All organic bodies, except the very lowest, consist of cells, small granules of albumen which are only visible when considerably magnified, with a nucleus inside. As a rule the cells also develop an outer membrane and the contents are then more or less fluid. The lowest cellular bodies consist of a single cell; the immense majority of organic beings are multi-cellular, congruous complexes of many cells which in lower organisms remain of a homogeneous type, but in higher organisms develop more and more varied forms, groupings and functions. In the human body, for example, bones, muscles, nerves, tendons, ligaments, cartilages, skin, in a word, all tissues are either composed of cells or originated from them. But in all organic cellular structure, from the amoeba, which is a simple and most of the time skinless albuminous particle with a nucleus inside, up to man, and from the tiniest unicellular desmids up to the most highly developed plant, the manner in which the cells multiply is the same: by fission. The cell nucleus first becomes constricted in the middle, the constriction separating the two halves of the nucleus gets more and more pronounced, and at last they separate from each other and form two cell nuclei. The same process takes place in the cell itself; each of the two nuclei becomes the centre of an accumulation of cellular substance, linked to the other by a strip which is steadily growing narrower, until at last the two separate from each other and continue to exist as independent cells. Through such repeated cell fission the whole animal is gradually developed in full out of the embryonal vesicle of the animal egg, after it has been fertilised, and the replacement of used-up tissues is effected in the same way in the adult animal. To call such a process composition, and to say that to describe it as development is pure imagination {D. Ph. 126}, certainly indicates a person who however difficult this may be to believe at the present day knows absolutely nothing of this process; here it is precisely and exclusively development that is going on, and indeed development in the most literal sense, and composition has absolutely nothing to do with it! Later on we shall have something more to say about what Herr D hring understands in general by life. In particular his conception of life is as follows: In undertaking, therefore, to define real life in the narrower and stricter sense, Herr D hring gives us four characteristics of life which totally contradict one another, one of which condemns to eternal death not only the whole vegetable kingdom but also about half the animal kingdom. Really no one can say that he misled us when he promised us from the ground up original conclusions and views {525}! Another passage runs: Herr D hring further tells us: In the second place, we hear for the first time here of transitional structures, externally undecided or undecidable forms (fine gibberish!) between plant and animal. That these intermediate forms exist; that there are organisms of which we cannot say flatly whether they are plants or animals; that therefore we are wholly unable to draw a sharp dividing line between plant and animal precisely this fact makes it a logical necessity for Herr D hring to establish a criterion of differentiation which in the same breath he admits will not hold water! But we have absolutely no need to go back to the doubtful territory between plants and animals; are the sensitive plants which at the slightest touch fold their leaves or close their flowers, are the insect-eating plants devoid of the slightest trace of sensation and do they even lack any capacity for it? This cannot be maintained even by Herr D hring without unscientific semi-poetry {D. Ph. 56, 142}. In the third place, it is once again a free creation and imagination on Herr D hring's part when he asserts that sensation is physiologically bound up with the presence of some kind of nerve apparatus, however simple. Not only all primitive animals, but also the zoophytes, or at any rate the great majority of them, show no trace of a nerve apparatus. It is only from the worms on that such an apparatus is regularly found, and Herr D hring is the first person to make the assertion that those animals have no sensation because they have no nerves. Sensation is not necessarily associated with nerves, but undoubtedly with certain albuminous bodies which up to now have not been more precisely determined. At any rate, Herr D hring's biological knowledge is sufficiently characterised by the question which he does not hesitate to put to Darwin: Of life in general Herr D hring is only able to tell us: That organic exchange of matter is the most general and most characteristic phenomenon of life has been said times out of number during the last thirty years by physiological chemists and chemical physiologists, and it is here merely translated by Herr D hring into his own elegant and clear language. But to define life as organic metabolism is to define life as life; for organic exchange of matter or metabolism with plastically creating schematisation is in fact a phrase which itself needs explanation through life, explanation through the distinction between the organic and the inorganic, that is, that which lives and that which does not live. This explanation therefore does not get us any further. Exchange of matter as such takes place even without life. There is a whole series of processes in chemistry which, given an adequate supply of raw material, constantly reproduce their own conditions, and do so in such a way that a definite body is the carrier of the process. This is the case in the manufacture of sulphuric acid by the burning of sulphur. In this process sulphur dioxide, SO2, is produced, and when steam and nitric acid are added, the sulphur dioxide absorbs hydrogen and oxygen and is converted into sulphuric acid, H2SO4. The nitric acid gives off oxygen and is reduced to nitric oxide; this nitric oxide immediately absorbs new oxygen from the air and is transformed into the higher oxides of nitrogen, but only to transfer this oxygen immediately to sulphur dioxide and to go through the same process again; so that theoretically an infinitely small quantity of nitric acid should suffice to change an unlimited quantity of sulphur dioxide, oxygen and water into sulphuric acid. Exchange of matter also takes place in the passage of fluids through dead organic and even inorganic membranes, as in Traube's artificial cells.  Here too it is clear that we cannot get any further by means of exchange of matter; for the peculiar exchange of matter which is to explain life needs itself to be explained through life. We must therefore try some other way. Life is the mode of existence of albuminous bodies, and this mode of existence essentially consists in the constant self-renewal of the chemical constituents of these bodies. The term albuminous body is used here in the sense in which it is employed in modern chemistry, which includes under this name all bodies constituted similarly to ordinary white of egg, otherwise also known as protein substances. The name is an unhappy one, because ordinary white of egg plays the most lifeless and passive role of all the substances related to it, since, together with the yolk, it is merely food for the developing embryo. But while so little is yet known of the chemical composition of albuminous bodies, this name is better than any other because it is more general. Wherever we find life we find it associated with an albuminous body, and wherever we find an albuminous body not in process of dissolution, there also without exception we find phenomena of life. Undoubtedly, the presence of other chemical combinations is also necessary in a living body in order to induce particular differentiations of these phenomena of life; but they are not requisite for naked life, except in so far as they enter the body as food and are transformed into albumen. The lowest living beings known to us are in fact nothing but simple particles of albumen, and they already exhibit all the essential phenomena of life. But what are these universal phenomena of life which are equally present among all living organisms? Above all the fact that an albuminous body absorbs other appropriate substances from its environment and assimilates them, while other, older parts of the body disintegrate and are excreted. Other non-living, bodies also change, disintegrate or enter into combinations in the natural course of events; but in doing this they cease to be what they were. A weather-worn rock is no longer a rock, metal which oxidises turns into rust. But what with non-living bodies is the cause of destruction, with albumen is the fundamental condition of existence. From the moment when this uninterrupted metamorphosis of its constituents, this constant alternation of nutrition and excretion, no longer takes place in an albuminous body, the albuminous body itself comes to an end, it decomposes, that is, dies. Life, the mode of existence of an albuminous body, therefore consists primarily in the fact that every moment it is itself and at the same time something else; and this does not take place as the result of a process to which it is subjected from without, as is the way in which this can occur also in the case of inanimate bodies. On the contrary, life, the metabolism which takes place through nutrition and excretion, is a self-implementing process which is inherent in, native to, its bearer, albumen, without which the latter cannot exist. And hence it follows that if chemistry ever succeeds in producing albumen artificially, this albumen must show the phenomena of life, however weak these may be. It is certainly open to question whether chemistry will at the same time also discover the right food for this albumen. From the metabolism which takes place through nutrition and excretion, as the essential function of albumen, and from its peculiar plasticity proceed also all the other most simple factors of life: irritability, which is already included in the mutual interaction between the albumen and its food; contractibility, which is shown, even at a very low stage, in the consumption of food; the possibility of growth, which in the lowest forms includes propagation by fission; internal movement, without which neither the consumption nor the assimilation of food is possible. Our definition of life is naturally very inadequate, inasmuch as, far from including all the phenomena of life, it has to be limited to those which are the most common and the simplest. From a scientific standpoint all definitions are of little value. In order to gain an exhaustive knowledge of what life is, we should have to go through all the forms in which it appears, from the lowest to the highest. But for ordinary usage such definitions are very convenient and in places cannot well be dispensed with; moreover, they can do no harm, provided their inevitable deficiencies are not forgotten. But back to Herr D hring. When things are faring badly with him in the sphere of earthly biology, he knows where to find consolation; he takes refuge in his starry heaven.
1877: Anti-Duhring - VIII. The Organic World, Conclusion