THEORY OF THE CELLS. 199 



contents of the cell are different from those which are produced 

 by change in the external cytoblastema. What is the cause 

 of this difference, if the metamorphosing power of the cell- 

 membrane be limited to its immediate neighbourhood merel; 



Might we not much rather expect that converted substance 

 would be found without distinction on the inner as on the 

 outer surface of the cell-membrane? It might be said that the 

 cell-membrane converts the substance in contact with it without 

 distinction, and that the variety in the products of this con- 

 version depends only upon a difference between the convertible 

 substance contained in the cell and the external cytoblastema. 

 But the question then arises, as to how it happens that the 

 contents of the cell differ from the external cytoblastema. If 

 it be true that the cell-membrane, which at first closely sur- 

 rounds the nucleus, expands in the course of its growth, so as 

 to leave an interspace between it and the cell, and that the 

 contents of the cell consist of fluid which has entered this 

 space merely by imbibition, they cannot differ essentially from 

 the external cytoblastema. I think therefore that, in order to 

 explain the distinction between the cell-contents and the ex- 

 ternal cvtoblastema, we must ascribe to the cell-membrane not 

 only the power in general of chemically altering the substances 

 which it is either in contact with, or has imbibed, but also of 

 so separating them that certain substances appear on its inner, 

 and others on its outer surface. The secretion of substances 

 already present in the blood, as, for instance, of urea, by the 

 cells with which the urinary tubes are lined, cannot be ex- 

 plained without such a faculty of the cells. There is, however, 

 nothing so very hazardous in it, since it is a fact that different 

 substances are separated in the decompositions produced by 

 the galvanic pile. It might perhaps be conjectured from tl 

 peculiarity of the metabolic phenomena in the cells, that a 

 particular position of the axes of the atoms composing the cell- 

 membrane is essential for the production of these appearances. 

 Chemical changes occur, however, not only in the cytobla- 

 stema and the cell-contents, but also in the solid parts of 

 which the cells arc composed, particularly the cell-membrane. 

 Without wishing to assert that there is any intimate connexion 

 between the metabolic power of the cells and galvanism, I may 

 yet, for the sake of making the representation of the process 



