WEISMANNISM, the essential teaching of August Weismann (q.v.), sometimes referred to as 'Nco-Darwinism.' Interest and contro versy have gathered mainly round his answer to the question, 'How is it that a single cell of the body can contain within itself all the hered itary tendencies of the whole organism?' In all theories of heredity (q.v.) biologists have assumed that characters acquired by the indi vidual are transmitted to offspring. This Weis mann denies and while biologists have con cerned themselves with speculation as to the mode by which such transmissions are effected, he challenges them to prove that they are ef fected at all. The burden of proof is thus thrown upon his opponents, whose assumptions must give way to experimental evidence, which alone can determine, and that only after pro tracted record of cases, whether individually acquired characters are transmitted or not. Death, he contends, is not a primary attribute of living matter; the protozoans, or one-celled organisms, being immortal in so far that they do not die naturally. The protozoan, a micro scopic jelly-like, apparently—not really — structureless with no seeming unlike ness of parts, multiplies by division. Each half becomes a complete individual and grows in like manner as the whole to which it belonged, till it also divides and so on with the multi plication of protozoans ad infinition. It cannot be said of either half that one is parent and the other offspring, for both arc of the same age, and only, in a limited sense, as the subdivisions into separate individuals are repeated, can we speak of succession of generations. In these processes there is nothing analogous to death. "There are,' Weismann says, 'no grounds for the assumption that the two halves of an arm- 14. are differently constituted internally, so that, alter a time, one of them will die while the Other continues to live. Observations show that %%Inn division is almost complete the proto plasm of Loth IR gins to circulate and for some time passes backward and forward be tween the two A complete mingling of the whole substance of the animal and a re suiting identity in the constitution of each half is thus brought about before the final separa tion? Consequently, there is unlimited per sistence of the individual; potential, although not absolute, immortality so long as life lasts on the earth.
While the one-celled organisms are thus im mortal, only the reproductive cells of the meta zoans, the many-celled, are immortal. How has this come about? Weismann accounts for it by the failure of certain protozoans to divide equally, whereby unlikeness of parts and differ ences of position of parts resulted. 'The first multicellular organisms were probably clusters of similar cells, hut these units soon lost the original homogeneity. As the result of mere relative position there arose division of labor, some of the cells were especially fitted to pro vide for the nutrition of the colony, while others undertook the work of reproduction.'
Clearly, those on the outside, being exposed to the direct and constant action of their sur roundings, would be the media of nutrition, and the builders-up of the cell-commonwealth. So the result of this cell-clustering would be that the cells fell into two classes, body cells and germ-cells. While the body cells were solely concerned with the nutrition of the organism. losing in this specialization of function the power of reproduction, that power became con centrated in the germ-cells, or, speaking more precisely, in the germ-plasm, which is located in the nucleus of the germ-cell. It is these germ-cells which are the immortal part of the metazoans. With increasing subdivision of function there has been increasing modification of the organism, but the two-fold classification of the somatic or body cells and the germ-cells has remained. The death of the body cells is involved in the ultimate failure to repair waste, because a worn-out tissue cannot forever re new itself, and because cell-division has its limits. In brief, death is the penalty paid for complexity of structure. As it is impossible for the germ-cell to be, as it were, an extract of the whole body, and for all the cells of the body to dispatch particles to therm-cells whence these derive their power of heredity (the fundamental idea of Darwin's theory of pangencsis, q.v.), the germ-cells, so far as their essential and characteristic substance is con cerned, are not derived from the body of the individual, but directly from the parent germ cell. Heredity, Weismann contends, is se cured by the transference from one generation to another of a substance with a definite chem ical and molecular constitution—in other words, by the 'continuity of the germ-plasm' This germ-plasm (which. Weismann's critics argue, runs perilously near a metaphysical con cept) is assumed to possess a highly complex but extremely stable structure, so stable 'that it absorbs nourishment and grows enormously without the least change in its complex molec ular structure.' Of this germ-plasm it is fur ther assumed that a small portion contained in the parent egg-cell is not used up in the con struction of the body of the offspring. but is reserved unchanged for the formation of the germ-cells of the follow mg generations, Only variations of the germ-plasm itself are inher ited, and it is upon these s ariations that natural selection operates. Variations arc due not to the influence of external condition nor to use r•r disuse of organs, but to sexual conjugation. 1 he process combines two groups of hereditary tendencies derived from the mingled germ of the male and female parents, result in those individual differences which form the material from which new species are pro dewed by the action of natural selection. Those differences multiply in geometrical ratio.