Life and death

by A. Dastre

Nutrition is a manufacture of protoplasm at the expense of the materials of the cellular ambient medium, which are assimilated—i.e., made chemically and physically similar to living matter and to the reserves it stores up. This operation, which is peculiarly chemical, is therefore indicated by the borrowing of materials from the external world, a borrowing which is always going on, because the operation is permanent, and, let me add, because of the continual rejection of the waste products of this manufacture. Our formula is:—Nutrition is a chemistry which persists.

The Idea of the Vital Vortex is Erroneous.—Here the effect has hidden the cause from the eyes of the biologists. They have been struck by the incessant entry and exit, by the never-ceasing passage, by the cycle of matter through the living being without guessing its why and wherefore; and they have taken as a picture of the living being a vortex in which the essential form is maintained while the matter, which is accessory, flows on without a check. This is Cuvier’s vital vortex. But for what purpose is this circulating matter used? They thought that it was employed entirely for the reconstitution of the living substance, continually and inevitably destroyed by the vital Minotaur.

Destruction of Reserve-stuff.—Here again there is a mistake. Really living substance is but little destroyed, and consequently requires very little renewal by the functional activity of the animal machine. Its metabolism—destruction and renewal—is in every case infinitely less than is supposed in the classical image of the vital vortex. It is the merit of physiologists, and particularly of Pflüger and Chauveau, to have worked for nearly forty years to establish this truth. They have proved it, at least as far as the muscular tissue is concerned. Protoplasm, properly so-called, is only destroyed as the organs of a steam engine are destroyed—its tubes, its boiler, its furnace. And it matters little. We know that such an engine uses much coal, and we know very little of its machinery and its metallic frame. And so it is with the cell, the living machine. A very small portion of the food introduced will be assimilated in the living substance. By far the greater part of it is destined to be worked up by the protoplasm and placed in reserve under the form of glycogen, albumen, and fat, etc.—i.e., compounds which are not the really living substance, the hereditary protoplasm, but the products of its industry, just as they are or may be the products of the industry of the chemist working in his laboratory. They will be expended for the purpose of furnishing the necessary energy to the vital functional activity, muscular contraction, secretion, heat, etc., just as coal is expended to set the steam engine going. The proof as far as the muscle is concerned does not stand alone. There are other examples. In particular, micrographic physiologists who have studied nervous phenomena say that the anatomical elements of the brain last indefinitely, and that they continue as they are, without renewal from birth to death. The permanence of the consciousness, be it said in passing, is connected by them with the permanence of the cerebral element (Marinesco).

Thus destruction is very restricted. There is only a very slight disassimilation of the living matter, properly so-called, in the course of the vital functional activity. We may even go farther than this experimental fact. This is what Le Dantec has done when he claims that there is even an assimilation, an increase of the protoplasm. Strictly speaking, this is possible, but there is no certain proof of it; and in any case we cannot agree with him when he affirms that the increase is the direct result of the functional activity and blends with it in one single, unique operation. We must, on the contrary, agree with Claude Bernard that it is only a consequence of it, that it is produced in consequence of the existence of a bond of correlation between organic destruction and assimilating synthesis.

Why is there this bond? That is easily understood if we reflect that the assimilating synthesis, an operation of endothermic, chemical complexity, naturally requires an exothermic counterpart, the organic destruction which will set free this necessary energy.

Formative Assimilation of Reserve-stuff. Formative Assimilation of Protoplasm.—It follows that there are in nutritive assimilation itself two distinct acts. The one consisting of the manufacture of reserve-stuff is the more obvious but the less specific; the other, really essential, is assimilation properly so-called, the reconstitution of the protoplasm. The former is indispensable to the production of the most prominent acts of vitality—movement, secretion, production of heat. If it is suspended, functional activity is arrested. We get apparent death, or latent life. But if the real assimilation is arrested, we have real death.

According to this there would be a fundamental distinction between real and apparent death. The former would be characterized by an arrest of the protoplasmic assimilation which is externally indicated by no sign. On the other hand, apparent death would be characterized by the arrest of the formation and destruction of reserve-stuff. It would be externally manifested by two signs:—The suppression of material exchanges with the medium (respiration, alimentation) and the suppression of the functional acts (production of movement, of heat, of electricity, of glandular excretion).

Such would be the most expedient test for apparent or real death. The question occurs in the case of grains of corn in Egyptian tombs, and also of hibernating animals and reviviscent beings, and, in general, in the case of what has been called the state of latent life. But from the practical point of view it is extremely difficult to apply this test and to decide if the phenomena which are arrested in the grain at maturity, in Leeuwenhoek’s tardigrada,[18] and in the dried-up Anguillulidæ[19] of Baker and Spallanzani, in the encysted colpoda[20] that a drop of warm water will revive, in the animals exposed by E. Yung and Pictet to a cold of more than a 100° C. below zero, are due to the general arrest of the two forms of assimilation, or to the arrest of the manufacture and utilization of reserve-stuff alone, or finally, to the arrest of protoplasmic assimilation alone. The latter, which is already very restricted in beings in a normal condition whose growth is terminated, may fall to the lowest degree in the being which, having no functional activity, is assimilating nothing. So that, to cut the question short, the experimenter who measures the value of the exchanges between the being and the medium has seldom to do more than decide between little and nothing. Hence his perplexity. But if experiment hesitates, theory affirms: it admits a priori that the movement of protoplasmic assimilation, an essential sign of vitality, is neither checked nor renewed, but proceeds continuously.

Is Nutrition, the Assimilating Synthesis, interrupted?—Nevertheless, there are many reasons for suspending all judgment as to this interpretation. It is questioned by most biologists. According to A. Gautier, the preserved grain of corn and the dried up rotifera are not really alive; they are like clocks in working order, ready to tell the time, but awaiting in absolute repose the first vibration which will set them going. As for the grain, it is the air, heat, and moisture which supply the first impulse. In other words, the organization proper to the manifestation of life remains, but there is no life. The so-called arrested life is not a life.

It must be said, however, that the majority of physiologists refuse to accept this interpretation. They believe in an attenuation of the nutritive synthesis and not in its complete destruction. They think that this total suppression would be contrary to current ideas relative to the perpetuity of the protoplasm and the limited duration of the living element. The natural medium is variable, and even the mineral cannot remain eternally fixed. Still less is perennity a property of the living being. If ordinary life is for each individual of limited duration, the arrested life must also be of limited duration. We cannot believe that after an indefinitely prolonged sleep the grain of corn, or the paste-eel, or the colpoda, emerging from their torpor can resume their existence, like the Sleeping Beauty, at the point at which it was interrupted, and thus pass with a bound, as it were, through the centuries.