sometimes solely affected; the disorder is then termed lockjaw.
+
+Thorax (Gr. θώραξ, a breast-plate). The upper cavity of the trunk of
+the body, containing the lungs, heart, etc.; the chest.
+
+Thyroid (Gr. εἶδος, a shield, and εἶ̓δος, form). The largest of the
+cartilages of the larynx: its projection in front is called “Adam’s
+Apple.”
+
+Tissue. Any substance or texture in the body formed of various
+elements, such as cells, fibers, blood-vessels, etc., interwoven with
+each other.
+
+Tobacco (Indian _tabaco_, the tube, or pipe, in which the Indians
+smoked the plant). A plant used for smoking and chewing, and in snuff.
+
+Trachea (Gr. τραχύς, rough). The windpipe.
+
+Tragus (Gr. τράγος, a goat). The eminence in front of the opening of
+the ear; sometimes hairy, like a goat’s beard.
+
+Transfusion (Lat. _transfundo_, to pour from one vessel to another).
+The operation of injecting blood taken from one person into the veins
+of another.
+
+Trichina Spiralis. (A twisted hair). A minute species of parasite, or
+worm, which infests the flesh of the hog: may be introduced into the
+human system by eating pork not thoroughly cooked.
+
+Trochanter (Gr. τροχάω, to turn, to revolve). Name given to two
+projections on the upper extremities of the femur, which give
+attachment to the _rotator_ muscles of the thigh.
+
+Trypsin. The ferment principle in pancreatic juice, which converts
+proteid material into peptones.
+
+Tubercle (Lat. _tuber_, a bunch). A pimple, swelling, or tumor. A
+morbid product occurring in certain lung diseases.
+
+Tuberosity (Lat. _tuber, tuberis_, a swelling). A protuberance.
+
+Turbinated (Lat. _turbinatus_, from _turbo, turbinis_, a top). Formed
+like a _top_; a name given to the bones in the outer wall of the nasal
+fossæ.
+
+Tympanum (Gr. τύμπανον, a drum). The cavity of the middle ear,
+resembling a drum in being closed by two membranes.
+
+Umbilicus (Lat., the navel.) A round cicatrix or scar in the median
+line of the abdomen.
+
+Urea (Lat. _urina_, urine). Chief solid constitutent of _urine_.
+Nitrogenous product of tissue decomposition.
+
+Ureter (Gr. οὐρέω, to pass urine). The tube through which the _urine_
+is conveyed from the kidneys to the bladder.
+
+Uvula (Lat. _uva_, a grape). The small, pendulous body attached to the
+back part of the palate.
+
+Vaccine Virus (Lat. _vacca_, a cow, and _virus_, poison). The material
+derived from heifers for the purpose of vaccination,—the great
+preventive of smallpox.
+
+Valvulae Conniventes. A name given to transverse folds of the mucous
+membrane in the small intestine.
+
+Varicose (Lat. _varix_, a dilated vein). A distended or enlarged vein.
+
+Vascular (Lat. _vasculum_, a little vessel). Pertaining to or
+possessing blood or lymph vessels.
+
+Vaso-motor (Lat. _vas_, a vessel, and _moveo, motum_, to move). Causing
+_motion_ to the _vessels_. Vaso-motor nerves cause contraction and
+relaxation of the blood-vessels.
+
+Venæ Cavæ, pl. of Vena Cava. “Hollow veins.” A name given to the two
+great veins of the body which meet at the right auricle of the heart
+
+Venous (Lat. _vena_, a vein). Pertaining to, or contained within, a
+vein.
+Ventilation. The introduction of fresh air into a room or building in
+such a manner as to keep the air within it in a pure condition.
+
+Ventral (Lat. _venter, ventris_, the belly). Belonging to the abdominal
+or belly cavity.
+
+Ventricles of the Heart. The two largest cavities of the heart.
+
+Vermiform (Lat. _vermis_, a worm, and _forma_, form). Worm-shaped.
+
+Vertebral Column (Lat. _vertebra_, a joint). The backbone; also called
+the spinal column and spine.
+
+Vestibule. A portion of the internal ear, communicating with the
+semicircular canals and the cochlea, so called from its fancied
+resemblance to the vestibule, or porch, of a house.
+
+Villi (Lat. _villus_, shaggy hair). Minute, thread-like projections
+upon the internal surface of the small intestine, giving it a velvety
+appearance.
+
+Virus (Lat., poison). Foul matter of an ulcer; poison.
+
+Vital Knot. A part of the medulla oblongata, the destruction of which
+causes instant death.
+
+Vitreous (Lat. _vitrum_, glass). Having the appearance of glass;
+applied to the humor occupying the largest part of the cavity of the
+eyeball.
+
+Vivisection (Lat. _vivus_, alive, and _seco_, to cut). The practice of
+operating upon living animals, for the purpose of studying some
+physiological process.
+
+Vocal Cords. Two elastic bands or ridges situated in the larynx; the
+essential parts of the organ of voice.
+
+Zygoma (Gr. ζυγώς, a yoke). The arch formed by the malar bone and the
+zygomatic process of the temporal bone.
+
+
+
+
+Index.
+
+
+Absorption
+  from mouth and stomach
+  by the intestines
+Accident and emergencies
+Achilles, Tendon of
+Air, made impure by breathing
+  Foul, effect of, on health
+Alcohol, Effect of, on bones
+  Effect of, on muscles
+  Effect of, on muscular tissue
+  Effect of, on physical culture
+  Nature of
+  Effects of, on human system
+    and digestion
+  Effect of, on the stomach
+    and the gastric juice
+  Final results on digestion
+  Effects of, on the liver
+  Fatty degeneration due to
+  Effect of, on the circulation
+  Effect of, on the heart
+  Effect of, on the blood-vessels
+  Effect of, on the lungs
+  Other results of, on lungs
+  Effect of, on disease
+  Effect of, on kidneys
+Alcohol
+  as cause of Bright’s disease
+  and the brain
+  How, injures the brain
+  Why brain suffers from
+  the enemy of brain work
+  Other physical results of
+  Diseases produced by
+  Mental and moral ruin by
+  Evil results of, inherited
+  Effect of, on taste
+  Effect of, on the eye
+  Effect of, on throat and voice
+Alcoholic beverages
+Alcoholic fermentation and Bacteria
+Anabolism defined
+Anatomy defined
+Antidotes for poisons
+Antiseptics
+Apparatus, Question of
+Arm, Upper
+Arteries
+Astigmatism
+Asphyxia
+Atlas and axis
+Atmosphere, how made impure
+
+Bacteria, Nature of
+Bacteria, Struggle for existence of
+  Importance of, in Nature
+  Action of
+  Battle against
+Baths and bathing
+Bathing, Rules and precautions
+Bicycling
+Bile
+Biology defined
+Bladder
+Bleeding, from stomach
+  from lungs
+  from nose
+  How to stop
+Blood, Circulation of
+  Physical properties of
+  corpuscles
+  Coagulation of
+  General plan of circulation
+Blood-vessels, Nervous control of
+  connected with heart
+  Effect of alcohol on
+  Injuries to
+Bodies, living, Characters of
+Body, General plan of
+Bone, Chemical composition of
+  Physical properties of
+  Microscopic structure of
+Bones, uses of, The
+  Kinds of
+  in infancy and childhood
+  positions at school
+  in after life
+  Broken
+  broken, Treatment for
+  Effect of alcohol on
+  Effect of tobacco on
+Breathing, Movements of
+Breathing, Mechanism of
+  Varieties of
+  Nervous control of
+  change in the air
+  Air, made impure by
+Brain, as a whole
+  Membranes of
+  as a reflex center
+  Effects of alcohol on
+Brain center, Functions of, in perception of impressions
+Bright’s disease caused by alcohol
+Bronchial tubes
+Burns or scalds
+
+Capillaries
+Carbohydrates
+Carpus
+Cartilage
+  Hyaline
+  White fibro-
+  Yellow fibro-
+  Thyroid
+  Arytenoid
+  Cricoid
+Cells
+  and the human organism
+  Kinds of
+  Vital properties of
+  Epithelial
+  Nerve
+Cerebrum
+Cerebellum
+Chemical compounds in the body
+Chloral
+Chyle
+Chyme
+Cilia of air passages
+Circulation
+  General plan of
+  Portal
+  Pulmonic
+  Systemic
+  Effect of alcohol on
+Clavicle
+Cleanliness, Necessity for
+Clothing, Use of
+  Material used for
+  Suggestions for use of
+  Effects of tight-fitting
+  Miscellaneous hints on use of
+  Catching, on fire
+Coagulation of blood
+Cocaine, ether, and chloroform
+Cochlea of ear
+Cocoa
+Coffee
+Colon
+Color-blindness
+Complemental air
+Compounds, Chemical
+  Organic
+Condiments
+Conjunctiva
+Connective tissue
+Consonants
+Contagious diseases
+Contraction, Object of
+Contusions and bruises
+Convulsions
+Cooking
+Coughing
+Cornea
+Corpuscles, Blood
+  Red
+  Colorless
+Corti, Organ of
+Cranial Nerves
+Cranium, Bones of
+Crying
+Crystalline lens
+Cuticle
+Cutis vera, or true skin
+
+Degeneration, Fatty, due to alcohol
+Deglutition, or swallowing
+Deodorants
+Diet, Important articles of
+  Effect of occupation on
+  Too generous
+  Effect of climate on
+Digestion, Purpose of
+  General plan of
+  in small intestines
+  in large intestines
+  Effect of alcohol on
+Disease, Effect of alcoholics upon
+Diseases, infectious and contagious, Management of
+  Care of
+  Hints on nursing
+Disinfectants
+  Air and water as
+  How to use
+Dislocations
+Dogs, mad, Bites of
+Drowning, Apparent
+  Methods of treating
+  Sylvester method
+  Marshall Hall method
+Duct, Hepatic
+  Cystic
+  Common bile
+  Thoracic
+  Nasal
+Duodenum
+Dura mater
+
+Ear, External
+  Middle
+  Bones of the
+  Internal
+  Practical hints on care of
+  Foreign bodies in
+Eating, Practical points about
+Eggs as food
+Elements, Chemical, in the body
+Epidermis, or cuticle
+Epiglottis
+Epithelium
+  Squamous
+  Columnar
+  Glandular
+  Ciliated
+Epithelial tissues, Functions of
+Erect position
+Ethmoid bone
+Eustachian tube
+Excretion
+Exercise, Physical
+  Importance of
+  Effect of, on muscles
+  Effect of, on important organs
+  Effect of, on personal appearance
+  Effect of excessive
+  Amount of, required
+  Time for
+  Physical, in school
+  Practical points about
+  Effect of alcohol and tobacco on
+Experiments, Limitations of
+  Value of
+Eye
+  Inner structure of
+  Compared to camera
+  Refractive media of
+  Movements of
+  Foreign bodies in
+  Practical hints on care of
+  Effect of alcohol on
+  Effect of tobacco on
+Eyeball, Coats of
+Eyelids and eyebrows
+Eyesight in schools
+
+Face
+  Bones of the
+Fainting
+Fats
+  and oils
+Femur
+Fibrin
+Fibula
+Fish as food
+Food and drink
+Food, why we need it
+  Absorption of, by the blood
+  Quantity of, as affected by age
+  Kinds of, required
+Foods, Classification of
+  Nitrogenous
+  Proteid
+  Saline or mineral
+  Vegetable
+  Proteid vegetable
+  Non-proteid vegetable
+  Non-proteid animal
+  Table of
+Food materials, Table of
+  Composition of
+Foot
+Foul air, Effect of, on health
+Frontal bone
+Frost bites
+Fruits as food
+
+Gall bladder
+Garden vegetables
+Gastric glands
+Gastric juice, Effect of alcohol on
+Glands
+  Mesenteric
+  Lymphatic
+  Ductless
+  Thyroid
+  Thymus
+  Suprarenal
+  Lacrymal
+Glottis
+
+Hair
+  Structure of
+Hair and nails, Care of
+Hall, Marshall, method for apparent drowning
+Hand
+Haversian canals
+Head and spine, how joined
+Head, Bones of
+Hearing, Sense of
+  Mechanism of
+  Effect of tobacco on
+Heart
+  Valves of
+  General plan of blood-vessels connected with
+  Rhythmic action of
+  Impulse and sounds of
+  Nervous control of
+  Effect of alcohol on
+  Effect of tobacco on
+Heat, Animal
+  Sources of
+Hiccough
+Hip bones
+Histology defined
+Humerus
+Hygiene defined
+Hyoid bone
+Hypermetropia
+
+Ileum
+Injured, Prompt aid to
+Insalivation
+Intestine, Small
+  Coats of small
+  Large
+Intoxicants, Physical results of
+Iris of the eye
+
+Jejunum
+Joints
+  Imperfect
+  Perfect
+  Hinge
+  Ball-and-socket
+  Pivot
+
+Katabolism defined
+Kidneys
+  Structure of
+  Function of
+  Action if, how modified
+  Effect of alcohol on
+Kidneys and skin
+
+Lacrymal apparatus
+  gland
+Lacteals
+Landmarks, Bony
+  Muscular
+  heart
+  arteries
+Larynx
+Laughing
+Lens, Crystalline
+Levers in the body
+Life, The process of
+Ligaments
+Limbs, Upper
+  Lower
+Liver
+  Minute structure of
+  Blood supply of
+  Functions of
+  Effect of alcohol on
+Lungs
+  Minute structure of
+  Capacity of
+  Effect of alcohol on
+  Bleeding from
+Lymph
+Lymphatics
+
+Mad dogs, Bites of
+Malar bone
+Mastication
+Maxillary, Superior
+  Inferior
+Meals, Hints about
+Meats as food
+Medulla oblongata
+Membrane, Synovial
+  Serous
+  Arachnoid
+Membranes, Brain
+Mesentery
+Metabolism defined
+Metacarpal bones
+Metatarsal bones
+Microscope, Use of
+Milk
+Mineral foods
+Morphology defined
+Motion in animals
+Mouth
+Movement, Mechanism of
+Muscles, Kinds of
+  voluntary, Structure of
+  involuntary, Structure of
+  Arrangement of
+  Important
+  Effect of alcohol on
+  Effect of tobacco on
+  Review analysis of
+  Rest for
+Muscular tissue, Effect of alcohol on
+  Changes in
+  Properties of
+  activity
+  contraction
+  fatigue
+  sense
+Myopia
+
+Nails
+  Care of
+Nasal bones
+Nerve cells
+  fibers
+  cells and fibers, Function of
+Nerves, Cranial
+  Spinal
+  Motor
+  Sensory
+  spinal, Functions of
+Nervous system, General view of
+  compared to telegraph system
+  Divisions of
+  Effect of alcohol on
+  Effect of tobacco on
+Nitrogenous foods.
+Non-proteid vegetable foods
+  animal foods
+Nose, Bleeding from
+  Foreign bodies in
+
+Occipital bone
+Œsophagus
+Opium
+  Poisonous effects of
+  In patent medicines
+  Victim of the, habit
+Organic compounds
+Outdoor games
+Oxidation
+
+Pain, Sense of
+Palate bones
+Pancreas
+Pancreatic juice
+Parietal bones
+Patella
+Pepsin
+Pericardium
+Periosteum
+Peritoneum
+Phalanges
+Pharynx and œsophagus
+Physical exercise
+Physical education in school
+Physical exercises in school
+Physiology defined
+  Study of
+  what it should teach
+  Main problems of, briefly stated.
+Physiological knowledge, Value of
+Pia mater
+Pneumogastric nerve
+Poisons
+Poisons, Table of
+  Antidotes for
+  Practical points about
+Poisoning, Treatment of
+Portal circulation
+Portal vein
+Presbyopia
+Pressure, Where to apply
+Proteids
+Proteid vegetable foods
+Protoplasm
+Pulmonary artery
+  veins
+Pulmonary infection
+Pulse
+Pupil of the eye
+
+Radius
+Receptaculum chyli
+Rectum
+Reflex centers
+  in the brain
+Reflex action, Importance of
+Renal secretion
+Residual air
+Respiration, Nature and object of
+  Nervous control of
+  Effect of, on the blood
+  Effect of, on the air
+  Modified movements of
+  Effect of alcohol on
+  Effect of tobacco on
+  artificial, Methods of
+Rest, for the muscles
+  Need of
+  Benefits of
+  The Sabbath, a day of
+  of mind and body
+Retina
+Ribs and sternum
+
+Saline or mineral foods
+Saliva
+Salt as food
+Salts, Inorganic, in the body
+Scalds or burns
+Scapula
+School, Physical education in
+  Positions at
+School and physical education
+Secretion
+Semicircular canals
+Sensations, General
+Sensation, Conditions of
+Sense, Organs of
+Sense organ, The essentials of
+Serous membranes
+Sick-room, Arrangement of
+  Ventilation of
+  Hints for
+  Rules for
+Sighing
+Sight, Sense of
+Skating, swimming, and rowing
+Skeleton
+  Review analysis of
+Skeleton and manikin, Use of
+Skin, The
+  regulating temperature
+  Action of, how modified
+  Absorbent powers of
+  and the kidneys
+Skull
+  Sutures of
+Sleep, a periodical rest
+  Effect of, on bodily functions
+  Amount of, required
+  Practical rules about
+Smell
+  Sense of
+Sneezing
+Snoring
+Sobbing
+Special senses
+Speech
+Sphenoid bone
+Spinal column
+Spinal cord
+  Structure of
+  Functions of
+  conductor of impulses
+  as a reflex center
+Spinal nerves
+  Functions of
+Spleen
+Sprains and dislocations
+Stammering
+Starches and sugars
+Sternum
+Stomach
+  Coats of
+  Digestion in
+  Effect of alcohol on
+  Bleeding from
+Strabismus
+Stuttering
+Sunstroke
+Supplemental air
+Suprarenal capsules
+Sutures of skull
+Sweat glands
+Sweat, Nature of
+Sylvester method for apparent drowning
+Sympathetic system
+  Functions of
+Synovial membrane
+  sheaths and sacs
+
+Taste, Organ of
+  Sense of
+Taste, Physiological conditions of
+  Modifications of the sense
+  Effect of alcohol on
+  Effect of tobacco on
+Tea
+Tear gland and tear passages
+Tears
+Technical terms defined
+Teeth
+  Development of
+  Structure of
+  Proper care of
+  Hints about saving
+Temperature, Regulation of bodily
+  Skin as a regulator of
+  Voluntary regulation of
+  Sense of
+Temporal bones
+Tendon of Achilles
+Tendons
+Thigh
+Thoracic duct
+Throat
+  Care of
+  Effect of alcohol on
+  Effect of tobacco on
+  Foreign bodies in
+Thymus gland
+Thyroid gland
+Tibia
+Tidal air
+Tissue, White fibrous
+  Connective
+  Yellow elastic
+  Areolar
+  Adipose
+  Adenoid
+  Muscular
+Tissues, Epithelial
+Tissues, epithelial, Varieties of
+  Functions of
+  Connective
+Tobacco, Effect of, on bones
+  Effect of, on muscles
+  Effect of, on physical culture
+  Effect of, on digestion
+  Effect of, on the heart
+  Effect of, on the lungs
+  Effect of, on the nervous system
+  Effect of, on the mind
+  Effect of, on the character
+  Effect of, on taste
+  Effect of, on hearing
+  Effect of, on throat and voice
+Touch, Organ of
+  Sense of
+Trachea
+Trunk, Bones of
+Tympanum, Cavity of
+
+Ulna
+Urine
+
+Valve, Mitral
+Valves of the heart
+Valves, Tricuspid
+  Semilunar
+Vegetable foods
+Veins
+Ventilation
+  Conditions of efficient
+  of sick-room
+Vestibule of ear
+Vermiform appendix
+Vision, Common defects of
+  Effect of tobacco on
+Vivisection and dissection
+Vocal cords
+Voice, Mechanism of
+  Factors in the production of
+  Care of
+  Effect of alcohol on
+  Effect of tobacco on
+Vowel sounds
+
+Walking, jumping, and running
+Waste and repair
+Waste material, Nature of
+Waste products, Elimination of
+Water as food
+Whispering
+Wounds, Incised and lacerated
+
+Yawning
+
+
+
+
+Footnotes
+
+ [1] The Value of Physiological Knowledge. “If any one doubts the
+ importance of an acquaintance with the fundamental principles of
+ physiology as a means to complete living, let him look around and see
+ how many men and women he can find in middle life, or later, who are
+ thoroughly well. Occasionally only do we meet with an example of
+ vigorous health continued to old age; hourly do we meet with examples
+ of acute disorder, chronic ailment, general debility, premature
+ decrepitude. Scarcely is there one to whom you put the question, who
+ has not, in the course of his life, brought upon himself illness from
+ which a little knowledge would have saved him. Here is a case of heart
+ disease consequent on a rheumatic fever that followed a reckless
+ exposure. There is a case of eyes spoiled for life by overstudy.
+    “Not to dwell on the natural pain, the gloom, and the waste of time
+    and money thus entailed, only consider how greatly ill health
+    hinders the discharge of all duties,—makes business often
+    impossible, and always more difficult; produces irritability fatal
+    to the right management of children, puts the functions of
+    citizenship out of the question, and makes amusement a bore. Is it
+    not clear that the physical sins—partly our ancestors’ and partly
+    our own—which produce this ill health deduct more from complete
+    living than anything else, and to a great extent make life a
+    failure and a burden, instead of a benefaction and a
+    pleasure?”—Herbert Spencer.
+
+ [2] The word protoplasm must not be misunderstood to mean a substance
+ of a definite chemical nature, or of an invariable morphological
+ structure; it is applied to any part of a cell which shows the
+ properties of life, and is therefore only a convenient abbreviation
+ for the phrase “mass of living matter.”
+
+ [3] “Did we possess some optic aid which should overcome the grossness
+ of our vision, so that we might watch the dance of atoms in the double
+ process of making and unmaking in the living body, we should see the
+ commonplace, lifeless things which are brought by the blood, and which
+ we call food, caught up into and made part of the molecular whorls of
+ the living muscle, linked together for a while in the intricate
+ figures of the dance of life, giving and taking energy as they dance,
+ and then we should see how, loosing hands, they slipped back into the
+ blood as dead, inert, used-up matter.”—Michael Foster, Professor of
+ Physiology in the University of Cambridge, England.
+
+ [4] “Our material frame is composed of innumerable atoms, and each
+ separate and individual atom has its birth, life, and death, and then
+ its removal from the ‘place of the living.’ Thus there is going on a
+ continuous process of decay and death among the individual atoms which
+ make up each tissue. Each tissue preserves its vitality for a limited
+ space only, is then separated from the tissue of which it has formed a
+ part, and is resolved into its inorganic elements, to be in due course
+ eliminated from the body by the organs of excretion.”—Maclaren’s
+ _Physical Education_.
+
+ [5] The periosteum is often of great practical importance to the
+ surgeon. Instances are on record where bones have been removed,
+ leaving the periosteum, within which the entire bone has grown again.
+ The importance of this remarkable tissue is still farther illustrated
+ by experiments upon the transplantation of this membrane in the
+ different tissues of living animals, which has been followed by the
+ formation of bone in these situations. Some years ago a famous surgeon
+ in New York removed the whole lower jawbone from a young woman,
+ leaving the periosteum and even retaining in position the teeth by a
+ special apparatus. The entire jawbone grew again, and the teeth
+ resumed their original places as it grew.
+
+ [6] The mechanism of this remarkable effect is clearly shown by an
+ experiment which the late Dr. Oliver Wendell Holmes used to take
+ delight in performing in his anatomical lectures at the Harvard
+ Medical College. He had a strong iron bar made into a ring of some
+ eight inches in diameter, with a space left between the ends just
+ large enough to be filled by an English walnut. The ring was then
+ dropped to the floor so as to strike on the convexity just opposite to
+ the walnut, which invariably was broken to pieces.
+
+ [7] For the treatment of accidents and emergencies which may occur
+ with reference to the bones, see Chapter XIII.
+
+ [8] “Besides the danger connected with the use of alcoholic drinks
+ which is common to them with other narcotic poisons, alcohol retards
+ the growth of young cells and prevents their proper development. Now,
+ the bodies of all animals are made up largely of cells, ... and the
+ cells being the living part of the animal, it is especially important
+ that they should not be injured or badly nourished while they are
+ growing. So that alcohol in all its forms is particularly injurious to
+ young persons, as it retards their growth, and stunts both body and
+ mind. This is the theory of Dr. Lionel S. Beale, a celebrated
+ microscopist and thinker, and is quite generally accepted.”—Dr. Roger
+ S. Tracy, of the New York Board of Health.
+
+ [9] “In its action on the system nicotine is one of the most powerful
+ poisons known. A drop of it in a concentrated form was found
+ sufficient to kill a dog, and small birds perished at the approach of
+ a tube containing it.”—Wood’s _Materia Medica_.
+    “Tobacco appears to chiefly affect the heart and brain, and I have
+    therefore placed it among cerebral and cardiac poisons.”—Taylor’s
+    _Treatise on Poisons_.
+
+ [10] “Certain events occur in the brain; these give rise to other
+ events, to changes which travel along certain bundles of fibers called
+ nerves, and so reach certain muscles. Arrived at the muscles, these
+ changes in the nerves, which physiologists call nervous impulses,
+ induce changes in the muscles, by virtue of which these shorten
+ contract, bring their ends together, and so, working upon bony levers,
+ bend the arm or hand, or lift the weight.”—Professor Michael Foster.
+
+ [11] The synovial membranes are almost identical in structure with
+ serous membranes (page 176), but the secretion is thicker and more
+ like the white of egg.
+
+ [12] “Smoking among students or men training for contests is a
+ mistake. It not only affects the wind, but relaxes the nerves in a way
+ to make them less vigorous for the coming contest. It shows its
+ results at once, and when the athlete is trying to do his best to win
+ he will do well to avoid it.” Joseph Hamblen Sears, Harvard Coach, and
+ Ex-Captain of the Harvard Football Team, Article in _In Sickness and
+ in Health_.
+
+ [13] “There is no profession, there is no calling or occupation in
+ which men can be engaged, there is no position in life, no state in
+ which a man can be placed, in which a fairly developed frame will not
+ be valuable to him; there are many of these, even the most purely and
+ highly intellectual, in which it is essential to success—essential
+ simply as a means, material, but none the less imperative, to enable
+ the mind to do its work. Year by year, almost day by day, we see men
+ (and women) falter and fail in the midst of their labors; ... and all
+ for want of a little bodily stamina—a little bodily power and bodily
+ capacity for the endurance of fatigue, or protracted unrest, or
+ anxiety, or grief.”—Maclaren’s _Physical Education_.
+
+ [14] “One half the struggle of physical training has been won when a
+ boy can be induced to take a genuine interest in his bodily
+ condition,—to want to remedy its defects, and to pride himself on the
+ purity of his skin, the firmness of his muscles, and the uprightness
+ of his figure. Whether the young man chooses afterwards to use the
+ gymnasium, to run, to row, to play ball, or to saw wood, for the
+ purpose of improving his physical condition, matters little, provided
+ he accomplishes that object.”—Dr. D. A. Sargent, Director of the
+ Hemenway Gymnasium at Harvard University.
+
+ [15] “It is _health_ rather than _strength_ that is the great
+ requirement of modern men at modern occupations; it is not the power
+ to travel great distances, carry great burdens, lift great weights, or
+ overcome great material obstructions; it is simply that condition of
+ body, and that amount of vital capacity, which shall enable each man
+ in his place to pursue his calling, and work on in his working life,
+ with the greatest amount of comfort to himself and usefulness to his
+ fellowmen.”—Maclaren’s _Physical Education_.
+
+ [16] To this classification may be added what are called albuminoids,
+ a group of bodies resembling proteids, but having in some respects a
+ different nutritive value. Gelatine, such as is found in soups or
+ table gelatine is a familiar example of the albuminoids. They are not
+ found to any important extent in our raw foods, and do not therefore
+ usually appear in the analyses of the composition of foods. The
+ albuminoids closely resemble the proteids, but cannot be used like
+ them to build up protoplasm.
+
+ [17] The amount of water in various tissues of the body is given by
+ the following table in parts of 1000:
+
+         Solids.                   Liquids.
+         Enamel, 2 Blood, 791 Dentine, 100 Bile, 864
+         Bone, 486 Blood plasma, 901
+         Fat, 299 Chyle, 928
+         Cartilage, 550 Lymph, 958
+         Liver, 693 Serum, 959 Skin, 720 Gastric
+         juice,  973 Brain, 750 Tears, 982
+         Muscle, 757 Saliva, 995
+         Spleen, 758 Sweat, 995 Kidney, 827 Vitreous
+         humor, 987
+
+ [18] The work of some kinds of moulds may be apparent to the eye, as
+ in the growths that form on old leather and stale bread and cheese.
+ That of others goes on unseen, as when acids are formed in stewed
+ fruits. Concerning the work of the different kinds of moulds.
+ Troussart says: “_Mucor mucedo_ devours our preserves; _Ascophora
+ mucedo_ turns our bread mouldy; _Molinia_ is nourished at the expense
+ of our fruits; _Mucor herbarium_ destroys the herbarium of the
+ botanist; and _Choetonium chartatum_ develops itself on paper, on the
+ insides of books and on their bindings, when they come in contact with
+ a damp wall.”—Troussart’s _Microbes, Ferments, and Moulds_.
+
+ [19] “The physiological wear of the organism is constantly being
+ repaired by the blood; but in order to keep the great nutritive fluid
+ from becoming impoverished, the matters which it is constantly losing
+ must be supplied from some source out of the body, and this
+ necessitates the ingestion of articles which are known as
+ food.”—Flint’s _Text-book of Human Physiology_.
+
+ [20] Glands. Glands are organs of various shapes and sizes, whose
+ special work it is to separate materials from the blood for further
+ use in the body, the products being known as secretion and excretion.
+ The means by which secretion and excretion are effected are, however,
+ identical. The essential parts of a gland consist of a basement
+ membrane, on one side of which are found actively growing cells, on
+ the other is the blood current, flowing in exceedingly thin-walled
+ vessels known as the capillaries. The cells are able to select from
+ the blood whatever material they require and which they elaborate into
+ the particular secretion. In Fig. 47 is illustrated, diagrammatically,
+ the structure of a few typical secreting glands. The continuous line
+ represents the basement membrane. The dotted line represents the
+ position of the cells on one side of the basement membrane. The
+ irregular lines show the position of the blood-vessels.
+
+ [21] Tablets and other material for Fehling and additional tests for
+ sugar can be purchased at a drug store. The practical details of these
+ and other tests which assume some knowledge of chemistry, should be
+ learned from some manual on the subject.
+
+ [22] The Peritoneum. The intestines do not lie in a loose mass in the
+ abdominal cavity. Lining the walls of this cavity, just as in a
+ general way, a paper lines the walls of a room, is a delicate serous
+ membrane, called the peritoneum. It envelops, in a greater or less
+ degree, all the viscera in the cavity and forms folds by which they
+ are connected with each other, or are attached to the posterior wall.
+ Its arrangement is therefore very complicated. When the peritoneum
+ comes in contact with the large intestine, it passes over it just as
+ the paper of a room would pass over a gas pipe which ran along the
+ surface of the wall, and in passing over it binds it down to the wall
+ of the cavity. The small intestines are suspended from the back wall
+ of the cavity by a double fold of the peritoneum, called the
+ mesentery. The bowels are also protected from external cold by several
+ folds of this membrane loaded with fat. This is known as the _great
+ omentum_.
+    The peritoneum, when in health, secretes only enough fluid to keep
+    its surface lubricated so that the bowels may move freely and
+    smoothly on each other and on the other viscera. In disease this
+    fluid may increase in amount, and the abdominal cavity may become
+    greatly distended. This is known as _ascites_ or dropsy.
+
+ [23] The human bile when fresh is generally of a bright golden red,
+ sometimes of a greenish yellow color. It becomes quite green when
+ kept, and is alkaline in reaction. When it has been omited it is
+ distinctly yellow, because of its action on the gastric juice. The
+ bile contains a great deal of coloring matter, and its chief
+ ingiedients are two salts of soda, sodium taurocholate and
+ glycocholate.
+
+ [24] Nansen emphasizes this point in his recently published work,
+ _Farthest North_.
+
+ [25] We should make it a point not to omit a meal unless forced to do
+ so. Children, and even adults, often have the habit of going to school
+ or to work in a hurry, without eating any breakfast. There is almost
+ sure to be a fainting, or “all-gone” feeling at the stomach before
+ another mealtime. This habit is injurious, and sure to produce
+ pernicious results.
+
+ [26] The teeth of children should be often examined by the dentist,
+ especially from the beginning of the second dentition, at about the
+ sixth year, until growth is completed. In infancy the mother should
+ make it a part of her daily care of the child to secure perfect
+ cleanliness of the teeth. The child thus trained will not, when old
+ enough to rinse the mouth properly or to use the brush, feel
+ comfortable after a meal until the teeth have been cleansed. The habit
+ thus formed is almost sure to be continued through life.
+
+ [27] “If the amount of alcohol be increased, or the repetition become
+ frequent, some part of it undergoes acid fermentation in the stomach,
+ and acid eructations or vomitings occur. With these phenomena are
+ associated catarrh of the stomach and liver with its characteristic
+ symptoms,—loss of appetite, feeble digestion, sallowness, mental
+ depression, and headache.”—James C. Wilson, Professor in the Jefferson
+ Medical College, Philadelphia.
+    “Man has recourse to alcohol, not for the minute quantity of energy
+    which may be supplied by itself, but for its powerful influence on
+    the distribution of the energy furnished by other things. That
+    influence is a very complex one.”—Professor Michael Foster.
+
+ [28] “When constantly irritated by the direct action of alcoholic
+ drinks, the stomach gradually undergoes lasting structural changes.
+ Its vessels remain dilated and congested, its connective tissue
+ becomes excessive, its power of secreting gastric juice diminishes,
+ and its mucous secretions abnormally abundant.”—H. Newell Martin, late
+ Professor of Physiology in Johns Hopkins University.
+    “Chemical experiments have demonstrated that the action of alcohol
+    on the digestive fluids is to destroy its active principle, the
+    pepsin, thus confirming the observations of physiologists that its
+    use gives ride to the most serious disorders of the stomach and the
+    most malignant aberrations of the entire economy.”—Professor E. C.
+    Youmans, author of standard scientific works.
+    “The structural changes induced by habitual use of alcohol and the
+    action of this agent on the pepsin, seriously impair the digestive
+    power. Hence it is, that those who are habitual consumers of
+    alcoholic fluids suffer from disorders o digestion.”—Robert
+    Bartholow, recently Professor of Materia Medica in the University
+    of Pennsylvania.
+    “Alcohol in any appreciable quantity diminishes the solvent power
+    of the gastric fluid so as to interfere with the process of
+    digestion instead of aiding it.”—Professor W. B. Carpenter, the
+    eminent English physiologist.
+
+ [29] “Cirrhosis of the liver is notoriously frequent among drunkards,
+ and is in fact almost, though not absolutely, confined to
+ them.”—Robert T. Edes, formerly Professor of Materia Medica in Harvard
+ Medical College.
+    “Alcohol acts on the liver by producing enlargement of that organ,
+    and a fat deposit, or ‘hob-nailed’ liver mentioned by the English
+    writers.”—Professor W. B. Carpenter.
+
+ [30] Preparation of Artificial Gastric Juice. _(a)_ Take part of the
+ cardiac end of the pig’s stomach, which has been previously opened and
+ washed rapidly in cold water, and spread it, mucous surface upwards,
+ on the convex surface of an inverted capsule. Scrape the mucous
+ surface firmly with the back of a knife blade, and rub up the
+ scrapings in a mortar with fine sand. Add water, and rub up the whole
+ vigorously for some time, and filter. The filtrate is an artificial
+ gastric juice.
+    _(b)_ From the cardiac end of a pig’s stomach detach the mucous
+    membrane in shreds, dry them between folds of blotting-paper, place
+    them in a bottle, and cover them with strong glycerine for several
+    days. The glycerine dissolves the pepsin, and on filtering, a
+    glycerine extract with high digestive properties is obtained.
+    These artificial juices, when added to hydrochloric acid of the
+    proper strength, have high digestive powers.
+    Instead of _(a)_ or _(b)_ use the artificial pepsin prepared for
+    the market by the wholesale manufacturers of such goods.
+
+ [31] The cause of the clotting of blood is not yet fully understood.
+ Although the process has been thoroughly investigated we have not yet
+ a satisfactory explanation why the circulating blood does not clot in
+ healthy blood-vessels. The ablest physiologists of our day do not, as
+ formerly, regard the process as a so-called vital, but a purely
+ chemical one.
+
+ [32] Serous Membranes.—The serous membranes form shut sacs, of which
+ one portion is applied to the walls of the cavity which it lines; the
+ other is reflected over the surface of the organ or organs contained
+ in the cavity. The sac is completely closed, so that no communication
+ exists between the serous cavity and the parts in its neighborhood.
+ The various serous membranes are the _pleura_ which envelops the
+ lungs; the _pericardium_ which surrounds the heart; the _peritoneum_
+ which invests the viscera of the abdomen, and the _arachnoid_ in the
+ spinal canal and cranial cavity. In health the serous membranes
+ secrete only sufficient fluid to lubricate and keep soft and smooth
+ the opposing surfaces.
+
+ [33] A correct idea may be formed of the arrangement of the
+ pericardium around the heart by recalling how a boy puts on and wears
+ his toboggan cap. The pericardium encloses the heart exactly as this
+ cap covers the boy’s head.
+
+ [34] “Alcohol taken in small and single doses, acts almost exclusively
+ on the brain and the blood-vessels of the brain, whereas taken in
+ large and repeated doses its chief effects are always nervous effects.
+ The first effects of alcohol on the function of inhibition are to
+ paralyze the controlling nerves, so that the blood-centers are
+ dilated, and more blood is let into the brain. In consequence of this
+ flushing of the brain, its nerve centers are asked to do more
+ work.”—Dr. T. S. Clouston, Medical Superintendent of the Royal Asylum,
+ Edinburgh.
+    “Alcoholic drinks prevent the natural changes going on in the
+    blood, and obstruct the nutritive and reparative
+    functions.”—Professor E. L. Youmans, well-known scientist and
+    author of _Class Book of Chemistry_.
+
+ [35] The word “cell” is not used in this connection in its technical
+ signification of a histological unit of the body (sec. 12), but merely
+ in its primary sense of a small cavity.
+
+ [36] “The student must guard himself against the idea that arterial
+ blood contains no carbonic acid, and venous blood no oxygen. In
+ passing through the lungs venous blood loses only a part of its
+ carbonic acid; and arterial blood, in passing through the tissues,
+ loses only a part of its oxygen. In blood, however venous, there is in
+ health always some oxygen; and in even the brightest arterial blood
+ there is actually more carbonic acid than oxygen.”—T. H. Huxley.
+
+ [37] “Consumption is a disease which can be taken from others, and is
+ not simply caused by colds. A cold may make it easier to take the
+ disease. It is usually caused by germs which enter the body with the
+ air breathed. The matter which consumptives cough or spit up contains
+ these germs in great numbers—frequently millions are discharged in a
+ single day. This matter spit upon the floor, wall, or elsewhere is apt
+ to dry, become pulverized, and float in the air as dust. The dust
+ contains the germs, and thus they enter the body with the air
+ breathed. The breath of a consumptive does not contain the germs and
+ will not produce the disease. A well person catches the disease from a
+ consumptive only by in some way taking in the matter coughed up by the
+ consumptive.”—Extract from a circular issued by the Board of Health of
+ New York City.
+
+ [38] “The lungs from the congested state of their vessels produced by
+ alcohol are more subject to the influence of cold, the result being
+ frequent attacks of bronchitis. It has been recognized of late years
+ that there is a peculiar form of consumption of the lungs which is
+ very rapidly fatal and found only in alcohol drinkers.”—Professor H.
+ Newell Martin.
+
+ [39] “The relation to Bright’s Disease is not so clearly made out as
+ is assumed by some writers, though I must confess to myself sharing
+ the popular belief that alcohol is one among its most important
+ factors.”—Robert T. Edes, M.D.
+
+ [40] Thus the fibers which pass out from the sacral plexus in the
+ loins, and extend by means of the great sciatic nerve and its branches
+ to the ends of the toes, may be more than a yard long.
+
+ [41] Remarkable instances are cited to illustrate the imperative
+ demand for sleep. Gunner boys have been known to fall asleep during
+ the height of a naval battle, owing to the fatigue occasioned by the
+ arduous labor in carrying ammunition for the gunner. A case is
+ reported of a captain of a British frigate who fell asleep and
+ remained so for two hours beside one of the largest guns of his
+ vessel, the gun being served vigorously all the time. Whole companies
+ of men have been known to sleep while on the march during an arduous
+ campaign. Cavalrymen and frontiersmen have slept soundly in the saddle
+ during the exhausting campaigns against the Indians.
+
+ [42] According to the Annual Report of New York State Reformatory, for
+ 1896, drunkenness among the inmates can be clearly traced to no less
+ than 38 per cent of the fathers and mothers only.
+    Drunkenness among the parents of 38 per cent of the prisoners in a
+    reformatory of this kind is a high and a serious percentage. It
+    shows that the demoralizing influence of drink is apt to destroy
+    the future of the child as well as the character of the parent.
+    “There is a marked tendency in nature to transmit all diseased
+    conditions. Thus the children of consumptive parents are apt to be
+    consumptive. But, of all agents, alcohol is the most potent in
+    establishing a heredity that exhibits itself in the destruction of
+    mind and body. There is not only a propensity transmitted, but an
+    actual disease of the nervous system.”—Dr. Willard Parker.
+
+ [43] “It is very certain that many infants annually perish from this
+ single cause.”—Reese’s _Manual of Toxicology_.
+
+ [44] If an eye removed from its socket be stripped posteriorly of the
+ sclerotic coat, an inverted image or the field of view will be seen on
+ the retina; but if the lens or other part of the refractive media be
+ removed, the image will become blurred or disappear altogether.
+
+ [45] This change in the convexity of the lens is only a slight one, as
+ the difference in the focal point between rays from an object twenty
+ feet distant and one four inches distant is only one-tenth of an inch.
+ While this muscular action is taking place, the pupil contracts and
+ the eyeballs converge by the action of the internal rectus muscles.
+ These three acts are due to the third nerve (the motor oculi). This is
+ necessary in order that each part should he imprinted on the same
+ portion of the retina, otherwise there would be double vision.
+
+ [46] The Germans have a quaint proverb that one should never rub his
+ eyes, except with his elbows!
+
+ [47] “The deleterious effect of tobacco upon eyesight is an
+ acknowledged fact. The Belgian government instituted an investigation
+ into the cause of the prevalence of color-blindness. The unanimous
+ verdict of the experts making the examination was that the use of
+ tobacco was one of the principal causes of this defect of vision.
+    “The dimness of sight caused by alcohol or tobacco has long been
+    clinically recognized, although not until recently accurately
+    understood. The main facts can now be stated with much assurance,
+    since the publication of an article by Uhthoff which leaves little
+    more to be said. He examined one thousand patients who were
+    detained in hospital because of alcoholic excess, and out of these
+    found a total of eye diseases of about thirty per cent.
+    “Commonly both eyes are affected, and the progress of the disease
+    is slow, both in culmination and in recovery.... Treatment demands
+    entire abstinence.”—Henry D. Noyes, Professor of Otology in the
+    Bellevue Hospital Medical College, New York.
+
+ [48] “The student who will take a little trouble in noticing the ears
+ of the persons whom he meets from day to day will be greatly
+ interested and surprised to see how much the auricle varies. It may be
+ a thick and clumsy ear or a beautifully delicate one; long and narrow
+ or short and broad, may have a neatly formed and distinct lobule, or
+ one that is heavy, ungainly, and united to the cheek so as hardly to
+ form a separate part of the auricle, may hug the head closely or flare
+ outward so as to form almost two wings to the head. In art, and
+ especially in medallion portraits, in which the ear is a marked
+ (because central) feature, the auricle is of great importance”—William
+ W. Keen, M.D., editor of Gray’s _Anatomy_.
+
+ [49] The organ of Corti is a very complicated structure which it is
+ needless to describe in this connection. It consists essentially of
+ modified ephithelial cells floated upon the auditory epithelium, or
+ basilar membrane, of the cochlea. There is a series of fibers, each
+ made of two parts sloped against each other like the rafters of a
+ roof. It is estimated that there are no less than 3000 of these arches
+ in the human ear, placed side by side in a continuous series along the
+ whole length of the basilar membrane. Resting on these arches are
+ numbers of conical epithelial cells, from the free surface of which
+ bundles of stiff hairs (cilia) project. The fact that these hair-cells
+ are connected with the fibers of the cochlear division of the auditory
+ nerve suggests that they must play an important part in auditory
+ sensation.
+
+ [50] The voices of boys “break,” or “change,” because of the sudden
+ growth or enlargement of the larynx, and consequent increase in length
+ of the vocal cords, at from fourteen to sixteen years of age. No such
+ enlargement takes place in the larynxes of girls: therefore their
+ voices undergo no such sudden change.
+
+ [51] This experiment and several others in this book, are taken from
+ Professor Bowditch’s little book called _Hints for Teachers of
+ Physiology_, a work which should be mastered by every teacher of
+ physiology in higher schools.
+
+ [52] The teacher or student who is disposed to study the subject more
+ thoroughly and in more detail than is possible in a class text-book,
+ will find all that is needed in the following excellent books, which
+ are readily obtained by purchase, or may be found in the public
+ libraries of larger towns: Dulles’ _Accidents and Emergencies;_
+ Pilcher’s _First Aid in Illness and Injury_; Doty’s _Prompt Aid to the
+ Injured;_ and Johnston’s “Surgical Injuries and Surgical Diseases,” a
+ special article in Roosevelt’s _In Sickness and in Health_.
+
+ [53] “A tourniquet is a bandage, handkerchief, or strap of webbing,
+ into the middle of which a stone, a potato, a small block of wood, or
+ any hard, smooth body is tied. The band is tied loosely about the
+ limb, the hard body is held over the artery to be constricted, and a
+ stick is inserted beneath the band on the opposite side of the limb
+ and used to twist the band in such a way that the limb is tightly
+ constricted thereby, and the hard body thus made to compress the
+ artery (Fig. 160).
+    “The entire circumference of the limb may be constricted by any
+    sort of elastic band or rubber tube, or any other strong elastic
+    material passed around the limb several times on a stretch, drawn
+    tight and tied in a knot. In this way, bleeding may be stopped at
+    once from the largest arteries. The longer and softer the tube the
+    better. It requires no skill and but little knowledge of anatomy to
+    apply it efficiently.” Alexander B. Johnson, Surgeon to Roosevelt
+    Hospital, New York City.
+
+ [54] Corrosive sublimate is probably the most powerful disinfectant
+ known. A solution of one part in 2000 will destroy microscopic
+ organisms. Two teaspoonfuls of this substance will make a solution
+ strong enough to kill all disease germs.
+
+ [55] The burning of sulphur produces sulphurous acid, which is an
+ irrespirable gas. The person who lights the sulphur must, therefore,
+ immediately leave the room, and after the lapse of the proper time,
+ must hold his breath as he enters the room to open the windows and let
+ out the gas. After fumigation, plastered walls should be white-washed,
+ the woodwork well scrubbed with carbolic soap, and painted portions
+ repainted.
+
+ [56] Put copperas in a pail of water, in such quantity that some may
+ constantly remain undissolved at the bottom. This makes a saturated
+ solution. To every privy or water-closet, allow one pint of the
+ solution for every four persons when cholera is about. To keep privies
+ from being offensive, pour one pint into each seat, night and morning.
+
+ [57] “While physiology is one of the biological sciences, it should be
+ clearly recognized that it is not, like botany or zoology, a science
+ of observation and description; but rather, like physics or chemistry,
+ a science of experiment. While the amount of experimental instruction
+ (not involving vivisection or experiment otherwise unsuitable) that
+ may with propriety be given in the high school is neither small nor
+ unimportant, the limitations to such experimental teaching, both as to
+ kind and as to amount, are plainly indicated.
+    “The obvious limitations to experimental work in physiology in the
+    high school, already referred to, make it necessary for the student
+    to acquire much of the desired knowledge from the text-book only.
+    Nevertheless, much may be done by a thoughtful and ingenious
+    teacher to make such knowledge real, by the aid of suitable
+    practical exercises and demonstrations.”—_Report of the Committee
+    of Ten on Secondary School Studies_.
+
+ [58] This ingenious and excellent experiment is taken from the _New
+ York School Journal_ for May, 1897, for which paper it was prepared by
+ Charles D. Nason, of Philadelphia.
+
+
+
+
+End of the Project Gutenberg EBook of A Practical Physiology, by Albert F. Blaisdell
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