The Mechanism of Life

. 47. Capsnlar osmotic growth. The capsule has been broken to show the interior structure. of the cap shows traces of radiating lamellae, 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. FlG. 48. An osmotic growth in which the terminal organs are differently coloured from the stems, showing that the chemical evolution is different.

mineral in a very shallow layer of concentrated solution, a centimetre or less in depth, and pouring over this a less con- centrated layer of solution. By varying the solution or concen- tration 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 man- ganese, the chloride, citrate or sulphate, the stages of evolution of the growth are distinguished not only by diversities of form, but also by modifi- cations 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 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. FIG. 50. Amoeboid osmotic growth, floating free in the mother liquor. The calcareous capsules grown in a saturated solution of potassium carbonate or phosphate often take a regular ovoid form. If these arc allowed to thicken, they may be taken out of the water without breaking, and then present the aspect of veritable ooliths. Osmotic produc- tions may be divided into two groups. Some like the silicate growths are fixed. Like vegetables, they develop, become or- gan i/ed, grow, decline, die, and are disin-

Fin. 51. Transparent osmotic cell, in which may tcgl'ated at the spot be seen the white calcareous nucleus. The where they are SOWll. summit of the cell bears osmotic prolongations. Others especiallv 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 Flc;. 52. Amctboid osmotic growth with long crystalline cilia swimming about in the mother liquor.

at the bottom of the vessel in which they are sown. As they grow, they absorb water and their specific gravity diminishes. FlG. 53. Osmotic growth swimming in mother liquor. The fin-like pro- longation grew out between two liquid layers of different concentrations. 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 crys- talline in structure, and are spread over the whole surface of the swimming vesicle. An osmotic growth in- creases by the absorp- tion of water from a concentrated solution. When the solution is originally saturated it thus becomes super- saturated, and deposits these long ciliary crys- tals 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 oper- valves separated showing the colloidal con- floats away ill the tents. liquid. We thus obtain a free swimming organ- ism, 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 con- traction increases till a portion of the vesicle is cut off* and swims away free like an amoeba. The same phenomenon may be observed with vermiform growths, a single seed often giving

rise in this way to a whole series of amoebifortn 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 draw- ing 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.

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. Simi- arly, if we suddenly dilute the mother liquor around an osmotic cell, it bursts by a process of dehiscence, and pro- jects into the liquid a part of its contents, which may thus become an independent vesicle, 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.

FIG. 55. Microphotograph showing the structure of various osmotic stems. (Magnified 25 diameters.) 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 FIG. 56. Microphotograph showing the structure of osmotic stems. (Magnified 40 diameters.) 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 lacunae, but all these lacunae 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 resem- blance 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.

FIG. 58. Photomicrograph of an osmotic leaf showing the cellular structure. The geologist may well consider what role osmotic growth may have played in the formation of the various rocks, siliceous, calcareous, barytic, magnesian, the fibrous and nodular rocks and atolls. The palaeontologist 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

FlG. 59. Osmotic growth with nucleated terminal organs. (One-third of the natural size.) 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. 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?

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 o, 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-r-water, carbon, nitrogen, phosphorus, sulphur before their absorption and assimilation belonged to the mineral 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 pro- duction 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 reali/e 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 im- pressions. 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, vi/. 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 elimina- tion. 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 absorp- tion 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 sur- rounding 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 organiza- tion 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. Ana- logous phenomena are met with in living organisms, the calcareous infiltration of the vessels representing the thicken- ing 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 them- selves 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 si em 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 accom- panied 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.