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diff --git a/33862-8.txt b/33862-8.txt new file mode 100644 index 0000000..25680fe --- /dev/null +++ b/33862-8.txt @@ -0,0 +1,5947 @@ +The Project Gutenberg EBook of The Mechanism of Life, by Stéphane Leduc + +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: The Mechanism of Life + +Author: Stéphane Leduc + +Translator: W Deane Butcher + +Release Date: October 15, 2010 [EBook #33862] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE MECHANISM OF LIFE *** + + + + +Produced by David Garcia, James Nugen, Keith Edkins and +the Online Distributed Proofreading Team at +http://www.pgdp.net + + + + + +Transcriber's note: A few typographical errors have been corrected: they +are listed at the end of the text. + + * * * * * + + +THE MECHANISM OF LIFE + +[Illustration: Osmotic Productions. [_Frontispiece_] + +THE + +MECHANISM OF LIFE + +BY + +DR. STÉPHANE LEDUC + +PROFESSEUR À L'ÉCOLE DE MÉDECINE DE NANTES + +TRANSLATED BY + +W. DEANE BUTCHER + +FORMERLY PRESIDENT OF THE RÖNTGEN SOCIETY, AND OF THE +ELECTRO-THERAPEUTICAL SECTION OF THE ROYAL SOCIETY OF MEDICINE + + + + + "La nature a formé, et forme tous + les jours les êtres les plus simples par + génération spontanée." LAMARCK. + + + + +[Illustration] + +NEW YORK + +REBMAN COMPANY + +HERALD SQUARE BUILDING +141-145, WEST 36TH STREET + + _First Impression March 1911_ + + _Second Impression January 1914_ + + _Printed in England_ + + * * * * * + + +{vii} + +TRANSLATOR'S PREFACE + +Professor Leduc's _Théorie Physico-chimique de la Vie et Générations +Spontanées_ has excited a good deal of attention, and not a little +opposition, on the Continent. As recently as 1907 the Académie des Sciences +excluded from its _Comptes Rendus_ the report of these experimental +researches on diffusion and osmosis, because it touched too closely on the +burning question of spontaneous generation. + +As the author points out, Lamarck's early evolutionary hypothesis was +killed by opposition and neglect, and had to be reborn in England before it +obtained universal acceptance as the Darwinian Theory. Not unnaturally, +therefore, he turns for an appreciation of his work to the free air and +wide horizon of the English-speaking countries. + +He has entitled his book "The Mechanism of Life," since however little we +may know of the origin of life, we may yet hope to get a glimpse of the +machinery, and perhaps even hear the whirr of the wheels in Nature's +workshop. The subject is of entrancing interest to the biologist and the +physician, quite apart from its bearing on the question of spontaneous +generation. Whatever view may be entertained by the different schools of +thought as to the nature and significance of life, all alike will welcome +this new and important contribution to our knowledge of the mechanism by +which Nature constructs the bewildering variety of her forms. + +There is, I think, no more wonderful and illuminating spectacle than that +of an osmotic growth,--a crude lump of brute inanimate matter germinating +before our very eyes, putting forth bud and stem and root and branch and +leaf and fruit, with no stimulus from germ or seed, without even {viii} the +presence of organic matter. For these mineral growths are not mere +crystallizations as many suppose; they increase by intussusception and not +by accretion. They exhibit the phenomena of circulation and respiration, +and a crude sort of reproduction by budding; they have a period of vigorous +youthful growth, of old age, of death and of decay. They imitate the forms, +the colour, the texture, and even the microscopical structure of organic +growth so closely as to deceive the very elect. When we find, moreover, +that the processes of nutrition are carried on in these osmotic productions +just as in living beings, that an injury to an osmotic growth is repaired +by the coagulation of its internal sap, and that it is able to perform +periodic movements just as an animal or a plant, we are at a loss to define +any line of separation between these mineral forms and those of organic +life. + +In the present volume the author has collected all the data necessary for a +complete survey of the mechanism of life, which consists essentially of +those phenomena which are exhibited at the contact of solutions of +different degrees of concentration. Whatever may be the verdict as to the +author's case for spontaneous generation, all will agree that the book is a +most brilliant and stimulating study, founded on the personal investigation +of a born experimenter. + + + +The present volume is a translation of Dr. Leduc's French edition, but it +is more than this, the work has been translated, revised and corrected, and +in many places re-written, by the author's own hand. I am responsible only +for the English form of the treatise, and can but regret that I have been +able to reproduce so imperfectly the charm of the original. + + W. DEANE BUTCHER. + + EALING. + + * * * * * + + +{ix} + +PREFACE TO THE ENGLISH EDITION + +C'est par l'initiative du Dr. Deane Butcher que cette ouvrage est presenté +aux lecteurs anglais, à la race qui a doté l'humanité de tant de +découvertes originales, geniales et d'une portée très générale. + +Comme un être vivant, une idée exige pour naître et se développer le germe +et le milieu de développement. Il est indéniable que le peuple +anglo-américain constitue un milieu particulièrement favorable à la +naissance et au développement des idées nouvelles. + +Pendant notre collaboration le Dr. Deane Butcher a été un critique +judicieux et éclairé, tous les changements dans l'édition anglaise sont dus +à ses observations. Il s'est assimilé l'ouvrage pour le traduire, et dans +beaucoup de parties, il a mis plus de clarté et de concision qu'il n'y en +avait dans le texte original. + + STÉPHANE LEDUC. + + NANTES, 1911. + + * * * * * + + +{xi} + +TABLE OF CONTENTS + + PAGE + + TRANSLATOR'S PREFACE vii + + AUTHOR'S PREFACE ix + + INTRODUCTION xiii + + I. LIFE AND LIVING BEINGS 1 + + II. SOLUTIONS 14 + + III. ELECTROLYTIC SOLUTIONS 24 + + IV. COLLOIDS 36 + + V. DIFFUSION AND OSMOSIS 43 + + VI. PERIODICITY 67 + + VII. COHESION AND CRYSTALLIZATION 78 + + VIII. KARYOKINESIS 89 + + IX. ENERGETICS 97 + + X. SYNTHETIC BIOLOGY 113 + + XI. OSMOTIC GROWTH: A STUDY IN MORPHOGENESIS 123 + + XII. THE PHENOMENA OF LIFE AND OSMOTIC PRODUCTIONS: + A STUDY IN PHYSIOGENESIS 147 + + XIII. EVOLUTION AND SPONTANEOUS GENERATION 160 + + * * * * * + + +{xiii} + +INTRODUCTION + +Life was formerly regarded as a phenomenon entirely separated from the +other phenomena of Nature, and even up to the present time Science has +proved wholly unable to give a definition of Life; evolution, nutrition, +sensibility, growth, organization, none of these, not even the faculty of +reproduction, is the exclusive appanage of life. + +Living things are made of the same chemical elements as minerals; a living +being is the arena of the same physical forces as those which affect the +inorganic world. + +Life is difficult to define because it differs from one living being to +another; the life of a man is not that of a polyp or of a plant, and if we +find it impossible to discover the line which separates life from the other +phenomena of Nature, it is in fact because no such line of demarcation +exists--the passage from animate to inanimate is gradual and insensible. +The step between a stalagmite and a polyp is less than that between a polyp +and a man, and even the trained biologist is often at a loss to determine +whether a given borderland form is the result of life, or of the inanimate +forces of the mineral world. + +A living being is a transformer of matter and energy--both matter and +energy being uncreateable and indestructible, i.e. invariable in quantity. +A living being is only a current of matter and of energy, both of which +change from moment to moment while passing through the organism. + +That which constitutes a living being is its form; for a living thing is +born, develops, and dies with the form and structure of its organism. This +ephemeral nature of the living being, which perishes with the destruction +of its form, is in {xiv} marked contrast to the perennial character of the +matter and the energy which circulate within it. + +The elementary phenomenon of life is the contact between an alimentary +liquid and a cell. For the essential phenomenon of life is nutrition, and +in order to be assimilated all the elements of an organism must be brought +into a state of solution. Hence the study of life may be best begun by the +study of those physico-chemical phenomena which result from the contact of +two different liquids. Biology is thus but a branch of the +physico-chemistry of liquids; it includes the study of electrolytic and +colloidal solutions, and of the molecular forces brought into play by +solution, osmosis, diffusion, cohesion, and crystallization. + +In this volume I have endeavoured to give as much of the science of +energetics as can be treated without the use of mathematical formulæ; the +conception of entropy and Carnot's law of thermodynamics are also +discussed. + +The phenomena of catalysis and of diastatic fermentation have for the first +time been brought under the general laws of energetics. This I have done by +showing that catalysis is only one instance of the general law of the +transformation of potential into kinetic energy, viz. by the intervention +of a foreign exciting and stimulating energy which may be infinitely +smaller than the energy it transforms. This conception brings life into +line with other catalytic actions, and shows us a living being as a store +of potential energy, to be set free by an external stimulus which may also +excite sensation. + +In a subsequent chapter I have dealt with the rise of Synthetic Biology, +whose history and methods I have described. It is only of late that the +progress of physico-chemical science has enabled us to enter into this +field of research, the final one in the evolution of biological science. + +The present work contains some of the earliest results of this synthetic +biology. We shall see how it is possible by the mere diffusion of liquids +to obtain forms which imitate with the greatest accuracy not only the +ordinary cellular tissues, but the more complicated striated structures, +such as muscle and mother-of-pearl. We shall also see how it is {xv} +possible by simple liquid diffusion to reproduce in ordered and regular +succession complicated movements like those observed in the karyokinesis of +the living cell. + +The essential character of the living being is its Form. This is the only +characteristic which it retains during the whole of its existence, with +which it is born, which causes its development, and disappears with its +death. The task of synthetic biology is the recognition of those +physico-chemical forces and conditions which can produce forms and +structures analogous to those of living beings. This is the subject of the +chapter on Morphogenesis. + +The last chapter deals with the doctrine of Evolution. The chain of life is +of necessity a continuous one, from the mineral at one end to the most +complicated organism at the other. We cannot allow that it is broken at any +point, or that there is a link missing between animate and inanimate +nature. Hence the theory of evolution necessarily admits the +physico-chemical nature of life and the fact of spontaneous generation. +Only thus can the evolutionary theory become a rational one, a stimulating +and fertile inspirer of research. We seek for the physico-chemical forces +which produce forms and structures analogous to those of living beings, and +phenomena analogous to those of life. We study the alterations in +environment which modify these forms, and we seek in the past history of +our planet for those natural phenomena which have brought these +physico-chemical forces into play. In this way we may find the road which +will, we hope, lead some day to the discovery of the origin and the +evolution of life upon the earth. + + * * * * * + + +{1} + +THE MECHANISM OF LIFE + +CHAPTER I + +LIFE AND LIVING BEINGS + +Primitive man distinguished but two kinds of bodies in nature, those which +were motionless and those which were animated. Movement was for him the +expression of life. The stream, the wind, the waves, all were alive, and +each was endowed with all the attributes of life--will, sentiment, and +passion. Ancient Greek mythology is but the poetic expression of this +primitive conception. + +In the evolution of the intelligence, as in that of the body, the +development of the individual is but a repetition of the development of the +race. Even now children attribute life to everything that moves. For them a +little bird still lives in the inside of a watch, and produces the +tick-tick of the wheels. In modern times, however, we have learnt that +everything in nature moves, so that motion of itself cannot be considered +as the characteristic of life. + +Heraclitus aptly compares life to a flame. Aristotle says, "Life is +nutrition, growth, and decay,--having for its cause a principle which has +its end in itself, namely [Greek: entelecheia]." This principle is itself +in need of definition, and Aristotle only substitutes one unknown epithet +for another. + +Bichat defined life as the ensemble of the functions which resist death. +This is to define life in terms of death,--but death is but the end of +life, and cannot be defined without first defining life. Claude Bernard +rejects all definition of life as insufficient, and incompatible with +experimental science. {2} + +Some modern physiologists regard sensibility, others irritability, as the +characteristic of life, and define life as the faculty of responding, by +some sort of change, to an external stimulus. As in the case of movement, +we have found by more attentive observation that this faculty also is +universal in nature. There is no action without reaction; an elastic body +repels the body that strikes it. Every object in nature dilates with heat, +contracts with cold, and is modified by the light which it absorbs. +Everything in nature responds to exterior action by a change, and hence +this faculty cannot be the characteristic of life. + +A distinguished professor of physiology was accustomed to teach that the +disproportion between action and reaction was the characteristic of life. +"Allow a gramme weight to fall on a nerve, and the muscle will raise a +weight of ten grammes. This disproportion is the characteristic of life." +But there is a much greater disproportion between action and reaction when +the friction of a match blows up a powder factory, or the turning of a +switch lights the lamps and animates the tramways and the motors of a great +city. The disproportion between action and reaction is therefore no +characteristic of life. + +The essential characteristic of life is often said to be nutrition--the +phenomenon by which a living organism absorbs matter from its environment, +subjects it to chemical metamorphosis, assimilates it, and finally ejects +the destructive products of metamorphosis into the surrounding medium. But +this characteristic is also common to a great number of ordinary chemical +reactions, so that we cannot call it peculiar to life. Consider, for +instance, a fragment of calcium chloride immersed in a solution of sodium +carbonate. It absorbs the carbonic ion, incorporates it into a molecule of +calcium carbonate, and ejects the chlorine ion into the surrounding medium. + +It may be argued that this is merely a chemical process, since the +substance which determines the reaction is also modified, the chloride of +calcium changing into carbonate of calcium. But every living thing is also +changing its chemical {3} constitution during every moment of its +existence,--it is this change which constitutes the process of senile +involution. The substance of the child is other than that of the ovum, and +the substance of the adult is not that of the child. Hence we cannot regard +nutrition as the exclusive characteristic of life. + +Other authorities regard growth and organization as the essentials of life. +But crystals also grow. It was said that the growth of a crystal differed +from that of a living thing, in that the former grew by the addition of +material from without--the juxtaposition of bricks, as it were--while the +latter grew by intussusception, an introduction of fresh material into the +substance of the organism. A crystal, moreover, was homogeneous, while the +tissues of a living being were differentiated--such differentiation +constituting the organization. At the present time, however, we recognize +the existence of a great variety of purely physical productions, the +so-called "osmotic growths," which increase by a process of +intussusception, and develop therefrom a marvellous complexity of +organization and of form. Hence growth and organization cannot be +considered as the essential characteristics of life. + +Since, then, we are totally unable to define the exact boundary which +separates life from the physical phenomena of nature, we may fairly +conclude that no such separation exists. This is in conformity with the +"law of continuity,"--the principle which asserts that all the phenomena of +nature are continuous in time and space. Classes, divisions, and +separations are all artificial, made not by nature but by man. All the +forms and phenomena of nature are united by insensible transition; it is +impossible to separate them, and in the distinction between living and +non-living things we must content ourselves with relative definitions, +which are far from being precise. + +Life can only be defined as the sum of all phenomena exhibited by living +beings, and its definition thus becomes a mere corollary to the definition +of a living being. + +The true definition of a living being is that it is a transformer of +energy, receiving from its environment the energy {4} which it returns to +that environment under another form. All living organisms are transformers +of energy. + +A living organism is also a transformer of matter. It absorbs matter from +its environment, transforms it, and returns it to its environment in a +different chemical condition. Living things are chemical transformers of +matter. + +Living beings are also transformers of form. They commence as a very simple +form, which gradually develops and becomes more complicated. + +The matter of which a living organism is constituted consists essentially +of certain solutions of crystalloids and colloids. To this we may add an +osmotic membrane to contain the liquids, and a solid skeleton to support +and protect them. Finally, it would seem that a colloid of one of the +albuminoid groups is a necessary constituent of every living being. + +We may say, then, that a living being is a transformer of energy and of +matter, containing certain albuminoid substances, with an evolutionary +form, the constitution of which is essentially liquid. + +A living being has but a limited duration. It is born, develops, becomes +organized, declines and dies. Through all the metamorphoses of form, of +substance, and of energy, informing the whole course of its existence, +there is a certain co-ordination, a certain harmony, which is necessary for +the conservation of the individual. This harmony we call Life. Discord is +disease,--the total cessation of the harmony is Death. When the form is +profoundly altered and the substance changed, the transformation of energy +no longer follows its regular course, the organism is dead. + +After death the colloids which have constituted the form of the living +thing pass from their liquid state as "sols" into their coagulated state as +"gels." The metamorphoses of form, substance, and energy still continue, +but no longer harmoniously for the conservation of the individual, but in +dis-harmony for its dissolution. Finally, the form of the individual +disappears, the substance and the energy of the living being is resolved +and dispersed into other bodies and other phenomena. {5} + +The results hitherto obtained from the study of life seem but +inconsiderable when compared with the time and labour devoted to the +question. Max Verworn exclaims, "Are we on a false track? Do we ask our +questions of Nature amiss, or do we not read her answers aright?" + +Each branch of science at its commencement employs only the simpler methods +of observation. It is purely descriptive. The next step is to separate the +different parts of the object studied--to dissect and to analyse. The +science has now become analytical. The final stage is to reproduce the +substances, the forms, and the phenomena which have been the subject of +investigation. The science has at last become synthetical. + +Up to the present time, biology has made use only of the first two methods, +the descriptive and the analytical. The analytical method is at a grave +disadvantage in all biological investigations, since it is impossible to +separate and analyse the elementary phenomena of life. The function of an +organ ceases when it is isolated from the organism of which it forms a +part. This is the chief cause of our lack of progress in the analysis of +life. + +It is only recently that we have been able to apply the synthetic method to +the study of the phenomena of life. Now that we know that a living organism +is but the arena for the transformation of energy, we may hope to reproduce +the elementary phenomena of life, by calling into play a similar +transformation of energy in a suitable medium. + +Organic chemistry has already obtained numerous victories in the same +direction, and the rapid advance in the production of organic bodies by +chemical synthesis may be considered the first-fruits of synthetic biology. + +A phenomenon is determined by a number of circumstances which we call its +causes, and of which it is the result. Every phenomenon, moreover, +contributes to the production of other phenomena which are called its +consequences. In order therefore to understand any phenomenon in its +entirety, we must determine all its causes both qualitatively and +quantitatively. + +Phenomena succeed one another in time as consequences {6} one of another, +and thus form an uninterrupted chain from the infinite of the past into the +infinite of the future. A living being gathers from its entourage a supply +of matter and of energy, which it transforms and returns. It is part and +parcel of the medium in which it lives, which acts upon it, and upon which +it acts. The living being and the medium in which it exists are mutually +interdependent. This medium is in its turn dependent on its entourage,--and +so on from medium to medium throughout the regions of infinite space. + +One of the great laws of the universe is the law of continuity in time and +space. We must not lose sight of this law when we attempt to follow the +metamorphoses of matter, of energy and of form in living beings. Evolution +is but the expression of this law of continuity, this succession of +phenomena following one another like the links of a chain, without +discontinuity through the vast extent of time and space. + +The other great universal law, that of conservation, applies with equal +force to living and to inanimate things. This law asserts the +uncreateability and the indestructibility of matter and of energy. A given +quantity of matter and of energy remains absolutely invariable through all +the transformations through which it may pass. + +We need not here discuss the question of the possible transformation of +matter into ether, or of ether into ponderable matter. Such a +transformation, if it exists, would have but little bearing on the +phenomena of life. Moreover, it also will probably be found to conform to +the law of conservation of energy. + +In marked contrast to the permanence of matter and of energy is the +ephemeral nature of form, as exhibited by living beings. Function, since it +is but the resultant of form, is also ephemeral. All the faculties of life +are bound up with its form,--a living being is born, exists, and dies with +its form. + +The phenomena of life may in certain cases slow down from their normal +rapidity and intensity, as in hibernating {7} animals, or be entirely +suspended, as in seeds. This state of suspension of life, of latent life as +it were, reminds us of a machine that has been stopped, but which retains +its form and substance unaltered, and may be started again whenever the +obstacle to its progress is removed. + +During the whole course of its life a living being is intimately dependent +on its entourage. For example, the phenomena of life are circumscribed +within very narrow limits of temperature. A living organism, consisting as +it does essentially of liquid solutions, can only exist at temperatures at +which such solutions remain liquid, i.e. between 0° C. and 100° C. Certain +organisms, it is true, may be frozen, but their life remains in a state of +suspension so long as their substance remains solid. Since the albuminoid +substances which are a necessary component of the living organism become +coagulated at 44° C., the manifestations of life diminish rapidly above +this temperature. The intensity of life may be said to augment gradually as +the temperature rises from 0° to 40°, and then to diminish rapidly as the +temperature rises above that point, becoming nearly extinct at 60° C. + +Another condition indispensable to life is the presence of oxygen. Life, +compared by Heraclitus to a flame, is a combustion, an oxydation, for which +the presence of oxygen at a certain pressure is indispensable. There are, +it is true, certain anærobic micro-organisms which apparently exist without +oxygen, but these in reality obtain their oxygen from the medium in which +they grow. + +Life is also influenced by light, by mechanical pressure, by the chemical +composition of its entourage, and by other conditions which we do not as +yet understand. In each case the conditions which are favourable or noxious +vary with the nature of the organism, some living in air, some in fresh +water, and others in the sea. + +Formerly it was supposed that the substance of a living being was +essentially different from that of the mineral world, so much so that two +distinct chemistries were in existence--organic chemistry, the study of +substances derived from bodies which had once possessed life, and inorganic +chemistry, dealing {8} with minerals, metalloids, and metals. We now know +that a living organism is composed of exactly the same elements as those +which constitute the mineral world. These are carbon, oxygen, hydrogen, +nitrogen, phosphorus, calcium, iron, sulphur, chlorine, sodium, potassium, +and one or two other elements in smaller quantity. It was formerly supposed +that the organic combinations of these elements were found only in living +organisms and could be fashioned only by vital forces. In more recent +times, however, an ever increasing number of organic substances have been +produced in the laboratory. + +Organic bodies may be divided into four principal groups. (1) +_Carbohydrates_, including the sugars and the starches, all of which may be +considered as formed of carbon and water. (2) _Fats_, which may be +considered chemically as the ethers of glycerine, combinations of one +molecule of glycerine and three molecules of a fatty acid, with elimination +of water. (3) _Albuminoids_, substances whose molecules are complex, +containing nitrogen and sulphur in addition to carbon, oxygen, and +hydrogen. The albuminoid of the cell nucleus also contains phosphorus, and +the hæmoglobin of the blood contains iron. (4) _Minerals_ or inorganic +elements, such as chloride of sodium, phosphate of calcium, and carbonic +acid. This group also includes water, which is the most important +constituent, since it forms more than a moiety of the substance of all +living creatures. + +Wöhler in 1828 accomplished the first synthesis of an organic substance, +urea, one of the products of the decomposition of albumin. Since then a +large number of organic substances have been prepared by the synthesis of +their inorganic elements. The most recent advance in this direction is that +of Emile Fischer, who has produced polypeptides having the same reactions +as the peptones, by combining a number of molecules of the amides of the +fatty acids. + +In the further synthesis of organic compounds the problems we have before +us are of the same order as those already solved. There is no essential +difference between organic and inorganic chemistry; living organisms are +formed of the {9} same elements as the mineral world, and the organic +combinations of these elements may be realized in our laboratories, just as +in the laboratory of the living organism. + +Not only so, but a living being only borrows for a short time those mineral +elements which, after having passed through the living organism, are +returned once again to the mineral kingdom from which they came. + +All matter has life in itself--or, at any rate, all matter susceptible of +incorporation in a living cell. This life is potential while the element is +in the mineral state, and actual while the element is passing through a +living organism. + +Mineral matter is changed into organic matter in its passage through a +vegetable organism. The carbonic acid produced by combustion and +respiration is absorbed by the chlorophyll of the leaves under the stimulus +of light--the oxygen of the carbonic acid being returned to the air, while +the carbon is utilized by the plant for the formation of sugar, starch, +cellulose, and fats. + +Thus plants are fed in great part by their leaves, taking an important part +of their nourishment from the air, while by their roots they draw from the +earth the water, the phosphates, the mineral salts, and the nitrates +required for the formation of their albuminoid constituents. A vegetable is +a laboratory in which is carried out the process of organic synthesis by +which mineral materials are changed into organic matter. The first +synthetic reaction is the formation of a molecule of formic aldehyde, +CH_2O, by the combination of a molecule of water with an atom of carbon. + +From this formic aldehyde, or formol, we may obtain all the various +carbohydrates by simple polymerization, i.e. by the association of several +molecules, with or without elimination of water. Thus two molecules of +formol form one molecule of acetic acid, 2CH_2O = C_2H_4O_2. Three +molecules of formol form a molecule of lactic acid, 3CH_2O = C_3H_6O_3. Six +molecules of formol represent glucose and levulose, 6CH_2O = C_6H_{12}O_6. +Twelve molecules of formol minus one molecule of water form saccharose, +lactose, cane sugar, and sugar of milk, 12CH_2O = C_{12}H_{22}O_{11} + +H_2O; _n_ times six {10} molecules of formol minus one molecule of water, +_n_(C_6H_{10}O_5), form starch and cellulose. + +Animals derive their nourishment from vegetables either directly, or +indirectly through the flesh of herbivorous animals. The mineral matter, +rendered organic in its passage through a vegetable growth, is finally +returned by the agency of animal organisms to the mineral world again, in +the form of carbonic acid, water, urea, and nitrates. Thus vegetables may +be regarded as synthetic agents, and animals and microbes as agents of +decomposition. Here also the difference is only relative, for in certain +cases vegetables produce carbonic acid, while some animal organisms effect +synthetic combinations. Moreover, there are intermediary forms, such as +fungi, which possessing no chlorophyll are nourished like animals by +organic matter, and yet like vegetables are able to manufacture organic +matter from mineral salts. + +The work of combustion begun by the animal organism is finished by the +action of micro-organisms, who complete the oxydation--the +re-mineralization of the chemical substances drawn originally from the +inorganic world by the agency of plant life. + +To sum up. Vegetables obtain their nourishment from mineral substances, +which they reduce, de-oxydize, and charge with solar energy. Animal +organisms on the contrary oxydize, and micro-organisms complete the +oxydation of these substances, returning them to the mineral world as +water, carbonates, nitrates, and sulphates. + +Thus matter circulates eternally from the mineral to the vegetable, from +the vegetable to the animal world, and back again. The matter which forms +our structure, which is to-day part and parcel of ourselves, has formed the +structure of an infinite number of living beings, and will continue to +pursue its endless reincarnation after our decease. + +This endless cycle of life is also an endless cycle of energy. The +combination of carbon with water carried out by the agency of chlorophyll +can only take place with absorption of energy. This energy comes directly +from the sun, the red and orange light radiations being absorbed by the +chlorophyll. {11} The arrest of vegetation during the winter months is due +not so much to the lowering of temperature as to the diminution of the +radiant energy received from the sun. In the same way shade is harmful to +vegetation, since the radiant energy required for growth is prevented from +reaching the plant. + +The energy radiated by the sun is accumulated and stored in the plant +tissues. Later on, animals feed on the plants and utilize this energy, +excreting the products of decomposition, _i.e._ the constituents of their +food minus the energy contained in it. Thus the whole of the energy which +animates living beings, the whole of the energy which constitutes life, +comes from the sun. To the sun also we owe all artificial heat, the energy +stored up in wood and coal. We are all of us children of the sun. + +The radiant energy of the sun is transformed by plants into chemical +energy. It is this chemical energy which feeds the vital activity of +animals, who return it to the external world under the form of heat, +mechanical work, and muscular contraction, light in the glow-worm, +electricity in the electric eel. + +There is a marked difference between the forms affected by organic and +inorganic substances. The forms of the mineral world are those of +crystals--geometrical forms, bounded by straight lines, planes, and regular +angles. Living organisms, on the contrary, affect forms which are less +regular--curved surfaces and rounded angles. The physical reason for this +difference in form lies in a difference of consistency, crystals being +solid, whereas living organisms are liquids or semi-liquids. The liquids of +nature, streams and clouds and dewdrops, affect the same rounded forms as +those of living organisms. + +Living beings for the most part present a remarkable degree of symmetry. +Some, like radiolarians and star-fish, have a stellate form. In plants the +various organs often radiate from an axis, in such a manner that on turning +the plant about this axis the various forms are superposed thrice, four, or +more often five times in one complete revolution. It is remarkable how +often this number five recurs in the {12} divisions and parts of a living +organism. In other cases the similar parts are disposed symmetrically on +either side of a median line or plane, giving a series of homologous parts +which are not superposable. + +The most important characteristic of a living being is its form. This is +implicitly admitted by naturalists, who classify animals and plants in +genera and species according to the differences and analogies of their +form. + +All living beings are composed of elementary organizations called cells. In +its complete state, a cell consists of a membrane or envelope containing a +mass of protoplasm, in the centre of which is a nucleus of differentiated +protoplasm. This nucleus may in its turn contain a nucleolus. In some cases +the cell is merely a protoplasmic mass without a visible envelope, so that +a cell may be defined as essentially a mass of protoplasm provided with a +nucleus. + +A living organism may consist merely of a single cell, which is able alone +to accomplish all the functions of life. Most living beings, however, +consist of a collection of innumerable cells forming a cellular association +or community. When a number of cells are thus united to constitute a single +living being, the various functions of life are divided among different +cellular groups. Certain cells become specialized for the accomplishment of +a single function, and to each function corresponds a different form of +cell. It is thus easy to recognize by their form the nerve cells, the +muscle cells which perform the function of movement, and the glandular +cells which perform the function of secretion. The cells of a living being +are microscopic in size, and it is remarkable that they never attain to any +considerable dimensions. + +In order that life may be maintained in a living organism, it is necessary +that a continual supply of aliment should be brought to it, and that +certain other substances, the waste-products of combustion, should be +eliminated. In order to be absorbed and assimilated, the alimentary +substances must be presented to the living organism in a liquid or gaseous +state. Thus the essential condition necessary for the {13} maintenance of +life is the contact of a living cell with a current of liquid. The +elementary physical phenomenon of life is the contact of two different +liquids. This is the necessary condition which renders possible the +chemical exchanges and the transformations of energy which constitute life. +It is in the study of the phenomena of liquid contact and diffusion that we +may best hope to pierce the secrets of life. The physics of vital action +are the physics of the phenomena which occur in liquids, and the study of +the physics of a liquid must be the preface and the basis of all inquiry +into the nature and origin of life. + + * * * * * + + +{14} + +CHAPTER II + +SOLUTIONS + +We have seen that living beings are transformers of energy and of matter, +evolutionary in form and liquid in consistency; that they are solutions of +colloids and crystalloids separated by osmotic membranes to form +microscopic cells, or consisting merely of a gelatinous mass of protoplasm, +with a nucleus of slightly differentiated material. The elementary +phenomenon of life is the contact of two different solutions. This is the +initial physical phenomenon from which proceed all the other phenomena of +life in accordance with the ordinary chemical and physical laws. Thus the +basis of biological science is the study of solution and of the phenomena +which occur between two different solutions, either in immediate contact or +when separated by a membrane. + +A solution is a homogeneous mixture of one or more solutes in a liquid +solvent. Before solution the solute or dissolved substance may be solid, +liquid, or gaseous. + +Solutes, or substances capable of solution, may be divided into two +classes--substances which are capable of crystallization, or crystalloids; +and those which are incapable of crystallization, the colloids. +Crystalloids may be divided again into two classes, those whose solutions +are ionizable and therefore conduct electricity, chiefly salts, acids, and +bases; and those whose solutions are non-ionizable and are therefore +non-conductors. These latter are for the most part crystallizable +substances of organic origin, such as sugars, urea, etc. + +Avogadro's law asserts that under similar conditions of temperature and +pressure, equal volumes of various gases {15} contain an equal number of +molecules. Under similar conditions, the molecular weights of different +substances have therefore the same ratio as the weights of equal volumes of +their vapours. Hence if we fix arbitrarily the molecular weight of any one +substance, the molecular weight of all other substances is thereby +determined. The molecular weight of hydrogen has been arbitrarily fixed as +two, and hence the molecular weight of any substance will be double its +gaseous density when compared with that of hydrogen. + +_Gramme-Molecule._--A gramme-molecule is the molecular weight of a body +expressed in grammes. Occasionally for brevity a gramme-molecule is spoken +of as a "molecule." Thus we may say that the molecular weight of oxygen is +16 grammes, meaning thereby that there are the same number of molecules in +16 grammes of oxygen as there are atoms in 1 gramme of hydrogen. + +_Concentration._--The concentration of a solution is the ratio between the +quantity of the solute and the quantity of the solvent. The concentration +of a solution is expressed in various ways. (_a_) The weight of solute +dissolved in 100 grammes of the solvent. (_b_) The weight of solute present +in 100 grammes of the solution. (_c_) The weight of solute dissolved in a +litre of the solvent. (_d_) The weight of solute in a litre of the +solution. The most usual method is to give the concentration as the weight +of solute dissolved in 100 grammes or in one litre of the solvent. + +_Molecular Concentration._--Many of the physical and biological properties +of a solution are proportional, not to its mass or weight concentration, +but to its molecular concentration, _i.e_. to the number of +gramme-molecules of the solute contained in a litre of the solution. Many +physical properties are quite independent of the nature of the solute, +depending only on its degree of molecular concentration. + +_Normal Solution._--A normal solution is one which contains one +gramme-molecule of the solute per litre. A decinormal solution contains +one-tenth of a gramme-molecule of the solute per litre, and a centinormal +solution one-hundredth of a gramme-molecule. A normal solution of urea, for +example, {16} contains 60 grammes of urea per litre, while a normal +solution of sugar contains 342 grammes of sugar per litre. + +_The Dissolved Substance is a Gas._--Van t' Hoff, using the data obtained +by the botanist Pfeffer, showed that the dissolved matter in a solution +behaved exactly as if it were a gas. The analogy is complete in every +respect. Like the gaseous molecules, the molecules of a solute are mobile +with respect to one another. Like those of a gas, the molecules of a solute +tend to spread themselves equally, and to fill the whole space at their +disposal, _i.e._ the whole volume of the solution. The surface of the +solution represents the vessel containing the gas, which confines it within +definite limits and prevents further expansion. + +_Osmotic Pressure._--Like the molecules of a gas, the molecules of a solute +exercise pressure on the boundaries of the space containing it. This +osmotic pressure follows exactly the same laws as gaseous pressure. It has +the same constants, and all the notions acquired by the study of gaseous +pressure are applicable to osmotic pressure. Osmotic pressure is in fact +the gaseous pressure of the molecules of the solute. + +When a gas dilates and increases in volume, its temperature falls, and cold +is produced. Similarly, when a soluble substance is dissolved, it increases +in volume, and the temperature of the liquid falls. This phenomenon is well +known as a means of producing cold by a refrigerating mixture. + +The phenomena of life are governed by the laws of gaseous pressure, since +all these phenomena take place in solutions. The fundamental laws of +biology are those of the distribution of substances in solution, which is +regulated by the laws of gaseous pressure, since all these laws are +applicable also to osmotic pressure. + +_Boyle's Law_.--When a gas is compressed its volume is diminished. If the +pressure is doubled, the volume is reduced to one-half. The quantity V × P, +that is the volume multiplied by the pressure, is constant. + +_Gay-Lussac's Law._--For a difference of temperature of a degree Centigrade +all gases dilate or contract by 1 / 273 of their volume at 0° Centigrade. +{17} + +_Dalton's Law._--In a gaseous mixture, the total pressure is equal to the +sum of the pressures which each gas would exert if it alone filled the +whole of the receptacle. + +_Pressure proportional to Molecular Concentration._--The above laws are +completely independent of the chemical nature of the gas, they depend only +on the number of gaseous molecules in a given space, _i.e._ on the +molecular concentration. If we double the mass of the gas in a given space, +we double the number of molecules, and we also double the pressure, +whatever the nature of the molecules. We may also double the pressure by +compressing the molecules of a gas, or of several gases, into a space half +the original size. The molecular concentration of a gas, or of a mixture of +gases, is the ratio of the number of molecules to the volume they occupy. +The pressure of a gas or of a mixture of gases is proportional to its +molecular concentration. This is a better and a shorter way of expressing +both Boyle's law and Dalton's law. + +One gramme-molecule of a gas, whatever its nature, condensed into the +volume of 1 litre, has a pressure of 22.35 atmospheres. Similarly one +gramme-molecule of a solute, whatever its nature, when dissolved in a litre +of water, has the same pressure, viz. 22.35 atmospheres. + +_Absolute Zero._--According to Gay-Lussac's law, the volume of a gas +diminishes by 1 / 273 of its volume at 0° C. for each degree fall of +temperature. Thus if the contraction is the same for all temperatures, the +volume would be reduced to zero at -273° C. This is the absolute zero of +temperature. Temperatures measured from this point are called absolute +temperatures, and are designated by the symbol T. If _t°_ indicates the +Centigrade temperature above the freezing point of water, then the absolute +temperature is equal to _t°_ + 273°. + +_The Gaseous Constant._--Consider a mass of gas at 0° C. under a pressure +P_o, with volume V_o. At the absolute temperature T, if the pressure be +unaltered, the volume of this gas will be V_oT / 273. Therefore the +constant PV, the product of the pressure by the volume, will be represented +by P_oV_oT / 273. {18} + +At the same temperature, but under another pressure P' the gas will have a +different volume V'. Since, according to Boyle's law, PV is constant (P'V' += P_oV_o), it will still equal P_oV_oT / 273. Therefore P_oV_o / 273 is +also constant. This quantity is called "the gaseous constant," and if we +represent it by the symbol R, we obtain the general formula PV = RT for all +gases, or PV / T = R. + +Suppose, for instance, we have a gramme-molecule of a gas at 0° C. in a +space of 1 litre. It has a pressure of 22.35 atmospheres at 0° C., or 273° +absolute temperature. Since PV = RT, R = PV / T = 1 × 22.35 / 273 = .0819. +This number .0819 is the numerical value of the constant R for all gases, +volume being measured in litres and pressure in atmospheres. + +Substances in solution behave exactly like gases, they follow the same laws +and have the same constants. All the conceptions which have been acquired +by the study of gases are applicable to solutions, and therefore to the +phenomena of life. The osmotic pressure of a solution is the force with +which the molecules of the solute, like gaseous molecules, strive to +diffuse into space, and press on the limits which confine them, the +containing vessel being represented by the surfaces of the solution. +Osmotic pressure is measured in exactly the same way as gaseous pressure. +To measure steam pressure we insert a manometer in the walls of the boiler. +In the same way we may use a manometer to measure osmotic pressure. We +attach the tube to the walls of the porous vessel, allow the solvent to +increase in volume under the pressure of the solute, and measure the rise +of the liquid in the manometer tube. + +_Pfeffer's Apparatus._--Pfeffer has designed an apparatus for the +measurement of osmotic pressure. It consists of a vessel of porous +porcelain, the pores of which are filled with a colloidal solution of +ferrocyanide of copper. This forms a semi-permeable membrane which permits +the passage of water into the vessel, but prevents the passage of sugar or +of any {19} colloid. The stopper which hermetically closes the vessel is +pierced for the reception of a mercury manometer. The vessel is filled with +a solution of sugar and plunged in a bath of water. The volume of the +solution in the interior of the vessel can vary, since water passes easily +in either direction through the pores of the vessel. The boundary of the +solvent has become extensible, and its volume can increase or diminish in +accordance with the osmotic pressure of the solute. Under the pressure of +the sugar water is sucked into the vessel like air into a bellows, the +solution passes into the tube of the manometer, and raises the column of +mercury until its pressure balances the osmotic pressure of the sugar +molecules. + +_Osmotic Pressure follows the Laws of Gaseous Pressure._--This osmotic +pressure is in fact gaseous pressure, and may be measured in millimetres of +mercury in just the same way. We may thus show that osmotic pressure +follows the laws of gaseous pressure as defined by Boyle, Dalton, and +Gay-Lussac. The coefficient of pressure variation for change of temperature +is the same for a solute as for a gas. The formula PV = RT is applicable to +both. The numerical value of the constant R is also the same for a solute +as for a gas. being .0819 for one gramme-molecule of either, when the +volume is expressed in litres and the pressure in atmospheres. The formula +PV = RT shows that for a given mass, with the same volume, the pressure +increases in proportion to the absolute temperature. + +_Osmotic Pressure of Sugar._--A normal solution of sugar, containing 342 +grammes of sugar per litre, has a pressure of 22.35 atmospheres, and it may +well be asked why such an enormous pressure is not more evident. The reason +will be found in the immense frictional resistance to diffusion. Frictional +resistance is proportional to the area of the surfaces in contact, and this +area increases rapidly with each division of the substance. When a solute +is resolved into its component molecules, its surface is enormously +increased, and therefore the friction between the molecules of the solute +and those of the solvent. + +_Isotonic Solutions._--Two solutions which have the same {20} osmotic +pressure are said to be iso-osmotic or isotonic. When comparing two +solutions of different concentration, the solution with the higher osmotic +pressure is said to be hypertonic, and that with the lower osmotic pressure +hypotonic. + +_Lowering of the Freezing Point._--Pure water freezes at 0° C. Raoult +showed that the introduction of a non-ionizable substance, such as sugar or +alcohol, lowers the freezing point of a solution in proportion to the +molecular concentration of the solute. One gramme-molecule of the solute +introduced into one litre of the solution lowers its temperature of +congelation by 1.85° C. Thus a normal solution of any non-ionizable +substance in water freezes at -1.85° C. The measurement of this lowering of +the freezing point is called Cryoscopy, a method which is becoming of great +utility in medicine. + +_Cryoscopy of Blood._--In order to determine the osmotic pressure of the +blood at 37° C., _i.e._ 98.6° F., the normal temperature, we proceed as +follows. On freezing the blood, we find that it congeals at -.56°. Its +molecular concentration is therefore .56 / 1.85 = .30, or about one-third +of a gramme-molecule per litre. Its osmotic pressure at 0° C. is therefore +.3 × 22.35 = 6.7 atmospheres. The increase of pressure with temperature is +the same as for a gas, viz. 1/273, or .00367 of its pressure at 0° for +every degree rise of temperature. The increase of pressure at 37° is +therefore .00367 × 37 × 6.7 = .9 atmospheres. The total osmotic pressure at +37° is therefore 6.7 + .9 = 7.6 atmospheres. + +_Rise of Boiling Point._--Water under atmospheric pressure boils at a +temperature of 100° C. The addition of a solute whose solution does not +conduct electricity, such as sugar, causes a rise in the boiling point +proportional to the molecular concentration of that solute. + +_Lowering of the Vapour Tension._--The vapour tension of a liquid is +lowered by the addition of a solute. A liquid boils at the temperature at +which its vapour tension equals that of the atmosphere. Since an aqueous +solution of sugar at atmospheric pressure does not begin to boil at 100° +C., it is manifest that its vapour tension is then less than that of the +{21} atmosphere. The addition of a solute such as sugar, whose solution is +not ionizable, and therefore does not conduct electricity, lowers the +vapour tension of the solution in proportion to the molecular concentration +of the solute. + +_Corresponding Values._--We have thus found five properties of a solution +which vary proportionally, so that from the measurement of any one of them +we can determine the corresponding values of all the others. These are-- + + 1. The Molecular Concentration. + 2. The Osmotic Pressure. + 3. The Diminution of Vapour Tension. + 4. The Raising of the Boiling Point. + 5. The Lowering of the Freezing Point. + +_Cryoscopy._--The usual method employed for the determination of the +molecular concentration and osmotic pressure of a solution is by +cryoscopy--the measurement of its temperature of congelation. A very +sensitive thermometer is used, the scale of which extends over only 5° and +is divided into hundredths of a degree. The liquid under examination is +placed in a test tube, in which the bulb of the thermometer is plunged, and +this is supported in a second tube with an air space all round it. The +whole is then suspended to the under side of the cover of the refrigerating +vessel, which may be cooled either by filling it with a freezing mixture, +or by the evaporation of ether. During the whole of the operation the +liquid is agitated by a mechanical stirrer. The first step is to determine +the freezing point of distilled water. As the water cools the mercury +gradually descends in the stem of the thermometer till it reaches a point +below the zero mark at 0° C. As soon as ice begins to form the mercury +rises, at first rapidly and then more slowly, reaches a maximum, and +finally descends again. This maximum reading is the true point of +congelation. The inner tube is then emptied, care being taken to leave a +few small ice crystals to serve as centres of congelation for the +subsequent experiment, thus avoiding supercooling of the solution. The +process is then repeated with the solution under examination. The +difference between {22} the two freezing points is the required "lowering +of the freezing point." + +Cryoscopy is the method most used in biological research to determine +molecular concentration. It has, however, some grave defects. It +necessitates several cubic centimetres of the liquid under examination. It +gives us the constants of the solution at the temperature of freezing, +which is far below that of life. Organic liquids are easily altered and are +extremely sensible to minute differences of temperature, cryoscopy +therefore gives us no information as to the constitution of solutions under +normal conditions. It is desirable to have some other method of determining +molecular concentration and the other interdependent constants at the +normal temperature of life. A much better method, were it possible, would +be the direct determination of the vapour tension of the solutions under +normal conditions of temperature and pressure. + +_Molecular Lowering of the Freezing Point._--For every substance whose +solution is not ionized and therefore does not conduct electricity, the +lowering of the freezing point is the same, viz. 1.85° C. for each +gramme-molecule of the solute per litre of the solution. + +_Determination of the Molecular Concentration._--In order to obtain the +molecular concentration of a non-ionizable substance, we have only to +determine the lowering of the freezing point. Let A be the lowering of the +freezing point of any solution. On dividing it by 1.85 (the lowering of the +freezing point for a normal solution), we obtain the number of +gramme-molecules in a litre of the solution. If n be the number of +gramme-molecules per litre, then n = A / 1.85. + +_Determination of the Osmotic Pressure._--The osmotic pressure P of a +solution may be obtained by multiplying its molecular concentration n by +22.35 atmospheres. P = n × 22.35 = A / 1.85 × 22.35. + +_Determination of Molecular Weight._--The lowering of the freezing point +also enables us to calculate the molecular {23} weight of any non-ionizable +solute. Thus Bouchard has been able to determine by means of cryoscopy the +mean molecular weight of the substances eliminated by the urine. A weight +_x_ of the substance is dissolved in a litre of water, and the lowering of +the freezing point is observed. The value thus found divided by 1.85 gives +us n, the number of gramme-molecules per litre. The molecular weight M may +be determined by dividing the original weight x by n. + +The study of osmotic pressure was begun by the Abbé Nollet; and one of his +disciples, Parrot, at an early date thus described its importance: "It is a +force analogous in all respects to the mechanical forces, a force able to +set matter in motion, or to act as a static force in producing pressure. It +is this force which causes the circulation of heterogeneous matter in the +liquids which serve as its vehicle. It is this force which produces those +actions which escape our notice by their minuteness and bewilder us by +their results. It is for the infinitely small particles of matter what +gravitation is for heavy masses. It can displace matter in solution upwards +against gravity as easily as downwards or in a horizontal direction." + +Thus the recognition of the fact that a substance in solution is really a +gas, has at a single stroke put us in possession of the laws of osmotic +pressure--laws slowly and laboriously discovered by the long series of +investigations on the pressure of gases. + +Osmotic pressure plays a most important rôle in the arena of life. It is +found at work in all the phenomena of life. When osmotic pressure fails, +life itself ceases. + + * * * * * + + +{24} + +CHAPTER III + +ELECTROLYTIC SOLUTIONS + +_Solutions which conduct Electricity._--The laws of solution which we have +studied in the previous chapter apply only to those solutions, chiefly of +organic origin, which do not conduct electricity. Solutions of electrolytes +such as the ordinary salts, acids, and bases, which are ionized on +solution, give values for the various constants of solution which do not +accord with those required by theory. If, for instance, we take a +gramme-molecule of an electrolyte such as chloride of sodium, and dissolve +it in a litre of water, we find that the lowering of the freezing point is +nearly double the theoretical value of 1.85°. The same holds good for the +osmotic pressure, and for all the constants which are proportional to the +molecular concentration of the solute. The solution behaves, in each case, +as if it contained more than one gramme-molecule of sodium chloride per +litre. It behaves, in fact, as if it contained i times the number of +molecules of solute originally introduced into it. If n be the original +number of molecules, then it will apparently contain n' = in molecules. +This law is universal for all electrolytic solutions; the theoretical value +for their concentration, osmotic pressure, and all the proportional +physical constants must be multiplied by this quantity, i = n'/n, which is +the ratio of the apparent number of the molecules present to the number +originally introduced. + +A similar dissociation of the molecule is observed in the case of many +gases. The vapour of chloride of ammonium, for instance, is decomposed by +heat, and it may be shown experimentally that the increase of pressure on +heating above {25} that which theory demands, is due to an increase in the +number of the gaseous molecules present. Some of the vapour particles are +dissociated into two or more fragments, each of which plays the part of a +single molecule. + +Arrhenius, in 1885, advanced the hypothesis that the apparent increase in +the number of molecules of an electrolytic solution was also due to +dissociation. This interpretation at once threw a flood of light on a +number of phenomena hitherto obscure. + +_Coefficient of Dissociation._--We have seen that in order to obtain values +which accord with experiment we have to multiply the number of +gramme-molecules of the solute by the coefficient i, which is called the +Coefficient of Dissociation. + +This coefficient of dissociation, i, may be found by observing the lowering +of the freezing point of a normal solution, and dividing it by 1.85. i = +t/1.85. + +The coefficient of dissociation varies with the degree of concentration of +the solution, rising to a maximum when the solution is sufficiently +diluted. + +If we know i, the coefficient of dissociation for a given solute, contained +in a solution of a definite concentration, we can find n', the number of +particles present in a solution containing n gramme-molecules of the solute +per litre, since n' = in. On the other hand, if from a consideration of its +freezing point and other constants we find that an electrolytic solution +appears to contain n' gramme-molecules per litre, the real number of +chemical gramme-molecules in one litre of the solution will be only n' / i += n. + +Very concentrated solutions do not conform to these laws. In this they +resemble gases, which as they approach their point of condensation tend +less and less to conform to the laws of gaseous pressure. + +_Electrolysis._--If we take a solution of an acid, a salt, or a base, and +dip into it two metallic rods, one connected to the positive and the other +to the negative pole of a battery, we {26} find that the metals or metallic +radicals of the solution are liberated at the negative pole, while the acid +radicals of the salts and acids and the hydroxyl of the bases are liberated +at the positive pole. The liberated substances may either be discharged +unchanged, or they may enter into new combinations, causing a series of +secondary reactions. + +_Electrolytes._--Solutions which conduct electricity are called +Electrolytes, and the conducting metallic rods dipping into the solution +are the Electrodes. Faraday gave the names of Ions to the atoms or +atom-groups liberated at either electrode. The ions liberated at the +positive electrode are the Anions, and those at the negative electrode are +the Cations. The only solutions which possess any notable degree of +electrical conductivity are the aqueous solutions of the various salts, +acids, and bases, and in these solutions only do we meet with those +phenomena of dissociation which are evidenced by anomalies of osmotic +pressure, freezing point and the like,--anomalies which show that the +solution contains a greater number of molecules than that indicated by its +molecular concentration. These anomalies are due to dissociation, the +division of some of the molecules into fragments, each of which plays the +part of a separate molecule, contributing its quota to the osmotic tension +and vapour pressure of the solution, in fact to all the phenomena which are +dependent on the degree of molecular concentration. The electrical +conductivity of a solution is therefore proved to be dependent on its +molecular dissociation. + +_Arrhenius' Theory of Electrolysis._--In 1885, Arrhenius brought forward +his theory of the transport of electricity by an electrolyte. According to +this hypothesis, the electric current is carried by the ions, the positive +charges by the cations, and the negative charges by the anions. In virtue +of the attraction between charges of different sign, and repulsion between +charges of like sign, the cations are repelled by the positive charge on +the anode, and attracted by the negative charge on the cathode. Similarly +the anions are repelled by the cathode and attracted by the anode. {27} + +An electrolytic solution contains three varieties of particles, positive +ions or cations, negative ions or anions, and undissociated neutral +molecules. The molecular concentration of such a solution, with the +corresponding constants, depends on the total number of these particles, +_i.e._ the sum of the ions and the undissociated neutral molecules. We may +indicate an ion by placing above it the sign of its electrical charge, one +sign for each valency. Thus Na^+ and Cl^- indicate the two ions of a salt +solution; Cu^{++} and SO_4^{--} the two ions of a solution of sulphate of +copper. A point is sometimes substituted for the + sign, and a comma for +the - sign. Thus Na^. and Cl^,; Cu^{..} and SO_4^{,,}. + +My friend Dr. Lewis Jones has given a very vivid picture of the processes +which go on in an electrolytic solution when an electric current is +passing. He compares an electrolytic cell to a ballroom, in which are +gyrating a number of dancing couples, representing the neutral molecules, +and a number of isolated ladies and gentlemen representing the anions and +cations respectively. If we suppose a mirror at one end of the ballroom and +a buffet at the other, the ladies will gradually accumulate around the +mirror, and the gentlemen around the buffet. Moreover, the dancing couples +will gradually be dissociated in order to follow this movement. + +_Degree of Dissociation._--The degree of dissociation is the fraction of +the molecules in the solution which have undergone dissociation. Let n be +the total number of molecules of the solute, and n" the number of +dissociated molecules. Then n" / n = a will represent the degree of +dissociation. Let k be the number of ions into which each molecule is +split. Then a = n"k / nk, _i.e._ the degree of dissociation is the ratio of +the number of ions actually present in a solution to the number which would +be present if all the molecules of the solute were dissociated. + +Let n' be the total number of particles present in a solution {28} +containing n molecules, each of which is composed of k ions. Then if a is +the degree of dissociation, + + n' = n - an + ank, + n' = n[1 + a (k - 1)], + n' / n = 1 + a (k - 1) = i. + +We thus obtain i the coefficient of dissociation, in terms of the degree of +dissociation a and the number of ions in each molecule k. + +If there is no dissociation, _i.e._ if a = 0, then n' = n, and i = 1. If +all the molecules are dissociated, a = 1, and i = k. + +_Faraday's Law._--Faraday found that the quantity of electricity required +to liberate one gramme-molecule of any radical is 96.537 coulombs for each +valency of the radical. + +_Electrochemical Equivalent._--The electrochemical equivalent of a radical +is the weight liberated by one coulomb of electricity. It is equal to the +molecular weight of the ion, divided by 96.537 times its valency. + +_Electrolytic Conductivity._--The conductivity of an electrolyte is the +inverse of its resistance. C = 1/R. + +For a given difference of potential the conductivity of an electrolyte is +proportional to the number of ions in unit volume, the electrical charge on +each ion, and the velocity of the ions. + +_The specific conductivity_ [Delta] of an electrolyte is the conductivity +of a cube of the solution, each face of which is one square centimetre in +area. The _molecular conductivity_ of an electrolyte is the conductivity of +a solution containing one gramme-molecule of the substance placed between +two parallel conducting plates, one centimetre apart. The molecular +conductivity is independent of the volume occupied by the gramme-molecule +of the solute, depending only on the degree of dissociation. The molecular +conductivity U is equal to the product of V, the volume of the molecule, by +[Delta], its specific conductivity. U = V[Delta]. Whence [Delta] = U / V, +_i.e._ the specific {29} conductivity equals the molecular conductivity +divided by the volume. + +The conductivity of an electrolyte is proportional to the number of ions in +a volume of the solution containing one gramme-molecule. Let M_{[infinity]} +be the conductivity for complete dissociation and M_v the molecular +conductivity at the volume V. Then + + M_v / M_{[infinity]} = n"k / nk = n" / n = a, + +the degree of dissociation. This is Ostwald's law, which says that the +degree of dissociation is equal to the ratio of conductivity when the +gramme-molecule occupies a volume V, to its conductivity when the solution +is so dilute that dissociation is complete. Hence the degree of +dissociation may also be determined by comparing the electrical +conductivities of two solutions of different degrees of concentration. + + | -- -- -- | -- -- -- | + | SO_4 SO_4 SO_4 | SO_4 SO_4 SO_4 | + | | | + | ++ ++ ++ | ++ ++ ++ | + | Cu Cu Cu | Cu Cu Cu | + | | | + +----------------------------+--------------------------------+ + +FIG. 1.--Before the passage of the current. + + | -- | -- -- | + | SO_4 | SO_4 SO_4 SO_4 SO_4 SO_4 | + - | | | + + | ++ | ++ ++ | + | Cu Cu Cu Cu | Cu Cu | + | | | + +---------------------------+---------------------------------+ + +FIG. 2.--After the passage of the current. + +_Velocity of the Ions._--If the electrolytic cell is divided into two +segments by means of a porous diaphragm, we shall find after a time an +unequal distribution of the solute on the two sides. For instance, with a +solution of sulphate of copper, after the current has passed for some time +there will be a diminution of concentration in the liquid on both sides of +the diaphragm, but the loss will be very unequally divided. Two-thirds of +the loss of concentration will be on the side of the negative electrode and +only one-third on the positive side. In 1853, Hittorf gave the following +ingenious explanation of this phenomenon:-- {30} + +Fig. 1 represents an electrolytic vessel containing a solution of sulphate +of copper, the vertical line indicating a porous partition separating the +vessel into two parts. Fig. 2 shows the same vessel after the passage of +the current. The acid radical has travelled twice as fast as the metal. For +each copper ion which has passed through the porous plate towards the +cathode two acid radicals have passed through it towards the anode. Three +ions have been liberated at either electrode, but in consequence of the +difference of velocity with which the positive and the negative ions have +travelled, the negative side of the vessel contains only one molecule of +copper sulphate and has lost two-thirds of its molecular concentration, +while the positive side contains two molecules of copper sulphate and has +only lost one-third of its concentration. This proves clearly that the ions +move in different directions with different velocities. Let u be the +velocity of the anions, and v the velocity of the cations. Let n be the +loss of concentration at the cathode, and 1 - n the loss of concentration +at the anode. Then + + u / v = n / (1 - n), + +_i.e._ the loss of concentration at the cathode is to the loss of +concentration at the anode as the velocity of the anions is to that of the +cations. Hence by measuring the loss of concentration at the two +electrodes, we have an easy means of determining the comparative velocity +of different ions. + +In 1876, Kohlrausch compared the conductivity of the chlorides, bromides, +and iodides of potassium, sodium, and ammonium respectively. He found that +altering the cation did not affect the _differences_ of conductivity +between the three salts, thus showing that these differences of +conductivity were dependent on the nature of the anion only, and not on the +particular base with which it was combined. The difference of conductivity +between an iodide and a bromide, for example, is the same whether +potassium, sodium, or ammonium salts are compared. A similar experiment has +been made with a series of cations combined with various anions. The +difference of conductivity of the salts in the series is the same whichever +anion is used, _i.e._ the difference of conductivity between potassium +chloride and sodium chloride is the same as that between {31} potassium +bromide and sodium bromide. Hence we may conclude that the conductivity of +any salt is an ionic property. + +Kohlrausch's law may be expressed by the formula c = d(u + v), where c is +the conductivity of the salt, d the degree of dissociation, _i.e._ the +fraction of the electrolyte broken up into ions, and u and v the velocity +of the anions and cations respectively. When all the molecules of the +electrolyte are dissociated, d = 1, and the formula becomes c_{[infinity]} += u + v. + +As we have already seen, a salt is formed by the union of a metal M with an +acid radical R. Potassium sulphate, K_2SO_4, consists of the metal K_2 and +the acid radical SO_4. Ammonium chloride, NH_4Cl, consists of the basic +radical NH_4 and the acid radical Cl. The various acids may be considered +as salts of the metal hydrogen. Thus sulphuric acid, H_2SO_4, is the +sulphate of hydrogen. Bases may be considered as salts with the hydroxyl +group, OH, replacing the acid radical. Thus potash, KOH, is the hydroxyl of +potassium. The various electrolytic combinations may be represented by the +following symbols:-- + + Salts = MR. + Acids = HR. + Bases = MOH. + +The various chemical reactions of an electrolyte are all ionic reactions, +the chemical activity of an electrolytic solution being proportional to its +electric conductivity, _i.e._ the degree of dissociation of its ions. The +acidity of an electrolytic solution is due to the presence of the +dissociated ion H^+, and its strength is determined by the concentration of +these free hydrogen ions. Hence the greater the degree of dissociation the +stronger the acid. + +The basic character of a solution is determined by the presence of the +hydroxyl radical OH^-. The greater the concentration of the hydroxyl ions, +_i.e._ the greater the dissociation, the stronger is the base. + +The ions H^+ and OH^- are of special importance, since they are the ions of +water, H_2O = H^+ + OH^-. The degree of {32} dissociation of pure water is +but small. Water is, however, the most important of all the various agents +in the chemical reactions of life, since a large number of organic +substances are decomposed by water by a process of hydrolysis, and a vast +number of organic substances are but combinations of carbon with the ions +H^+ and OH^-, their diversity being due to variations in the relative +proportions and grouping. + +_The Chemical, Therapeutic, and Toxic Actions of Ions._--The chemical, +therapeutic, antiseptic, and toxic actions of electrolytic solutions are +almost exclusively due to ionization. Take, for instance, a solution of +nitrate of silver in which the addition of chlorine produces a white +precipitate of chloride of silver. This precipitate occurs only when the +solution added is one such as NaCl, where the chlorine is present as the +free ion Cl^-. No such precipitate is produced in a solution of chlorate of +potassium or chloracetic acid, where the chlorine is entangled in the +complex ion ClO_3 or C_2H_3ClO_2. + +Since, then, the toxic and pharmacological properties of an electrolyte +depend entirely on the ionic grouping, it behoves the physician and the +biologist to study the structure and grouping of the ions in a molecule, +rather than that of the atoms. Consider for a moment the totally different +properties of the phosphides and the phosphates. The former are extremely +toxic, while the latter are perfectly harmless. There is not the slightest +analogy between their actions on the living organism. On the other hand, +all the phosphides produce the same toxic and therapeutic effects, whatever +the cation with which they are united. Their toxic properties are derived +from the presence of the free phosphorus ion P^{---}. The phosphates +contain phosphorus in the same proportion as the phosphides, but this +phosphorus is harmlessly entangled in the complex ion PO_4^{---}, whose +properties are absolutely different from those of the ion P^{---}. + +The above considerations apply equally to the chlorides and chlorates, the +iodides and iodates, the sulphides and sulphates, and in general to all +chemical salts. {33} + +The question has an intimate bearing on practical pharmacology. When we +prescribe a cacodylate or an amylarsinate, we are not prescribing an +arsenical treatment whose effects can be compared with those of an +arsenide, an arsenite, or an arsenate. This fact is sufficiently indicated +by the difference in the toxic doses of the different salts. Each variety +of arsenical ion has its own special physiological and therapeutic +properties. We do not expect to obtain the results of a ferruginous +treatment from the administration of a ferrocyanide or a ferricyanide. Both +contain iron, it is true, but neither possess the properties of the cation +Fe^{+++}, but rather those of the complex anion of which they form a part. + +We have already said that most of the therapeutic, toxic, and caustic +actions of an electrolyte are due to ionic action, and the substances can +therefore have no toxic action unless they are dissociated. Many of the +solvents employed in medicine, such as alcohol, glycerine, vaseline, and +chloroform dissolve the electrolytes but do not dissociate them into ions, +and these solutions therefore do not conduct electricity. Such solutions +have no therapeutic action. With the absence of dissociation all the ionic +toxic and caustic effects also disappear entirely, and only re-appear as +the water of the tissue is able slowly to effect the necessary +dissociation. + +Carbolic acid dissolved in glycerine is hardly caustic and but very +slightly toxic. We have met with several instances in which a tablespoonful +of carbolized glycerine, in equal parts, has been swallowed without any ill +effect, either caustic or toxic, whereas the same dose dissolved in water +would have been fatal. This absence of dissociation has enabled the surgeon +Mencière to inject carbolic and glycerine in equal proportions into the +larger joints, the part being subsequently washed out with pure alcohol. +Thus by employing vaseline, oil, or glycerine as a solvent, and avoiding +the access of water, we are able to use electrolytic antiseptics in very +concentrated form. Their action is brought out very slowly, as the water of +the organism effects the necessary dissociation of the electrolyte. {34} + +Since all chemical, toxic, and therapeutic actions are ionic, they are +proportional to the degree of ionic concentration, _i.e._ to the number of +ions in a given volume. The only point of importance, that which determines +their activity, whether chemical or therapeutic, is the degree of +ionization or dissociation. For example, all acids have the same cation +H^+. They have all identical properties, but they differ widely in the +intensity of their action. There are weak acids such as acetic acid, and +strong acids like sulphuric acid. The stronger acids are those which are +more thoroughly dissociated, and in which the ion H^+ is very concentrated; +whereas the feeble acids are but slightly dissociated, so that the ion H^+ +is less concentrated. + +Paul and Krönig have shown that the bactericidal action of different salts +also varies with their degree of dissociation, _i.e._ with the +concentration of the active ions. They made a series of observations on the +bactericidal action of various salts of mercury, the bichloride, the +bibromide, and the bicyanide, on the spores of _Bacillus anthracis_. The +following results were obtained from a comparison of solutions containing 1 +gramme-molecule of the salt in 64 litres of water. With the bichloride +solution, after exposure to the solution for twenty minutes, only 7 +colonies of the bacillus were developed. After exposure to a similar +solution of the bibromide the number of colonies was 34. The antiseptic +action of the bichloride was therefore five times as great as that of the +bibromide. The bicyanide of mercury, however, even when four times as +concentrated, permitted the growth of an enormous number of colonies, +showing that it had no appreciable antiseptic action whatever. +Nevertheless, the proportion of Hg is the same in all the solutions, and if +there were any difference one would naturally expect that the ion Cy^- +would be more toxic than Cl^- or Br^-. The real condition which varies in +these solutions and determines their activity is the degree of +dissociation. The whole of the antiseptic property resides in the ion +Hg^{++}. This ion is very {35} concentrated in the highly dissociated +solution HgCl_2, less concentrated in the less ionized solution HgBr_2, and +exceedingly dilute in the HgCy_2, which is hardly ionized at all. + +What is true of the bactericidal action of the salts of mercury is equally +true of their therapeutic effect. It is a great mistake to estimate the +medicinal activity of a solution of a salt of mercury, or indeed of any +electrolytic solution, simply by its degree of molecular concentration. The +important point is the degree of dissociation, which is the only true +measure of its activity. In the intramuscular injection of mercury salts it +is by no means a matter of indifference what salt we employ. A salt should +be used such as the bichloride or the biniodide, which is easily +dissociated. Other salts are often employed because they occasion less pain +at the site of injection; but the pain is a sign of the degree of activity +of the preparation. The pain, it is true, may be avoided by using a salt +which is less easily dissociated, or in which the mercury is bound up in a +complex ion, but by so doing we diminish the efficacy of the remedy. It is +moreover quite easy to diminish, or even entirely to suppress, the pain, by +using a very dilute solution of an active ionized salt. A one-half per +cent. or even one-quarter per cent. solution of the bichloride or biniodide +of mercury may be injected very slowly in sufficient quantity without +producing the slightest discomfort. Local action depends entirely on ionic +concentration. One drop of pure sulphuric acid will destroy the skin, +whereas the same amount if diluted in a tumblerful of water will furnish a +refreshing drink. + + * * * * * + + +{36} + +CHAPTER IV + +COLLOIDS + +As we have already seen, living organisms are formed essentially of +liquids. These liquids are solutions of crystallizable substances or +crystalloids, and non-crystallizable substances or colloids--a +classification which we owe to Graham. + +The liquids are the most important constituents of a living organism, since +they are the seat of all the chemical and physical phenomena of life. The +junction of two liquids of different concentration is the arena in which +takes place both the chemical transformation of matter and the correlative +transformation of energy. In a former chapter we have passed in review the +class of crystalloids, we will now turn our attention to the characteristic +properties of colloids. + +_Colloids._--Colloids differ from crystalloids in that they do not form +crystals from solution, being completely amorphous when in the solid state. +The solution of a colloid solidifies in the same form which it possessed in +the liquid state, the solvent being enclosed in the meshes of a sort of +network formed by the solute. This form is approximately retained even +after the water has evaporated by drying, the passage from the liquid state +of solution to the solid state being effected through a series of +intermediary states, such as a clot, coagulum, or jelly. This passage from +the state of solution into a state of jelly is called coagulation. Some +colloids, such as gelatine, coagulate with cold; while others, such as +egg-albumin, coagulate with heat. Some, like the caseine of milk, require +the addition of certain chemical substances to set up coagulation; while +still others, such as the fibrin of blood, appear to coagulate +spontaneously. The physical phenomena of {37} coagulation are still but +little understood. In some cases it is a reversible phenomenon, thus +gelatine coagulated by cold is redissolved by heat; whereas with other +colloids the process is irreversible, albumin coagulated by heat is not +redissolved on cooling. + +Colloids in a state of coagulation have a vacuolar or sponge-like +structure. The solvent is imprisoned in the vacuoles of the clot, and is +expelled little by little by its retraction. Colloids diffused in water are +usually called colloidal solutions, but they are not true solutions. Such a +pseudo-solution of a colloid is called a "sol," while a colloid in a state +of coagulation is called a "gel." Colloidal solutions spread but little, +diffuse very slowly in the liquids of the body, and cannot penetrate +organic membranes. + +Colloidal solutions diffuse light, unlike crystalloid solutions, which are +transparent. We all know how the trajectory of a beam of sunlight through a +darkened room is rendered visible by the particles of dust. In the same way +if a colloidal solution is illuminated by a transverse ray of light, the +light is diffused by the molecules of the colloid in semi-solution, and the +liquid appears faintly illuminated on a dark background. The light diffused +by a colloidal solution is polarized, which shows that it is reflected +light, + +Siedentopf and Sigmondy have applied this principle of lateral illumination +on a dark background to the construction of the ultra-microscope. With the +aid of this instrument we may not only see, but count the particles in a +colloidal solution, which is in reality merely a pseudo-solution or +suspension, in contradistinction to the true solution of a crystalloid. + +Colloidal solutions possess only a very feeble osmotic pressure. The +lowering of the freezing point and the other corresponding constants are +also quite insignificant. This arises from the fact that the molecules of a +colloid are extremely large when compared with those of a crystalloid. For +example let us take colloidal substance whose molecular weight is 2000. A +solution containing 40 grammes per litre would have an osmotic pressure +only one-fiftieth of that of a {38} solution of similar strength of a +crystalloid whose molecular weight was 40. + +Not only so, but on measuring the molecular concentration, the osmotic +pressure, and the other constants of a colloidal solution, we find values +even lower than those which we should expect from a consideration of its +molecular weight. This is probably due to the tendency of a colloid to +polymerization, i.e. to form groups or associations of molecules. Suppose, +for instance, that the molecules of a colloidal solution are aggregated +into groups of ten. Since each group plays the part of a simple molecule, +the osmotic pressure will be ten times less than that corresponding to the +quantity of the solute present. Such a group of molecules is called by +Naegeli a "micella." + +Similar phenomena of aggregation may be observed in the molecules of many +inorganic substances. The molecule of iodine, for example, is monatomic at +1200° C., but becomes diatomic at the ordinary temperature. Sulphur at 860° +C. is a gas with a vapour density of 2.2, while at 500° C. its vapour +density rises to 6.6. In both of these cases two or more molecules of the +element have been condensed into one as a result of the fall of +temperature. + +We frequently find that two successive cryoscopic observations on the +freezing point of the same colloidal solution will vary. This is due to the +extreme sensitiveness of the micellæ, which absorb or abandon their extra +molecules under the slightest influence. This mobility in the constitution +of the micellæ appears to be one of the principal causes of the peculiar +properties of colloidal solutions. + +The phenomenon of polymerization appears to be reversible. The micellæ are +formed under certain conditions, and are disintegrated when these +conditions are removed. The osmotic pressure varies in the same manner, +diminishing with polymerization and augmenting with the disintegration of +the micellæ. One may easily understand what an important rôle is played by +this alternate polymerization and disintegration in the phenomena of life. + +Most colloidal substances are precipitated from their solutions by the +addition of very small quantities of electrolytic {39} solutions. +Non-electrolytic solutions do not appear to provoke this precipitation. +This is not a chemical action, for an exceedingly small quantity of an +electrolyte is able to precipitate an indefinite quantity of the colloid. +The precipitation is probably due to the electric charges carried by the +dissociated ions of the electrolytes. + +When an electric current is passed through a colloid solution, the course +of the molecules of the colloid is sometimes towards the cathode and +sometimes towards the anode, according to the nature of the colloid and of +the solvent. This displacement would appear to indicate a difference of +electric potential between the molecules of the colloid and those of the +solvent. Hardy has shown that in an alkaline solution the molecules of +albumin travel towards the anode, while in an acid solution they travel +towards the cathode. + +_Metallic Colloids._--Carey Lea and afterwards Credé succeeded in obtaining +silver in colloidal solution by ordinary chemical means. Professor Bredig +has introduced a more general method of obtaining a number of metals in +colloidal solutions in a state of great purity. He causes an electric arc +to pass between two rods of the metal immersed in distilled water. The +cathode is thus pulverized into a very fine powder which rests in +suspension in the liquid, constituting a colloidal solution. Bredig has in +this way prepared sols of platinum, palladium, iridium, silver, and +cadmium. + +_Catalytic Properties of Colloids._--Catalysis is the property possessed by +certain bodies of initiating chemical reaction. The mass of the catalyzing +body has no definite proportion to that of the substances entering into the +reaction, and the appearance of the catalyzer is in no way altered by the +reaction. + +Ostwald has shown that catalysis consists essentially in the acceleration +or retardation of chemical reactions which would take place without the +action of the catalyzer, but more slowly. + +Catalytic reactions are very numerous in chemistry. The inversion of sugar +by acids, the etherization of alcohol by sulphuric acid, the decomposition +of hydrogen peroxide by {40} platinum black are all instances of catalysis. +Fermentation by means of a soluble ferment or diastase, a phenomenon which +may almost be called vital, is also a catalytic action. The action of +pepsin, of the pancreatic ferment, of zymase, and of other similar ferments +has a great analogy with the purely physical phenomenon of catalysis. The +diastases are all colloids, and so are many other catalyzers. + +A catalyzer is a stimulus which excites a transformation of energy. The +catalyzer plays the same rôle in a chemical transformation as does the +minimal exciting force which sets free the accumulation of potential energy +previous to its transformation into kinetic energy. A catalyzer is the +friction of the match which sets free the chemical energy of the powder +magazine. + +Bredig has studied the catalytic decomposition of hydrogen peroxide by +metallic colloids prepared by his electric method. He found that 1 +atom-gramme of colloidal platinum gives a sensible catalytic effect when +diluted with 70 million litres of water. Caustic soda and other chemical +substances inhibit the catalytic action of colloidal platinum in the same +way as they inhibit the fermenting action of diastase. The curve of +decomposition of hydrogen peroxide by colloidal platinum may be compared +with the curve of fermentation by emulsin. Both are equally affected by the +addition of an alkali. Many other chemical and physical agents have a +similar inhibitory action on the catalysis of colloidal metals and on +diastasic fermentation. Thus a mere trace of sulphuretted hydrogen or +hydrocyanic acid will paralyse the action of a colloidal metal, just as it +does that of a ferment. This is what Bredig calls the poisoning of metallic +ferments. + +We may hope that the further study of catalysis, a purely physico-chemical +phenomenon, may throw more light on the mechanism of diastasic +fermentation, which is essentially a vital reaction. + +It must not be forgotten that all classification is artificial and +arbitrary, and only to be used as long as it facilitates study. This +observation is particularly applicable to the classification of substances +into crystalloids and colloids. {41} There is no sharp line between the two +groups, the passage is gradual, and it is impossible to say where one group +ends and the other begins. Many colloids such as hæmoglobin are +crystallizable, and many crystallizable substances are coagulable. Many +substances appear at one time in the crystalloid state and at another time +in the colloidal state, so that instead of dividing substances into +colloids and crystalloids, we should rather consider these expressions as +denoting different phases assumed by the same substance. + +In order to define clearly our various classes and divisions, we are apt to +exaggerate slight differences of properties or composition. We say that +colloids have no osmotic pressure, whereas in fact the osmotic pressure of +the colloids though feeble plays a very important part in the phenomena of +life. + +So in other departments of science--a factor which is almost infinitesimal +may yet exercise a vast influence on the results. It is by infinitesimal +variations of pressure, a thousandth of a millimetre or less, that we +obtain the various degrees of penetration in the Röntgen rays. + +The division into solutions and pseudo-solutions or suspensions is also an +arbitrary one. A true solution is also a suspension of the molecules of the +solute. There is no essential difference between a solution and a +suspension, but only a difference in the size of the molecules, or +agglomerations of molecules, in one case so small as to be transparent, and +in the other case just big enough to diffuse light. There are moreover many +properties common to colloidal solutions and suspensions of fine powders, +such as kaolin, mastic, charcoal, or Indian ink. These particles in +suspension are precipitated by solutions of electrolytes in a manner +similar to the coagulation of colloids. + +The surface of every liquid is covered by a very thin layer, a sort of +membrane slightly differentiated from the rest of the liquid. This membrane +may be a chemical one, a pellicular precipitate like that which is formed +by the contact of two membranogenous liquids. On the other hand, the +membrane may not differ from the subjacent liquid in chemical composition, +but only in physical properties. If we {42} consider the molecules in the +middle of a liquid, each molecule is subjected to the cohesive attraction +of molecules on every side, attractions which neutralize one another. At +the surface of the liquid, however, there are quite other conditions of +equilibrium. There each molecule is drawn downwards towards the centre of +the liquid, and there is no compensating attraction in an opposite +direction. The resultant pressure is normal to the surface of the liquid, +and is mechanically equivalent to an elastic membrane which tends to +diminish the surface, and hence the volume of the liquid. We may therefore +regard this surface tension as acting the part of a veritable physical +membrane. + +There is a still further differentiation of the surface of a liquid. When +the liquid is not a simple one, but complex as in a solution, we find that +the concentration of the solute is greater at the surface than in the +interior. This is the so-called phenomenon of "adsorption," which is +another cause for the production of a physical membrane covering the +surface of a liquid. + +Substances in a colloidal state have a great tendency to form these +chemical or physical membranes at the point of contact between the +colloidal solute and the solvent. This is probably the reason why the +coagulum of a colloidal liquid usually presents a vacuolar or spongy +structure. + + * * * * * + + +{43} + +CHAPTER V + +DIFFUSION AND OSMOSIS + +_Diffusion and Osmosis._--If we place a lump of sugar in the bottom of a +glass of water, it will dissolve, and spread by slow degrees equally +throughout the whole volume of the liquid. If we pour a concentrated +solution of sulphate of copper into the bottom of a glass vessel, and +carefully pour over it a layer of clear water, the liquids, at first +sharply separated by their difference of density, will gradually mix, so as +to form a solution having exactly the same composition in all parts of the +jar. The process whereby the sugar and the copper sulphate spread uniformly +through the whole mass of the liquid in opposition to gravity is called +Diffusion. This diffusion of the solute is a phenomenon exactly analogous +to the expansion of a gas. It is the expression of osmotic pressure, or +rather of the difference of the osmotic pressure of the solute in different +parts of the vessel. The molecules of the solute move from a place where +the osmotic pressure is greater towards a position where the osmotic +pressure is less. The water molecules on the other hand pass from positions +where the osmotic pressure of the solute is less towards positions where it +is greater. As a consequence of this double circulation the osmotic +pressure tends to become equalized in all parts of the vessel. + +Diffusion appears to be the fundamental physical phenomenon of life. It is +going on continually in the tissues of all living beings, and a study of +the laws of diffusion and osmosis is therefore absolutely necessary for a +just conception of vital phenomena. + +_Coefficient of Diffusion._--The coefficient of diffusion has {44} been +defined by Fick as the quantity of a solute which in one second traverses +each square centimetre of the cross section of a column of liquid 1 +centimetre long, between the opposite sides of which there is unit +difference of concentration. Nernst in his definition substitutes "unit +difference of osmotic pressure" for "unit difference of concentration." + +Until recently it was generally believed that diffusion took place in +colloids and plasmas just as in pure water. This is, however, by no means +the case: the differences are considerable. When a solute is introduced +into a colloidal solution, the greater the concentration of the colloid the +slower will be the diffusion. This may be shown by a simple experiment. +Several glass plates are prepared, by spreading on each a solution of +gelatine of different concentration, to which a few drops of phenol +phthalein have been added. If now a drop of an alkaline solution be placed +on each plate, we can see that the drop diffuses more slowly through the +more concentrated gelatine solution, since the presence of the alkali is +rendered visible by the coloration of the phenol phthalein. A similar +demonstration may be made by allowing drops of acid to diffuse through +solutions of gelatine made slightly alkaline and coloured with phenol +phthalein. In general, we find on experiment that when similar drops of any +coloured or colouring solution are left for an equal time on plates of +gelatine of different degrees of concentration, the greater the +concentration of the gelatine the smaller will be the circle of coloration +obtained. + +We may show that the rapidity of diffusion diminishes as the gelatinous +concentration increases, by another experiment. If we put side by side on +our gelatine plate a drop of sulphate of copper and another of ferrocyanide +of potassium, the point of contact of the two fluids will be sharply marked +by a line of precipitate. We find that under similar conditions the time +between the sowing of the drops and the formation of this line of +precipitate is longer when the gelatine is more concentrated. + +_Osmosis._--In 1748, l'Abbé Nollet discovered that when a pig's bladder +filled with alcohol was plunged into water, the {45} water passed into the +bladder more rapidly than the alcohol passed out; the bladder became +distended, the internal pressure increased, and the liquid spirted out when +the bladder was pricked by a pin. This passage of certain substances in +solution through an animal membrane is called Osmosis, and membranes which +exhibit this property are called osmotic membranes. + +_Precipitated Membranes._--In 1867, Traube of Breslau discovered that +osmotic membranes could be made artificially. Certain chemical precipitates +such as copper ferrocyanide can form membranes having properties analogous +to those of osmotic membranes. With these precipitated membranes Traube +made a number of interesting experiments. These have lately been collected +in the volume of his memoirs published by his son. + +_Osmotic Membranes._--Osmotic membranes were formerly called semi-permeable +membranes, being regarded as membranes which allow water to pass through +them, but arrest the passage of the solute. This definition is inexact, +since no membrane permeable to water is absolutely impermeable to the +solutes. All we can say is that certain membranes are more permeable to +water than to the substances in solution, and are moreover very unequally +permeable to the various substances in solution. As a rule a membrane is +much more permeable to a solute whose molecule is of small dimensions. +Molecules of salt, for instance, pass through such a membrane much more +quickly than do those of sugar. The term "osmotic membrane" should +therefore in all cases replace that of "semi-permeable membrane." + +Osmotic membranes behave exactly like colloids. The resistance which they +oppose to the passage of different substances varies with the nature of the +liquid or solute concerned. There is no real difference between the passage +of a solution through an osmotic membrane and its diffusion through a +colloid. The protoplasm of a living organism, being a colloid, acts exactly +like an osmotic membrane so far as regards the distribution of solutions +and substances in solution. {46} + +The diffusion of molecules through a colloid, a plasma, or a membrane is +governed by laws precisely analogous to Ohm's law, which governs the +transport of electricity. The intensity or rapidity of diffusion is +proportional to the difference of osmotic pressure, and varies inversely +with the resistance. + +In the case of molecular diffusion, however, the rapidity of diffusion +depends also on the size and nature of the molecules of the diffusing +substance. The theory of the resistance of the various plasmas and +membranes to diffusion has been but little understood; we can discover +hardly any reference to it in the literature of the subject. + +The laws of diffusion apply equally to the diffusion of ions. Nernst has +shown that there is a difference of electric potential at the surface of +contact of two electrolytic solutions of different degrees of +concentration. Both the positive and negative ions of the more concentrated +solution pass into the less concentrated solution, but the ions of one sign +will pass more rapidly than those of the other sign, because being smaller, +they meet with less resistance. + +The resistance of the medium plays a most important part in all the +phenomena of diffusion. When two solutions of different concentration come +into contact, the interchange of molecules and ions which occurs is unequal +owing to the differences in resistance. Hence both solutions become +modified not only in concentration but also in composition. It has long +been known that diffusion can cause the decomposition of certain easily +decomposed substances, and it would appear probable that diffusion is also +capable of producing new chemical combinations. + +The separation of the liberated ions in consequence of the unequal +resistance which they meet with in the medium they traverse often +determines chemical reaction. This ionic separation is a fertile agent of +chemical transformation in the living organism, and may be the determinant +cause in those chemical reactions which constitute the phenomena of +nutrition. + +When different liquids come into contact there are two distinct series of +phenomena, those due to osmotic pressure and those due to differences of +chemical composition. Even {47} with isotonic solutions there will be a +transfer of the solutes if these are of different chemical constitution. +Take, for instance, two isotonic solutions, one of salt and another of +sugar. When these are brought into contact there is no transference of +water from one solution to the other, but there is a transference of the +solutes. In the salt solution the osmotic pressure of the sugar is zero. +Hence the difference of osmotic pressure of the sugar in the two solutions +will cause the molecules of sugar to diffuse into the salt solution. For +the same reason the salt will diffuse into the sugar solution. + +A disregard of this fact, that a solute will always pass from a solution +where its osmotic pressure is high, into one where its osmotic pressure is +low, is a frequent source of error. Thus it is said to be contrary to the +laws of osmosis that solutes should pass from the blood, with its low +osmotic pressure, into the urine, where the general osmotic pressure is +higher; the more so because in consequence of the exchange the osmotic +pressure of the urine is still further increased. Such an exchange, it is +argued, is contrary to the ordinary laws of physics, and can therefore only +be accomplished by some occult vital action. This, however, is not the +fact, as is proved by experiment. + +Consider an inextensible osmotic cell containing a solution of sugar, the +walls of the cell being impermeable to sugar but permeable to salt. Let us +plunge such a cell into a solution of salt, which has a lower osmotic +pressure than the sugar solution. Since the walls of the cell are +inextensible, the quantity of water in the cell cannot increase. The salt, +however, will pass into the cell, since the osmotic pressure of the salt is +greater on the outside than on the inside, and the walls are permeable to +the molecules of salt. This passage will continue until the osmotic +pressure of the salt is equal inside and outside the cell; at the same time +the total osmotic pressure within the cell will have increased, in spite of +its being originally greater than the osmotic pressure outside. + +_Plasmolysis._--We all know that a cut flower soon dries {48} up and fades. +When, however, we place the shrivelled flower in water, the contracted +protoplasm swells up again and refills the cells, which become turgid, and +the flower revives. This phenomenon is due to the fact that vegetable +protoplasm holds in solution substances like sugars and salts which have a +high osmotic pressure. Consequently water has a tendency to penetrate the +cellular walls of plants, to distend the cells and render them turgescent. +De Vries has used this phenomenon for the measurement of osmotic tension. +He employs for this purpose the turgid cells of the plant _Tradescantia +discolor_. The cells are placed under the microscope and irrigated with a +solution of nitrate of soda. On gradually increasing the concentration of +the solution there comes a moment when the protoplasmic mass is seen to +contract and to detach itself from the walls of the cell. This phenomenon, +which is known as plasmolysis, occurs at the moment when the solution of +nitrate of soda begins to abstract water from the protoplasmic juice, +_i.e._ when the osmotic tension of the nitrate of soda becomes greater than +that of the protoplasmic liquid. So long as the osmotic tension of the soda +solution is less than that of the protoplasm, there will be a tendency for +water to penetrate the cell wall and swell the protoplasm. When the osmotic +tension of the solution which bathes the cell is identical with that of the +cellular juice, there is no change in the volume of the protoplasm. In this +way we are able to determine the osmotic pressure of any solution. We have +only to dilute the solution till it has no effect on the protoplasm of the +vegetable cells. Since the osmotic tension of this protoplasm is known, we +can easily calculate the osmotic tension of the solution from the degree of +dilution required. + +_Red Blood Corpuscles as Indicators of Isotony._--In 1886, Hamburger showed +that the weakest solutions of various substances which would allow the +deposition of the red blood cells, without being dilute enough to dissolve +the hæmoglobin, were isotonic to one another, and also to the blood serum, +and to the contents of the blood corpuscles. This is Hamburger's method of +determining the osmotic {49} tension of a liquid. The diluted solution is +gradually increased in strength until, when a drop of blood is added to it, +the corpuscles are just precipitated, and no hæmoglobin is dissolved. + +_The Hæmatocrite._--In 1891, Hedin devised an instrument for determining +the influence of different solutions on the red blood corpuscles. This +instrument, the hæmatocrite, is a graduated pipette, designed to measure +the volume of the globules separated by centrifugation from a given volume +of blood under the influence of the liquid whose osmotic pressure is to be +measured. The method depends on the principle that solutions isotonic to +the blood corpuscles and to the blood serum will not alter the volume of +the blood corpuscles, whereas hypertonic solutions decrease that volume. + +_Action of Solutions of Different Degrees of Concentration on Living +Cells_.--We have just seen that a living cell, whether vegetable or animal, +is not altered in volume when immersed in an isotonic solution that does +not act upon it chemically. When immersed in a hypertonic solution, it +retracts; in a slightly hypotonic solution it absorbs water and becomes +turgescent, while in a very hypotonic solution it swells up and bursts. In +a hypertonic solution the red blood cells retract and fall to the bottom of +the glass, the rapidity with which they are deposited depending on the +amount of retraction. In a hypotonic solution they swell up and burst, the +hæmoglobin dissolving in the liquid and colouring it red. This is the +phenomenon of hæmatolysis. According to Hamburger, the serum of blood may +be considerably diluted with water before producing hæmatolysis. +Experimenting with the blood of the frog, he found that the globules +remained intact in size and shape when irrigated with a salt solution +containing .64 per cent. of salt, this solution being isotonic with the +frog's blood serum. On the other hand, they did not begin to lose their +hæmoglobin till the proportion of salt was reduced to below .22 per cent. +Thus frog's serum may be diluted with 200 per cent. of water before +producing hæmatolysis. In mammals the blood corpuscles remain invariable in +a salt solution of about .9 per cent., and begin to lose their {50} +hæmoglobin approximately in a .6 per cent. solution. A solution of .9 per +cent. of NaCl is therefore isotonic to the contents of the red blood +corpuscles, to the serum of the blood, and to the cells of the tissues. It +by no means follows that the cells of the blood and tissues undergo no +change when irrigated with a .9 per cent. solution of chloride of sodium. +They do not lose or gain water, it is true, and they retain their volume +and their specific gravity. But they do undergo a chemical alteration, by +the exchange of their electrolytes with those of the solution. Hamburger +has pointed out that in mammals the shape of the red corpuscles is altered +in every liquid other than the blood serum; even in the lymph of the same +animal there is a diminution of the long diameter, and an increase of the +shorter diameter, while the concave discs become more spherical. + +All the cells of a living organism are extremely sensitive to slight +differences of osmotic pressure--the cells of epithelial tissue and of the +nervous system as well as the blood cells. For instance, the introduction +of too concentrated a saline solution into the nasal cavity will set up +rhinitis and destroy the terminations of the olfactory nerves. Pure water, +on the other hand, is itself a caustic. There is a spring at Gastein, in +the Tyrol, which is called the poison spring, the "Gift-Brunnen." The water +of this spring is almost absolutely pure, hence it has a tendency to +distend and burst the epithelium cells of the digestive tract, and thus +gives rise to the deleterious effects which have given it its name. +Ordinary drinking water is never pure, it contains in solution salts from +the soil and gases from the atmosphere. These give it an osmotic pressure +which prevents the deleterious effects of a strongly hypotonic liquid. +During a surgical operation it is of the first importance not to injure the +living surfaces by flooding them with strongly hypertonic or hypotonic +solutions. This precaution becomes still more important when foreign +liquids are brought into contact with the delicate cells of the large +surfaces of the serous membranes. Gardeners are well aware of the noxious +influence of a low osmotic pressure. They water the soil around the roots +of a plant, so that the water may take up {51} some of the salts from the +soil before being absorbed by the plant. Pure water poured over the heart +of a delicate plant may burst its cells owing to its low osmotic pressure. +In many medical and surgical applications, on the other hand, a low osmotic +pressure is of advantage. Thus, in order to remove the dry crusts of eczema +and impetigo, the most efficacious application is a compress of cotton wool +soaked in warm distilled water. Under the influence of such a hypotonic +solution the dry cells rapidly swell up, burst, and are dissolved. + +Cooking is also very much a question of osmotic pressure. If salt is put +into the water in which potatoes and other vegetables are boiled, osmosis +is set up and a current of water passes from the vegetable cells to the +salt water. The cellular tissue of the vegetable becomes contracted and +dried, and the membranes become adherent, the vegetable loses weight and +becomes difficult of digestion, in consequence of its hard and waxy +consistency, which prevents the action of the digestive juices. Vegetables +should be cooked in soft water, and should be salted after cooking. When so +treated, a potato absorbs water, the cells swell up, the skin bursts, the +grains of starch also swell up and burst, and the pulp becomes more +friable. The digestive juice is thus able to penetrate the different parts +of the vegetable rapidly, and digestion is facilitated. Any one can easily +prove for himself that a potato boiled in salt water diminishes in weight, +whilst its weight increases when it is cooked in soft water. + +The method of cryoscopy is also of considerable service in forensic +medicine. As shown by Carrara, the cryoscopy of the blood is an important +aid in determining the question whether a body found in the water was +thrown in before or after death. In the former case the concentration of +the blood will be much diminished. In certain experiments on dogs the +cryoscopic examination of the blood showed a freezing point of -.6° C. The +dog was then drowned, when the freezing point of the blood in the left +ventricle was increased to -.29° C., and that in the right ventricle to +-.42° C. On the other hand, when a dog was killed before being thrown into +the water, the {52} osmotic pressure of the blood was hardly decreased even +after an immersion of 72 hours. In the case of persons or animals drowned +in sea water, a similar alteration of the point of congelation is observed, +but in the reverse direction. In this case the osmotic pressure is raised +considerably in those who are drowned, whereas no such rise is observed in +those who are thrown into the sea after death. + +The circulation of the sap in plants and trees is also in great part due to +osmotic pressure. The aspiration of the water from the soil is due to the +intracellular osmotic pressure in the roots, which causes the sap to rise +in the stem of a plant as it would in the tube of a manometer. From a +knowledge of the osmotic pressure of the intracellular liquid of the roots, +we may calculate the height to which the sap can be raised in the trunk of +a tree, _i.e._ the maximum height to which the tree can possibly grow. +Suppose, for instance, the plasma of the rootlets has an osmotic pressure +of six atmospheres, corresponding to that of a 9 per cent. solution of +sugar. A pressure of six atmospheres is equal to the weight of a column of +water 6 × .76 × 13.596 = 61.95 metres high. This, then, is the maximum +height to which this osmotic pressure is able to lift the sap. That is to +say, a tree whose rootlets contain a solution of sugar of 9 per cent. +concentration, or its equivalent, can grow to a height of 62 metres. + +Cryoscopy is also of great use in practical medicine, more especially for +the examination of the urine. The freezing point of urine varies from +-1.26° C. to -2.35°. Koryani has studied the ratio of the point of +congelation of urine to that of a solution containing an equal quantity of +chloride of sodium. He finds that the ratio (freezing point of urine) / +(freezing point of NaCl) increases when the circulation through the tubules +of the kidney is diminished. + +Hans Koeppe has shown that the hydrochloric acid of the gastric juice is +produced by the osmotic exchanges between the blood and the gastric +contents. The ion Na^+ of the salt in the stomach contents exchanges with +an ion H^+ of the monobasic salts of the blood, NaHCO_3 + NaCl = HCl + +Na_2CO_3. {53} + +_Influence of Muscular Contraction on the Intramuscular Osmotic +Pressure._--When a muscle is immersed in an isotonic salt solution it does +not change in weight. In a hypertonic solution it loses weight in +consequence of a loss of water, which passes from the muscle into the +solution to equalize the osmotic pressure. It gains weight in a hypotonic +solution, the water current setting towards the point of higher +concentration. It is easy, therefore, to tell whether the osmotic pressure +in a muscle is above or below that of a given solution, by observing +whether the muscle gains or loses weight when immersed in it. Thus we may +measure the osmotic pressure in a muscle by finding a salt solution in +which the muscle neither gains nor loses weight. In this way we have been +able to prove that the osmotic pressure of a tired muscle is higher than +that of the normal muscle. Our experiments were carried out on the muscles +of frogs. After having pithed the frog, one of the hind legs is removed by +a single stroke of the scissors. The leg is skinned, dried with blotting +paper, and weighed. It is then placed in a salt solution whose freezing +point is -.53° C. At 15° C. such a solution has an osmotic pressure of 6.6 +atmospheres. We next proceed to determine the osmotic pressure of the +corresponding leg after it has been tired by muscular work. For this it is +stimulated by an intermittent faradic current passing once a second for +five minutes. The leg is then skinned, dried, weighed, and placed in the +same salt solution. After eight hours' immersion the legs are weighed +again. The following are the results of six experiments, the numbers +representing fractions of the original weight:-- + +Change of weight of untired leg-- + + After 8 hours -.000. + After 16 hours -.000. + After 24 hours -.006. + +Change of weight of stimulated leg-- + + After 8 hours +.050. + After 16 hours +.080. + After 24 hours +.101. + +{54} + +This result shows that muscular work provoked by electric stimulation +noticeably increases the osmotic pressure of the muscle. + +In order to discover the exact osmotic pressure in the stimulated muscles +we repeated the series of experiments, using more and more concentrated +solutions. In a solution whose freezing point was -.57°, we obtained the +following values:-- + +Change of weight of untired leg-- + + After 8 hours -.000. + After 16 hours -.004. + After 24 hours -.006. + +Change of weight of stimulated leg-- + + After 8 hours +.039. + After 16 hours +.072. + After 24 hours +.099. + +Finally, in a solution freezing at -.72°, _i.e._ with an osmotic pressure +at 15° C. of 9.176 atmospheres, we obtained the following mean values for +the untired leg:-- + + After 8 hours -.04. + After 16 hours -.05. + After 24 hours -.05. + +In this solution, freezing at -.72° C., some of the stimulated muscles +showed no diminution in weight, while others showed a very small +diminution, and others again a slight augmentation, the maximum increase +being .085 of the initial weight. The solution is therefore practically +isotonic with the stimulated muscle. + +In this case the elevation of the intramuscular osmotic pressure produced +by the electrical excitation and the muscular contractions was therefore +2.5 atmospheres, or more than 2.6 kilogrammes per square centimetre of +surface. + +I made further experiments in order to discover whether the variation in +osmotic pressure depended on the duration of {55} the muscular contraction. +For this purpose I used a solution freezing at -.53° C. and immersed in it +untired muscles, and muscles which had been electrically excited for two, +four, and six minutes respectively. The following are the results:-- + + Untired muscles. Muscles stimulated once a second during + 2 Minutes. 4 Minutes. 6 Minutes. + .000 +.026 +.084 +.094 + +.001 +.034 +.065 +.093 + +.005 +.045 +.079 +.097 + .000 +.037 +.070 +.095 + .000 +.032 +.072 +.096 + +Mean of all the observations-- + + +.0012 +.0348 +.074 +.095 + +These experiments show clearly that the osmotic intramuscular pressure +rises in proportion to the duration of the electrical stimulation. + +In order to determine the influence of the work accomplished by the muscle +on the elevation of the osmotic pressure, I made the following experiment. +The two hind legs of a frog were submitted to the same electrical +excitation, one leg being left at liberty, and the other being stretched by +a hundred-gramme weight, acting by a cord and pulley. After exciting them +electrically for five minutes, the legs were immersed for twenty-four hours +in a saline solution freezing at .53° C. The free limb showed an +augmentation of .085 of the initial weight, and the stretched limb an +increase of .106 of the initial weight. It is evident, therefore, that the +osmotic pressure increases with the amount of work done by a muscle. + +Briefly, then, the results of our experiments are as follow:-- + +1. Muscular contraction electrically produced causes an increase of the +osmotic pressure in a muscle. + +2. The intramuscular osmotic pressure may reach, or even exceed, 2.5 +atmospheres, or 2.6 kilogrammes per square centimetre of surface. + +3. When a muscle is made to contract once a second, the {56} elevation of +the osmotic pressure increases with the number of contractions. + +4. The intramuscular osmotic pressure increases with the work done by the +muscle. + +5. Fatigue is caused by the increase of osmotic pressure in a contracting +muscle. + +[Illustration: FIG. 3.--Fields of diffusive force. + +(_a_) Monopolar field of diffusion. A drop of blood in a saline solution of +higher concentration. + +(_b_) Bipolar field of diffusion. Two poles of opposite signs. On the right +a grain of salt forming a hypertonic pole of concentration, on the left a +drop of blood forming a hypotonic pole of dilution. ] + +_The Field of Diffusion._--Just as Faraday introduced the conception of a +field of magnetic force and a field of electric force to explain magnetic +and electrical phenomena, so we may elucidate the phenomena of diffusion by +the conception of a field of diffusion, with centres or poles of diffusive +force. If we consider a solution as a field of diffusion, any point where +the concentration is greater than that of the rest may be considered as a +centre of force, attractive for the molecules of water, and repulsive for +the molecules of the solute. In the same way any point of less +concentration may be regarded as a centre of attraction for the molecules +of the solute, and a centre of repulsion for the molecules of water. + +A field of diffusion may be monopolar or bipolar. A bipolar field has a +hypertonic pole or centre of concentration, and a hypotonic pole or centre +of dilution. By analogy with the magnetic and electric fields we may +designate the hypertonic pole as the positive pole of diffusion, and the +hypotonic as the negative pole. {57} + +The positive and negative poles and the lines of force in the field of +diffusion may be illustrated by the following experiment. A thin layer of +salt water is spread over an absolutely horizontal plate of glass. If now +we take a drop of blood, or of Indian ink, and drop it carefully into the +middle of the salt solution, we shall find that the coloured particles will +travel along the lines of diffusive force, and thus map out for us a +monopolar field of diffusion, as in Fig. 3 a. Again, if we place two +similar drops side by side in a salt solution, their lines of diffusion +will repel one another, as in Fig. 4. + +[Illustration: FIG. 4.--Two drops of blood in a more concentrated solution, +showing a field of diffusion between two poles of the same sign.] + +Now let us put into the solution, side by side, one drop of less +concentration and another of greater concentration than the solution. The +lines of diffusion will pass from one drop to the other, diverging from the +centre of one drop and converging towards the centre of the other (Fig. 3 +_b_). In this manner we are able to obtain diffusion fields analogous to +the magnetic fields between poles of the same sign and poles of opposite +signs. + +The conception of poles of diffusion is of the greatest importance in +biology, throwing a flood of light on a number of phenomena, such as +karyokinesis, which have hitherto been regarded as of a mysterious nature. +It also enables us to appreciate the rôle played by diffusion in many other +biological phenomena. Consider, for example, a centre of anabolism in a +living organism. Here the molecules of the living protoplasm are in process +of construction, simpler molecules being united and built up to form larger +and more complex groups. As a result of this aggregation the number of +molecules in a given area is diminished, _i.e._ the concentration and the +osmotic pressure fall, producing a hypotonic centre of diffusion. We may +thus regard every centre of anabolism as a negative pole of diffusion. {58} + +Consider, on the other hand, a centre of catabolism, where the molecules +are being broken up into fragments or smaller groups. The concentration of +the solution is increased, the osmotic pressure is raised, and we have a +hypertonic centre of diffusion. Every centre of catabolism is therefore a +positive pole of diffusion. Similar considerations as to the formation and +breaking up of the molecules in anabolism and catabolism apply to +polymerization. + +The diffusion field has similar properties to the magnetic and the electric +field. Thus there is repulsion between poles of similar sign, and +attraction between poles of different signs. A simple experiment will show +this. A field of diffusion is made by pouring on a horizontal glass plate a +10 per cent. solution of gelatine to which 5 per cent. of salt has been +added. The gelatine being set, we place side by side on its surface two +drops, one of water, and one of a salt solution of greater concentration +than 5 per cent. We have thus two poles of diffusion of contrary signs, a +hypotonic pole at the water drop, and a hypertonic pole at the salt drop. +Diffusion immediately begins to take place through the gelatine, the drops +become elongated, advance towards one another, touch, and unite. If, on the +contrary, the two neighbouring drops are both more concentrated or both +less concentrated than the medium, they exhibit signs of repulsion as in +Fig. 4. + +Diffusion not only sets up currents in the water and in the solutes, but it +also determines movements in any particles that may be in suspension, such +as blood corpuscles, particles of Indian ink, and the like. These particles +are drawn along with the water stream which passes from the hypotonic +centres or regions toward those which are hypertonic. + +These considerations suggest a vast field of inquiry in biology, pathology, +and therapeutics. Inflammation, for example, is characterized by +tumefaction, turgescence of the tissues, and redness. The essence of +inflammation would appear to be destructive dis-assimilation with intense +catabolism. We have seen that a centre of catabolism is a hypertonic focus +of diffusion. Hence the osmotic pressure in an inflamed region is +increased, turgescence is produced, and {59} the current of water carries +with it the blood globules which produce the redness. + +The phenomenon of agglutination may also possibly be due to osmotic +pressure, a positive centre of diffusion attracting and agglomerating the +particles held in suspension. + +_Tactism and Tropism._--The phenomena of tactism and tropism may also be +partly explained by the action of these diffusion currents of particles in +suspension, these polar attractions and repulsions. In all experiments on +this subject we should take into account the possible influence of osmotic +pressure, since many of the causes of tactism or tropism also modify the +osmotic pressure at the point of action, and it is possible that this +modification is the true cause of the phenomenon. Osmotactism and +osmotropism have not as yet been sufficiently studied. + +[Illustration: FIG. 5.--Liquid figures of diffusion. + +The six negative poles of diffusion are coloured with Indian ink. The +positive pole in the centre is uncoloured and is formed by a drop of KNO_3 +solution.] + +Thus it may be said that osmotic pressure dominates all the kinetic and +dynamic phenomena of life, all those at least which are not purely +mechanical, like the movements of respiration and circulation. The study of +these vital phenomena is greatly facilitated by the conception of the field +of diffusion and poles of diffusion, and of the lines of force, which are +the trajectories of the molecules of the solutes, and the particles and +globules in suspension. + +_The Morphogenic Effects of Diffusion._--Many interesting experiments may +be made showing variations of the lines of force in a field of diffusion, +and how liquids subjected only to differences of osmotic pressure diffuse +and mix with one {60} another in definite patterns. When a liquid diffuses +in another undisturbed by the influence of gravity, it produces figures of +geometric regularity, and we may thus obtain figures and forms of infinite +variety. The following is our method of procedure. A glass plate is placed +absolutely horizontal and is covered with a thin layer of water or of +saline solution. Then with a pipette we introduce into the solution, in a +regular pattern, a number of drops of liquid coloured with Indian ink. A +wonderful variety of patterns and figures may be obtained by employing +solutions of different concentration and varying the position of the drops. + +[Illustration: FIG. 6.--Pattern produced in gelatine by the diffusion of +drops of concentrated solutions of nitrate of silver and bromide of +ammonium.] + +Instead of the water or salt solution, we may spread on the plate a 5 or 10 +per cent. solution of gelatine, containing various salts in solution. If +now we sow on this gelatine drops of various solutions which give +colorations with the salts in the gelatine, we may obtain forms of perfect +regularity, presenting most beautiful colours and contrasts. The drops, of +course, must be placed in a symmetrical pattern. In this way we may obtain +an endless number of ornamental figures. + +In order to cover a lantern slide 8½ cm. × 10 cm., about 5 c.c. of gelatine +is required. To this amount of gelatine we add a single drop of a saturated +solution of salicylate of sodium, and spread the liquid gelatine evenly +over the plate. When the gelatine has set, we put the plate over a diagram, +a hexagon for instance, and place a drop of ferrous sulphate solution at +each of the six angles. The drops immediately diffuse {61} through the +gelatine, and the result after a time is the production of a beautiful +purple rosette. The gelatine must be carefully covered to prevent its +drying until the diffusion is complete. The preparation may then be dried +and mounted as a lantern slide, and will give the most brilliant effect on +projection. If the gelatine has been treated with a drop of potassium +ferrocyanide solution instead of salicylate of sodium, a few drops of +FeSO_4 will give a blue pattern. Or we may treat the gelatine with +ferrocyanide of potassium and salicylate of sodium mixed, and thus obtain +an intermediary colour on the addition of FeSO_4. We may, indeed, vary +indefinitely the nature and concentration of the solution, as well as the +number and position of the drops. The results have all the charm of the +unexpected, which adds greatly to the interest of the experiment. + +[Illustration: FIG. 7.--Pattern produced in gelatine by the diffusion of +drops of silver nitrate and sodium carbonate.] + +These experiments are not merely a scientific toy. They show us the +possibility, hitherto unsuspected, that a vast number of the forms and +colours of nature may be the result of diffusion. Thus many of the +phenomena of life, hitherto so mysterious, present themselves to us as +merely the consequences of the diffusion of one liquid into another. One +cannot help hoping that the study of diffusion will throw still further +light on the subject. + +If a number of spheres, each capable of expansion and deformation, are +produced simultaneously in a liquid, they will form polyhedra when they +expand by growth. This is the {62} precise architecture of a vast number of +living organisms and tissues, which are formed by the union of microscopic +polyhedra or cells. A section of such a polyhedral structure would appear +as a tissue of polygons. It is interesting to note that the simple process +of diffusion will produce such structures under conditions closely allied +to those which govern the development of the tissues of a living organism. + +[Illustration: FIG. 8.--Pattern produced in gelatine by the diffusion of +drops of a solution of nitrate of silver and of citrate of potassium.] + +We may obtain this cellular structure by a simple experiment. On a glass +plate we spread a 5 per cent. solution of pure gelatine, and when set sow +on it a number of drops of a 5 to 10 per cent. solution of ferrocyanide of +potassium. The drops must be placed at regular intervals of 5 mm. all over +the plate. When these have been allowed to diffuse and the gelatine has +dried, we obtain a preparation which exactly resembles the section of a +vegetable cellular tissue (Fig. 9). The drops have by mutual pressure +formed polygons, which appear in section as cells, with a membranous +envelope, a {63} nucleus, and a cytoplasm, which is in many cases entirely +separated from the membrane. These cells when united form a veritable +tissue, in all respects similar to the cellular structure of a living +organism. + +[Illustration: FIG. 9.--Tissue of artificial cells formed by the diffusion +in gelatine of drops of potassium ferrocyanide.] + +In the preparation showing artificial cells the cellular structure is not +directly visible until the gelatine has dried. One sees only a gelatinous +mass analogous to the protoplasm of a living organism. This mass is +nevertheless organized, or at least in process of organization, as we may +see by the refraction when its image is projected on the screen. + +During the cell-formation, and as long as there is any difference of +concentration in the gelatine, each cell is the arena of active molecular +movement. There is a double current, as in the living cell, a stream of +water from the periphery to the centre, and of the solute from the centre +to the periphery. This molecular activity--the life of the artificial +cell--may be prolonged by appropriate nourishment, {64} _i.e._ by +continually repairing the loss of concentration at the centre of the cell. + +The life of the artificial cell may also be prolonged by maintaining around +it an appropriate medium. If we prematurely dry such a preparation of +artificial cells, the molecular currents will cease, to recur again when we +restore the necessary humidity to the preparation. This to my mind gives us +a most vivid picture of the conditions of latent life in seeds and many +rotifera. + +These artificial cells, like living organisms, have an evolutionary +existence. The first stage corresponds to the process of organization, the +gelatine representing the blastema, and the drop the nucleus. Thus the cell +becomes organized, forming its own cytoplasm and its own enveloping +membrane. + +The second stage in the life of this artificial cell is the period during +which the metabolism of the cell is active and tends to equalize the +concentration of the liquid in the cell and in the surrounding medium. + +The third stage is the period of decline. The double molecular current +gradually slows down as the difference of concentration decreases between +the cell contents and its entourage. When this equality of concentration +has become complete the molecular currents cease, the cell has terminated +its existence; it is dead. The currents of substance and of energy have +ceased to flow--the form only remains. + +These artificial cells are sensible to most of the influences which affect +living organisms. Like living cells they are influenced both in their +organization and in their development by humidity, dryness, acidity, or +alkalinity. They are also greatly affected by the addition of minute +quantities of chemical substances either to the gelatinous blastema or to +the drops which represent the primary nuclei. We may in this way obtain +endless varieties, nuclei which are opaque or transparent, with or without +a nucleolus, and cells containing homogeneous cytoplasm without a nucleus. +We may also obtain cells with cytoplasm filling the whole of the cellular +cavity or separated from the cell-membrane. We may obtain {65} cells +imitating all the natural tissues, cells without a membranous envelope, +cells with thick walls adhering to one another, or cells with wide +intracellular spaces. + +[Illustration: FIG. 10.--Artificial liquid cells, formed by coloured drops +of concentrated salt solution in a less concentrated salt solution.] + +The forms of these artificial cells depend on the number and relative +position of the drops which represent the nuclei, and on the molecular +concentration or osmotic tension of the solution. The number of the +cellular polyhedra is determined by the number of centres of diffusion. The +magnitude of the dihedral angles, from which radiate three and occasionally +four walls, depends on the position of the hypertonic poles of diffusion. +The curvature of a surface is determined by the differences of +concentration on either side. Between isotonic solutions the surface is +plane, whilst it is curved between solutions of different osmotic +pressures, the convexity being directed towards the hypertonic solution. + +[Illustration: FIG. 11.--Liquid cells with a fringe of cilia, obtained by +sowing coloured drops of concentrated salt solution in a weaker salt +solution. The contents of the cells have undergone segmentation.] + +The time required for these artificial cells to grow varies from two to +twenty-four hours, according to the concentration of the gelatine, the +growth being most rapid in dilute solutions. + +Similar cells may be produced in water. If we pour a thin layer of water on +a horizontal plate, and with a pipette {66} sow in it a number of drops of +salt water coloured with Indian ink, we may obtain artificial cells +composed entirely of liquid, having the same characters as those produced +in a gelatinous solution. + +It is possible by liquid diffusion to produce not only ordinary cells but +ciliated cells. If we spread a layer of salt water on a horizontal glass +plate, and sow in it drops of Indian ink, artificial cells are produced by +diffusion. At the edge of the preparation there is often to be seen a sort +of fringe, analogous to the cilia of living cells (Fig. 11). + +These tissues of artificial cells demonstrate the fact that inorganic +matter is able to organize itself into forms and structures analogous to +those of living organisms under the action of the simple physical forces of +osmotic pressure and diffusion. The structures thus produced have functions +which are also analogous to those of living beings, a double current of +diffusion, an evolutionary existence, and a latent vitality when desiccated +or congealed. + + * * * * * + + +{67} + +CHAPTER VI + +PERIODICITY + +_Periodic Precipitation._--A phenomenon is said to be periodic when it +varies in time and space and is identically reproduced at equal intervals. +We are surrounded on all sides by periodic phenomena; summer and winter, +day and night, sleep and waking, rhythm and rhyme, flux and reflux, the +movements of respiration and the beating of the heart, all are periodic. +Our first sorrows were appeased by the periodic rhythm of the cradle, and +in our later years the periodic swing of the rocking-chair and the hammock +still soothe the infirmities of old age. + +Sound is a periodic movement of the atmosphere which brings to us harmony +and melody. Light consists of periodic undulations of the ether which +convey to us the beauty of form and colour. Periodic ethereal waves waft to +us the wireless message through terrestrial space and the radiant energy of +the sun and stars. + +It is therefore not to be wondered at that the phenomena of diffusion are +also periodic. According to Professor Quinke of Heidelberg, the first +mention of the periodic formation of chemical precipitates must be +attributed to Runge in 1885. Since that time these precipitates have been +studied by a number of authors, and particularly by R. Liesegang of +Düsseldorf, who in 1907 published a work on the subject, entitled _On +Stratification by Diffusion_. + +In 1901 I presented to the Congress of Ajaccio a number of preparations +showing concentric rings, alternately transparent and opaque, obtained by +diffusing a drop of potassium ferrocyanide solution in gelatine containing +a trace of ferric {68} sulphate. At the Congress of Rheims in 1907 I +exhibited the result of some further experiments on the same subject. + +These periodic precipitates may be obtained from a great number of +different chemical substances. The following is the best method of +demonstrating the phenomenon. A glass lantern slide is carefully cleaned +and placed absolutely level. We then take 5 c.c. of a 10 per cent. solution +of gelatine and add to it one drop of a concentrated solution of sodium +arsenate. This is poured over the glass plate whilst hot, and as soon as it +is quite set, but before it can dry, we allow a drop of silver nitrate +solution containing a trace of nitric acid to fall on it from a pipette. +The drop slowly spreads in the gelatine, and we thus obtain magnificent +rings of periodic precipitates of arsenate of silver, with which any one +may easily repeat the experiments detailed in this chapter. + +[Illustration: FIG. 12.--Lines of diffusion precipitate, showing the +simultaneous propagation of "undulations of different wave-length.] + +_Circular Waves of Precipitation._--The wave-front of the periodic rings of +precipitates is always perpendicular to the rays of diffusion. The distance +between the rings depends on the concentration of the diffusing solution. +The greater the fall of concentration, the less is the interval between the +rings. Each ring represents an equipotential line in the field of +diffusion. These equipotential lines of diffusion give us the best and most +concrete reproduction of the mode of propagation of periodic waves in +space. They are, in fact, a visible diagram of the propagation of the waves +of light and sound. Occasionally we may observe in the gelatine the +simultaneous propagation of undulations of different wave-length, just as +we have them in the ether and the air. These diffusion wavelets {69} give +us a very beautiful representation of the simultaneous propagation of +undulations of different wave-length in the same medium. + +[Illustration: FIG. 13.--Waves of diffusion refracted at a plane surface on +passing from a less concentrated into a more concentrated solution. The +refracted wave-front is flattened, the wave-length being less in the denser +medium.] + +Like waves of light and sound, these waves of diffusion are refracted when +they pass from one medium into another of a different density, where they +have a different velocity. When, for instance, a diffusion wave passes from +a 5 per cent. solution of gelatine into a 10 per cent. solution, the +wave-front is retarded, the retardation being proportional to the length of +the path through the denser medium. Hence the wave-front is flattened, the +curvature of the refracted wave being less than that of the original wave +of diffusion. The contrary is the case when the wave-front passes into a +medium where its velocity is greater. The middle of the wave-front now +travels faster than the flanks, and the curvature is increased. + +[Illustration: FIG. 14.--Transformation of a spherical wave-front into a +plane wave-front by a convergent diopter.] + +These diffusion rings furnish us with most excellent diagrams of refraction +at a "diopter," _i.e._ a spherical surface separating two media of +different densities. Fig. 14 shows the refraction at a convergent diopter, +_i.e_. a surface where the denser medium is convex. The diffusion waves in +this case emanate from the principal focus of the diopter, and therefore +become plane on passing through the convex surface of the denser gelatine. + +These periodic diffusion rings also illustrate the phenomena of colour +diffraction. Diffusion waves of different {70} wavelength are unequally +refracted by a gelatine lens. Hence rings of different wave-length which, +originating at the same spot, are at first concentric, are no longer +parallel after passing through a gelatine lens. A convergent lens which +will change the long spherical incident waves into shorter plane waves, +will transform the short incident waves into concave waves whose curvature +is opposite to that of the original waves, _i.e._ it will transform a +divergent into a convergent beam. This is an illustration of what is called +the aberration of refrangibility. + +In the same way we may demonstrate the course of diffusion waves through a +gelatine prism, showing the refraction on their incidence and again on +emergence. The prism is made of a stronger gelatine solution, which is more +refractive than the gelatine around it. The waves of diffusion whilst +traversing the prism are retarded, and this retardation is greatest at the +base where the passage is longer. Hence the wave-front is tilted towards +the base of the prism, and this tilting is repeated when the wave-front +leaves the prism. + +If we examine diffusion waves of different wave-length on their emergence +from the gelatine prism, we shall see that they cut one another. With a +dense prism, the wave-front of the shorter waves is more tilted towards the +base than the wave-front of the longer waves. For diffusion as for light +the shorter waves are the most refracted. Both refraction and dispersion +are due to the unequal resistances of the medium to undulatory movements of +different periodicity. + +[Illustration: FIG. 15.--Diffraction of diffusion waves on passing through +a narrow aperture.] + +_Diffraction._--When light traverses a minute orifice, instead {71} of +passing on in a straight line, it spreads out like a fan, forming a +diverging cone of light, just as if the orifice were itself a luminous +point. This is the phenomenon of diffraction which has hitherto been +considered incompatible with the emission theory of light. Diffusion waves +may also be made to pass through a narrow orifice, when they will behave +exactly like the waves of light. The new waves radiate from the orifice +like a fan, instead of giving a cone of waves bounded by lines passing +through the circumference of the orifice and the original centre of +radiation. Thus on passing through a small orifice diffusion waves exhibit +the phenomenon of diffraction just as light waves do. + +[Illustration: FIG. 16.--Interference of diffusion waves.] + +_Interference._--The phenomenon of interference may also be illustrated by +waves of diffusion. If on a gelatine plate we produce two series of +diffusion waves from two separate centres, we get at certain points an +appearance corresponding to the interference of two sets of light waves. +This appearance is best shown by sowing on the gelatine film a straight row +of drops equidistant from one another. It should be remarked that this +phenomenon of the production of circles of precipitate separated by +transparent spaces, although periodic, is not of necessity vibratory or +undulatory. It would thus appear that periodic phenomena may be propagated +through space without vibratory or oscillatory motion. If we submit to a +critical examination the various experiments which have established the +undulatory theory of light, we find that they do indeed demonstrate the +periodic nature of light, but in no wise prove that light is a vibratory +movement of the ether. {72} On the contrary, the hypothesis that light is +propagated by vibratory movements is open to many objections. Even the +Zeeman effect, although it may tend to establish the fact that light is +produced by vibratory movement, by no means proves that it is propagated in +the same manner. When the theory was accepted that the transmission of +light was periodic it was supposed that this periodic transmission could +only be vibratory or undulatory in character, since waves or vibrations +were the only periodic phenomena known at that time. We now know that there +are other means of periodic transmission which are apparently not +undulatory. The periodic precipitates produced by diffusion show us the +transmission of spherical waves through space, which follow the laws of +light, although the periodic phenomenon is apparently emissive rather than +vibratory. + +It will be remembered that Newton considered light to be produced by +projectile-like particles emanating from a centre, and proceeding in +straight lines in all directions. This emission theory of light was +abandoned in favour of Huygens' undulatory theory. + +It was said that the phenomena of interference and diffraction could not be +explained by the theory of emission, while the undulatory theory gave a +simple explanation. The scientific mind was unable to conceive the idea of +emission and periodicity as taking part in the same phenomenon. The savants +and thinkers who have meditated on this question have always considered the +theory of emission and that of periodicity as incompatible. Nevertheless, +we are here in presence of a phenomenon in which emission and periodicity +exist simultaneously. The molecules emanating from our drop are diffused in +straight radiating lines, and yet produce periodic precipitates which are +subject to interference and diffraction like the undulations of Huygens. + +The phenomena associated with the pressure of light, the {73} discovery of +the cathode rays and the radiations of radium, together with the +introduction of the electron theory of electricity, all seem to have +brought again into greater prominence Newton's original conception of the +emissionary nature of light. + +Some of the phenomena of radiation can be explained only by the emission +theory, and others by the undulatory theory of light. All these +difficulties would be solved if we admitted the hypothesis that radiating +bodies project electrons, which produce in the ether periodic waves similar +to those formed in our gelatine films by the molecules of diffusion. + +These diffusion films are of the greatest possible service in the practical +teaching of optics. They place before the eye of the student a working +model as it were of the undulations of light. When projected on the screen, +they give excellent pictures of the phenomena of refraction, diffraction, +and interference, and the simultaneous propagation of undulation of +different wave-lengths, and they show in a visible manner the changes of +wave-length in media of different densities. + +Diffusion waves differ greatly in length, varying from several millimetres +to 2 [mu]. Many are even shorter than this, too short to be separately +distinguished even under the highest power of the microscope, when they +give the effect of moiré or mother-of-pearl. + +It is easy to construct a spectroscopic grating in this way with fine lines +whose distance apart is of the order of a micron, separated by clear +spaces. Every physical laboratory may thus produce its own spectroscopic +gratings, rectilinear, circular, or of any desired form. + +The most beautiful colour effects may be produced with these diffusion +gratings, as we have shown at the Congress of Rheims in 1907. We have a +considerable collection of these diffusion gratings, some with very fine +lines, giving a very extended spectrum, and others with coarser striations +which give a large number of small spectra. + +This study of periodic precipitates is of the highest interest when we come +to investigate the production of colour in natural objects, such as the +wings of insects or the plumage of {74} birds. Many tissues have this lined +or striated structure and exhibit interference colours like those of the +periodic precipitates, their structure showing alternate transparent and +opaque lines, whose width is of the order of a micron. This is the +structure of muscle, and to this striated surface is also attributable many +of the most beautiful colours of nature, the gleam of tendon and +aponeurosis, the fire of scarab and beetle, the colours of the peacock, and +the iridescence of the mollusc and the pearl. The study of liquid diffusion +has given us an idea of the physical mechanism by which these striated +tissues are produced, a mechanism which up to the present time has not been +even suspected. Our experiments show how readily such striped or ruled +structures may be produced in a colloidal solution by the simple diffusion +of salts such as are found in every living organism. + +[Illustration: FIG. 17.--Photomicrograph of striated structure of a +periodic precipitate of carbonate and phosphate of lime (magnified 500 +times).] + +To make a spectroscopic grating by diffusion we proceed as follows. We take +5 c.c. of a 10 per cent. solution of gelatine, and add to it one drop of a +concentrated solution {75} of calcium nitrate. We spread the gelatine +evenly over a plain glass lantern slide and allow it to set. After it is +set, but before it dries, we place in the centre of the slide a drop of +concentrated solution containing two parts of sodium carbonate (Na_2CO_3) +to one of dibasic sodium phosphate (Na_2HPO_4). Tribasic sodium phosphate +alone without the addition of the carbonate will also give good results. If +the phosphate solution is placed on the gelatine in the form of a drop, we +obtain circular periodic precipitates. If it is desired to make a +rectilineal grating, we deposit the phosphate solution on the gelatine in a +straight line by means of two parallel glass plates. In this way we may +obtain lines of periodic precipitation to the number of 500 to 1000 per +millimetre, forming gratings which produce most beautiful spectra. + +Pearls and mother-of-pearl both owe their iridescence to a similar ruled +structure, which is developed in the living tissue of a mollusc. They are, +in fact, periodic precipitates of phosphate and carbonate of lime deposited +in the colloidal organic substance of the mollusc. They have the same +structure and the same chemical composition; they have the same physical +properties, the glow, the fire, and the brilliancy of our spectroscopic +gratings. In these experiments, indeed, we have realized the synthesis of +the pearl, not only a chemical synthesis, but the synthesis of its +structure and organism. + +We have been able to make these periodic precipitates by the reaction of a +great number of chemical substances, giving a bewildering variety of form +and structure. Some of these recall the form of various organisms, and +especially of insects, as may be seen in Fig. 18. + +All the phenomena of life are periodic. The movement of heart and lungs, +sleep and waking, all nervous phenomena, have a regular periodicity. It is +possible that the study of these purely physical phenomena of periodic +precipitation may give us the key to the causation of rhythm and +periodicity in living beings. + +Besides this periodic precipitation there appear to be other chemical +reactions which are periodic. Professor Bredig of Heidelberg has lately +described a curious phenomenon, the {76} periodic catalysis of peroxide of +hydrogen by mercury. He thus describes his experiment: "We place in a +perfectly clean test tube a few cubic centimetres of perfectly pure +mercury. Upon this we pour 10 c.c. of a 10 per cent. solution of hydrogen +peroxide. The mercury speedily becomes covered with a thin, brilliant +bronze-coloured pellicle which reflects light. Then little by little +catalysis of the hydrogen peroxide begins, with liberation of oxygen. After +some time, from five to twenty minutes, the liberation of gas at the +surface of the mercury ceases, the cloud formed by the gas bubbles +disappears, and the bronze mirror at the surface of the mercury lights up +with the glint of silver. There is a pause of one or more seconds, and then +the catalytic action begins afresh, commencing at the edges of the mirror. +The cloud is again formed and again disappears. This beautiful and +surprising rhythmic phenomenon may continue at regular intervals for an +hour or more." + +[Illustration: FIG. 18.--Articulate form produced by periodic +precipitation.] + +A slight alkalinity of the liquid is necessary to start the phenomenon. +This explains the retardation at the beginning {77} of the experiment, +since the rhythmic catalysis cannot begin until the hydrogen peroxide has +dissolved a little of the glass so as to render it slightly alkaline. The +catalytic process may, however, be set going at once by adding a trace of +potassium acetate to the solution. + +We may even obtain a curve giving an automatic record of the periodicity of +this catalytic action. For this purpose the oxygen given off is led to a +manometer, which registers on a revolving drum the periodic variation in +pressure. The curve thus obtained presents a remarkable resemblance to a +tracing of the pulse. The frequency and character of the undulatory curve +is modified by physical and chemical influences. Like circulation or +respiration, periodic catalysis has its poisons, and exhibits signs of +fatigue, and of paralysis by cold. + +The rhythmic catalysis of Bredig produces an electrical current of action +between the mercury and the water just like that produced by the rhythmic +contraction of the heart, and this current may be registered in a similar +way by means of the Einthoven galvanometer. Thus the heart-beat may be but +an instance of rhythmic catalysis, since both produce the same phenomena, +movement, chemical action, and periodic currents. In the chapter on +physiogenesis we shall return to the study of this question and consider +another rhythmic phenomenon which is the result of osmotic growth. + + * * * * * + + +{78} + +CHAPTER VII + +COHESION AND CRYSTALLIZATION + +Chemical affinity is the force which holds together the different atoms in +a molecule. Cohesion is the force which holds together molecules which are +chemically similar. Although physical science distinguishes three states of +matter, solid, liquid, and gaseous, yet here as elsewhere there are no +sharp dividing lines, but rather an absolute continuity. We have in fact +many intermediate states; between liquids and gases there are the various +conditions of vapour, and between liquids and solids we get viscous, +gelatinous, and paste-like conditions. The only real difference between +solids, liquids, and gases is the intensity of the force of cohesion, which +is considerable in solids, feeble in liquids, and absent in gases. + +A living organism is the arena in which are brought into play the opposing +forces of cohesion and disintegration. The study of cohesion is therefore a +vital one for the biologist, and especially cohesion under the conditions +which obtain in living beings, viz. in liquids of heterogeneous +constitution. The forces of cohesion brought into play under these +conditions may be beautifully illustrated by a simple experiment. We take a +plate of glass, well cleaned and absolutely horizontal. On it we pour a +layer of salt water, and in the middle we carefully drop a spot of Indian +ink. The drop at once begins to diffuse, and we obtain a circular figure, +like the monopolar field of diffusion already described, the rays of +diffusion radiating from the centre in all directions. + +[Illustration: FIG. 19.--Muriform cohesion figure formed by a drop of +Indian ink in a solution of salt.] + +If we keep the plate carefully protected from all disturbing influences, +after some ten to twenty minutes we shall see the coloured particles +returning on their path, and the centre of {79} the drop becoming more and +more black. Each line of force becomes segmented into granules, which +gradually increase in size, and approach nearer to one another and to the +centre of the drop, until it assumes the mulberry appearance shown in the +photograph (Fig. 19). + +[Illustration: FIG. 20.--Seven similar drops of Indian ink diffusing in a +salt solution. Two minutes after introducing the drops.] + +If we sow a number of drops of Indian ink in regular order on the surface +of a salt solution, we obtain most beautiful patterns formed by the mutual +repulsion of the drops. Figs. 20, 21, and 22 represent the successive +aspects of seven drops of Indian ink thus sown on a layer of salt solution, +and kept undisturbed long enough to allow of their evolution. Fig. 20 shows +the aspect after two minutes, when the diffusion is almost complete. In +Fig. 21, photographed after fifteen {80} minutes, the colouring matter has +almost entirely reunited to form separate granulations; whilst in Fig. 22, +taken after thirty minutes, these granulations are rearranged to form an +agglomeration around the centre of each drop. + +[Illustration: FIG. 21.--The same drops 15 minutes later, showing the +granulation appearance.] + +The following experiment, which is more difficult, will show the cohesive +attraction of one drop for another. A plate of glass is adjusted absolutely +horizontal, and covered as before with a layer of salt solution. On this we +sow a number of drops of the same salt solution coloured with Indian ink. +The drops must be of exactly the same concentration as the salt medium, so +as to avoid any difference of osmotic pressure between the drops and the +medium, otherwise the drops would not remain intact but would diffuse into +the solution. Since under these conditions the liquid of the medium around +the drops is perfectly symmetrical and homogeneous, it cannot exercise any +influence on the liquid of the drops. + +[Illustration: FIG. 22.--The same drops after 30 minutes. The granulations +have agglomerated at the centre of the drops.] + +It is otherwise, however, with the colouring matter of the {81} drops. The +particles of Indian ink may be seen passing from one drop to another, the +coloured circles become elongated towards one another, touch, and finally +unite. If, as in Fig. 23, the drops are of different size, the larger one +will have a preponderating attractive action and eat up the smaller drops. +In the figure, six small drops are placed around a large one, and the +smaller drops have begun to be deformed and to move towards the larger +drop. This central drop is also deformed, and has assumed a more or less +hexagonal form, under the influence of the attraction of the six smaller +ones. It may be noticed that the least prominent angle of the hexagon is +opposite the small drop which is farthest away from it, whilst one of the +smaller drops has already begun to be swallowed up by the large one. This +cohesion phenomenon is very slow in its action, but after an hour or two +the central drop will be found to have {82} completely absorbed the six +smaller ones, and only one large drop will remain. + +[Illustration: FIG. 23.--Attraction between coloured drops in an isotonic +solution.] + +_Incubation._--In the living organism we frequently find conditions similar +to those realized in this experiment, viz. very slow movements of diffusion +in liquids containing particles in suspension. In such cases the +consequences must be the same, viz. granulation and segmentation. Consider +for a moment the incubation of an egg. The heat of incubation determines a +certain amount of evaporation through the shell, with a concentration of +the liquid near the surface. As a consequence of this superficial +concentration we get segmentation of the vitellus, with the production of a +morula. + +_Artificial Parthenogenesis._--The experimental parthenogenesis of Loeb and +Delage consists in plunging the egg into a liquid other than sea water, and +returning it again to its original medium. This operation will necessarily +determine slow movements of diffusion in the egg, which will give rise to +segmentation. It may be objected that segmentation is also produced by a +solution which is isotonic with sea water. Such a solution would not indeed +produce an exchange of water with the egg, but it would set up an exchange +of electrolytes, since there would be a difference of their osmotic +pressure in the egg and in the new isotonic medium. The extremely slow +movements of diffusion thus produced would be very favourable to the action +of the cohesive force on the particles in suspension, and hence to the +segmentation of the egg. + +[Illustration: FIG. 24.--A circle of eight drops of Indian ink 30 minutes +after they have been sown in a salt solution. The drops have undergone +diffusion and subsequent cohesion, resulting in a reticulate structure.] + +Few physical phenomena give us a deeper insight into the phenomena of life +than those which we here contemplate. There is still another experiment +which is even more convincing. On the surface of our horizontal salt +solution we sow a number of drops of a more concentrated salt solution at +equal distances around the circumference of a circle. Movements of +diffusion are thus set up in the interior of the circle, and after a time, +when this diffusion has become so slow as to be almost imperceptible, a +furrow begins to appear in the coloured mass. Then a second and third +appear, and others crossing the former break up the mass {83} into +segments. Finally the segmentation becomes complete, and the preparation +presents a muriform appearance, looking in fact something like a mulberry +(Fig. 24). If the preparation is preserved for several hours longer, we may +see the cells formed by segmentation unite around the circumference so as +to form a hollow bag corresponding to a gastrula, as shown in Fig. 25. + +[Illustration: FIG. 25.--The same preparation several hours later, showing +a cellular gastrula-like structure.] + +These preparations are extremely sensitive to external influences, which +renders the demonstration of cohesion phenomena difficult. I have +nevertheless on several occasions been able to project the experiment on +the screen during a lecture. The segmentation is influenced by very slight +currents of diffusion, and I have many preparations showing the +segmentation regularly distributed in various ways along radial diffusion +lines. We may in this way produce many varieties of structure lamellar, +vacuolate, or cellular, in fact {84} all the tissue structures which are +met with in living organisms. All these structures are retractile, the +retraction going on very slowly for a long time, as if the force of +cohesion continued to act in the web of the structure even after its +formation was complete. The phenomenon is a purely physical synthetic +reproduction of the phenomenon of coagulation, the cohesion figure being in +fact a retractile clot. + +[Illustration: FIG. 26.--Field of crystallization of sodium chloride +(magnified 60 diameters).] + +_Crystallization._--When we evaporate a solution of a crystalloid it +becomes more concentrated, slow movements of diffusion are set up, and at a +given moment agglomeration occurs, the agglomerates taking the form of +crystals. Thus crystallization may be regarded as a particular case of +conglomeration by cohesion, differing only in the regularity of the +arrangement of the molecules, which gives the geometrical form of the +crystal. Hence we can easily understand how the presence of a crystalline +fragment may facilitate the process of crystallization. Consider a liquid +in which extremely slow movements of diffusion are taking place. If the +liquid is perfectly homogeneous there will be no centre of attraction to +which the molecules may become attached. {85} + +[Illustration: FIG. 27.--Field of crystallization around a crystal of +sodium chloride in process of formation.] + +If, however, a crystal or other heterogeneous structure is present, it +forms a centre of cohesion which will attach any molecules that are brought +by diffusion into its sphere of attraction. We have succeeded in +photographing the arrangement of the molecules of a liquid around a crystal +in the act of formation (Fig. 26). For this purpose we add to the solution +traces of some colloidal substance, such as gelatine or gum, so as to delay +the crystallization. It may thus be shown that the molecules of the +surrounding liquid are already arranged in crystalline order for some +distance from the crystal, forming a sort of field of crystallization. The +arrangement of this regular field varies in different cases, and is more or +less complicated according to circumstances. One of the most frequent forms +is that shown in Fig. 27, which is the field around a crystal of sodium +chloride. In the centre {86} of the crystal is a square with well-marked +outline. At each corner of this square there is a straight line at right +angles to the diagonal, which will form the sides of the crystal in process +of formation. From the middle of each side arise yet other perpendiculars, +which in their turn bear other cross lines, each new line being set at +right angles to its predecessor. A later stage of crystallization is shown +in Fig. 27, where the two squares one inside the other at an angle of 45° +are clearly indicated. + +[Illustration: FIG. 28.--Three crystals of sodium chloride in process of +formation, each in the centre of a field of crystallization.] + +Every crystallizable substance gives a different characteristic field of +crystallization. In 1903, at the Congress of Angers, I terminated my +address by these words: "The field of crystallization may serve to +determine the character of a substance in solution." I have subsequently +received from Carbonell y Solès of Barcelona an interesting work on this +subject, which he contributed to the International Congress of Medicine at +Madrid in 1903, entitled _Applicacion de la crystalogenia experimental à la +investigacion toxicologica de cas alcaloïdes_. {87} + +Six years ago I received from Australia an exceedingly beautiful photograph +of a thin pellicle found in a rain gauge. My correspondent supposed that +this strange figure might have been produced under the influence of an +electric or magnetic field. I was able to assure him by return of post that +the figure was the result of the crystallization of copper sulphate in a +colloidal medium. In return I received a letter verifying this fact, and +saying that there were copper works in the neighbourhood, and the air was +filled with the dust of copper sulphate. + +Living beings are but solutions of colloids and crystalloids, and their +tissues are built up by the aggregation of these solutes. We have already +seen how the forces of crystallization are modified in colloid solutions. +This force of crystallization must play an important rôle in the +metamorphoses of the living organism, and influence their morphology. It +may therefore be of interest to investigate some of the numberless forms of +crystallization in colloidal solutions. + +[Illustration: FIG. 29.--Crystallization of sodium chloride in a colloidal +solution, giving a plant-like form.] + +[Illustration: FIG. 30.--Form produced by the crystallization of chloride +of ammonium in a colloidal solution.] + +Figs. 29 and 30 represent the forms produced by chloride of sodium and +chloride of ammonium respectively, in solutions of gelatine of different +degrees of concentration. Their resemblance to vegetable growth is so +remarkable that several observers on first seeing them have called them +"Fern-crystals." + +I should like here to recall to your notice the work of an English +observer, Dr. E. Montgomery of St. Thomas's {88} Hospital, which was +published as long ago as 1865. This work was recently brought to my notice +by the kindness of Professor Baumler of Freiburg. He says: "Crystals are +not strangers in the organic world. Many organic compounds are able to +assume crystalline forms under certain conditions. Rainey has shown that +many shells consist of globular crystals _i.e._ of mineral substances made +to crystallize by the influence of viscid material." In this connection I +may also mention the interesting work of Otto Lehmann of Karlsruhe on +liquid crystals. + +In conclusion, we may recall the words of Schwann himself, the originator +of the cell theory: "The formation of the elementary shapes of an organism +is but a crystallization of substances capable of imbibition. The organism +is but an aggregate of such imbibing crystals." + + * * * * * + + +{89} + +CHAPTER VIII + +KARYOKINESIS + +In 1873, Hermann Fol, writing of the eggs of Geryonia, thus describes the +phenomenon of karyokinesis: "On either side of the residue of the nucleus +there appears a concentration of plasma, thus forming two perfectly regular +star-like figures, whose rays are straight lines of granulations. There are +other curved rays which pass from one star or centre of attraction to the +other. The whole figure is extraordinarily distinct, recalling in a +striking manner the arrangement of iron filings surrounding the poles of a +magnet. Sachs' theory is that the division of the nucleus is caused by +centres of attraction, and I agree with him, not on theoretical grounds, +but because I have actually seen these centres of attraction." + +Since the discovery of Hermann Fol, a great number of explanations have +been given, all of them theoretical, to account for the figures and +phenomena of karyokinesis. Many of these so-called explanations are +mechanical, while others invoke the aid of magnetism or electricity to +account for the resemblance of the figures of karyokinesis to the magnetic +or electric phantom or spectre. Among the authors who have dealt with this +question we may mention Hartog of Cork, Gallardo of Buenos Ayres, and +Rhumbler of Göttingen. + +In 1904 I presented to the Grenoble Congress, and in 1906 to the Lyons +Congress, a series of photographs and preparations of experimental +karyokinesis. I showed how, in a solution analogous to that found in the +natural cell, the simple processes of liquid diffusion, without the +intervention of magnetism or electricity, may reproduce with perfect +accuracy and in their normal sequence the whole of the movements and {90} +figures which characterize the phenomenon of karyokinesis. This experiment +consists not merely in the production of a certain figure, such as is +obtained in the magnetic spectre, but in the reproduction of the movement +itself, and of all the successive forms which are seen in the natural +phenomenon. These are evolved before the eyes of the spectator in their +regular order and sequence. + +I may here reproduce the text of my communication at Grenoble: "Until I +introduced the conception of a field of diffusion, there was no proper +means of studying the phenomena of diffusion, which obey the laws of a +field of force as expounded by Faraday. Moreover, no one suspected the +possibility of reproducing by liquid diffusion a spectre analogous to the +electro-magnetic phantom. Guided by this theory of a diffusion field of +force, I have been able to reproduce experimentally the figures of +karyokinesis by simple diffusion. With regard to the achromatin spindle, +Professor Hartog has shown that the two poles of the spindle are of the +same sign, and not of opposite signs as was at first supposed. In the +process of karyokinesis the two centrosomes, _i.e._ the two poles of the +achromatin spindle, repel one another. They must therefore be poles of the +same sign. An electric or magnetic spectre showing a spindle between two +poles of the same sign is unknown; such a thing would appear to be an +absolute impossibility. What is impossible in electricity and magnetism, +however, is quite possible in the artificial diffusion field; we can here +have a spindle between two poles which repel one another--that is, between +poles of the same sign. Fig. 31 is a photograph of such a spindle produced +by diffusion. On either side are two poles of concentration, which +represent the centrosomes, each pole being surrounded by a star-like +radiation. These poles being alike, repel one another. In the preparation +one may see the distance between the two poles slowly increase, the poles +gradually separating from one another just as do the centrosomes of an ovum +during karyokinesis. This preparation, then, which is produced entirely by +diffusion, presents a perfect resemblance to the achromatin spindle in +karyokinesis. {91} + +[Illustration: FIG. 31.--Diffusion figure representing karyokinesis. +Achromatin spindle between two similar poles of concentration.] + +"The spindle of which we give a photograph in Fig. 31 was made by placing +in salt water a drop of the same solution pigmented with blood or Indian +ink, and placing on either side of this central drop a hypertonic drop of +salt solution more lightly coloured. After diffusion had gone on for some +minutes, we obtained the figure which we have photographed. I would draw +your attention to the equatorial plane, which shows that the spindle is not +formed by lines of force passing from one pole to the other, as would be +the case between two poles of contrary sign, but by two forces acting in +opposite directions. On either side the pigment of the central drop has +been drawn towards the hypertonic centre nearest to it. In the median line, +however, the pigment is attracted in opposite directions by equal forces, +and therefore remains undisturbed, marking the position of the equatorial +plane. This observation applies equally to the equatorial plane in natural +karyokinesis, whose existence is thus readily explained. + +"It is hardly necessary to insist on the fact that liquid preparations like +these are of extreme delicacy and sensitiveness, and require for their +production, and still more for their photography, the greatest care and +skill, which can only be acquired by long practice. {92} + +"We are able to produce by diffusion not only the achromatin spindle, but +also the segmentation of the chromatin, and the division of the nucleus. If +in the saline solution we place a coloured isotonic drop between two +coloured hypertonic drops, all the figures and movements of karyokinesis +appear successively in their due order. The central drop, representing the +nucleus between the two lateral drops or centrosomes, first becomes +granular. Next we see what appears to be a rolled-up ribbon analogous to +the chromatin band, which soon breaks into fragments analogous to the +chromosomes. These arrange themselves around, and are gradually attracted +towards the centrosomes, where they accumulate to form two pigmented +nuclear masses. A partition then makes its appearance in the median line, +and this partition becomes continuous with the boundary of the spheres +around the centrosomes. Finally we have two cells in juxtaposition, each +with its nucleus, its protoplasm, and its enveloping membrane. I have been +able to photograph these successive stages of the segmentation of the +chromatin just as I have those of the achromatin spindle" (Fig. 32). + +[Illustration: FIG. 32.--Four successive stages in the production of +artificial karyokinesis by diffusion.] + +This memoir, written in 1904, clearly asserts the homopolarity of the +centrosomes, and shows that the nuclear division is the result of a bipolar +action, two poles of the same sign exerting their influence on opposite +sides of the nucleus. It also emphasizes the important fact that diffusion, +{93} and as far as we know diffusion alone, is able to produce a spindle +between homologous poles. + +A glance at the photograph is enough to show that the spindle is formed +between poles of the same sign. The lines of diffusion radiate from one +centre and converge towards the other centre in curves, giving the double +convergence characteristic of a spindle. The central drop merely supplies +the necessary material, and should have a concentration but slightly less +than that of the plasma, so as not to set up its own lines of diffusion. +The photograph shows clearly that the rays of the spindle traverse the +equator without any break. It has been objected that these lines form not +so much a spindle as two hemi-spindles, but it is clear that these two +hemi-spindles are continuous and form a single sheaf of rays uniting the +two poles of concentration. This is a phenomenon entirely unknown in the +magnetic or electric fields, where two poles of the same sign, one on +either side of a pole of the contrary sign, give two separate spindles. In +a magnetic field it is impossible to make the lines emanating from one pole +converge, except to a pole of opposite sign. Hence if we admit the +homopolarity of the centrosomes, we must also admit that diffusion is the +_vera causa_ of karyokinesis, since, as I showed at the Grenoble Congress +in 1904, diffusion and diffusion alone is capable of producing a spindle +between two poles of the same sign. + +_Nuclear Division._--In order to reproduce artificially the phenomena +attending the division of the nucleus, we may proceed as follows. We cover +a perfectly horizontal glass plate with a semi-saturated solution of +potassium nitrate to represent the cytoplasm of the cell. The nucleus in +the centre is reproduced by a drop of the same solution coloured by a trace +of Indian ink, the solid particles of which will represent the chromatin +granules of the nucleus. The addition of the Indian ink will have slightly +lowered the concentration of the central drop, and this is in accordance +with nature, since the osmotic pressure of the nucleus is somewhat less +than that of the plasma. We next place on either side of the drop which +represents the {94} nucleus a coloured drop of solution more concentrated +than the cytoplasm solution. The particles of Indian ink in the central +drop arrange themselves in a long coloured ribbon, apparently rolled up in +a coil, the edges of the ribbon having a beaded appearance. After a short +time the ribbon loses its beaded appearance and becomes smooth, with a +double outline, as is shown in A, Fig. 32. This coil or skein of ribbon +subsequently divides, forming a nuclear spindle, while the chromatin +substance collects together in the equatorial plane as in B, Fig. 32. + +A more advanced stage of the nuclear division is shown at C, Fig. 32, where +the chromatin bands of artificial chromosomes are grouped in two conical +sheafs converging towards the two centrosomes. For some considerable time +these conical bundles remain united by fine filaments, the last vestiges of +the nuclear spindle. The final stage is that of two artificial cells in +juxtaposition, whose nuclei are formed by the original centrosomes +augmented by the chromatin bands or chromosomes (Fig. 32, D). + +[Illustration: FIG. 33.--Equatorial crown produced by diffusion.] + +The resemblance of these successive phenomena to those of natural +karyokinesis is of the closest. The experiment shows that diffusion is +quite sufficient to produce organic karyokinesis, and that the only +physical force required is that of osmotic pressure. If in the cytoplasm of +a cell there are two points of molecular concentration greater than that of +the general mass, the nucleus must necessarily divide with all the +phenomena which accompany karyokinesis. In nature these two centres of +positive concentration are introduced into the protoplasm of the cell by +fecundation--that is, by the entrance of the centrosomes of the sperm cell. +In certain abnormal cases the concentration may be produced in the cell +itself by the formation of two centres of catabolism or molecular +disintegration, since, as we have seen, molecular disintegration raises the +osmotic pressure. This phenomenon, namely the production of karyokinesis +from centres of catabolism, may account for the abnormal karyokinesis of +cancer cells and the like. The subject is one which would well repay +further investigation. {95} + +[Illustration: FIG. 34.--A triaster produced by diffusion.] + +It has been found in our experiments that in order to obtain the regular +division of the artificial nucleus represented by the intermediary drop, +the latter must have an osmotic pressure slightly below that of the plasma. +This leads to the supposition that a similar condition must obtain in the +natural cell. It may be noticed, moreover, that the grains of pigment +follow the direction of the flow of water, being carried along by the +stream. This would appear to show that the nucleus of a natural cell has +also a molecular concentration less than that of the plasma--a result +either of dehydration of the plasma, or of some diminution in the molecular +concentration of the nucleus. + +Other phenomena of karyokinesis may also be closely imitated by diffusion. +For instance, in the diffusion preparation we notice at each extremity of +the equator a V-shaped figure with its apex towards the centre, +corresponding exactly to what in natural karyokinesis is called the +equatorial crown. + +We may also produce diffusion figures of abnormal karyokinesis. Fig. 34 +represents such a form, a triaster produced by diffusion. + +Artificial karyokinesis may also be produced by hypotonic poles of +concentration--that is to say, when the central drop representing the ovum +is positive and the lateral drops representing the centrosomes are negative +with respect to the plasma. In this case, however, the resemblance to +natural karyokinesis is less perfect. {96} + +Without attaching to it an importance which is not warranted by +experimental results, it is interesting to note that we have here two +methods of fertilization, hypertonic and hypotonic, _i.e._ by centrosomes +of greater concentration and by centrosomes of less concentration than that +of the plasma of the ovum, and that we have in nature two corresponding +results, viz. two different sexes. It is possible that we have in these two +methods of producing nuclear division the secret of the difference of sex. + + * * * * * + + +{97} + +CHAPTER IX + +ENERGETICS + +Movement is everywhere; there is no such thing as immobility; the very idea +of rest is itself an illusion. Immobility is only apparent and relative, +and disappears under closer examination. All terrestrial objects are driven +with prodigious velocity around the sun, and the dwellers on the earth's +equator travel each day around the 40,000 kilometres of its circumference. +All objects on the globe are in motion, the inanimate as well as the +living. The waters rise in vapour from the sea, float over mountain and +valley, and return down the rivers to the sea again. Still more marvellous +is the current of water which flows eternally from dew and rain, through +the sap of plants and the blood of animals to the mineral world again. The +very mountains crumble and their substance is washed down into the plains; +the winds move the air and raise the waves of the sea, whilst the strong +ocean currents are produced by variations of temperature in different +parts. This agitation, this incessant and universal motion, has been a +favourite subject of poetic contemplation. Heraclitus writes: "There is a +perpetual flow, all is one universal current; nothing remains as it was, +change alone is eternal." Ovid writes in his _Metamorphoses_: "Believe me, +nothing perishes in this vast universe, but all varies, and changes its +figure. I think that nothing endures long under the same appearance. What +was solid earth has become sea, and solid ground has issued from the bosom +of the waters." + +The French poetess Mme. Ackermann has expressed the same idea in beautiful +verse:-- + + "Ainsi, jamais d'arrêt. L'immortelle matière, + Un seul instant encore n'a pu se reposer. + La Nature ne fait, patiente ouvrière, + Que défaire et recomposer. + {98} + Tout se métamorphose entre ses mains actives; + Partout le mouvement incessant et divers, + Dans le cercle éternel des formes fugitives, + Agitant l'immense univers." + +It was only towards the middle of last century that mankind in the long +search after unity in nature began to realize that all the movements of the +universe are the manifestations of a single agent, which we call energy. In +reality all the phenomena of nature may be conceived as diverse forms of +motion, and the word "energy" is the common expression applied to all the +various modes of motion in the universe. It was by the study of heat, and +more especially of thermodynamics, that we obtained our conceptions of the +science of energetics. + +It was in Munich in 1798 that the English engineer Count Rumford first +observed that in the operation of boring a cannon the copper was heated to +such a degree that the shavings became red-hot. This suggested his famous +experiment, in which a heavy iron pestle was turned by horse power in a +metal mortar filled with water. The water boiled, and when more water was +added this also became heated to ebullition, and so on indefinitely. +Rumford argued that the heat thus obtained in an indefinite quantity could +not be a material substance; that motion was the only thing added to the +water without limit, and that therefore heat must be motion. + +While Rumford's experiment showed the transformation of motion into heat, +the steam engine was soon afterwards to demonstrate the opposite +transformation, viz. that of heat into motion. + +The actual state of our knowledge with regard to the science of energy +rests on two principles, that of Mayer and that of Carnot. + +The first principle was defined by J. R. Mayer, a medical practitioner of +Heilbronn, whose work, _Bemerkungen ueber die Kräfte der unbelebten Natur_, +was published in 1842. "All physical phenomena," says Mayer, "whether vital +or chemical, are forms of motion. All these forms of motion are susceptible +of change into one another, and in all the transformations the {99} +quantity of mechanical work represented by different modes of motion +remains invariable." + +The energy of a given body is the amount of transferable motion stored up +in that body, and is measured by its capacity of producing mechanical work. + +Ostwald thus defines energy: "Energy is work, all that can be obtained from +work, and all that can be changed into work." Different forms of energy may +be measured in different ways, but all forms of energy can be measured +either in units of mechanical work or in units of heat, in +kilogramme-metres or foot-pounds or in calories, according as the energy in +question is transformed into mechanical work or into heat. The first +principle of energetics, the conservation of energy, may be thus expressed: +"Energy is eternal; none is ever created, and none is ever lost. The +quantity of energy in the universe is invariable, and is conserved for ever +in its integrity." + +The unit by which we measure quantities of heat is the calory, the amount +of heat required to raise the temperature of one kilogramme of water one +degree Centigrade. + +The practical unit of mechanical work is the kilogramme-metre, the work +required to raise the weight of one kilogramme to the height of one metre. +The theoretical unit of work is one erg, the work required to move a mass +of one gramme through one centimetre against a force of one dyne. + +Joule of Manchester was the first to verify Mayer's law quantitatively. By +an experiment analogous to that of Rumford, he transformed work into heat, +arranging his apparatus so that he might measure the amount of heat +produced and the work expended. On dividing the quantity of work that had +disappeared by the quantity of heat which had been disengaged, he found +that 424 kilogramme-metres of work had been expended for each calory of +heat produced. + +Hirn of Colmar measured the ratio of work to heat in the steam engine. He +found that for each calory of heat which had disappeared there were +produced 425 kilogramme-metres of work. {100} + +This number 425 has therefore been accepted as representing in calories and +kilogramme-metres the transformation of work into heat, and of heat into +work. + +Further measurements on the transformations of other forms of energy, +chemical energy and electrical energy, have shown that Joule's law of +equivalents is general, and that the quantity of mechanical work +represented by any form of energy remains undiminished after +transformation, whatever the nature of that transformation. + +Energy presents itself to us under two forms, potential and actual. +Potential energy is slumbering energy, energy localized or locked up in the +body. In order to transform potential energy into actual energy, there is +required the intervention of an additional awakening, stimulating, or +exciting energy from without. This stimulating energy may be almost +infinitesimal in amount and bears no quantitative relation to the amount of +energy transformed. It is the small amount of work required to turn the key +which liberates an indeterminate quantity of potential energy. + +Actual energy, on the other hand, is energy in movement, awake and alert, +ready to be transformed into any other form of energy without the +intervention of any such external stimulating force. + +The passage of a given quantity of energy from the potential into the +actual state is effected gradually, and during the time of transformation +the sum of the actual and the potential energy remains constant. + +A weight suspended by a cord possesses a quantity of potential energy equal +to the product of its weight into the height through which it can fall. +This energy is locked up in a certain space, it cannot be transformed +without the intervention of some external energy to cut the cord. During +the falling of the weight, at the middle of its path, half of this +slumbering energy has become kinetic, and is represented by the _vis viva_ +of the weight, while the other half is still potential and is equivalent to +the work which the weight will accomplish during the second half of its +fall. At any moment the sum of these two energies, the sleeping and the +waking {101} energies, represents the total potential energy of the weight +before it began to fall. + +So with the powder in a gun. The potential energy of the powder cannot +become actual without some stimulus, some exciting force from without to +set it free. It is the external work of pressing the trigger that liberates +the potential energy of the powder, transforming it into the actual energy +of combustion, and the kinetic energy of the projectile. + +Since energy is work, and work is a function of motion, there is in reality +no such thing as energy in repose. Matter according to our modern +conception is a complex of molecules, atoms, and electrons; we conceive the +molecules of matter as always in movement, animated with cyclic or +vibratory motion, these oscillatory or rotatory movements representing the +potential energy of the body in question. Potential energy is thus the +expression of molecular motion without translation of the molecules as a +whole in space. + +When this potential energy is transformed into actual energy by the +intervention of some external force, we get a current of energy, a +transference of the molecules in space. Thus, when an external force has +released the weight, the molecular orbits in the falling body change in +form, and the potential energy of the molecular motion becomes the kinetic +energy of the falling body. Similarly in the conduction of heat, the energy +of the hot body is transferred to a colder body by transmission of the +vibratory motion from molecule to molecule. So again with chemical energy, +the molecular motion of combustion may be transformed into the radiant +energy of the ethereal waves. + +Actual energy may be regarded as a current of molecular motion. To make the +matter clearer, let a mass of matter be represented by a regiment of +soldiers. Then each soldier will represent an electron, a company will be +an atom, and a battalion will be a molecule. As long as the soldiers mark +time, turn, or otherwise exercise without advancing, we have simply an +accumulation of potential energy. The word of command, "March," is the +exciting force which suddenly transforms this potential into kinetic +energy. The marching {102} regiment is a representation of a body +possessing kinetic energy. Potential energy is energy confined to a certain +point in space, whereas actual energy is a current of energy, continually +changing its place or form. Energy is like water-power--potential in the +lake, actual in the waterfall or river. + +Any mechanism capable of causing one form of energy to pass into another is +a transformer of energy. A steam engine is a transformer of energy, +changing caloric energy into mechanical work. An electrical machine is a +transformer of energy, converting mechanical motion into a current of +electricity, whilst an electro-motor changes the movement of electrons into +mechanical movement. Every living being, and even man himself, is but a +transformer of energy, changing the energy derived from the earth and air +and sun into mechanical motion, nervous energy, and heat. + +The first law of energetics, that of the conservation of energy, is +analogous to Lavoisier's principle in chemistry, the conservation of +matter. The sign of equality which unites the terms of a chemical equation +expresses the fact that after every chemical reaction the same total mass +of matter is present as before the transformation. This is also true of +energy; after every transformation we find exactly the same total quantity +of energy as before it. This, however, tells us nothing as to the +conditions of the transformation, or the causes, _i.e._ the anterior +phenomena, which determined such transformation. + +The second principle of energetics, that of Carnot, enunciated in 1824, +deals with the conditions under which a transformation of energy is +possible. A mass of water at a certain height represents a quantity of +potential energy equal to the product of its weight by its height; but this +energy cannot produce mechanical work unless the water is allowed to fall. +Consider two lakes at the same altitude and of the same capacity, one of +which is entirely landlocked, while the other has an open channel leading +to the sea. Each lake represents the same quantity of potential energy, but +the energy of the landlocked lake is useless, it cannot be {103} +transformed; whereas the other lake whose water can run into the sea +realizes the conditions necessary for utilization, viz. the +transformability of its energy. The same may be said of all forms of +energy; a heat engine can only act as a transformer, change heat into work, +if there is a difference of temperature between its source and its sink; an +electric motor can only work if there is a fall of potential between the +entrance and the exit of the electric current. + +Energy presents itself to us as the product of two factors, weight and +height in the waterfall, quantity and temperature in the heat engine, +current intensity and potential in the electric motor. + +In considering these two factors we may note that one factor is always a +quantity (Q) and the other an intensity (I). This latter expresses some +sort of difference of position or condition, the height of the weight, a +difference of temperature in the heat engine, of pressure in the gas +engine, or of electric potential in the dynamo or electric furnace. There +can be no current of energy without this difference of potential, and +therefore no transformation from one form of energy to another. + +The second law of thermodynamics, Carnot's law, may therefore be enunciated +thus: "Energy cannot be transformed without a fall of potential." + +We may also derive this principle from a consideration of the formula of +efficiency, the ratio of the work done by the transformer to the work done +on the transformer. + + Efficiency = energy transformed / total energy absorbed + +The total energy is the product QI, _i.e._ the product of the total +quantity by the total intensity at our disposal. The transformed energy is +Q(I - I'), the product of the total quantity by the difference of intensity +at the inlet and at the outlet of the machine. The formula for efficiency +thus becomes + + Q(I - I') / QI = (I - I') / I. + + If I represents a temperature, then in order that the efficiency may be +positive I' must be less than I, {104} there must be a fall of temperature +in the machine. If I' were greater than I, _i.e._ if the temperature at the +outlet were greater than that at the inlet, the efficiency would be a +negative one, and the transformer would have to borrow heat from some +external source. + +_Entropy._--In every transformation of energy a certain portion of the +energy is transformed into heat: a lamp gives out useless heat as well as +light, a machine gives out useless heat as well as mechanical work. This +loss of useful energy as heat occurs in every transference or +transformation of energy; it is only in the case of heat passing from a +hotter to a colder body that there is no such transformation. When equality +of temperature is established there has been no loss of energy, but the +whole of the energy has become unutilizable, i.e. untransformable. In the +formula of efficiency the fall of intensity I - I' is now zero, and +therefore the efficiency of the machine + + (I - I') / I + +is also zero. + +Since in all its transformations a certain fraction of the energy is +changed into heat, there is a tendency in nature for all differences of +temperature to become equalized. Hence the quantity of utilizable energy in +the universe tends to diminish. Clausius called this unutilizable energy +enmeshed in the substance of a body its entropy, and showed that in every +transformation the amount of this unutilizable energy tended to increase. +"The entropy of a system always tends towards a maximum value." + +If this gradual incessant increase of entropy is universal in nature, and +if there is no compensatory mechanism, the universe must be tending towards +a definite end, when the whole of its energy shall have been transformed +into unutilizable heat with a uniform temperature. There is, however, +reason to suppose that some such compensatory mechanism does in fact exist. +Behind us stretches an infinite past, and in the future we believe that the +phenomena of nature will be unrolled in a cycle which has no end. But the +arguments derived from a study of entropy apply only to the facts and +phenomena actually under our notice, the supposed {105} impossibility, +without borrowing energy from without, of re-establishing the differences +of temperature by drawing heat from a colder in order to concentrate it in +a hotter body, and may not be absolutely identical with those obtaining in +other ages. Our ignorance of such a phenomenon and our powerlessness to +produce it in no way argue that it is impossible. It may exist for aught we +know in some other region of space, or in another time than ours. We may +perhaps some day obtain artificially the conditions which would render +possible such a phenomenon, since it may be possible to produce in the +experimental laboratory conditions which are not spontaneously realized in +nature under present conditions. The future may perchance reveal to us +absolutely new phenomena which have not hitherto been realized. In his work +on the evolution of matter and of energy Gustave le Bon gives expression to +some interesting and original ideas on this subject. + +The laws of Mayer and Carnot alone are not sufficient to explain the +phenomena of life, without some consideration of the laws of stimulus. +Mayer's principle asserts the conservation of energy, and Carnot's the +conditions necessary for its transformation, but these alone cannot account +for the transformation of potential into actual energy. A weight suspended +by a cord does not fall merely because there is room for its descent. We +need the intervention of some outside force to cut the cord. In every +transformation of energy this external force is required to cut the cord, +or pull the trigger, some external force of excitation or liberation, an +energy which may be infinitesimal in amount, and which bears no proportion +to the quantity of potential energy it sets free. This intervention of an +excitatory, stimulating, or liberating energy is universal. Every +phenomenon of nature is but a transformation or a transference of energy, +determined by the intervention of a minimal quantity of energy from +without. This liberation of large quantities of potential energy by an +exceedingly small external stimulus has not hitherto received the +consideration it demands. Certain phenomena, such as those of chemical +catalysis or the action of soluble ferments, excite our astonishment +because such extremely small quantities of {106} certain substances will +determine the chemical transformations of large quantities of matter, there +being no proportion between the amount of the catalytic substance and of +the matter transformed. These phenomena are, however, only particular cases +of the general law of energetics that transformation requires a stimulus. +The catalyzer, or ferment, does not contribute matter to the reaction, but +only the minimal energy necessary to liberate the chemical potential energy +stored in the fermenting substance. + +We must therefore add a third to the two laws of energetics, Mayer's law of +conservation, and Carnot's law of fall of potential. This third law is the +law of stimulus, the necessity of the intervention of an external +excitatory force capable of setting in motion the current of energy +required for a transformation. This stimulus is the primary phenomenon, the +determinant cause of such transformation. + +Three conditions, then, are required for a transformation or displacement +of energy:-- + +1. _The cause_, the intervention of a stimulus which starts the +transformation or displacement. + +2. _The possibility_, the necessary fall of potential. + +3. _The condition_, the conservation of the energy concerned, since being +indestructible its total quantity cannot alter. + +Every living being is a transformer of energy. The lower animals and man +himself receive from food and air the potential energy which becomes actual +under the process of oxydation. This chemical combustion is the source of +all vital energy; the ancients aptly compared life to a flame, and +Lavoisier has shown that life, like the flame, is maintained by a process +of oxydation. The energy derived from food and air is restored by the +organism to the external world in the form of heat and mechanical motion. +The celebrated experiments of Atwater show that there is an absolute +equality between the energy obtained from the oxydation of the various +aliments and the sum of the calorific and mechanical energy liberated by a +living being. + +Man obtains his supply of energy either directly from the {107} vegetable +world, or indirectly from vegetables which have passed through the flesh of +animals. Vegetables in their turn obtain their substance from the mineral +world and their energy from the sun. The salts, the water, and the carbonic +acid absorbed by plants possess no store of potential energy. Whence then +can they obtain the potential energy which they transmit to animals and +man, if not from the sun? The energy of the solar radiations is absorbed by +the chlorophyll of the leaves, and stored up in the organic carbohydrates +formed by the synthesis of water and carbon. Chlorophyll has the peculiar +property of reducing carbonic acid, and uniting the carbon with water in +different proportions to form sugar and starch, whilst fats and vegetable +albumens are also formed by an analogous reaction. All these complex bodies +are stores of energy; the vital processes of oxydation do but liberate in +the human body the energy which the chlorophyll of plants has absorbed from +the solar rays. + +We must look, then, to the sun as the direct source of all the energy which +animates the surface of the earth. The sun looses the winds, and raises the +waters of the sea to the mountain-tops, to form the rivers and torrents +which return again to the sea; the sun warms our hearths, drives our ships, +and works our steam engines. There is no sign of life or movement on our +planet which does not come directly or indirectly from the solar rays. + +It may be asked by what path does the chemical energy of the living +organism pass into the mechanical energy of motion. It would appear that +the intermediary step cannot be heat, as in the steam engine, since the +necessary temperature would be quite incompatible with life. + +The formula for the efficiency of a thermic transformer is + + (T - T') / T, + +the ratio of the difference of the absolute temperatures at the source and +at the sink, to the absolute temperature at the source. Calorimetric +measurements have shown that the efficiency of the human machine is about +one-fifth, _i.e._ it can transform 20 per cent. of the energy absorbed. The +ordinary temperature of muscle is 38° C., or 311° absolute. We have {108} +therefore (T - 311) / T = .20, or T = 388.75° absolute, _i.e._ 115.75° C. +Thus, in order to obtain an efficiency of 20 per cent. with an ordinary +thermic transformer, having a temperature of 38° at the sink, we should +need a temperature of over 115° C. at the source. Such a temperature would +be quite incompatible with the integrity of living tissues, and we may +therefore conclude that the human organism is not a heat engine. + +We are indeed completely ignorant of the mode of transformation of chemical +into kinetic energy in the living organism; we know only that muscular +contraction is accompanied by a change of form; at the moment of +transformation the combustion of the muscle is increased, and during +contraction the stretched muscular fibre tends to acquire a spherical +shape. It is this shortening of the muscular fibre which produces the +mechanical movement. The step which we do not as yet fully understand is +the physical phenomenon which intervenes between the disengagement of +chemical energy and the occurrence of muscular contraction. Professor +d'Arsonval supposes that this missing step is a variation in the surface +tension of the liquid in the muscular fibre. The surface tension of a +liquid is due to the unbalanced forces of cohesion acting on the surface +layer of molecules. Under the attraction of cohesion the molecules within +the liquid are in a state of equilibrium, being equally attracted in all +directions, but those at the surface of the liquid are drawn towards the +centre. The resultant of these attractive forces is a pressure normal to +the surface, which is mechanically equivalent to an elastic tension tending +to diminish the surface. In consequence of this surface tension the liquid +has a tendency to assume the form in which its surface area is a minimum, +_i.e._ the spherical form. If such a sphere is stretched into a cylinder or +fibre by mechanical tension, it will shorten itself when released; and if +by any means we increase the surface tension of such a liquid fibre it will +tend to assume a spherical form and contract just as a muscular fibre does. +The surface tension of a liquid varies with its chemical composition; the +slightest chemical modification of a liquid alters the force of {109} this +tension. We may therefore explain the mechanism of muscular contraction by +supposing that a nervous impulse alters in some way the rate of combustion +in a muscular fibre, that this alteration produces a momentary change in +the chemical composition of the muscular cell, and that this change of +chemical composition increases the surface tension of the cell sufficiently +to provoke its contraction into a more spherical form. + +Ostwald has introduced a very useful conception for the study of this +question of surface energy. A liquid surface contains a quantity of energy +equal to its surface tension multiplied by its area, hence any variation +either of area or of tension corresponds to a variation of its energy. This +novel conception constitutes a valuable addition to the experimental study +of the physiology of muscular action, since it gives us some idea of the +mechanism by which chemical energy may be transformed into muscular +contraction. + +Whatever the mechanism of transformation in the animal machine, we have to +consider the same quantities as in other motor machines. These are: (1) the +efficiency; (2) the potential energy; (3) the power; (4) the energy given +up to the medium under the form of heat; (5) the temperature. + +Muscles, then, are merely transformers which change chemical energy into +mechanical work, the diminution of stored-up energy in a muscle being +expressed by the sensation of fatigue. A muscle may be studied in four +different phases: (1) in repose; (2) in a state of tension; (3) when doing +positive work; (4) when work is being done on it. + +When a muscle is in a state of tension, as when a weight is sustained by +the outstretched arm, the muscle is producing no external work. The entire +work done is converted into heat; just as it is in a dynamo or steam engine +which is prevented from turning by a brake. Muscular contraction produces +fatigue even when it does no external work. It is impossible for the muscle +to support even the weight of the outstretched arm itself for any +considerable time. + +A muscle is doing positive work when it is raising a weight or moving a +body from one point to another. {110} + +The fourth state of muscular contraction is when the muscle is doing +negative work, _i.e._ when work is being done on it, as for instance when +we go downstairs, or when a descending weight forces down the opposing arm +which attempts to support it. In this case the muscles receive a portion of +the energy lost by the descending weight, and this energy shows itself in +the muscle in the form of heat. This increase of heat in a muscle doing +negative work has been clearly demonstrated by the calorimetric experiments +of Hirn and the thermometric experiments of Béclard. Hirn's observations on +muscular calorimetry show a production of heat corresponding to 150 +calories per hour when in repose, 248 calories per hour during positive +work, and 287 during negative work. Béclard's thermometric measurements +also show that the temperature of a muscle rises each time that it +contracts, and that the rise of temperature is greatest when the muscle is +doing negative work, least during positive work, and intermediate when in a +state of tension. + +It is of the greatest importance in medical practice to distinguish between +these different forms of muscular activity. There is a vast physiological +difference between muscular contraction with the production of positive +work, and muscular contraction without the production of work, or with +negative work. To climb a flight of stairs is to contract the muscles with +the production of work equal to the weight of the body multiplied by the +height of the stairs. To descend the stairs is to contract the same +muscles, but with the production of negative work, and consequently a +maximum of heat. To walk on level ground is to contract the muscles with +the production of little or no external work; as in a machine turning +without friction in a vacuum. + +We have seen that a fall of potential and a current of energy are the +necessary conditions for the production of any natural phenomenon. Hence we +may assume that the phenomenon of sensation is also accompanied by a fall +of potential and a current of energy. When we touch a hot body, there is a +flow of energy from the hot body to the hand. When we touch a cold body, +there is a current of energy in the opposite direction, {111} from the hand +to the body. It was formerly held, and is still held by some physiologists, +that the chief characteristic of life is the disproportion between an +excitation and the response which it invokes from the organism. Such a +doctrine can only be held by one who believes, at least implicitly, that +the phenomena of life are supernatural, or at all events different in their +nature from all other phenomena; for the disproportion between an +excitation and the response it evokes is by no means confined to living +things. This disproportion is universal in nature, and quite in conformity +with the physical laws which govern the transformation of energy. The +energy of living things is potential energy--a fact which has been too +little recognized. In the case of reflex actions it is self-evident, +because the response is immediate, and always the same for the same +stimulus. As in all other transformations, the stimulus consists in the +intervention of a minimal quantity of external energy. + +Long before the discovery of the laws of energy, Lamarck had recognized and +formulated this fact. He writes: "What would vegetable life be without +excitations from without, what would be the life even of the lower animals +without this cause?" In another passage, seeking for a power capable of +exciting the action of the organism, he says: "The lower animal forms, +without nervous system, live only by the aid of excitations which they +receive from without. In the lowest forms of life this exciting force is +borrowed directly from the environment, while in the higher forms the +external exciting force is transferred to the interior of the living being +and placed at the disposal of the individual." + +This remark, that the movements of living things are not communicated but +excited, that the external excitation only sets free latent or potential +energy in the organism, shows that Lamarck had penetrated more deeply than +many of the modern physiologists into the secrets of biological energy. We +seek in vain in the text-books of physiology for any conception of +potential energy in living beings, or the notion of an exciting force as +the cause of sensation. All action of a living organism is reflex action. +Every action has a cause, and {112} the cause of an organic action is an +exciting energy from without, either immediate, or stored up in the nervous +system from an external impression made at some previous epoch. Actions +which are not evidently reflex are merely delayed reflexes; we have +acquired the power of inhibiting, delaying, or modifying the response to an +external stimulus, so that the same excitation may determine responses of +very different kinds according to the mood produced by previous +impressions. When carefully investigated, no action of ours is automatic; +every movement is determined by impressions derived from without. An action +without a motive, that is without an external determining cause, would be +an action without reason. + +In conclusion, we may formulate this general principle: The energy of a +living being is potential energy; sensations represent the intervention of +an external exciting energy which provokes the response, _i.e._ the +transformation of the potential energy already stored in the organism into +the actual energy of motion and vital activity. + + * * * * * + + +{113} + +CHAPTER X + +SYNTHETIC BIOLOGY + +The course of development of every branch of natural science has been the +same. It begins by the observation and classification of the objects and +phenomena of nature. The next step is to decompose the more complex +phenomena in order to determine the physical mechanism underlying them--the +science has become analytical. Finally, when the mechanism of a phenomenon +is understood, it becomes possible to reproduce it, to repeat it by +directing the physical forces which are its cause--the science has now +become synthetical. + +Modern biology admits that the phenomena of life are physico-chemical in +their nature. Although we have not as yet been able to define the exact +nature of the physical and chemical processes which underlie all vital +phenomena, yet every further discovery confirms our belief that the +physical laws of life are identical with those of the mineral world, and +modern research tends more and more to prove that life is produced by the +same forces and is subject to the same laws that regulate inanimate matter. + +The evolution of biology has been the same as that of the other sciences; +it has been successively descriptive, analytical, and synthetic. Just as +synthetic chemistry began with the artificial formation of the simplest +organic products, so biological synthesis must content itself at first with +the fabrication of forms resembling those of the lowest organisms. Like +other sciences, synthetic biology must proceed from the simpler to the more +complex, beginning with the reproduction of the more elementary vital +phenomena. Later on we may hope to {114} unite and associate these, and to +observe their development under various external influences. + +The synthesis of life, should it ever occur, will not be the sensational +discovery which we usually associate with the idea. If we accept the theory +of evolution, then the first dawn of the synthesis of life must consist in +the production of forms intermediate between the inorganic and the organic +world--forms which possess only some of the rudimentary attributes of life, +to which other attributes will be slowly added in the course of development +by the evolutionary action of the environment. + +Long ago, the penetrating genius of Lamarck seized on the idea that a +knowledge of life could only be obtained by the comparison of organic with +inorganic phenomena. He writes: "If we would acquire a real knowledge of +what constitutes life, of what it consists, what are the causes and the +laws which give rise to this wonderful phenomenon of nature, and how life +can be the source of the multitude of forms presented to us by living +organisms, we must before all consider with great attention the differences +which exist between inorganic and living bodies; and for this purpose we +must compare side by side the essential characters of these two classes of +bodies." + +Synthetic biology includes morphogeny, physiogeny, and synthetic organic +chemistry, which is also a branch of synthetic biology, since it deals with +the composition of the constituents of living organisms. Synthetic organic +chemistry is already a well-organized science, important by reason of the +triumphs which it has already gained. The other two branches of biological +synthesis, morphogeny, the synthesis of living forms and structures, and +physiogeny, the synthesis of functions, can hardly as yet be said to exist +as sciences. They are, however, no less legitimate and no less important +than the sister science of synthetic chemistry. + +Although morphogeny and physiogeny do not exist as well-organized and +recognized sciences, there are already a number of works on the subject by +enthusiastic pioneers--independent seekers, who have not feared to abandon +the paths of official science to wander in new and hitherto unexplored +domains. {115} + +The first experiment in physiogeny was the discovery of osmosis by the Abbé +Nollet in 1748. He filled a pig's bladder with alcohol, and plunged it into +water. He noticed that the bladder gradually increased in volume and became +distended, the water penetrating into the interior of the bladder more +quickly than the alcohol could escape. This was the first recorded +experiment in the physics of nutrition and growth. + +In 1866, Moritz Traube of Breslau discovered the osmotic properties of +certain chemical precipitates. As I pointed out in the _Revue Scientifique_ +of March 1906, Traube made the first artificial cell, and studied the +osmotic properties of membranes and their mode of production. This +remarkable research should have been the starting-point of synthetic +biology. The only result, however, was to give rise to numberless +objections, and it soon fell into complete oblivion. "There are," says +Traube, "a number of persons quite blind to all progress, who in the +presence of a new discovery think only of the objections which may be +brought against it." The works of Traube have been collected and published +by his son (_Gesammelte Abhandlungen von Moritz Traube_, 1899). + +In 1867 there appeared in England a paper by Dr. E. Montgomery, of St. +Thomas's Hospital, _On the Formation of so-called Cells in Animal Bodies_. +This paper, published by Churchill & Sons, is a most interesting +contribution and one of great originality. The author says: "There can be +no compromise between the tenets of the cell theory and the conclusions +arrived at in this paper; the distinction is thorough. Either the units of +which an organism is composed owe their origin to some kind or other of +procreation, a mysterious act of that mysterious entity life, by which, in +addition to their material properties, they become endowed with those +peculiar metaphysical powers constituting vitality. Or, on the other hand, +the organic units, like the crystalline units of inorganic bodies, form the +organism by dint of similar inherent qualities, form in fact a living being +possessed of all its inherent properties, as soon as certain chemical +compounds are placed under certain physical conditions. If the former +opinion be {116} true, then we must clearly understand that there exists +naturally a break in the sequence of evolution, a chasm between the organic +and the inorganic world never to be bridged over. If, on the contrary, the +latter view be correct, then it strongly argues for a continuity of +development, a gradual chemical elaboration, which culminates in those high +compounds which, under surrounding influences, manifest those complex +changes called vital. + +"Surely it is not a matter of indifference or of mere words, if the extreme +aim of physiology avowedly be the detection of the different functions +dependent on the vital exertions of a variety of ultimate organisms, and +the discovery of the specific stimulants which naturally incite these +functions into play. Or, on the other hand, if it be understood to consist +rather in the careful investigation of the succession of chemical +differentiations and their accompanying physical changes, which give rise +to the formation of a variety of tissues that are found to possess certain +specific properties, to display certain definite actions due to a further +flow of chemical and physical modifications." + +In 1871 there appeared a memoir by the Dutch savant Harting entitled +_Recherche de Morphologie synthetique sur la production artificielle de +quelques formations calcaires organiques_. This memoir, says Professor R. +Dubois, had cost Harting more than thirty years of work. "Synthetic +morphology is yet only in its infancy, let us hope that in a time equal to +that which has already expired since the first artificial production of +urea, it will have made a progress equal to that of its older sister, +synthetic chemistry." + +In the _Comptes Rendues_ of 1882 is the following note by D. Monnier and +Karl Vogt:-- + +"1. Figured forms presenting all the characteristics of organic growth, +cells, porous canals, tubes with partition walls, and heterogeneous +granules, may be produced artificially in appropriate liquids by the mutual +action of two salts which form one or more insoluble salts by double +decomposition. One of the component salts should be in solution, while the +other salt must be introduced in the solid form. {117} + +"2. Such forms of organic elements, cells, tubes, etc., may be produced +either in an organic liquid or a semi-organic liquid such as sucrate of +lime, or in an absolutely inorganic liquid such as silicate of soda. Thus +there can no longer be any question of distinctive forms as characterizing +organic bodies in contradistinction to inorganic bodies. + +"3. The figured elements of these pseudo-organic forms depend on the +nature, the viscosity, and the concentration of the liquids in which they +are produced. Certain viscous liquids such as solutions of gum arabic or +chloride of zinc do not produce these forms. + +"4. The form of these artificial pseudo-organic products is constant, as +constant as that of the crystalline forms of mineral salts. This form is so +characteristic that it may often serve for the recognition of a minimal +proportion of a substance in a mixture. The observation of these forms is a +means of analysis as sensitive as that of the spectrum. We may, for +example, differentiate in this way the alkaline bicarbonates from the +sesqui-carbonates or the carbonates. + +"5. The form of these artificial pseudo-organic elements depends +principally on the nature of the acid radical of the solid salt. Thus the +sulphates and the phosphates generally produce tubes, while the carbonates +form cells. + +"6. As a rule these pseudo-organic forms are engendered only by substances +which are found in the living organism. Thus sucrate of calcium will +engender organic forms, whereas sucrate of strontium or barium does not do +so. There are, however, some exceptions to this rule, such as the sulphates +of copper, cadmium, zinc, and nickel. + +"7. These artificial pseudo-organic elements are surrounded by veritable +membranes, dializing membranes which allow only liquids to pass through +them. These artificial cells have heterogeneous cell-contents, and produce +in their interior granulations which are disposed in a regular order. Thus +they are both in constitution and in form absolutely similar to the +cellular elements which constitute living organisms. + +"8. It is probable that the inorganic elements which are present in the +natural protoplasm may play an important part {118} in determining the form +which is assumed by the figured elements of the organism." + +In 1902, Professor Quinke of Heidelberg, who has consecrated his life with +such distinction to the physics of liquids, writes thus of the organogenic +power of liquids in a paper published in the _Annalen der Physik_ under the +title "Unsichtbare Flüssigkeitschichten": "In 1837, Gustav Rose obtained +organic forms by precipitation from inorganic solutions. By precipitating +chloride of calcium with the carbonates of ammonium and other alkaline +carbonates, he obtained small spheres which grew and were transformed into +calcic rhombohedra. He also obtained a flocculent precipitate which later +became granular and showed under the microscope forms like the starfish, +and discs with undulated borders. At Freiberg, in certain stalactites, Rose +also discovered forms consisting of six pyramidal cells around a spherical +nucleus. + +"In 1839, Link obtained spherical granulations by the precipitation of +calcic or plumbic solutions by potash, soda, or carbonic acid. These +spherical granulations united after a time to form crystals. Sulphate of +iron, ammoniated sulphate of zinc, sulphate of copper precipitated by +sulphuretted hydrogen, and saline solutions precipitated by ferrocyanide of +potash, all give granular precipitates or discs, of which the granular +origin is quite perceptible. + +"Runge in 1855 was the first to describe the formation of periodic chemical +precipitates. He used blotting paper as the medium in which various +chemical substances met by diffusion. In this way he studied the mutual +reactions of solutions of ferrocyanide of potash, chloride of iron, and the +sulphates of copper, iron, manganese, and zinc. The coloured precipitates +appeared at different positions in the paper, and disappeared periodically +at greater or longer intervals. The designs formed by these coloured +precipitates change with the concentration of the saline solutions, or on +the addition of oxalic acid, salts of potash or ammonia, and other +substances. These designs are shown in a number of beautiful illustrations +which accompany the work. In this {119} case the capillarity of the paper +necessarily exerts a certain influence on the formation of the figures, but +in addition to this, Runge admits the intervention of another force +hitherto unknown, which he calls 'Bildungstrieb,' the formative impulse, +which he considers to be the elementary vital force in the formation of +plants and animals. + +"In 1867, R. Böttger obtained arborescent forms and ramifications of +metallic vegetation by sowing fragments the size of a pea of crystals of +the iron chlorides, chloride of cobalt, sulphate of manganese, nitrate and +chloride of copper, etc., in an aqueous solution of silicate of sodium of +specific gravity 1.18. These forms are due, as I shall show later on, to +the surface tension of the oily precipitate; Böttger gives no explanation +of the phenomenon. + +"To this force, viz. that of surface tension, is also due the cellular +forms obtained by Traube in 1866. These were obtained from gelatine and +tannin, from acetate of copper or lead, and from nitrate of mercury in an +aqueous solution of ferrocyanide of potassium. These cells and precipitated +membranes have also been studied by Reinke, F. Cohn, H. de Vries, and +myself, who all observed the regression of these membranes, which although +colloidal at the beginning of the reaction speedily become friable. This +entirely refutes the opinion of Traube as to the constitution of the +precipitated membranes. He supposed them to consist of masses of solid +substance, with smaller orifices which do not permit the passage of the +membranogenous substance, whilst the larger orifices through which it can +pass are soon closed by the precipitate, the membrane itself thus growing +by a process of intussusception. + +"Later on Traube himself considered the precipitated membrane to be a thin, +solid gelatinous layer in which the water was mechanically entangled. + +"Tamman has also made a number of experiments with solutions of the +chlorides and sulphates of the heavy metals, and solutions of phosphates, +silicates, ferrocyanides, and other salts. He found that most of these +membranes were permeable to the membranogenous solution. According to +Tamman, all {120} precipitated membranes are hydrated substances, and some +of them, like the ferrocyanide of copper and the tannate of gelatine are, +when first formed, entirely comparable to liquid membranes in all their +properties. + +"Graham had already obtained colourless jellies by the interaction of +concentrated solutions of ferrocyanide of potassium and sulphate of copper. +Bütschli also has recently described the microscopic appearance of +precipitated membranes produced by ferrocyanide of potassium and acetate or +chloride of iron. + +"Like Linke and Gustav Rose, Famintzin has obtained spheroidal precipitates +by the reciprocal action of concentrated solutions of chloride of calcium +and carbonate of potassium. These grow rapidly and suddenly, with +concentric layers showing a spherical or flattened nucleus. He also +obtained forms resembling sphero-crystals and starch grains. + +"Harting, Vogelsang, Hansen, Bütschli, and others have studied the +structures which are formed by the reciprocal action of chloride of calcium +and the alkaline carbonates. Vogelsang has found small calcareous bodies in +the amorphous and globular precipitate formed by chloride of calcium and +carbonate of ammonium. He describes spheres attached to one another, +vesicles, and muriform structures. The number of these spheroids is +increased by the addition of gelatine. Hansen has also studied Harting's +method for the formation of sphero-crystals by the action of the alkaline +carbonates and phosphates on the salts of calcium in presence of albumen +and gelatine. He considers that the latter retard the crystallization and +assist the formation of the sphero-crystals. + +"I shall show later on that gelatine and albumen essentially modify the +precipitate and do not merely act as catalytic substances. The researches +of Famintzin, repeated and extended by Bütschli, show that sphero-crystals +are produced by the reaction of chloride of calcium on carbonate of +potassium without the presence of gelatine or albumen. Bütschli studied the +spheroids of carbonate of lime by means of polarized light, and found that +the layers were alternately positively and negatively polarized." {121} + +Such is the history of morphogenesis as described in 1902 by the authority +most qualified for the task, Professor Quinke of Heidelberg. + +In 1904, Professor Moritz Benedikt of Vienna treated the whole question in +his book, _Crystallization and Morphogenesis_, of which a French +translation appeared in the Maloine Library. This book is full of original +and suggestive ideas; it describes the work of Harting, and more especially +that of Van Schroën, who considers that crystals like living beings begin +as a cell and grow by a process of intussusception. Professor Benedikt has +made a complete résumé of the question in an article, "The Origins of the +Forms of Life," which appeared in the _Revue Scientifique_ in 1905. + +In 1904, Professor Dubois of Lyons presented a report to the Society of +Biology on his interesting experiments on mineral cytogenesis. The same +year he gave a discourse at the university of Lyons on "The Creation of +Living Beings," which has been published by A. Storck of Lyons. + +One of the most active of the modern morphogenists is Professor Herrera of +Mexico, whose work is illustrated in the _Atlas de Plasmogenie_ by Dr. +Jules Félix of Brussels, one of the most enthusiastic disciples of the new +science. There is a résumé of Herrera's work in the _Memoirs of the Societé +Alzate, Mexico_. + +A bibliography of the works which have appeared on this subject may be +found in the book of Professor Rhumbler of Göttingen, _Aus dem +Lückengebiete zwischen Organischer und Anorganischer Materie_, 1906. + +In 1907, Dr. Luiz Razetti of Carracas published a magnificent study of the +subject under the title _Que es la vida_. + +In 1907, Dr. Martin Kuckuck of St. Petersburg repeated and extended the +experiments of R. Dubois, and published his results under the title +_Archigonia, Generatio Spontanea_, Leipzig, Ambrosius Barth. + +Butler Burke of Cambridge has also made a series of experiments with radium +and barium salts analogous to those of Dubois. + +In 1909, Albert and Alexandre Mary of Beauvais published {122} an +interesting study of this question under the title _Études expérimentales +sur la génération primitive_, published by Jules Rousset. + +I should mention also among the works of synthetic biology the publications +of Professor Otto Lehmann of Karlsruhe, and in particular _Flüssige +Krystalle und die Theorien des Lebens_, Leipzig, Ambrosius Barth. + +Professor Ulenhuth of Berlin has published his study on the osmotic growth +of iron in alkaline hypochlorites under the title _Untersuchungen ueber +Antiformin_, Berlin, Julius Springer. + +Professor Gariel has made a series of researches on osmotic growth which +are published in Abraham's _Recueil d'expériences de physique_. + +A. Lecha Marzo of Valladolid published his researches on the growth of +aniline colours in the _Gaceta Medica Catalana_, 1909, under the title +_Otra nueva flora artificiale_. + +Dr. Maurice d'Halluin of Lille has also published a volume on osmotic +growths under the title, _Stéphane Leduc a-t-il créé la vie?_ + +The subjects of the numerous memoirs that I have myself published during +the last ten years upon the question are treated anew in the pages of this +volume, and a résumé of my researches on osmotic growth has already +appeared in the _Documents du Progrès_, Sept. 1909. + +We have thus shown that synthetic morphogenesis has already attracted the +attention of a certain number of ardent investigators. Morphogeny has now +its methods and its results, and physiogeny is also developing side by side +with it, since function is but the result of form. The field of research is +opened, and workers alone are needed in order to reap an abundant harvest. + + * * * * * + + +{123} + +CHAPTER XI + +OSMOTIC GROWTH--A STUDY IN MORPHOGENESIS + +The phenomenon of osmotic growth has doubtless presented itself to the eyes +of every chemist; but to discover a phenomenon it is not enough merely to +have it under our eyes. Before Newton many a mathematician had seen a +spectrum, if only in the rainbow; many an observer before Franklin had +watched the lightning. To discover a phenomenon is to understand it, to +give it its due interpretation, and to comprehend the importance of the +rôle which it plays in the scheme of nature. + +_Osmotic Membranes._--Certain substances in concentrated solution have the +property of forming osmotic membranes when they come in contact with other +chemical solutions. When a soluble substance in concentrated solution is +immersed in a liquid which forms with it a colloidal precipitate, its +surface becomes encased in a thin layer of precipitate which gradually +forms an osmotic membrane round it. + +An osmotic membrane is not a semi-permeable membrane, as sometimes +described, _i.e._ a membrane permeable to water but impermeable to the +solute. It is a membrane which opposes different resistances to the passage +of water and of the various substances in solution, being very permeable to +water, but much less so to the different solutes. + +A soluble substance thus surrounded by an osmotic membrane represents what +Traube has called an artificial cell. In such a cell the dissolved +substances have a very high osmotic pressure, an expansive force like that +of steam in a boiler; the molecules of the solute exerting pressure on the +walls of the extensible cell, and distending it like the {124} gas in a +balloon. This pressure increases the volume of the cell, and in consequence +water rushes in through the permeable membrane and still further distends +the cell. Most beautiful osmotic cells may be produced by dropping a +fragment of fused calcium chloride into a saturated solution of potassium +carbonate or tribasic potassium phosphate, the calcium chloride becoming +surrounded by an osmotic membrane of calcium carbonate or calcium +phosphate. This mineral membrane is beautifully transparent and perfectly +extensible. It is astonishing to contemplate the contrast between the hard +crystalline forms of ordinary chalk and these soft transparent elastic +membranes which have the same chemical constitution. These osmotic cells of +carbonate of lime or phosphate of lime consist of a transparent membrane +enclosing liquid contents and a solid nucleus of chloride of calcium. Their +form is that of an ovoid or flattened sphere, and they may attain a +diameter of seven centimetres or more. + +More frequently the osmotic growth consists of a number of cells instead of +one large cell. The first cell gives birth to a second cell or vesicle, and +this to a third, and so on, so that we finally obtain an association of +microscopic cellular cavities, separated by osmotic walls--a structure +completely analogous to that which we meet with in a living organism. + +We may easily picture to ourselves the mechanism by which an osmotic cell +gives birth to such a colony of microscopic vesicles. The membranogenous +substance, the chloride of calcium, diffuses uniformly on all sides from +the solid nucleus, and forms an osmotic membrane where it comes into +contact with the solution. This spherical membrane is extended by osmotic +pressure, and grows gradually larger. Since the area of the surface of a +sphere increases as the square of its radius, when the cell has grown to +twice its original diameter, each square centimetre of the membrane will +receive by diffusion but a quarter as much of the membranogenous substance. +Hence, after a time, the membrane will not be sufficiently nourished by the +membranogenous substance, it will break down, and an aperture will occur +through which the interior liquid oozes out, forming in its turn a new +{125} membranous covering for itself. This is the explanation of the fact +that all living organisms are formed by colonies of microscopical elements, +although we must not forget that Nature often produces similar results in +different ways. + +[Illustration: FIG. 35. FIG. 36. + +Osmotic growths of ferrocyanide of copper.] + +Osmotic growths may be obtained from a great number of chemical substances. +The most easily grown are the soluble salts of calcium in solutions of +alkaline phosphates and carbonates, to which we have already alluded. We +may also reverse the phenomenon by growing phosphates and carbonates in +solutions of calcium salts, but in this case the osmotic growths are not so +beautiful. + +The various silicates play an important part in the constitution of shells +and of the skeletons of marine animals. Most of the metallic salts, and +more especially the soluble salts of calcium, give rise to the phenomenon +of osmotic growth when sown in solutions of the alkaline silicates. In this +way, by using different silicates and varying the proportions and the +concentrations, we may obtain an immense variety of osmotic growths. + +A good solution to commence with is the following:-- + + Silicate of potash, sp. gr. 1.3 (33° Beaumé) 60 gr. + Saturated solution of sodium carbonate 60 gr. + Saturated solution of dibasic sodium phosphate 30 gr. + Distilled water make up to 1 litre. + +{126} + +A fragment of fused calcium chloride dropped into this solution will +produce a rapid growth of slender osmotic forms which may attain a height +of 20 or 30 centimetres. + +Small pellets may also be made of one part of sugar and two of copper +sulphate and sown in the following solution, which must be kept warm until +the growth is complete:-- + + Ten per cent. solution of gelatine 10 to 20 c.c. + Saturated solution of potassium ferrocyanide 5 to 10 c.c. + Saturated solution of sodium chloride 5 to 10 c.c. + Warm water (32° to 40° C.) 100 c.c. + +In this solution we can obtain osmotic growths which may attain to a height +of 40 centimetres or more, vegetable forms, roots, arborescent twigs, +leaves, and terminal organs. These growths are stable as soon as the +gelatine has cooled and set, and may be carried about without fear of +injury (Fig. 35). + +Precipitated osmotic membranes are very widely distributed in nature. +Professor Ulenhuth has seen iron growths in alkaline sodium hypochlorite +(Javelle water), and Lecha-Marzo has demonstrated the osmotic growth of the +various {127} stains used for microscopy, in the liquids used for fixing +preparations. + +[Illustration: FIG. 37.--Osmotic vermiform growth. + +(_a_) The sickle-shaped growth. + +(_b_) The growth broken by the upward pressure of the solution. + +(_c_) The wound having cicatrized, the stem continues to grow downwards. ] + +We now know that the physical force which builds up these growths is that +of osmotic pressure, since the slightest consideration will show the +inadequacy of the usual explanation that the growth is due to mere +differences of density, or to amorphous precipitation around bubbles of +gas. These may indeed affect the phenomenon, but can in no way be regarded +as its cause. + +One of our experiments throws considerable light on this question. In a +glass vessel we placed a concentrated solution of carbonate of potassium, +to which had been added 4 per cent. of a saturated solution of tribasic +potassium phosphate. Into this solution we dropped a fragment of fused +calcium chloride, and obtained a vermiform growth some 6 millimetres in +diameter. This growth was curved, at first growing upwards, then for a +short distance horizontally, and finally downwards. The upward pressure of +the solution, which was heavier than the growth, ultimately broke it at the +top of the curve, as shown at _b_, Fig. 37. The liquid contents of the +growth began to ooze out through the wound, but this after a time became +cicatrized, and the stem continued to grow obstinately downwards once more, +in opposition to the hydrostatic pressure. In consequence of this pressure +the growth is sinuous, tacking as it were from side to side like a boat +against the wind. We give three successive photographs of this growth, +which attained a length of over 10 inches. We have frequently obtained +these vermiform growths forming a series of such loops, growing upwards and +falling again many times in succession. + +_Osmotic Growths in Air._--Certain of these artificial cells may be made to +grow out of the solution into the air. For this purpose we place a fragment +of CaCl_2 in a shallow flat-bottomed glass dish, just covering the fragment +with liquid. The best solution is as follows:-- + + Potassium carbonate, saturated solution 76 parts. + Sodium sulphate, saturated solution 20 " + Tribasic potassium phosphate, saturated solution 4 " + +{128} + +The calcium chloride surrounds itself with an osmotic membrane; water +penetrates into the interior of the cell thus formed, and a beautiful +transparent spherical cell is the result, the summit of which soon emerges +from the shallow liquid. The cell continues to increase by absorption of +the liquid at its base, and may grow up out of the liquid into the air for +as much as one or two centimetres. + +This is a most impressive spectacle, an osmotic production, half aquatic +and half aerial, absorbing water and salts by its base, and losing water +and volatile products by evaporation from its summit, while at the same +time it absorbs and dissolves the gases of the atmosphere. + +The aerial portion of an osmotic growth will sometimes become specialized +in form. The summit of the growth develops a sort of crown or cup +surrounded by a circular wall. This cup contains liquid, and continues to +grow up into the air like the stem of a plant, carrying with it the liquid +which has been absorbed by the base of the growth. + +The preceding experiments give us an explanation of the curious phenomena +exhibited by so-called creeping salts. A saline solution left at the bottom +of a vessel will sometimes be found after some months to have crept up to +the top of the vessel. Cellular partitions formed in this way will be found +extending from the bottom to the top of the vessel, and not only so, but +the whole of the remaining liquid will be imprisoned in the upper cells. + +[Illustration: FIG. 38.--Osmotic growth produced by sowing a mixture of +CaCl_2 and MnCl_2 in a solution of alkaline carbonate, phosphate, and +silicate. The stem and terminal organs are of different colours. (One-third +of the natural size.)] + +[Illustration: FIG. 39.--An osmotic growth photographed by transverse light +to show the construction of the terminal organs.] + +_Assimilation and Excretion._--Like a living being, an osmotic growth +absorbs nutriment from the medium in which it grows, and this nutriment it +assimilates and organizes. If we compare the weight of an osmotic growth +with that of the mineral fragment which produced it, we shall find that the +mineral seed has increased many hundred times in weight. Similarly, if we +weigh the liquid before and after the experiment, we shall find that it has +lost an equivalent weight. The absorbed substance of an osmotic production +must also undergo chemical transformation before it can be +assimilated--that is, before it can form part of the growth. Calcium +chloride, for example, growing in a solution of potassium {130} carbonate, +is transformed into calcium carbonate. CaCl_2 + K_2CO_3 = CaCO_3 + 2KCl. +Thus an osmotic growth can make a choice between the substances offered to +it, rejecting the potassium of the nutrient liquid, and absorbing water and +the radical CO_3, while at the same time it eliminates and excretes {131} +chlorine, which may be found in the nutrient liquid after the reaction. + +Of all the ordinary physical forces, osmotic pressure and osmosis alone +appear to possess this remarkable power of organization and morphogenesis. +It is a matter of surprise that this peculiar faculty has hitherto remained +almost unsuspected. + +[Illustration: FIG. 40.--Osmotic growth in a solution of KNO_3, showing +spine-like organs.] + +_Osmotic Growths._--If we sow fragments of calcium chloride in solutions of +the alkaline carbonates, phosphates, or silicates, we obtain a wonderful +variety of filiform and linear growths which may attain to a height of 30 +or 40 centimetres. Some are so flexible that the stems bend, falling in +curves around the centre of growth, like leaves of grass. If we dilute this +same liquid, as it becomes less concentrated the growths are more curved, +ramified, dendritic, like those of trees or corals. + +[Illustration: FIG. 41.--Terminal organs like catkins, developing in a +solution of ammonium chloride.] + +In the culture of osmotic growths we may also by appropriate means produce +terminal organs resembling flowers and seed-capsules. To do this we wait +till the growth is considerably advanced, and then add a large quantity of +liquid to the nutrient solution so as to diminish the concentration a +hundredfold or more. Spherical {132} terminal organs will then grow out +from the ends of the stems, which may during their further growth become +conical or piriform in shape. + +By superposing layers of liquid of different concentration and decreasing +density, one may obtain knots and swellings in the osmotic growths marking +the surfaces of separation of the liquid. When a young growth in the vigour +of its youth reaches the surface of the water, it spreads out horizontally +over the surface of the liquid in thin leaves or foliaceous expansions of +different forms. + +[Illustration: FIG. 42.--An osmotic madrepore.] + +The preponderating influence in morphogenesis is osmotic pressure, the +osmotic forms varying with its intensity, distribution, and mode of +application. Whatever the chemical composition of the liquid, similar +osmotic forces, modified in the same manner, give rise to forms which have +a family resemblance. The chemical nature of the liquid, however, is not +entirely without influence on the form. Thus the presence of a nitrate in +the mother liquor tends to produce points or thorns. Ammonium chloride in a +potassium ferrocyanide solution produces growths shaped like catkins, and +the alkaline chlorides tend to produce vermiform growths. {133} + +Coralline growths may also be obtained by using appropriate chemical +solutions. For this purpose the solution of silicate, carbonate, and +dibasic phosphate should be diluted to half strength, with the addition of +2 to 4 per cent. of a concentrated solution of sodium sulphate or potassium +nitrate. + +[Illustration: FIG. 43.--An osmotic mushroom form.] + +[Illustration: FIG. 44.--Osmotic fungi.] + +Coral-like forms may also be grown from a semi-saturated solution of +silicate, carbonate, and dibasic phosphate, to which has been added 4 per +cent. of a concentrated solution of sodium sulphate or potassium nitrate. +In this we may obtain beautiful growths like madrepores or corals, formed +by a central nucleus from which radiate large leaves like the petals of a +flower. The presence of nitrate of potassium produces pointed leaves with +thorn-like processes recalling the forms of the aloe and the agave. + +Most remarkable fungus-like forms may be obtained by commencing the growth +in a concentrated solution, and then {134} carefully pouring a layer of +distilled water over the surface of the liquid. The resemblance is so +perfect that some of our productions have been taken for fungi even by +experts. The {135} stem of these osmotic fungi is formed of bundles of fine +hollow fibres, while the upper surface of the cap is sometimes smooth, and +sometimes covered with small scales. The lower surface of the cap shows +traces of radiating lamellæ, which are sometimes intersected by concentric +layers parallel to the outer {136} surface of the cap. In this case the +lower surface of the cap shows a number of orifices or canals similar to +those seen in many varieties of fungus. + +[Illustration: FIG. 45.--A shell-like calcareous osmotic growth.] + +[Illustration: FIG. 46.--Osmotic growths in the form of shells.] + +[Illustration: FIG. 47.--Capsular osmotic growth. The capsule has been +broken to show the interior structure.] + +Shell-like osmotic productions may be grown by sowing the mineral in a very +shallow layer of concentrated solution, a centimetre or less in depth, and +pouring over this a less concentrated layer of solution. By varying the +solution or concentration we may thus grow an infinite variety of shell +forms. {137} + +Capsules or closed shells may be produced in the same way by superimposing +a layer of somewhat greater concentration. These capsules consist of two +valves joined together at their circumference. The lower valve is thick and +strong, while the upper valve may be transparent, translucent, or opaque, +but is always thinner and more fragile than the lower one. + +Ferrous sulphate sown in a silicate solution gives rise to growths which +are green in colour, climbing, or herbaceous, twining in spirals round the +larger and more solid calcareous growths. + +[Illustration: FIG. 48.--An osmotic growth in which the terminal organs are +differently coloured from the stems, showing that the chemical evolution is +different.] + +With salts of manganese, the chloride, citrate or sulphate, the stages of +evolution of the growth are distinguished not only by diversities of form, +but also by modifications of colour. We may thus obtain terminal organs +black or golden yellow in colour on a white stalk. In a similar way we may +obtain fungi with a white stalk and a yellow cap, of which the lower +surface is black. + +[Illustration: FIG. 49.--Osmotic capsular growth with figured belt.] + +Very beautiful growths may be obtained by sowing calcium chloride in a +solution of potassium carbonate, with the addition of 2 per cent. of a +saturated solution of tribasic potassium phosphate. This will give capsules +with figured belts, vertical lines at regular intervals, or transverse +stripes composed of projecting dots such as may be seen in many +sea-urchins. These capsules are closed at the summit by a cap, forming an +operculum, so that they sometimes appear as if formed of two valves. Now +and again we may see the upper valve raised by {138} the internal osmotic +pressure, showing the gelatinous contents through the opening. + +[Illustration: FIG. 50.--Amoeboid osmotic growth, floating free in the +mother liquor.] + +The calcareous capsules grown in a saturated solution of potassium +carbonate or phosphate often take a regular ovoid form. If these are +allowed to thicken, they may be taken out of the water without breaking, +and then present the aspect of veritable ooliths. + +[Illustration: FIG. 51.--Transparent osmotic cell, in which may be seen the +white calcareous nucleus. The summit of the cell bears osmotic +prolongations.] + +[Illustration: FIG. 52.--Amoeboid osmotic growth with long crystalline +cilia swimming about in the mother liquor.] + +[Illustration: FIG. 53.--Osmotic growth swimming in mother liquor. The +fin-like prolongation grew out between two liquid layers of different +concentrations.] + +Osmotic productions may be divided into two groups. Some like the silicate +growths are fixed. Like vegetables, they develop, become organized, grow, +decline, die, and are disintegrated at the spot where they are sown. +Others, especially those which are grown in alkaline carbonates and +phosphates, have two periods of evolution, the first a fixed period, and +the second a wandering {139} one. During the first period their specific +gravity is greater than that of the surrounding medium, and they rest +immobile at the bottom of the vessel in which they are sown. As they grow, +they absorb water and their specific gravity diminishes. Little by little +they rise up in the liquid, and finally acquire a considerable amount of +mobility, being readily displaced by every current. Hence it is very +difficult to photograph these {140} mobile osmotic growths, which swim +about in the mother liquor and are often provided with prolongations in the +forms of cilia, and sometimes with fins, which undulate as they move. Some +of these ciliary hairs are evidently osmotic in their origin, being +localized as a tuft at the summit of the growth. Others are apparently +crystalline in structure, and are spread over the whole surface of the +swimming vesicle. An osmotic growth increases by the absorption of water +from a concentrated solution. When the solution is originally saturated it +thus becomes supersaturated, and deposits these long ciliary crystals on +the surface of the growth. + +When a capsule splits in two under the influence of the internal osmotic +pressure, it may happen that the operculum or upper valve floats away in +the liquid. We thus obtain a free swimming organism, a transparent +bell-like form with an undulating fringe, like a Medusa. + +[Illustration: FIG. 54.--Capsular osmotic growth, the two valves separated +showing the colloidal contents.] + +Frequently a single seed or stock will give rise to a whole series of +osmotic growths. A vesicle is first produced, and then a contraction +appears around the vesicle, and this contraction increases till a portion +of the vesicle is cut off and swims away free like an amoeba. The same +phenomenon may be observed with vermiform growths, a single seed often +giving {141} rise in this way to a whole series of amoebiform or vermiform +productions. + +It must be remembered that in an osmotic growth the active growing portion +is the gelatinous contents in the interior, the external visible growth +being only a skeleton or shell. We may sometimes succeed in hooking up one +of these long vermiform growths, breaking the calcareous sheath, and +drawing out a long undulating translucid gelatinous cylinder. The outline +of this cylinder is so well defined as to make us doubt whether the fine +colloidal membrane which separates it clearly from the liquid can have been +formed so rapidly, or if it may not perhaps exist already formed in the +interior of its calcareous sheath. + +[Illustration: FIG. 55.--Microphotograph showing the structure of various +osmotic stems. (Magnified 25 diameters.) + +(_a_) Sodium sulphite. + +(_b_) Potassium bichromate. + +(_c_) Sodium sulphide. + +(_d_) Sodium bisulphite. ] + +When a large capsular shell such as we have described bursts, it expels a +part or the whole of its contents as a gelatinous mass which retains the +form of the cavity. Similarly, if we suddenly dilute the mother liquor +around an osmotic cell, it bursts by a process of dehiscence, and projects +into the liquid a part of its contents, which may thus become an +independent vesicle. In this way a single osmotic cell may produce a whole +series of independent vesicles. + +It is even possible to rejuvenate an osmotic growth that has become +degenerate through age. An osmotic production grows old and dies when it +has expended the osmotic force contained in the interior of its capsule. A +calcium osmotic growth which has thus become exhausted may be rejuvenated +by transferring it to a concentrated solution of calcium chloride. It will +absorb this, and thus be enabled to renew its evolution and growth when put +back again into the original mother liquor. {142} + +The structure of osmotic growths is no less varied than their form. Their +stems are formed of cells or vesicles juxtaposed, showing cavities +separated by osmotic walls. Sometimes the component vesicles have kept +their original form, so that the stem has the appearance of a row of beads. +Or the cells may be more or less flattened, the divisions being widely +separated. Or again, by the absorption of the divisions, a tube may be +formed, a veritable vessel or canal in which liquids can circulate. {143} + +[Illustration: FIG. 56.--Microphotograph showing the structure of osmotic +stems. (Magnified 40 diameters.)] + +[Illustration: FIG. 57.--Photograph of an osmotic leaf showing the veins.] + +The foliaceous expansions, or osmotic leaves, also present great varieties +both of appearance and of structure. The veins may be longitudinal, +fan-shaped, or penniform. We have occasionally met with leaves having a +lined or ruled surface, giving most beautiful diffraction colours. The +usual structure, however, is vesicular or cellular, as in Fig. 58. In +photographs we often get the appearance of lacunæ, but all these lacunæ are +closed cavities, the appearance being due to the transparency of the cell +walls. + +[Illustration: FIG. 58.--Photomicrograph of an osmotic leaf showing the +cellular structure.] + +In conclusion we may say that osmotic growths are formed of an ensemble of +closed cavities of various forms, containing liquids and separated by +osmotic membranes, constituting veritable tissues. This structure offers +the closest {144} resemblance to that of living organisms. Is it possible +to doubt that the simple conditions which produce an osmotic growth have +frequently been realized during the past ages of the earth? What part has +osmotic growth played in the evolution of living forms, and what traces of +its action may we hope to find to-day? Osmotic growth gives us fibrous +silicates, phosphatic nodules, corals, and madrepores; it also gives us +formations which remind one of the "atolls," calcareous growths rising like +a crown out of the water. The geologist may well consider what rôle osmotic +growth may have played in the formation of the various rocks, siliceous, +calcareous, barytic, magnesian, the fibrous and nodular rocks and atolls. +The palæontologist relies on the different forms found in his rocks to +classify his specimens; from the existence of a shell, he concludes the +presence of life. Since, however, forms which are apparently organic may be +merely the product of osmotic growth, it is evident that he must reconsider +his conclusions. The same may be said of the various forms of coral or of +fungoid growths. In the {146} presence of a calcified or silicated fungus +we can no longer argue with certainty as to the existence of life, without +taking into consideration the possibility that the specimen in question may +be an osmotic production. + +[Illustration: FIG. 59.--Osmotic growth with nucleated terminal organs. +(One-third of the natural size.)] + +[Illustration: FIG. 60.--A group of osmotic plants.] + +Whatever our opinion as to its signification, osmotic growth demands the +attention of every mind devoted to the study of nature. It is a marvellous +spectacle to see a formless fragment of calcium salt grow into a shell, a +madrepore, or a fungus, and this as the result of a simple physical force. +Why should the study of osmotic growth attract less attention than the +formation of crystals, on which so much time and labour has been bestowed +in the past? + + * * * * * + + +{147} + +CHAPTER XII + +THE PHENOMENA OF LIFE AND OSMOTIC PRODUCTIONS--A STUDY IN PHYSIOGENESIS + +It is impossible to define life, not only because it is complex, but +because it varies in different living beings. The phenomena which +constitute the life of a man are far other than those which make up the +life of a polyp or a plant; and in the more simple forms life is so greatly +reduced that it is often a matter of difficulty to decide whether a given +form belongs to the animal, vegetable, or mineral kingdom. Considering the +impossibility of defining the exact line of demarcation between animate and +inanimate matter, it is astonishing to find so much stress laid on the +supposed fundamental difference between vital and non-vital phenomena. +There is in fact no sharp division, no precise limit where inanimate nature +ends and life begins; the transition is gradual and insensible, for just as +a living organism is made of the same substances as the mineral world, so +life is a composite of the same physical and chemical phenomena that we +find in the rest of nature. All the supposed attributes of life are found +also outside living organisms. Life is constituted by the association of +physico-chemical phenomena, their harmonious grouping and succession. +Harmony is a condition of life. + +We are quite unable to separate living beings from the other productions of +nature by their composition, since they are formed of the same mineral +elements. All the aliments of plants--water, carbon, nitrogen, phosphorus, +sulphur--before their absorption and assimilation belonged to the mineral +kingdom. The carbon and the water are transformed into {148} sugar and fat, +the nitrogen and the sulphur into albumen, and the compounds so formed are +then said to belong to the organic world. These organic bodies are returned +once again to the mineral world by the action of animals and microbes, +which transform the carbon into carbonates, and the nitrogen, sulphur, and +phosphorus into nitrates, sulphates, and phosphates. Hence life is but a +phase in the animation of mineral matter; all matter may be said to have +within itself the essence of life, potential in the mineral, actual in the +animal and the vegetable. The flux and reflux of matter is alternate and +incessant, from the mineral world to the living, and back again from the +living to the mineral world. + +At the same time there is a continuous flux of energy. Organic matter +contains potential energy, the energy of chemical combination; and during +its passage through the living being it is gradually stripped of this +energy and returned to the mineral world. The first step in synthetic +biology is the addition of potential energy to matter, the reduction of an +oxide, the separation of a salt into its radicals, the production of some +endothermic chemical combination. The energy stored up by such processes +can be again liberated as heat, that fire which the ancients with wonderful +prescience long ago recognized as the symbol of life. + +Attempts have been made to differentiate a living being by the nature of +its chemical combinations, the so-called organic compounds. It was supposed +that life alone could realize these and cause the production of the various +substances which form the structure of living beings. Of late years, +however, a large number of these organic substances have been artificially +produced in the laboratory, and the synthetic problems which remain are of +the same order as those which have been already solved. + +As one learns to know the mineral kingdom and the living world more +intimately the differences between them disappear. Thus a living being was +supposed to be characterized by its sensibility, _i.e._ its faculty of +reaction against external impressions. But this reaction is a general +phenomenon of nature; there is no action without reaction. Neither can the +{149} reaction to internal impressions, immediate or deferred, be +considered as the characteristic of life, since osmotic growths exhibit a +most exquisite sensibility in this direction. Since, then, the faculty of +reaction is a general property of matter, the characteristics of life in +the lower organisms are only three in number, viz. nutrition, growth, and +reproduction by fission or budding. But crystals are also nourished and +grow in the water of crystallization. They have moreover a specific form, +and every biologist who wishes to establish a parallel between the +phenomena of the living and the mineral world is wont to compare living +beings with crystals. Crystals, it is said, affect regular geometric forms, +salient angles, and rectilinear edges, while living beings have rounded +forms without any geometric regularity. Another supposed distinction is +that living beings are nourished by intussusception, whereas crystals +increase by apposition. Again, living beings are said to assimilate and +transform the aliment they absorb, whereas crystals do not transform the +matter which is added externally to their structure. Another supposed +difference is that living things eliminate and discharge their products of +combustion, while the evolution of a crystal is accompanied by no such +elimination. Finally, the phenomenon of reproduction is said to be the +exclusive characteristic of a living being; but crystals may also be +reproduced and multiplied by the introduction of fragments of crystalline +matter into a supersaturated solution. + +The resemblance between an osmotic growth and a living organism is much +closer than that between a living being and a crystal, there being not only +an analogy of form, but also of structure and of function. In order to find +the physical parallel to life, we must turn to osmosis and osmotic growth +rather than to crystals and crystallization. + +The first and most striking analogy between living beings and osmotic +growths is that of form. The morphogenic power of osmosis gives rise to an +infinite variety of forms. An osmotic growth, even at the first sight, +suggests the idea of a living thing. One need only glance at the +photographs of osmotic productions to recognize the forms of madrepore, +fungus, alga, and shell. It is wonderful that a force capable {150} of such +marvellous results should have hitherto been almost entirely neglected. + +A second analogy between vital and osmotic growths is to be found in their +structure, both being formed by groups of cells or vesicles separated by +osmotic membranes. An osmotic stem, formed by a row of cellular cavities +separated by osmotic membranes, has a great structural resemblance to the +knotted stems of bamboos, reeds, and the like. The foliaceous expansions of +osmotic growths are formed by colonies of cells or vesicles disposed in +regular lines, which may present various patterns of innervation, parallel, +palmate, or pennate. Many of the lamellar osmotic growths are striped in +parallel lines alternately opaque and transparent. The terminal organs have +also their enveloping membranes, their pulp and nucleus, just like +vegetable forms. + +The analogies of function are no less remarkable than those of form and +structure. Nutrition is perhaps the most elementary and essential vital +phenomenon, since without nutrition life cannot exist. Nutrition consists +in the absorption of alimentary substances from the surrounding medium, the +chemical transformation of such substances, their fixation by +intussusception in every part of the organism, and the ejection of the +products of combustion into the surrounding medium. Osmotic growths absorb +material from the medium in which they grow, submit it to chemical +metamorphosis, and eject the waste products of the reaction into the +surrounding medium. An osmotic growth moreover exercises choice in the +selection of the substances which are offered for its consumption, +absorbing some greedily and entirely rejecting others. Thus osmotic growths +present all the phenomena of nutrition, the fundamental characteristic of +life. + +In the living organism nutrition results in growth, development, and +evolution. Growth and development also follow the absorption and fixation +of aliment by an osmotic production. An osmotic production grows, its form +develops and becomes more complicated, and its weight increases. An osmotic +growth may weigh many hundred times as much as the mineral sown in the +solution, the mother liquor losing a {151} corresponding weight. Thus +growth, which has hitherto been considered an essential phenomenon of life, +is also a phenomenon common to all osmotic productions. + +Osmotic growths like living things may be said to have an evolutionary +existence, the analogy holding good down to the smallest detail. In their +early youth, at the beginning of life, the phenomena of exchange, of +growth, and of organization are very intense. As they grow older, these +exchanges gradually slow down, and growth is arrested. With age the +exchanges still continue, but more slowly, and these then gradually fail +and are finally completely arrested. The osmotic growth is dead, and little +by little it decays, losing its structure and its form. + +The membranes of an osmotic growth thicken with age, and thus oppose to the +osmotic exchanges a steadily increasing resistance. Young osmotic cells +appear swollen and turgescent, whereas old ones become flaccid, relaxed, +and wrinkled. Analogous phenomena are met with in living organisms, the +calcareous infiltration of the vessels representing the thickening and +hardening of the osmotic membranes. The plumpness of a child and the +turgescence of young cells are but the expression of high osmotic tension, +while relaxation and flaccidity of the tissues in old age betrays the fall +of osmotic pressure in the intracellular tissues. + +Circulation of the nutrient fluid may also be observed in an osmotic growth +as in a living organism. If we take a calcareous growth with long ramified +stems and dilute the mother liquor considerably, we may see currents of +liquid issuing from the summit of the growth--currents which are made +visible by the cloudy precipitates which they cause. The same current is +also rendered visible in the stems themselves by the motion of the +granulations and gas bubbles in the interior of the osmotic cells. It is +plain that some such circulation must exist, for how could a membrane be +formed 30 centimetres from the seed if the membranogenous substance did not +circulate through the stem? A moment's consideration will show that the +propulsion is due to osmotic pressure and not to mere differences of +density, for the liquid {152} which rises in the stem is a concentrated +solution of calcium salt much denser than the mother liquor, and the +current of liquid after rising in the stem may be seen to fall back again +through the liquid. + +[Illustration: FIG. 61.--A group of osmotic forms.] + +Organization has long been considered as one of the principal +characteristics of life, _i.e._ the arrangement of matter so as to produce +an animated and evolutionary form accompanied by transformation of energy. +But osmotic growths are also organizations endowed with the same faculties, +and the physical mechanism which is at the basis of their formation is the +same as that which determines the organization of living matter. + +The phenomena of osmotic growth show how ordinary mineral matter, +carbonates, phosphates, silicates, nitrates, and chlorides, may imitate the +forms of animated nature without {153} the intervention of any living +organism. Ordinary physical forces are quite sufficient to produce forms +like those of living beings, closed cavities containing liquids separated +by osmotic membranes, with tissues similar to those of the vital organs in +form, colour, evolution, and function. + +It is only necessary to glance at the photographs of these osmotic growths +to appreciate the wonderful variety of form. The variety of function is not +less evident, and in many instances, especially with manganese salts, the +difference of function of various regions is marked by differences of +colour. When a large osmotic cell projects beyond the mother liquor and +grows up into the air, it is evident that the function of liquid absorption +must be localized in the submerged part. In other cases we have a local +evolution of gas, which may be demonstrated by growing a fragment of +calcium chloride in a mother liquor composed of the following saturated +solutions:-- + + Potassium carbonate 76 parts. + Potassium sulphate 16 " + Tribasic potassium phosphate 46 " + +During the whole period of growth there is an abundant liberation of +bubbles of gas, which is accurately limited to a belt around the base of +the growth, and sometimes also to a cap at the summit. + +Since morphological differentiations of different parts is but the result +of differences of evolution, _i.e._ of functional differences of the +various parts, we may consider that osmotic growths possess the faculty of +organization like living beings. + +An osmotic growth may be wounded, and a wound delays its growth and +development like a disease or an accident in a living being. A wound in an +osmotic production may also become cicatrized and covered with a membrane, +when the growth will recommence exactly as in a living being. + +An osmotic growth is a transformer of energy. It increases in bulk, pushing +aside the mother liquor, and thus doing external work. An osmotic growth +has a temperature above its medium, since the chemical reaction of which it +is the seat is accompanied by the production of heat. We know {154} but +little of the transformation of energy which takes place in an osmotic +production, but we may say with certainty that it is capable of +transforming both chemical energy and osmotic energy into heat and +mechanical motion. + +An osmotic production is the arena of complicated chemical phenomena which +produce a veritable metabolism. It has long been known that diffusion and +osmosis may determine various chemical transformations. H. St. Clair +Deville has demonstrated that certain unstable salts are partially +decomposed by diffusion. Thus during the diffusion of alum, the sulphate of +potash is separated from the sulphate of aluminium. Similarly, when the +chloride or acetate of aluminium is caused to diffuse, the acids become +separated from the aluminia. This decomposition is the result of the +different resistance which the medium offers to the diffusion of different +ions. This difference of resistance may even cause a difference of +potential between two media, similar to the differences of potential in +living organisms. Frequently also a difference of hydration in the chemical +substances on either side of an osmotic membrane will determine a chemical +reaction, which like all other chemical reactions is accompanied by a +corresponding transformation of energy. The study of these chemical +metamorphoses and the transformations of energy in osmotic growths has +opened up a new subject for experimental investigation in the field of +organic chemistry. + +_Coagulation._--There is a most remarkable analogy between the phenomena of +coagulation as seen in living beings and the phenomena which occur when the +liquid in the interior of an osmotic growth comes into contact with the +mother liquor. When the sap of a plant or the blood of an animal escapes +into the air or water of the surrounding medium, it coagulates, _i.e._ it +changes from a liquid to a gelatinous consistency. In the same way, when +the liquid in the interior of an osmotic growth leaks out into the mother +liquor it forms a gelatinous precipitate. This gelatinous precipitation is +a physico-chemical phenomenon of the same nature as coagulation. It is by +the study of coagulation in liquids less complex than blood that we may +hope to elucidate the mechanism of the process, {155} which is simply a +physico-chemical phenomenon exactly analogous to gelatinous precipitation. +Calcium phosphate is always prone to coagulate; it has been called the +gelatinous phosphate of lime, and we have already seen how readily tribasic +calcium phosphate takes the form of beautiful transparent colloidal +membranes which are gelatinous in texture. + +We may obtain colloidal precipitates exactly analogous to coagulated +albumin by mixing a weak solution of chloride of calcium with potassium +carbonate or tribasic phosphate. Like albumin this precipitate forms +flakes, and is deposited slowly as a gelatinous colloidal mass. Like +albumin also this calcic solution is coagulated by heat; a solution of a +calcic salt of a volatile acid on heating forms a precipitate which has all +the appearance of albumin coagulated by heat. + +Finally, Arthus and Pagès have shown that blood does not coagulate when +deprived of its calcium salts by the addition of alkaline oxalates, +fluorides, or citrates, and that the blood thus treated recovers its +coagulability on the addition of a soluble salt of calcium. The coagulation +of milk is also a calcium salt precipitation. Coagulation therefore would +seem to be merely the colloidal precipitation of a salt of calcium. + +Diffusion and osmosis are the elementary phenomena of life. All vital +phenomena result from the contact of two colloidal solutions, or of two +liquids separated by an osmotic membrane. Hence the study of the physics of +diffusion and osmosis is the very basis of synthetic biology. + +A living being exhibits two sorts of movements, those which are the result +of stimulus from without, and those which are determined by an excitation +arising from within. In the higher animals the stimulus or exciting energy +coming from the entourage may be infinitely small when compared with the +amount of energy transformed. Moreover, the response to an identical +excitation may so vary as to give to these different responses an +appearance of spontaneity. There is in reality no spontaneity, since the +difference in response is governed by previous external impressions which +have left their record on the machinery. There is in fact no such thing as +a spontaneous action, since every action of a living {156} being has as its +ultimate cause a stimulus or excitation coming from without. + +The movements of the second category are also conditioned by an excitation, +but the stimulus comes from within the organism. These movements consist +principally of changes of nutrition, or movements of the circulation and +respiration; they are rhythmic in character and are probably produced by +the same chemico-physical causes which determine rhythmic movements outside +the living body. + +Just in the same way osmotic growths present two sorts of movements, +external movements and those which are connected with their nutrition. A +free osmotic growth swimming in the mother liquor will alter its position +and form under the influence of the slightest exterior excitation or +vibration. It responds to every variation of temperature, or to a slight +difference of concentration produced by adding a single drop of water, and +reacts to every exterior influence by displacement or deformation. + +An osmotic growth also shows indications of movements which are connected +with its nutrition, and these movements are rhythmic, like those of +respiration or circulation in a living organism. The growth of an osmotic +production shows itself not as a continuous process but periodically. The +water traverses the membrane, raises the pressure, and distends the cell; +at first the cell wall resists by reason of its elasticity, it then +suddenly relaxes, yielding to the osmotic pressure and bulging out at a +thinner spot on the surface; the internal pressure falls suddenly, and +there is a pause in the growth. + +This rhythmic growth may be best observed by sowing in a solution of a +tribasic alkaline phosphate, pellets composed of powdered calcium chloride +moistened with glycerine, to which has been added 1 per cent. of monobasic +calcium phosphate. The experiment is so arranged as to bend or incline the +growing stems which shoot out from these grains. This may be done by +carefully pouring above the mother liquor a layer of water, or a less +concentrated solution. As the internal osmotic pressure rises, the drooping +extremity of the twig will become turgescent and gradually lift itself +{157} up, and then suddenly fall again for several millimetres. We have +frequently watched this rhythmic movement for an hour or more--a slow +gradual elevation of the extremity of the twig and a rapid fall recurring +every four seconds or so. + +It may be objected that the substance of an osmotic growth is continually +undergoing change, whereas a living organism transforms into its own +substance the extraneous matter which it borrows from its environment. The +distinction, however, is only an apparent one. The substance of a living +being is also continually undergoing chemical change; it does not remain +the same for a single instant. We see an evidence of this change in the +evolution of age; the substance of the adult is not that of the infant. In +some living organisms such as insects, especially the ephemeridæ who have +but a brief existence, this change of substance is even more rapid than +that in an osmotic growth. + +It has been objected that osmotic productions cannot be compared with +living organisms since they contain no albuminoid matter. This is to +consider life as a substance, and to confound the synthesis of life with +that of albumin. If albumin is ever produced by synthesis in the laboratory +it will probably be dead albumin. All living organisms contain albumin; +this is probably due to the fact that albuminoid matter is particularly +adapted for the formation of osmotic membranes. Our osmotic productions are +composed of the same elements as those which constitute living beings; an +osmotic growth obtained by sowing calcium nitrate in a solution of +potassium carbonate with sodium phosphate and sulphate contains all the +principal elements of a living organism, viz. carbon, oxygen, hydrogen, +nitrogen, sulphur, and phosphorus. + +The whole of the vegetable world is produced by the osmotic growth of +mineral substances, if we except the small amount of organic matter +contained in the seeds. + +The most important problem of synthetic biology is not so much the +synthesis of the albuminoids as the reduction of carbonic acid. In nature +this reduction is accomplished by the radiant energy of the sun, by the +agency of the catalytic action of chlorophyll. {158} + +The physico-chemical study of osmotic growth is as yet hardly begun; we +have but indicated the method, the way is open, and the problems awaiting +solution are legion. Only work and ever more work and workers are required. +Experiments should be made with substances which are chemically unstable +like the albuminoids, substances which readily combine and dissociate +again, alternately absorbing and giving up the potential energy which is +the essence of life. Experiments should also be made with substances which +readily unite or decompose under the influence of water, since hydration +and hydrolysis appear to be the dominant mechanism in all vital reaction, +as they undoubtedly are in osmotic growth, which consists of an increase of +hydration on one side of an osmotic membrane and a diminution on the other +side. + +Life is not a substance but a mechanical phenomenon; it is a dynamic and +kinetic transference of energy determined by physico-chemical reactions; +and the whole trend of modern research leads to the belief that these +reactions are of the same nature as those met with in the organic world. It +is the grouping of physical reactions and their mode of association and +succession, their harmony in fact, which constitutes life. The problem we +have to solve in the synthesis of life is the proper attuning and +harmonizing of these physical phenomena, as they exist in living beings, +and there should be no absolute impossibility in our some day realizing +this harmony in whole or in part. + +Albert Gaudry says: "I cannot conceive why in determining the connecting +links of the animal world the fact that an organic body is formed of such +and such elements should be of greater importance than the manner in which +these elements are grouped. Descartes regarded extension as the essential +property of an organized being; he supposed it to be inert of itself, and +that it had the Deity for its motive force. To-day the hypothesis of +Descartes has given way to that of Leibnitz, who regards force as the +essential property of the living being, the visible and tangible matter +being only of secondary importance. If we regard the living being as a +force, this force is able to aggregate matter under such and such a form, +{159} with such or such a structure, and such or such a chemical essence. +It does not seem that the classification depending on differences of +substance are any more important than those which depend on differences of +form." + +The biological interest of osmotic productions is quite independent of the +chemical nature of the substances which enter into their growth. All +substances which produce osmotic membranes by the contact of their +solutions exhibit phenomena analogous to those of nutrition. Osmotic +morphogenesis is a physical phenomenon resulting from the contact of the +most diverse substances. It has given us our first glimpse of the manner in +which a living being may be supposed to have been formed according to the +ordinary physical laws of nature. We cannot at present produce osmotic +growths with all the combinations found in living beings, but that is only +because chemistry still lags far behind physics in the synthesis of organic +forms. + +We are often told "not to force the analogy." But error is equally produced +by the exaggeration of unimportant differences. We have already seen that +nutrition, absorption, transformation, and excitation are not the +characteristics of living organisms alone; nor is reaction to external +impressions the appanage only of animate beings. To insist on the +resemblance between an osmotic production and a living being is not to +force an analogy but to demonstrate a fact. + +Let us briefly recapitulate. An osmotic growth has an evolutionary +existence; it is nourished by osmosis and intussusception; it exercises a +selective choice on the substances offered to it; it changes the chemical +constitution of its nutriment before assimilating it. Like a living thing +it ejects into its environment the waste products of its function. +Moreover, it grows and develops structures like those of living organisms, +and it is sensitive to many exterior changes, which influence its form and +development. But these very phenomena--nutrition, assimilation, +sensibility, growth, and organization--are generally asserted to be the +sole characteristics of life. + + * * * * * + + +{160} + +CHAPTER XIII + +EVOLUTION AND SPONTANEOUS GENERATION + +By many biologists, even at the present day, the origin and evolution of +living beings is considered to be outside the domain of natural phenomena, +and hence beyond the reach of experimental research. The change in our +views on this subject is due to a Frenchman, Jean Lamarck, who was the true +originator of the scientific doctrine of evolution. At a time when the +miraculous origin of every living being was regarded as an unchangeable +verity, and was defended like a sacred dogma, Lamarck boldly formulated his +theory of evolution, with all its attendent consequences, from spontaneous +generation to the genealogy of man. + +In his _Philosophie Zoologique_, which appeared in 1809, Lamarck put forth +his claim to regard all the phenomena of life, of living beings, and of man +himself as pertaining to the domain of natural phenomena. According to him, +all bodies which are met with in nature, organic and inorganic alike, are +subject to the same laws. Life is a physical phenomenon, and all the +processes of life are due to mechanical causes, either physical or +chemical. He writes: "À leur source le physique et le moral ne sont sans +doute qu'une seule et même chose. Il faut rechercher dans la considération +de l'organisation les causes mêmes de la vie." + +In the intellectual evolution of the human mind perhaps no advance has been +more important than that of Lamarck--the conquest of the domain of life by +human intelligence. In conformity with the true scientific method, he +founds his doctrine on the facts and phenomena of nature. "I confine +myself," he says, "within the bounds of a simple contemplation {161} of +nature." It was this observation of the gradual perfecting of living +organisms from the simplest to the most complicated that inspired Lamarck +with the idea of evolution and transformation. "How," he says, "can we help +searching for the cause of such wonderful results? Are we not compelled to +admit that nature has produced successively bodies endowed with life, +proceeding from the simplest to the most complex?" + +The various products of nature have been divided into classes, genera, and +species, simply to facilitate their study. Modern research tends to show +that there is no definite line of demarcation even between the animal, +vegetable, and mineral kingdoms. All our classification is artificial, and +the passage from one division to another is gradual and insensible. Lamarck +expresses this idea very clearly: "We must remember that classes, orders, +and families, and all such nomenclature, are methods of our own invention. +In nature there are no such things as classes or orders or families, but +only individuals. As we become better acquainted with the productions of +nature, and as the number of specimens in our collections increases, we see +the intervals between the classes gradually fill up, and the lines of +separation become effaced." + +Lamarck also raises his voice against the supposed immutability of species. +"Species have only a relative constancy, depending on the circumstances of +the individuals. The individuals of a given species perpetuate themselves +without variation only so long as there is no variation in the +circumstances which influence their existence. Numberless facts prove that +when an individual of a given species changes its locality, it is subjected +to a number of influences which little by little alter, not only the +consistency and proportions of its parts, but also its form, its faculty, +and even its organization; so that in time every part will participate in +the mutations which it has undergone." + +Lamarck also clearly affirms the fact of spontaneous generation. "I hope to +prove," he says, "that nature possesses means and faculties for the +production of all the forms which we so much admire. Rudimentary animals +and plants have {162} been formed, and are still being formed to-day, by +spontaneous generation." + +Lamarck himself gives a résumé of his doctrine in the following six +propositions:-- + +1. "All the organized bodies of our globe are veritable productions of +Nature, which she has successively formed during the lapse of ages. + +2. "Nature began, and still recommences day by day, with the production of +the simplest organic forms. These so-called spontaneous generations are her +direct work, the first sketches as it were of organization. + +3. "The first sketches of an animal or a vegetable growth being begun under +favourable conditions, the faculties of commencing life and of organic +movement thus established have gradually developed little by little the +various parts and organs, which in process of time have become diversified. + +4. "The faculty of growth is inherent in every part of an organized body; +it is the primary effect of life. This faculty of growth has given rise to +the various modes of multiplication and regeneration of the individual, and +by its means any progress which may have been acquired in the composition +and forms of the organism has been preserved. + +5. "All living things which exist at the present day have been successively +formed by this means, aided by a long lapse of time, by favourable +conditions, and by the changes on the surface of the globe--in a word, by +the power which new situations and new habits have of modifying the organs +of a body which is endowed with life. + +6. "Since all living things have undergone more or less change in their +organization, the species which have been thus insensibly and successively +produced can have but a relative constancy, and can be of no very great +antiquity." + +The admirable work of Lamarck was absolutely neglected in France, where it +was treated as unworthy even of consideration. This neglect profoundly +afflicted Lamarck, who gradually sank a victim to the opposition of his +contemporaries. He left, however, one disciple, Etienne Jeoffroy St. {163} +Hilaire, but he too was soon reduced to silence under the weight of +authority of his adversaries. + +[Illustration: FIG. 62.--Osmotic vegetation.] + +Before the doctrine of evolution could live and take its proper place, it +had to be reborn in England--the country of liberty. This resuscitation was +due to Darwin, who added to it his illuminating doctrine of natural +selection. But apart from this and a perfecting of its various details, +Lamarck had already formulated the doctrine of evolution with perfect +precision. Lamarck's work was still-born, whereas that of Darwin lived and +grew to its full development. This was due, not to any imperfection or +insufficiency in Lamarck's work, but {164} to the milieu into which it was +born. It was the environment that stifled the offspring of Lamarck. + +In 1868, Ernest Haeckel speaks of the genius of Lamarck in these words: +"The chief of the natural philosophers of France is Jean Lamarck, who takes +his place beside Goethe and Darwin in the history of evolution. To him +belongs the imperishable glory of being the first to formulate the theory +of descent, and of founding the philosophy of nature on the solid basis of +biology," and adds, "There is no country in Europe where Darwin's doctrine +has had so little influence as in France." Haeckel has but done tardy +justice in his discovery of and testimony to the genius of Lamarck. + +The spirit of opposition does not seem to have much changed in France since +Lamarck's time. In 1907 the Académie des Sciences de Paris excluded from +its _Comptes Rendus_ the report of my researches on diffusion and osmosis, +because it raised the question of spontaneous generation. + +The majority of scientists seem to consider that the question of +spontaneous generation was definitely settled once for all when Pasteur's +experiments showed that a sterilized liquid, kept in a closed tube, +remained sterile. + +Without the idea of spontaneous generation and a physical theory of life, +the doctrine of evolution is a mutilated hypothesis without unity or +cohesion. On this point Lamarck speaks most clearly: "Although it is +customary when one speaks of the members of the animal or vegetable kingdom +to call them products of nature, it appears that no definite conception is +attached to the expression. Our preconceived notions hinder us from +recognising the fact that Nature herself possesses all the faculties and +all the means of producing living beings in any variety. She is able to +vary, very slowly but without cessation, all the different races and all +the different forms of life, and to maintain the general order which we see +in all her works." + +The doctrine of Lamarck is frequently misinterpreted. We often hear it +expressed as "Function makes the organ," or even "Function creates the +organ." This is equivalent to saying, "Life makes the living being," which +is incomprehensible, {165} making of function a sort of immaterial and +independent entity which constructs a material organ in order to lodge +within it. No such idea is to be found in all the works of Lamarck. He +formulates his law in the following terms: "In every animal which is still +undergoing development, the frequent and sustained use of any one organ +increases its size and power, whereas the constant neglect of the use of +such organ weakens and deteriorates it, so that it finally disappears." + +In his expression of this law Lamarck insists on the fact that organization +precedes function. He affirms only that function, _i.e._ action and +reaction, modifies the organ; or, in other words, that organisms are +modelled by the action of exterior forces acting upon them. It is in this +sense only that function may be said to make an organ, but this mode of +expression should be avoided, as it is apt to be misunderstood. + +Astronomy teaches us that our globe was detached from the sun in an +incandescent state, and geology asserts that this earth has passed through +a period of long ages when its temperature was incompatible with the +existence of life. It was only with the cooling of the earth crust that it +was possible for living beings to make their appearance. Hence they must of +necessity have been produced spontaneously from terrestrial material under +the influences of chemical and physical forces. This opinion imposes itself +on all who reflect and judge freely. In the same way the doctrine of +evolution necessitates as a corollary the doctrine of spontaneous +generation. The doctrine of evolution should reconstitute every link in the +chain of beings from the simplest to the most complicated; it cannot afford +to leave out the most important of all, viz. the missing link between the +inorganic and the organic kingdoms. If there is a chain, it must be +continuous in all its parts, there can be no solution of continuity. + +Evolutionists like Lamarck and Haeckel admit spontaneous generation, not as +the most probable, but as the only possible explanation of the phenomenon +of life. + +Lamarck shows us the apparition of living things at a certain epoch of the +earth's evolution, and the gradual {166} development of more complicated +forms as the conditions changed on the surface of the globe. Darwin shows +how heredity and natural selection tend to accentuate the variations which +are favourable to existence. Haeckel demonstrates the parallelism between +ontogenesis and philogenesis--between the successive forms in the evolution +of the embryo and the successive forms of the individual in the evolution +of a race. These are great and admirable conquests of the human +intelligence, they have demonstrated the first appearance and the +progressive evolution of living beings; it now only remains for us to +explain them. + +[Illustration: FIG. 63.--Marine forms of osmotic growth.] + +The doctrine of evolution, while enforcing the fact of spontaneous +generation and progressive evolution, gives us no hint as to the physical +mechanism of such generation. It does not tell us by what forces, or +according to what laws, the simpler forms of life have been produced, or in +what manner differences of environment have acted in order to modify them. +The doctrine asserts the simultaneous variations in organic forms and in +the physical influences which produce them, but says {167} nothing as to +their mode of action. The Darwinian theory shows how acquired variations +are transmitted and accentuated by natural selection, but it says nothing +as to how these variations may be acquired. In the same way we are in +entire ignorance as to the physical mechanism of ontogenetic development, +the evolution of the embryo. + +The morphogenic action of diffusion produces osmotic growths of extreme +variety. Most of these forms recall those of living things--shells, fungi, +corals, and algæ. The analogy of function is quite as close as the +resemblance of form. The study of osmosis, however, is as yet in its +infancy, and osmotic productions vary with the physical conditions of +chemical constitution, temperature, concentration, and the like. The study +of the organizing action of osmosis on organic material has as yet been +hardly attempted. + +Osmosis produces growths of great complexity, much more complicated indeed +than the more simple forms of living organisms. This marvellous complexity +of an osmotic growth may be compared with another fact, the ontogenetic +development of the ovum, a single cell which under favourable conditions of +environment may evolve into a most complicated organism. These +considerations lead to the belief that the beginning of life has not been +the production of a simple primitive form from which all others are +descended, but that a number of such primitive forms may have been +produced, forms which by a rapid physical development attained a high +degree of complexity. Osmotic morphogenesis shows us that the ordinary +physical forces have in fact a power of organization infinitely greater +than has been hitherto supposed by the boldest imagination. + +When we consider the ignorance in which we still remain as to the phenomena +which pass before our very eyes, how can we expect to understand those +which occurred in past ages, when the physical and chemical conditions were +so immensely different from those which obtain in our own time? What do we +know even now of the physical and chemical phenomena which take place in +the unfathomed depths of the ocean, where for aught we know even at the +present time the same {168} process may be going on--the genesis of life, +and the emergence of living beings out of the inanimate mineral world? +"Even now," says Albert Gaudry, "polyps and oceanic animalculæ are building +up vast coral reefs and rocks. The oxygen and hydrogen which existed once +was water, the oxygen and nitrogen which once made air, the carbon, the +phosphorus, the silica and the lime which once were solid rock, now form +the substance of living beings. The silica is deposited in the skeleton of +a sponge or a radiolaria, the shell of a foraminifera or the carapace of a +crustacean, or unites with phosphorus to form the bones of a vertebrate. A +very tumult of life has succeeded to the primitive silence of inert matter. +Life has invaded the earth, and we see on all sides the inanimate mineral +kingdom being changed into a living world." + +The admission that life may have appeared on the earth under the influence +of natural forces and according to physical laws and conditions different +from those of the present era throws a vivid light on the study of +biogenesis, spontaneous generation, and evolution. The means of research +are now indicated, and we have only to study the documents already in our +possession in order to know the conditions which obtained when life first +appeared on the globe. We must endeavour to reproduce these conditions and +to study their effects. + +Since all living beings are formed of the same elements as those of the +mineral world, the term "organic" as applied to combinations can only be +used in order to emphasize the complexity of their constitution. It was +formerly believed that these organic combinations were the result of life, +and could not be reproduced except by living organisms. To-day many of +these organic substances are produced in the laboratory from inorganic +materials. In the past history of the globe it is easy to imagine +conditions which would facilitate the synthesis of organic substances +without the interposition of life. At the temperature of the electric +furnace, which was that of the earth at an early period of its evolution, +chemical combinations are possible quite other than those obtaining under +the present conditions of temperature and pressure. At the higher +temperature of the early {169} geological era, silicides, carbides, +phosphides, and nitrides were formed in stable combinations instead of the +oxides, silicates, carbonates, phosphates, and nitrates of the present +time. These combinations existed on the earth at a time when the conditions +of temperature precluded the existence of water in a liquid state. As the +temperature cooled, and the water vapour became condensed, it entered into +chemical combination with the various rocks, producing organic compounds +like acetylene, which results from the action of water on calcium carbide. +H. Lénicque has developed a theory as to the formation of various rocks +under these conditions, which he communicated in 1903 to the French Society +of Civil Engineers. + +The chemical evolution of the globe has undergone great changes as the +temperature gradually fell and the constitution of its crust altered. As +long as the temperature was higher than that at which water can exist, all +chemical reactions must have taken place between anhydric substances, +elements and salts in a state of fusion. These conditions are very +different from those of the present-day chemistry, which is the chemistry +of aqueous solutions. We may hope to be able to reproduce the earlier +conditions by the experimental study of anhydric substances in a state of +fusion. + +At a later period, that of the primary and secondary rocks, there was a +uniform and constant temperature of about 40° C. The atmosphere was charged +with water vapour, and all the conditions were present for the production +of storms and tempests. The atmosphere during long ages must have been the +seat of formidable and incessant electric discharges; these discharges are +the most powerful of all physical agents of chemical synthesis, and will +cause nitrogen to combine directly to form various compounds--nitrates, +cyanides, and ammonia. Carbonic acid would also be present in abundance and +would enter into combination with these nitrogenous compounds. In this way +we may imagine that compounds were formed which by some process of physical +synthesis subsequently gave rise to vast quantities of albuminoid matter. +At that time the seas and oceans contained all those substances which have +{170} since been fixed by the metamorphism of the primitive rocks, or +deposited in the sedimentary strata. Most of the elements in our minerals +were formerly in a state of solution in these primeval seas, which +contained carbonates, silicates, and soluble phosphates in great abundance. +As the crust gradually cooled, the terrestrial atmosphere of necessity +altered in composition, and the slow evolution of the atmosphere no doubt +also exercised an influence on the development of living beings. + +Palæontology teaches us that the earliest living organism appeared in the +sea. The most ancient of living things, those of the primary ages, which +were of greater duration than all other ages put together, were all +aquatic. We find moreover that every living organism consists of liquids, +solutions of crystalloids and colloids separated by osmotic membranes; and +it is significant that the ocean, that vast laboratory of life, is also a +solution of crystalloids and colloids. It is evident, then, that we must +look to the study of solutions if we would hope to discover the nature and +origin of life. + +Life is an ensemble of functions and of energy-transformations, an ensemble +which is conditioned by the form, the structure, and the composition of the +living being. Life, therefore, may be said to be conditioned by form, +_i.e._ the external, internal, and molecular forms of the living being. + +All living things consist of closed cavities, which are limited by osmotic +membranes, and filled with solutions of crystalloids and colloids. The +study of synthetic biology is therefore the study of the physical forces +and conditions which can produce cavities surrounded by osmotic membranes, +which can associate and group such cavities, and differentiate and +specialize their functions. Such forces are precisely those which produce +osmotic growths, having the forms and exhibiting many of the functions of +living beings. Of all the theories as to the origin of life, that which +attributes it to osmosis and looks on the earliest living beings as +products of osmotic growths is the most probable and the most satisfying to +the reason. + +[Illustration: FIG. 64.--Osmotic shells and corals.] + +We have already seen that the seas of the primary and {171} secondary ages +presented in a high degree the particular conditions favourable for the +production of osmotic growths. During these long ages an exuberant growth +of osmotic vegetation must have been produced in these primeval seas. All +the substances which were capable of producing osmotic membranes by mutual +contact sprang into growth,--the soluble salts of calcium, carbonates, +phosphates, silicates, albuminoid matter, became organized as osmotic +productions,--were born, developed, evolved, dissociated, and died. +Millions of ephemeral forms must have succeeded one another in the natural +evolution of that age, when the living world was represented by matter thus +organized by osmosis. + +The experimental study of osmotic morphogeny adds its weight of evidence in +the same direction. When we see under our own eyes the cells of calcium +become organized, develop and grow in close imitation of the forms of life, +we cannot doubt that such a transformation has often occurred in the past +history of our planet, and the conviction becomes irresistible {172} that +osmosis has played a predominant rôle in the history of our earth and its +inhabitants. It is a matter of astonishment that the scientist has taken no +notice of the active part which osmosis has played in the evolution of our +earth. On the effects of this most important physical phenomenon science +has hitherto remained entirely mute. + +_Printed by_ MORRISON & GIBB LIMITED, _Edinburgh_ + + * * * * * + + +Corrections made to printed original. + +Page 47. "into one where its osmotic pressure is low": 'into on' in +original. + +Page 90. "the achromatin spindle in karyokinesis.": 'karineyoksis' in +original. + +Page 120. "The researches of Famintzin": 'Famitzin' in original, +inconsistent with spelling 2 paragraphs earlier. + +Page 141. "Similarly, if we suddenly dilute": 'Simiarly' in original. + +Page 153. "which is accurately limited": 'acurately' in original. + +Page 158. "this force is able to aggregate matter": 'this orce' in +original. + + + + + + +End of the Project Gutenberg EBook of The Mechanism of Life, by Stéphane Leduc + +*** END OF THIS PROJECT GUTENBERG EBOOK THE MECHANISM OF LIFE *** + +***** This file should be named 33862-8.txt or 33862-8.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/3/3/8/6/33862/ + +Produced by David Garcia, James Nugen, Keith Edkins and +the Online Distributed Proofreading Team at +http://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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