Life and death

by A. Dastre

Impossibility of life without evolution—Law of increase and division—Immortality of the protozoa—Death, a phenomenon of adaptation which has appeared in the course of the ages—The infusoria—The death of the infusoria—Two kinds of reproduction—The caryogamic rejuvenescence of Maupas—Calkins on rejuvenescence—Causes of senescence—Impossibility of life without evolution.

We take into account, a priori, the conditions that must be fulfilled by the monocellular being in order to escape the inevitability of evolution, of the succession of ages, of old age, and of death. It must be able indefinitely to maintain itself in a normal régime, without changing, without increasing, maintaining its constant morphological and chemical composition, in an environment vast enough for it to be unaltered by the borrowings or the spendings resulting from its nutrition—i.e., it must remain constant in the presence of the constant being. We might conceive of a nutrition perfect enough, of exchanges exact enough, and regular enough, for the state of things to be indefinitely maintained. This would be absolute permanence realized in the vital mobility.

The Law of Growth and Division.—This model of a perfect and invariable machine does not exist in nature. Life is incompatible with the absolute permanence of the dimensions and the forms of the living organism.

In a word, it is a rigorous law of living nature that the cell can neither live indefinitely without growth, nor grow indefinitely without division.

Why is this so? Why is there this impossibility of a regular régime in which the cell would be maintained in magnitude without diminution or increase? Why has nutrition as a necessary consequence the growth of the element? This is what we do not positively know.

Things are so. It is an irreducible fact, peculiar to the protoplasm, a characteristic of the living matter of the cell. It is the fundamental basis of the property of generation. That is all we can say about it. Real living beings have therefore inevitably an evolution. They are not unchangeable. In its simple form this evolution consists in the fact that the cell grows, divides, and diminishes by this division, begins the upward march which ends in a new division. And so on.

Immortality of the Protozoa.—It may happen, and it does happen in fact, that this series of acts is repeated indefinitely at any rate unless an accidental cause should interrupt it. The animal thus describes an indefinite curve, constituted by a series of indentations, the highest point of which corresponds to the maximum of size, and the lowest point to the diminution which succeeds the division. This state of things has no inevitable end if the medium does not change. The being is immortal.

In fact, the compound beings of a single cell, protophytes and protozoa, the algae and the unicellular mushrooms, at the minimum stage of differentiation, escape the necessity of death. They have not, as Weismann remarks, the real immortality of the gods of mythology, who were invulnerable. On the contrary, they are infinitely vulnerable, fragile, and perishable; myriads die every moment. But their death is not inevitable. They succumb to accidents, never to old age.

Imagine one of these beings placed in a culture medium favourable to the full exercise of its activities, and, moreover, wide enough in its extent to be unaffected by the infinitely small quantities of material which the animal may take from it or expel into it. Suppose, for example, it is an infusorian in an ocean. In this invariable medium the being lives, increases, and grows continually. When it has reached the limits of a size fixed by its specific law, it divides into two parts, which are indistinguishable the one from the other. It leaves one of its halves to colonize in its neighbourhood, and it begins its evolution as before. There is no reason why the fact should not be repeated indefinitely, since nothing is changed, either in the medium or in the animal.

To sum up. The phenomena which take place in the cell of the protozoan do not behave as a cause of check. The medium allows the organism to revictual and to discharge itself in such a way and with such perfection that the animal is always living in a regular régime, and, with the exception of its growth and later on of its division, there is nothing changed in it.