(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 CaCl2 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 ,, |
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.
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 carbonate, is transformed into calcium carbonate. CaCl2 + K2CO3 = CaCO3 + 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 CO3, while at the same time it eliminates and excretes 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.
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.
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 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.
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.
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.
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 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 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 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.
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.
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.
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.
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 the internal osmotic pressure, showing the gelatinous contents through the opening.
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.
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 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 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.
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 amœba. The same phenomenon may be observed with vermiform growths, a single seed often giving rise in this way to a whole series of amœbiform 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.
(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.
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.
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.
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 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 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.
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?
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 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 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 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 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 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.
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 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 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, 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 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 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.
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, 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.
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 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 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. Hilaire, but he too was soon reduced to silence under the weight of authority of his adversaries.