422 SCIENTIFIC THOUGHT. 



literature, to have placed it at the entrance of his text- 

 book of physiology, and thus to have given the student 

 a somewhat more detailed description of the elementary 

 functions of living matter than was afforded by the older 

 term "vortex," employed by Cuvier. 

 33. These merits of Schwann, which attach more to the 



"Metabol- 

 ism." conception of " metabolism " than to that of the cell, 



are not reduced by our having to state that the latter 

 conception has been entirely changed since his time. 

 The cell of to-day is not the cell as Schwann conceived 

 it. Of the pretty clearly defined structure or organ- 

 isation of that biologist, with its wall (membrane), 

 its kernel (nucleus), and its fluid contents (cell sap), 

 nothing has remained but the cell contents, termed 

 protoplasm by von Mohl ; and the living process can no 

 longer be considered as the function of a well-defined 

 organ or machine. It is rather the fundamental property 

 of an almost homogeneous substance, the mass of proto- 

 plasm, in which the kernel is the only recognisable 

 differentiated portion. The immediate effect of this de- 

 structive analysis of the early conception of the cell was 

 to destroy the idea that the living processes carried on in 

 any special cell or organ are a result of its organisation, 

 as the function of an apparatus is dependent upon the 

 arrangement and combination of its parts. It has pro- 

 moted the view that for our understanding at least 

 the first thing to learn is the nature of the processes 

 themselves. We have to look upon the visible structure 

 of special cells and organs merely as " mechanical con- 

 trivances, serving only to modify in special ways the 

 results of the exercise of these fundamental activities, 



