The Mechanism of Life

In order to determine the influence of the work ac- complished by the muscle on the elevation of the osmotic pressure, I made the following experiment. The two hind legs of a frog were submitted to the same electrical excitation, one leg being left at liberty, and the other being stretched by a hundred-gramme weight, acting by a cord and pulley. After exciting them electrically for five minutes, the legs were immersed for twenty-four hours in a saline solution freezing at 53 C. The free limb showed an augmentation of *085 of the initial weight, and the stretched limb an increase of *106 of the initial weight. It is evident, therefore, that the osmotic pressure increases with the amount of work done by a muscle.

Briefly, then, the results of our experiments are as follow : 1. Muscular contraction electrically produced causes an increase of the osmotic pressure in a muscle. 2. The intramuscular osmotic pressure may reach, or even exceed, 2*5 atmospheres, or 2'6 kilogrammes per square centimetre of surface. elevation of the osmotic pressure increases with the number of contractions. 4. The intramuscular osmotic pressure increases with the work done by the muscle.

5. Fatigue is caused by the increase of osmotic pressure in a contracting muscle. The Field of Diffusion. Just as Faraday introduced the conception of a field of magnetic force and a field of electric force to explain magnetic and electrical phenomena, so we may elucidate the phenomena of diffusion by the conception of a field of diffusion, with centres or poles of diffusive force. If we (a) Monopolar field of diffusion. A drop of blood in a saline solution of higher

(b] Bipolar field of diffusion. Two poles of opposite signs. On the right a grain of salt forming a hypertonic pole of concentration, on the left a drop oi blood forming a hypotonic pole of dilution. consider a solution as a field of diffusion, any point where the concentration is greater than that of the rest may be considered as a centre of force, attractive for the molecules of water, and repulsive for the molecules of the solute. In the same way any point of less concentration may be regarded as a centre of attraction for the molecules of the solute, and a centre of repulsion for the molecules of water.

A field of diffusion may be monopolar or bipolar. A bipolar field has a hypertonic pole or centre of concentration, and a hypotonic pole or centre of dilution. By analogy with the magnetic and electric fields we may designate the hypertonic pole as the positive pole of diffusion, and the hypotonic as the negative pole. The positive and negative poles and the lines of force in the field of diffusion may be illustrated by the following experiment. A thin layer of salt water is spread over an absolutely horizontal plate of glass. If now we take a drop of blood, or of Indian ink, and drop it carefully into the middle of the salt solution, we shall find that the coloured particles will travel along the lines of diffusive force, and thus map out for us a monopolar field of diffusion, as in Fig. 3 a. Again, if we place two similar drops side by side in a salt solution, their lines of diffusion will repel one another, as in Fig. 4.

solution, side by side, one FIG. 4. Two drops of blood in a more drop Of less concentration concentrated solution, showing a field of The lines of diffusion will pass from one drop to the other, diverging from the centre of one drop and converging to- wards the centre of the other (Fig. 36). In this manner we are able to obtain diffusion fields analogous to the magnetic fields between poles of the same sign and poles of opposite signs. The conception of poles of diffusion is of the greatest importance in biology, throwing a flood of light on a number of phenomena, such as karyokinesis, which have hitherto been regarded as of a mysterious nature. It also enables us to appreciate the role played by diffusion in many other biological phenomena. Consider, for example, a centre of anabolism in a living organism. Here the molecules of the living protoplasm are in process of construction, simpler molecules being united and built up to form larger and more complex groups. As a result of this aggregation the number of molecules in a given area is diminished, i.e. the concentra- tion and the osmotic pressure fall, producing a hypotonic centre of diffusion. We may thus regard every centre of anabolism as a negative pole of diffusion.

Consider, on the other hand, a centre of catabolism, where the molecules are being broken up into fragments or smaller groups. The concentration of the solution is increased, the osmotic pressure is raised, and we have a hypertonic centre of diffusion. Every centre of catabolism is therefore a positive pole of diffusion. Similar considerations as to the formation and breaking up of the molecules in anabolism and catabolism apply to polymerization.

The diffusion field has similar properties to the magnetic and the electric field. Thus there is repulsion between poles of similar sign, and attraction between poles of different signs. A simple experiment will show this. A field of diffusion is made by pouring on a horizontal glass plate a 10 per cent, solution of gelatine to which 5 per cent, of salt has been added. The gelatine being set, we place side by side on its surface two drops, one of water, and one of a salt solution of greater concentration than 5 per cent. We have thus two poles of diffusion of contrary signs, a hypotonic pole at the water drop, and a hypertonic pole at the salt drop. Diffusion immediately begins to take place through the gelatine, the drops become elongated, advance towards one another, touch, and unite. If, on the contrary, the two neighbouring drops are both more concentrated or both less concentrated than the medium, they exhibit signs of repulsion as in Fig. 4.

Diffusion not only sets up currents in the water and in the solutes, but it also determines movements in any particles that may be in suspension, such as blood corpuscles, particles of Indian ink, and the like. These particles are drawn along with the water stream which passes from the hypotonic centres or regions toward those which are hypertonic. These considerations suggest a vast field of inquiry in biology, pathology, and therapeutics. Inff animation, for example, is characterized by tumefaction, turgescence of the tissues, and redness. The essence of inflammation would ap- pear to be destructive dis-assimilation with intense catabolism. We have seen that a centre of catabolism is a hypertonic focus of diffusion. Hence the osmotic pressure in an in- flamed region is increased, turgescence is produced, and

the current of water carries with it the blood globules which produce the redness. The phenomenon of agglutination may also possibly be due to osmotic pressure, a positive centre of diffusion attract- ing and agglomerating the particles held in suspension. Tactism and Tropism. The phenomena of tactism and tropism may also be partly explained by the action of these diffusion currents of particles in suspension, these polar attractions and repulsions. In all experiments on this subject we should take into account the possible influence of osmotic pres- sure, since many of the causes of tactism or tropism also modify the osmotic pressure at the point of action, and it is possible that this modifi- cation is the true cause of the phenomenon. Osmo- tactism and osmotropism have not as yet been suffi- ciently studied.

Thus it may be said that osmotic pressure dominates all the kinetic and dynamic phenomena of life, all those at least which are not purely mechanical, like the movements of respiration and circulation. The study of these vital phenomena is greatly facilitated by the concep- tion of the field of diffusion and poles of diffusion, and of the lines of force, which are the trajectories of the molecules of the solutes, and the particles and globules in suspension.

The Morphogenic Effects of Diffusion. Many interesting experiments may be made showing variations of the lines of force in a field of diffusion, and how liquids subjected only to differences of osmotic pressure diffuse and mix with one The six negative poles of diffusion are coloured with Indian ink. The positive pole in the centre is uncoloured and is formed by a drop of KNO 3 solution. another in definite patterns. When a liquid diffuses in another undisturbed by the influence of gravity, it produces figures of geometric regularity, and we may thus obtain figures and forms of infinite variety. The following is our method of procedure. A glass plate is placed absolutely horizontal and is covered with a thin layer of water or of saline solution. Then with a pipette we introduce into the solution, in a regular pattern, a number of drops of liquid coloured with Indian ink. A wonderful variety of patterns and figures may be obtained

by employing solutions of different concentra- tion and varying the position of the drops. Instead of the water or salt solution, we may spread on the plate a 5 or 10 per cent, solution of gela- ti ne, containing various salts in solution. If now we sow on this gelatine drops of vari- ous solutions which give colorations with the salts in the gela- tine, we may obtain forms of perfect regu- larity, presenting most beautiful colours and contrasts. The drops, of course, must be placed in a symmetrical pattern. In this way we may obtain an endless number of ornamental figures.

In order to cover a lantern slide 81 cm. x 10 cm., about 5 c.c. of gelatine is required. To this amount of gelatine we add a single drop of a saturated solution of salicylate of sodium, and spread the liquid gelatine evenly over the plate. When the gelatine has set, we put the plate over a diagram, a hexagon for instance, and place a drop of ferrous sulphate solution at each of the six angles. The drops immediately diffuse FlG. 6. Pattern produced in gelatine by the diffusion of drops of concentrated solutions of nitrate of silver and bromide of ammonium.

through the gelatine, and the result after a time is the production of a beautiful purple rosette. The gelatine must be carefully covered to prevent its drying until the diffusion is complete. The preparation may then be dried and mounted as a lantern slide, and will give the most brilliant effect on projection. If the gelatine has been treated with a drop of potassium ferrocyanide solution instead of salicylate of sodium, a few drops of FeS0 4 will give a blue pattern. Or we may treat the gelatine with ferrocyanide of potassium and salicylate of sodium mixed, and thus obtain an inter- mediary colour on the addition of FeSO 4 . We may, indeed, vary indef- initely the nature and concentration of the solution, as well as the number and position of the

FIG. 7. Pattern produced in gelatine by the diffusion of drops of silver nitrate and sodium carbonate. of the unexpected, which adds greatly to the interest of the These experiments are not merely a scientific toy. They show us the possibility, hitherto unsuspected, that a vast number of the forms and colours of nature may be the result of diffusion. Thus many of the phenomena of life, hitherto so mysterious, present themselves to us as merely the conse- quences of the diffusion of one liquid into another. One cannot help hoping that the study of diffusion will throw still further light on the subject.

If a number of spheres, each capable of expansion and deformation, are produced simultaneously in a liquid, they will form polyhedra when they expand by growth. This is the precise architecture of a vast number of living organisms and tissues, which are formed by the union of microscopic polyhedra or cells. A section of such a polyhedral structure would appear as a tissue of polygons. It is interesting to note that the simple process of diffusion will produce such structures under conditions closely allied to those which govern the development of the tissues of a living organism.

FiG. 8. Pattern produced in gelatine by the diffusion of drops of a solution of nitrate of silver and of citrate of potassium. periment. On a glass plate we spread a 5 per cent, solution of pure gelatine, and when set sow on it a number of drops of a 5 to 10 per cent, solution of ferrocyanide of potassium. The drops must be placed at regular intervals of 5 mm. all over the plate. When these have been allowed to diffuse and the gelatine has dried, we obtain a preparation which exactly resembles the section of a vegetable cellular tissue (Fig. 9). The drops have by mutual pressure formed polygons, which appear in section as cells, with a membranous envelope, a

nucleus, and a cytoplasm, which is in many cases entirely separated from the membrane. These cells when united form a veritable tissue, in all respects similar to the cellular structure of a living organism. In the preparation showing artificial cells the cellular structure is not directly visible until the gelatine has dried. One sees only a gelatinous mass analogous to the protoplasm of a living organism. This mass is nevertheless organized, or

FlG. g. Tissue of artificial cells formed by the diffusion in gelatine of drops of potassium ferrocyanide. at least in process of organization, as we may see by the refraction when its image is projected on the screen. During the cell-formation, and as long as there is any difference of concentration in the gelatine, each cell is the arena of active molecular movement. There is a double current, as in the living cell, a stream of water from the periphery to the centre, and of the solute from the centre to the periphery. This molecular activity the life of the artificial cell may be prolonged by appropriate nourishment,

i.e. by continually repairing the loss of concentration at the centre of the cell. The life of the artificial cell may also be prolonged by maintaining around it an appropriate medium. If we prematurely dry such a preparation of artificial cells, the molecular currents will cease, to recur again when we restore the necessary humidity to the preparation. This to my mind gives us a most vivid picture of the conditions of latent life in seeds and many rotifera.

These artificial cells, like living organisms, have an evolutionary existence. The first stage corresponds to the process of organization, the gelatine representing the blas- tema, and the drop the nucleus. Thus the cell becomes organized, forming its own cytoplasm and its own enveloping membrane. The second stage in the life of this artificial cell is the period during which the metabolism of the cell is active and tends to equalize the concentration of the liquid in the cell and in the surrounding medium.

The third stage is the period of decline. The double molecular current gradually slows down as the difference of concentration decreases between the cell contents and its entourage. When this equality of concentration has become complete the molecular currents cease, the cell has terminated its existence ; it is dead. The currents of substance and of energy have ceased to flow the form only remains. These artificial cells are sensible to most of the influences which affect living organisms. Like living cells they are influenced both in their organization and in their development by humidity, dryness, acidity, or alkalinity. They are also greatly affected by the addition of minute quantities of chemical substances either to the gelatinous blastema or to the drops which represent the primary nuclei. We may in this way obtain endless varieties, nuclei which are opaque or transparent, with or without a nucleolus, and cells containing homogeneous cytoplasm without a nucleus. We may also obtain cells with cytoplasm filling the whole of the cellular cavity or separated from the cell-membrane. We may obtain

cells imitating all the natural tissues, cells without a mem- branous envelope, cells with thick walls adhering to one another, or cells with wide intracellular spaces. The forms of these artificial cells depend on the number and relative position of the drops which represent the nuclei, and on the molecular concentration or osmotic tension of the solution. The number of the cellular polyhedra is determined by the number of centres of diffusion. The magnitude of the dihedral angles, from which radiate three and occasionally four

FlG. 10. Artificial liquid cells, formed by coloured drops of concentrated salt solution in a less concentrated salt solution. walls, depends on the position of the hypertonic poles of diffusion. The curvature of a surface is determined by the differences of concentration on either side. Between isotonic solutions the surface is plane, whilst it is curved between solutions of different osmotic pressures, the convexity being directed towards the hypertonic solution.

The time required for these artificial cells to grow varies from two to twenty -four hours, according to the concentra- tion of the gelatine, the growth being most rapid in dilute solutions. Similar cells may be produced in water. If we pour a thin layer of water on a horizontal plate, and with a pipette sow in it a number of drops of salt water coloured with Indian ink, we may obtain artificial cells composed entirely of liquid, 1 laving the same characters as those produced in a gelatinous solution.

It is possible by liquid diffusion to produce not only ordinary cells but ciliated cells. If we spread a layer of salt water on a horizontal glass plate, and sow in it drops of Indian ink, artificial cells are pro- duced by diffusion. At the edge of the preparation there is often to be seen a sort of fringe, analogous to the cilia of living cells (Fig. These tissues of artificial cells demonstrate the fact that inorganic matter is able to organize itself into forms and structures analogous to those of living organisms under the action of the simple physical forces of osmotic pressure and diffusion. The structures thus pro- duced have functions which are also analogous to those of living beings, a double current of diffusion, an evolutionary existence, and a latent vitality when desiccated or congealed.

FIG. ii. Liquid cells with a fringe of cilia, obtained by sowing coloured drops of con- centrated salt solution in a weaker salt solution. The contents of the cells have un- dergone segmentation. Periodic Precipitation. A phenomenon is said to be periodic when it varies in time and space and is identically reproduced at equal intervals. We are surrounded on all sides by periodic phenomena ; summer and winter, day and night, sleep and waking, rhythm and rhyme, flux and reflux, the movements of respiration and the beating of the heart, all are periodic. Our first sorrows were appeased by the periodic rhythm of the cradle, and in our later years the periodic swing of the rocking-chair and the hammock still soothe the infirmities of old age.

Sound is a periodic movement of the atmosphere which brings to us harmony and melody. Light consists of periodic undulations of the ether which convey to us the beauty of form and colour. Periodic ethereal waves waft to us the wireless message through terrestrial space and the radiant energy of the sun and stars. It is therefore not to be wondered at that the phenomena of diffusion are also periodic. According to Professor Quinke of Heidelberg, the first mention of the periodic formation of chemical precipitates must be attributed to Rungc in 1885. Since that time these precipitates have been studied by a number of authors, and particularly by R. Liesegang of Diisseldorf, who in 1907 published a work on the subject, entitled On Stratification by Diffusion.

In 1901 I presented to the Congress of Ajaccio a number of preparations showing concentric rings, alternately trans- parent and opaque, obtained by diffusing a drop of potassium ferrocyanide solution in gelatine containing a trace of feme sulphate. At the Congress of Rheims in 1907 I exhibited the result of some further experiments on the same subject. These periodic precipitates may be obtained from a great number of different chemical substances. The following is the best method of demonstrating the phenomenon. A glass lantern slide is carefully cleaned and placed absolutely level. We then take 5 c.c. of a 10 per cent, solution of gelatine and add to it one drop of a concentrated solution of sodium arsenate. This is poured over the glass plate whilst hot, and as soon as it is quite set, but before it can dry, we allow a drop of silver nitrate solution containing a trace of nitric