All the liquid atmospheres which surround the cells and form their ambient medium have intercommunication. A change having taken place in one cellular group, and therefore in the corresponding liquid, modifies the medium of the further or nearer groups, and therefore these groups themselves.
Nervous Solidarity.—But the real instrument of the solidarity of the part is the nervous system. Thanks to it in the living machine the component activities of the cellular multitude restrain and control one another. Nervous solidarity makes of the complex being not a mob of cells, but a connected system, an individual in which the parts are subordinated to the whole and the whole to the parts; in which the social organism has its rights just as the individual has his rights. The whole secret of the vital functional activity of the complex being is contained in these two factors:—the independence and the subordination of the elementary lives. General life is the harmony of the elementary lives, their symphony.
Independence and Subordination of the Anatomical Elements.—The independence of the anatomical elements results from the fact that they are the real depositaries of the vital properties, the really active components. On the other hand the subordination of the parts to the whole is the very condition of the preservation of form in animals and plants. The architecture which is characteristic of them, the morphological plan which they realize in their evolutive development which they are ever preserving and repairing, form a striking proof of this. This dependence in no way contradicts the autonomy of the elements. For when with Claude Bernard and Virchow we study the circumstances we see that the element accommodates itself to the organic plan without violence to its nature. It behaves in its natural place as it would behave elsewhere, if elsewhere it were to meet around it the same liquid medium which at once is a stimulant and a food. This at least is the conclusion we may draw from experiments on transplanting, or on animal and vegetable grafting. Neither the neighbouring elements, nor the whole system act on it at a distance by a kind of mysterious induction, according to the ideas of the vitalists, in order to regulate the activity of the element. They contribute solely to the composition of the liquid atmosphere which bathes it. They intervene in order to provide it with a certain environment whose very characteristic physical and chemical constitution regulates its activity. This constitution may be some day imitated by the devices of experiment. When that result is achieved the anatomical element will live in isolation exactly as it lives in the organic association, and the mysterious bond which causes its solidarity with the rest of the economy will become intelligible. In fact, we may defer more or less the maturity of this prophecy, but there is no doubt that we are daily nearing its fulfilment.
The general life of the complex being is therefore the more or less perfect synergy, the ordered process of elementary lives. General death is the destruction of these partial lives. The nervous system, the instrument of this harmony of the parts, represents the social bond. It keeps most of the partial elements under its sway, and is thus the intermediary of their relations. The closer this dependence, the higher the development of the nervous apparatus, and the better, also, is assured the universal solidarity and therefore the unity of the organism. Cellular federation assumes the characteristic of a unique individuality in proportion to the development of this nervous centralization. With an ideal perfect nervous system the correlation of the parts would also attain perfection. As Cuvier said: “None could experience change without a change in the rest.”
But no animal possesses this extreme solidarity of the parts of the living economy. It is a philosopher’s dream. It is the dream of Kant, to whom the perfect organism would be “a teleological system,” a system of reciprocal ends and means, a sum total of parts each existing for and by the rest, for and by the whole. An organism so completely connected would be unlikely to live. In fact, living organisms show a little more freedom in the interplay of their parts. Their nervous apparatus fortunately does not attain this imaginary perfection; their unity is not so rigorous. The idea of individuality, of individual existence, is therefore not absolute but relative. There are all degrees of it according to the development of the nervous system. What the man in the street and the doctor himself understand by death is the situation created by the stopping of the general wheels, the brain, the heart, and the lungs. If the breath leaves no trace on the glass held to the mouth, if the beating of the heart is no longer perceptible by the hand which touches or the ear which listens, if the movement and the reaction of sensitiveness have ceased to be manifest, these signs make us conclude that it is death. But this conclusion, as we have said before, is a prognostic rather than a judgment of fact. It expresses the belief that the subject will certainly die, and not that it is from this moment dead. To the physiologist the subject is only on the way to die. The process has started. The only real death is when the universal death of all the elements has been consummated.
CHAPTER III.
PHYSICAL AND CHEMICAL CHARACTERS OF CELLULAR DEATH. NECROBIOSIS. GROWING OLD.
Characteristic of elementary life—Changes produced by death in the composition and the death of the cell—Schlemm; Loew; Bokorny; Pflüger; A. Gautier; Duclaux—The processive character of death—Accidental death—Necrobiosis—Atrophy—Degeneration—So-called natural death—Senescence—Metchnikoff’s theory of senescence—Objections.
Elementary death is nothing but the suppression in the anatomical elements of all the phenomena of vitality.
Characteristics of Elementary Life.—The characteristic features of elementary life have been sufficiently fixed by science. First of all, there is morphological unity. All the living elements have an identical morphological composition. That is to say that life is only accomplished and sustained in all its fulness in organic units possessing the anatomical constitution of the cell, with its cytoplasm and its nucleus, constituted on the classical type. In the second place, there is chemical unity. The constituent matter, the matter of which the cell is built up, diverges but little from a chemical type—a proteid complex, with a hexonic nucleus, and from a physical model which is an emulsion of granulous, immiscible liquids, of different viscosities. The third character consists in the possession of a specific form acquired, preserved, and repaired by the element. The fourth character, and perhaps the most essential of all, is the property of growth or nutrition with its consequence, namely, a relation of exchanges with the external medium, exchanges in which oxygen plays considerable part. Finally, there is a last property, that of reproduction, which in a certain measure is a necessary consequence of the preceding,—i.e., of growth.
These five vital characters of the elements are most in evidence in cells living in isolation, in microscopical beings formed of a single cell, protophytes and protozoa. But we find them also in the associations formed by the cells among one another—i.e., in ordinary plants and animals, multicellular complexes, called for this reason metaphytes and metazoa. Free or associated, the anatomical elements behave in the same way—feed, grow, breathe, digest in the same manner. As a matter of fact, the grouping of the cells, the relations, proximity and contiguity, which they assume, introduce some variants into the expression of the common phenomena; but these slight differences cannot disguise the essential community of the vital processes.