THEORY OF THE CELLS. 193
it cannot continue long in existence after being separated from its swarm. The manifestation of the power which resides in the cell depends upon conditions to which it is subject only when in connexion with the whole (organism).
The question, then, as to the fundamental power of organized bodies resolves itself into that of the fundamental powers
of the individual cells. We must now consider the general
phenomena attending the formation of cells, in order to discover what powers may be presumed to exist in the cells to
explain them. These phenomena may be arranged in two
natural groups: first, those which relate to the combination of
the molecules to form a cell, and which may be denominated the
plastic phenomena of the cells; secondly, those which result
from chemical changes either in the component particles of the
cell itself, or in the surrounding cytoblastema, and which may
be called metabolic phenomena ((
Greek characters), implying that
which is liable to occasion or to suffer change).
The general plastic appearances in the cells are, as we have seen, the following: at first a minute corpuscle is formed, (the nucleolus); a layer of substance (the nucleus) is then precipitated around it, which becomes more thickened and ex- panded by the continual deposition of fresh molecules between those already present. Deposition goes on more vigorously at the outer part of this layer than at the inner. Frequently the entire layer, or in other instances the outer part of it only, becomes condensed to a membrane, which may continue to take up new molecules in such a manner that it increases more rapidly in superficial extent than in thickness, and thus an intervening cavity is necessarily formed between it and the nucleolus. A second layer (cell) is next precipitated around this first, im which precisely the same phenomena are repeated, with merely the difference that in this case the processes, especially the growth of the layer, and the formation of the space intervening between it and the first layer (the cell-cavity), go on more rapidly and more completely. Such were the phenomena in the formation of most cells; im some, however, there appeared to be only a single layer formed, while in others (those especially in which the nucleolus was hollow) there were three. The other varieties in the development of the elementary parts were (as we saw) reduced to these—that if two neighbouring
