MINUTE STRUCTURE OF THE NERVOUS TISSUES 27 



case with other white matter. It is always and exclusively 

 devoted to conduction. 



Gray matter is far more intricate in structure and its 

 physiology is less easily defined. It is massed for the most 

 part in the central nervous system. Small detached col- 

 lections, the ganglia, exist in other localities. An inspec- 

 tion of typical gray matter gives, first of all, the impression 

 of looseness of texture. Nerve-fibers are seen stray ing- 

 through the field, but never in a compact formation. 

 Attention is quickly attracted by the curious bodies which 



Fig. 4. A common type of nerve-cell (or perikaryon) giving rise 

 to the axon of a nerve-fiber. 



are most characteristic of this tissue, the so-called nerve- 

 cells. These vary widely in size, but probably have, on 

 the average, about the same dimensions as other cells. 

 In each one a conspicuous nucleus can be demonstrated. 

 But the most remarkable features of most nerve-cells 

 are the numerous processes which extend from them 

 (Fig. 4). 



It has been said that the cells in connective tissue some- 

 times show a highly irregular outline. The cells of the 

 nervous system, however, surpass all others in this re- 

 spect. Their protoplasm is spun out into prolongations 



