THE UPSHOT OF
our enquiry so far has been the drawing of a sharp distinction between the ‘ego instincts’ and the sexual instincts, and the view that the former exercise pressure towards death and the latter towards a prolongation of life. But this conclusion is bound to be unsatisfactory in many respects even to ourselves. Morever, it is actually only of the former group of instincts that we can predicate a conservative, or rather retrograde, character corresponding to a compulsion to repeat. For on our hypothesis the ego instincts arise from the coming to life of inanimate matter and seek to restore the inanimate state; whereas as regards the sexual instincts, though it is true that they reproduce primitive states of the organism, what they are clearly aiming at by every possible means is the coalescence of two germ-cells which are differentiated in a particular way. If this union is not effected, the germ-cell dies along with all the other elements of the multicellular organism. It is only on this condition that the sexual function can prolong the cell’s life and lend it the appearance of immortality. But what is the important event in the development of living substance which is being repeated in sexual reproduction, or in its fore-runner, the conjugation of two protista?*
We cannot say; and we should consequently feel relieved if the whole structure of our argument turned out to be mistaken. The opposition between the ego or death instincts†
and the sexual or life instincts would then cease to hold and the compulsion to repeat would no longer possess the importance we have ascribed to it.
If we do so, we may be astonished to find how little agreement there is among biologists on the subject of natural death and in fact that the whole concept of death melts away under their hands. The fact that there is a fixed average duration of life at least among the higher animals naturally argues in favour of there being such a thing as death from natural causes. But this impression is countered when we consider that certain large animals and certain gigantic arboreal growths reach a very advanced age and one which cannot at present be computed. According to the large conception of Wilhelm Fliess , all the phenomena of life exhibited by organisms—and also, no doubt, their death—are linked with the completion of fixed periods, which express the dependence of two kinds of living substance (one male and the other female) upon the solar year. When we see, however, how easily and how extensively the influence of external forces is able to modify the date of the appearance of vital phenomena (especially in the plant world)—to precipitate them or hold them back—doubts must be cast upon the rigidity of Fliess’s formulas or at least upon whether the laws laid down by him are the sole determining factors.
Let us turn back, then, to one of the assumptions that we have already made, with the expectation that we shall be able to give it a categorical denial. We have drawn far-reaching conclusions from the hypothesis that all living substance is bound to die from internal causes. We made this assumption thus carelessly because it does not seem to us to be
an assumption. We are accustomed to think that such is the fact, and we are strengthened in our thought by the writings of our poets. Perhaps we have adopted the belief because there is some comfort in it. If we are to die ourselves, and first to lose in death those who are dearest to us, it is easier to submit to a remorseless law of nature, to the sublime ‘Aváyxn
[Necessity], than to a chance which might perhaps have been escaped. It may be, however, that this belief in the internal necessity of dying is only another of those illusions which we have created ‘um die Schwere des Daseins zu ertragen’
It is certainly not a primaeval belief. The notion of ‘natural death’ is quite foreign to primitive races; they attribute every death that occurs among them to the influence of an enemy or of an evil spirit. We must therefore turn to biology in order to test the validity of the belief.
What strikes us in this is the unexpected analogy with our own view, which was arrived at along such a different path. Weismann, regarding living substance morphologically, sees it in one portion which is destined to die—the soma, the body apart from the substance concerned with sex and inheritance—and an immortal portion—the germ-plasm, which is concerned with the survival of the species, with reproduction. We, on the other hand, dealing not with the living substance but with the forces operating in it, have been led to distinguish two kinds of instincts: those which seek to lead what is living to death, and others, the sexual instincts, which are perpetually attempting and achieving a renewal of life. This sounds like a dynamic corollary to Weismann’s morphological theory.
The greatest interest attaches from our point of view to the treatment given to the subject of the duration of life and the death of organisms in the writings of Weismann (1882, 1884, 1892, etc.). It was he who introduced the division of living substance into mortal and immortal parts. The mortal part is the body in the narrower sense—the ‘soma’—which alone is subject to natural death. The germ-cells, on the other hand, are potentially immortal, in so far as they are able, under certain favourable conditions, to develop into a new individual, or, in other words, to surround themselves with a new soma. (Weismann, 1884.)
multicellular But the appearance of a significant correspondence is dissipated as soon as we discover Weismann’s views on the problem of death. For he only relates the distinction between the mortal soma and the immortal germ-plasm to
organisms; in unicellular organisms the individual and the reproductive cell are still one and the same (Weismann, 1882, 38). Thus he considers that unicellular organisms are potentially immortal, and that death only makes its appearance with the multicellular metazoa. It is true that this death of the higher organisms is a natural one, a death from internal causes; but it is not founded on any primal characteristic of living substance (Weismann, 1884, 84) and cannot be regarded as an absolute necessity with its basis in the very nature of life (Weismann, 1882, 33). Death is rather a matter of expediency, a manifestation of adaptation to the external conditions of life; for, when once the cells of the body have been divided into soma and germ-plasm, an unlimited duration of individual life would become a quite pointless luxury. When this differentiation had been made in the multicellular organisms, death became possible and expedient. Since then, the soma of the higher organisms has
died at fixed periods for internal reasons, while the protista have remained immortal. It is not the case, on the other hand, that reproduction was only introduced at the same time as death. On the contrary, it is a primal characteristic of living matter, like growth (from which it originated), and life has been continuous from its first beginning upon earth. (Weismann, 1884, 84 f.)
late acquisition of organisms, then there can be no question of there having been death instincts from the very beginning of life on this earth. Multicellular organisms may die for internal reasons, owing to defective differentiation or to imperfections in their metabolism, but the matter is of no interest from the point of view of our problem. An account of the origin of death such as this is moreover far less at variance with our habitual modes of thought than the strange assumption of ‘death instincts’. It will be seen at once that to concede in this way that higher organisms have a natural death is of very little help to us. For if death is a
* The discussion which followed upon Weismann’s suggestions led, so far as I can see, to no conclusive results in any direction. Soon afterwards research was directed to the experimental testing on unicellular organisms of the alleged immortality of living substance. An American biologist, Woodruff, experimenting with a ciliate infusorian, the ‘slipper-animalcule’, which reproduces by fission into two individuals, persisted until the 3029th generation (at which point he broke off the experiment), isolating one of the part-products on each occasion and placing it in fresh water. This remote descendant of the first slipper-animalcule was just as lively as its ancestor and showed no signs of ageing or degeneration. Thus, in so far as figures of this kind prove anything, the immortality of the protista seemed to be experimentally demonstrable.
Some writers returned to the views of Goette (1883), who regarded death as a direct result of reproduction. Hartmann (1906, 29) does not regard the appearance of a ‘dead body’—a dead portion of the living substance—as the criterion of death, but defines death as ‘the termination of individual development’. In this sense protozoa too are mortal; in their case death always coincides with reproduction, but is to some extent obscured by it, since the whole substance of the parent animal may be transmitted directly into the young offspring.
From the aggregate of these experiments two facts emerge which seem to offer us a firm footing. First: If two of the animalculae, at the moment before they show signs of senescence, are able to coalesce with each other, that is to ‘conjugate’ (soon after which they once more separate), they are saved from growing old and become ‘rejuvenated’. Conjugation is no doubt the fore-runner of the sexual reproduction of higher creatures; it is as yet unconnected with propagation and is limited to the mixing of the substances of the two individuals. (Weismann’s ‘amphimixis’.) The recuperative effects of conjugation can, however, be replaced by certain stimulating agents, by alterations in the composition of the fluid which provides their nourishment, by raising their temperature or by shaking them. We are reminded of the celebrated experiment made by J. Loeb, in which, by means of certain chemical stimuli, he induced segmentation in sea-urchins’ eggs—a process which can normally occur only after fertilization.
Other experimenters arrived at different results. Maupas, Calkins and others, in contrast to Woodruff, found that after a certain number of divisions these infusoria become weaker, diminish in size, suffer the loss of some part of their organization and eventually die, unless certain recuperative measures are applied to them. If this is so, protozoa would appear to die after a phase of senescence exactly like the higher animals—thus completely contradicting Weismann’s assertion that death is a late acquisition of living organisms.
own metabolism which had fatal results for the particular kind of animalcule. For the same animalculae which inevitably perished if they were crowded together in their own nutrient fluid flourished in a solution which was over-saturated with the waste products of a distantly related species. An infusorian, therefore, if it is left to itself, dies a natural death owing to its incomplete voidance of the products of its own metabolism. (It may be that the same incapacity is the ultimate cause of the death of all higher animals as well.) Secondly: It is probable nevertheless that infusoria die a natural death as a result of their own vital processes. For the contradiction between Woodruff’s findings and the others is due to his having provided each generation with fresh nutrient fluid. If he omitted to do so, he observed the same signs of senescence as the other experimenters. He concluded that the animalculae were injured by the products of metabolism which they extruded into the surrounding fluid. He was then able to prove conclusively that it was only the products of its
Thus our expectation that biology would flatly contradict the recognition of death instincts has not been fulfilled. We are at liberty to continue concerning ourselves with their possibility, if we have other reasons for doing so. The striking similarity between Weismann’s distinction of soma and germ-plasm and our separation of the death instincts from the life instincts persists and retains its significance.We may pause for a moment over this preeminently dualistic view of instinctual life. According to E. Hering’s theory, two kinds of processes are constantly at work in living substance, operating in contrary directions,...
At this point the question may well arise in our minds whether any object whatever is served by trying to solve the problem of natural death from a study of the protozoa. The primitive organization of these creatures may conceal from our eyes important conditions which, though in fact present in them too, only become visible
in higher animals where they are able to find morphological expression. And if we abandon the morphological point of view and adopt the dynamic one, it becomes a matter of complete indifference to us whether natural death can be shown to occur in protozoa or not. The substance which is later recognized as being immortal has not yet become separated in them from the mortal one. The instinctual forces which seek to conduct life into death may also be operating in protozoa from the first, and yet their effects may be so completely concealed by the life-preserving forces that it may be very hard to find any direct evidence of their presence. We have seen, moreover, that the observations made by biologists allow us to assume that internal processes of this kind leading to death do occur also in protista. But even if protista turned out to be immortal in Weismann’s sense, his assertion that death is a late acquisition would apply only to its manifest
phenomena and would not make impossible the assumption of processes tending