THE REGULATING MECHANISM 179 



the cytoplasm (protoplasm of the cell) and 

 in the nucleus, there are fine fibres and 

 networks, while chromatin is abundant in 

 the nucleus. In the protoplasm of the nerve 

 cell we find numerous granules. These are 

 more abundant after the cell has rested for a 

 while, and they seem to be used up during the 

 period when the cell is active. The exhausted 

 cell, during the next period of rest, again 

 becomes crowded with granules as it revives. 

 Thus it behaves like a secreting cell. Pro- 

 cesses, or as they have been called, poles, issue 

 from the cell. These are sometimes few in 

 number, but in many cases each cell may 

 have four, five, or six processes. All of these 

 processes, except one, divide and subdivide 

 so as to form smaller and smaller processes, 

 like a branch of a tree dividing until we 

 reach the ultimate twigs. The branch of 

 a tree seen against a winter sky is a picture 

 of the arrangement. The remaining process 

 is the beginning of the axis of a nerve fibre, 

 around which the white substance is developed 

 at a later period. The ultimate unit of the 

 nervous system therefore is now designated 



