Idioplasm

IDIOPLASM, a term introduced into science by the botanist Naegeli, denoting a substance contained in equal amounts in both sexual elements (in the egg and the spermatozoon) and which is the carrier of hereditary properties inherent to a given organism. This term later began to be used generally to denote the concept of "hereditary plasma" (alongside the term "germ plasm" of Weismann) in contrast to non-hereditary plasma ("stereoplasm" of Naegeli and "somatoplasm" of Weismann), although Naegeli's conception of the structure of idioplasm is completely different from the conception of "germ plasm" held by Weismann. According to Naegeli, idioplasm is complexly constructed. It consists of bundles of "micelles"—units of living matter, which in turn are formed by the combination of molecules. The bundles form a network with a specific dynamic relationship between the rows of the network. The more complex the organization, the more complex the structure of the idioplasm and the interrelationships between the rows of micelles. Thus, if in appearance the germ cells of different animals are similar to one another, then in the internal structure of the idioplasm they are sharply distinct. By this, Naegeli explains the difference between the organisms originating from them. Idioplasm, according to Naegeli, is present not only in eggs and spermatozoa, but also in all cells of the body. The bundles, forming a network, permeate the entire organism, passing from cell to cell. External influences, by changing the organism, cannot but reflect upon the idioplasm, and since the idioplasm of any cells is in connection with others, these changes must be transmitted to the germ cells as well. Thus, according to Naegeli, acquired traits are inherited. On the other hand, the presence of idioplasm in all cells also explains the phenomena of asexual reproduction. Modern genetics replaces the outdated and, to a significant degree, abstract concept of Naegeli's idioplasm with the doctrine of chromosomes as carriers of hereditary properties. Since the chromosomes contained in the nuclei of all body cells turn out, as a rule, to be identical to the chromosomes of the fertilized egg, Naegeli's doctrine regarding the distribution of idioplasm in all parts of the organism retains its significance even at the present time, although it takes on a different concrete meaning. Naegeli's doctrine of the "micellar" structure of idioplasm has received, in recent years, an especially deep development both in biology and in physical chemistry. By "micelles" one now understands colloidal particles having the appearance of minute crystals. There are grounds to think that at the foundation of chromosome structure lie, indeed, giant micelles—bundles of long chromosomal protein molecules, the individual linearly arranged links of which (radicals of the molecules) correspond to specific genes.