The Mechanism of Life Part 12

A. Lecha Marzo of Valladolid published his researches on the growth of aniline colours in the _Gaceta Medica Catalana_, 1909, under the t.i.tle _Otra nueva flora artificiale_.

Dr. Maurice d'Halluin of Lille has also published a volume on osmotic growths under the t.i.tle, _Stephane Leduc a-t-il cree 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 resume of my researches on osmotic growth has already appeared in the _Doc.u.ments du Progres_, 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.

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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 role 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 pa.s.sage of water and of the various substances in solution, being very permeable to water, but much less so to the different solutes.

A soluble substance thus surrounded by an osmotic membrane represents what Traube has called an artificial cell. In such a cell the dissolved substances have a very high osmotic pressure, an expansive force like that of steam in a boiler; the molecules of the solute exerting pressure on the walls of the extensible cell, and distending it like the {124} gas in a balloon. This pressure increases the volume of the cell, and in consequence water rushes in through the permeable membrane and still further distends the cell. Most beautiful osmotic cells may be produced by dropping a fragment of fused calcium chloride into a saturated solution of pota.s.sium carbonate or tribasic pota.s.sium 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 const.i.tution. 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 a.s.sociation of microscopic cellular cavities, separated by osmotic walls--a structure completely a.n.a.logous to that which we meet with in a living organism.

We may easily picture to ourselves the mechanism by which an osmotic cell gives birth to such a colony of microscopic vesicles. The membranogenous substance, the chloride of calcium, diffuses uniformly on all sides from the solid nucleus, and forms an osmotic membrane where it comes into contact with the solution. This spherical membrane is extended by osmotic pressure, and grows gradually larger. Since the area of the surface of a sphere increases as the square of its radius, when the cell has grown to twice its original diameter, each square centimetre of the membrane will receive by diffusion but a quarter as much of the membranogenous substance.

Hence, after a time, the membrane will not be sufficiently nourished by the membranogenous substance, it will break down, and an aperture will occur through which the interior liquid oozes out, forming in its turn a new {125} membranous covering for itself. This is the explanation of the fact that all living organisms are formed by colonies of microscopical elements, although we must not forget that Nature often produces similar results in different ways.

[Ill.u.s.tration: FIG. 35. FIG. 36.

Osmotic growths of ferrocyanide of copper.]

Osmotic growths may be obtained from a great number of chemical substances.

The most easily grown are the soluble salts of calcium in solutions of alkaline phosphates and carbonates, to which we have already alluded. We may also reverse the phenomenon by growing phosphates and carbonates in solutions of calcium salts, but in this case the osmotic growths are not so beautiful.

The various silicates play an important part in the const.i.tution of sh.e.l.ls and of the skeletons of marine animals. Most of the metallic salts, and more especially the soluble salts of calcium, give rise to the phenomenon of osmotic growth when sown in solutions of the alkaline silicates. In this way, by using different silicates and varying the proportions and the concentrations, we may obtain an immense variety of osmotic growths.

A good solution to commence with is the following:--

Silicate of potash, sp. gr. 1.3 (33 Beaume) 60 gr.

Saturated solution of sodium carbonate 60 gr.

Saturated solution of dibasic sodium phosphate 30 gr.

Distilled water make up to 1 litre.

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A fragment of fused calcium chloride dropped into this solution will produce a rapid growth of slender osmotic forms which may attain a height of 20 or 30 centimetres.

Small pellets may also be made of one part of sugar and two of copper sulphate and sown in the following solution, which must be kept warm until the growth is complete:--

Ten per cent. solution of gelatine 10 to 20 c.c.

Saturated solution of pota.s.sium ferrocyanide 5 to 10 c.c.

Saturated solution of sodium chloride 5 to 10 c.c.

Warm water (32 to 40 C.) 100 c.c.

In this solution we can obtain osmotic growths which may attain to a height of 40 centimetres or more, vegetable forms, roots, arborescent twigs, leaves, and terminal organs. These growths are stable as soon as the gelatine has cooled and set, and may be carried about without fear of injury (Fig. 35).

Precipitated osmotic membranes are very widely distributed in nature.

Professor Ulenhuth has seen iron growths in alkaline sodium hypochlorite (Javelle water), and Lecha-Marzo has demonstrated the osmotic growth of the various {127} stains used for microscopy, in the liquids used for fixing preparations.

[Ill.u.s.tration: FIG. 37.--Osmotic vermiform growth.

(_a_) The sickle-shaped growth.

(_b_) The growth broken by the upward pressure of the solution.

(_c_) The wound having cicatrized, the stem continues to grow downwards. ]

We now know that the physical force which builds up these growths is that of osmotic pressure, since the slightest consideration will show the inadequacy of the usual explanation that the growth is due to mere differences of density, or to amorphous precipitation around bubbles of gas. These may indeed affect the phenomenon, but can in no way be regarded as its cause.

One of our experiments throws considerable light on this question. In a gla.s.s vessel we placed a concentrated solution of carbonate of pota.s.sium, to which had been added 4 per cent. of a saturated solution of tribasic pota.s.sium phosphate. Into this solution we dropped a fragment of fused calcium chloride, and obtained a vermiform growth some 6 millimetres in diameter. This growth was curved, at first growing upwards, then for a short distance horizontally, and finally downwards. The upward pressure of the solution, which was heavier than the growth, ultimately broke it at the top of the curve, as shown at _b_, Fig. 37. The liquid contents of the growth began to ooze out through the wound, but this after a time became cicatrized, and the stem continued to grow obstinately downwards once more, in opposition to the hydrostatic pressure. In consequence of this pressure the growth is sinuous, tacking as it were from side to side like a boat against the wind. We give three successive photographs of this growth, which attained a length of over 10 inches. We have frequently obtained these vermiform growths forming a series of such loops, growing upwards and falling again many times in succession.

_Osmotic Growths in Air._--Certain of these artificial cells may be made to grow out of the solution into the air. For this purpose we place a fragment of CaCl_2 in a shallow flat-bottomed gla.s.s dish, just covering the fragment with liquid. The best solution is as follows:--

Pota.s.sium carbonate, saturated solution 76 parts.

Sodium sulphate, saturated solution 20 "

Tribasic pota.s.sium phosphate, saturated solution 4 "

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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 part.i.tions 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.

[Ill.u.s.tration: FIG. 38.--Osmotic growth produced by sowing a mixture of CaCl_2 and MnCl_2 in a solution of alkaline carbonate, phosphate, and silicate. The stem and terminal organs are of different colours. (One-third of the natural size.)]

[Ill.u.s.tration: FIG. 39.--An osmotic growth photographed by transverse light to show the construction of the terminal organs.]

_a.s.similation and Excretion._--Like a living being, an osmotic growth absorbs nutriment from the medium in which it grows, and this nutriment it a.s.similates 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 a.s.similated--that is, before it can form part of the growth. Calcium chloride, for example, growing in a solution of pota.s.sium {130} carbonate, is transformed into calcium carbonate. CaCl_2 + K_2CO_3 = CaCO_3 + 2KCl.

Thus an osmotic growth can make a choice between the substances offered to it, rejecting the pota.s.sium of the nutrient liquid, and absorbing water and the radical CO_3, while at the same time it eliminates and excretes {131} chlorine, which may be found in the nutrient liquid after the reaction.

Of all the ordinary physical forces, osmotic pressure and osmosis alone appear to possess this remarkable power of organization and morphogenesis.

It is a matter of surprise that this peculiar faculty has. .h.i.therto remained almost unsuspected.