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 orga- 

 nized 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 dis- 

 cover 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 (to ^Eraj3oA(/o)i', 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 pre- 

 cipitated 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, in which precisely the same phenomena arc repeated, 

 with merely the difference that in this case the processes, espe- 

 cially 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 pheno- 

 mena in the formation of most cells; in 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 



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