168 SOME RECENT DEVELOPMENTS 



of modern physiology, lead us to regard the proto- 

 plasm of which the cell-bodies consist, in rather a 

 different manner, and from a new standpoint. 

 Protoplasm may, to adopt the simile given above, 

 be regarded as the topmost point, the crest of the 

 physiological wave, consisting of matter in a con- 

 dition of extremely unstable equilibrium, and varying 

 greatly in structure and in composition in different 

 cells, or even in the same cell at different times. 

 The essential character however of protoplasm is 

 that it is alive ; and although we are unable to 

 formulate precisely what we mean by life, there is 

 at any rate one very definite idea which we asso- 

 ciate with living matter and with it alone, and this 

 is the power which living matter possesses of 

 building itself up, renewing itself from the dead 

 matter which is taken in as food. To define 

 protoplasm is difficult, perhaps impossible, but the 

 one essential thing to remember about it is that 

 it is alive. To speak of dead protoplasm is a 

 misnomer. 



Starting from this new position attempts were 

 soon made to determine whether the protoplasm of 

 which cell-bodies consist possesses any structure, 

 and more especially whether there are any structural 

 changes which occur normally in cell-bodies, in 

 association with vital acts. It was soon found that 

 the cell-body or cell-substance is not necessarily 

 homogeneous. In many, perhaps in most cases, a 

 more or less pronounced reticular structure is 

 present ; the protoplasm consisting of a network of 

 firmer strands, the meshes of which are filled with 



