The Mechanism of Life

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 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 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 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

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 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 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.

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, 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 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.

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 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.

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 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.

"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 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 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 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."

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 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.

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 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 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.

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:—

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:—

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 stains used for microscopy, in the liquids used for fixing preparations.