ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 433 



The cell body is usually much larger than that of other cells 

 in the body and is composed of granular protoplasm contain- 



Fig. 139. TWO CORPUSCLES OF PURKINJE FROM THE CEREBELLUM SHOWING THEIR IN- 

 VESTMENT WITH DENDRONS FROM CELLS OF THE OUTER GRAY MATTER. (After 



Ramon y Cajal.) 



a, axis-cylinder of corpuscle of Purkinje; &, network of dendrons. 



ing a relatively large nucleus. The cell body is really the 

 center of energy. We must imagine that here, in some 

 chemical way no doubt, energy is liberated which takes the 

 form of nervous activity. That such a breaking down of 

 the substance of nerve cells occurs when they are being 

 stimulated has been satisfactorily proved by experiments in 

 which nerve cells were subjected to long continued stimuli, 

 then examined with a microscope and compared with similar 

 cells not so stimulated. Such stimulated cells shrink in 

 volume, and in the plainest way indicate a severe loss of 

 their substance. The nucleus becomes much smaller. 

 Similar observations have been made on old nerve cells. 

 Here, too, the cell body becomes shrunken and the nucleus 

 practically disappears. Sometimes the cell body may dis- 

 appear altogether. 



The Nerves. 



While in a direct sense the term "nerve" might include 

 the dendrons it is more usually referred to the main fiber 

 leading from the cell to muscle, skin, sense-organ, or other 

 neurons. If such a nerve be examined a little distance 



28 



