THE NERVOUS SYSTEM ' 5 



gation of cells, such as skin cells, bone 

 cells, muscle cells, gland cells, and so forth, 

 arranged so as to constitute its organs. The 

 nervous system in the higher animals, like their 

 other sets of organs, is also composed of cells, 

 but nerve cells are very unlike other cells. 

 Although the analysis of the body from this 

 standpoint was undertaken three quarters of a 

 century ago, the unique character of the nerve 

 cell was only first fully grasped by Waldeyer 

 in 1891. Each nerve cell, or neurone, as Wal- 

 deyer designated it, consists of a nucleated cell 

 body, the so-called ganglion cell of the older 

 neurologists, from which extremely attenuated 

 processes, the nerve fibers, reach out to the 

 most distant parts of the animal. These proc- 

 esses, which for a long time were not recog- 

 nized as belonging to the nerve cell, are the 

 most characteristic parts of its structure. Ex- 

 tending as they do in the larger animals for even 

 some meters from their cell bodies, they afford 

 an example of the special extension of a single 

 cell such as is seen in no other histological 

 element. In man, for instance, neurone proc- 

 esses are known to begin in the middle of the 

 back and extend to the toes, a distance well 

 over a meter. Although the human body con- 



