PROPERTIES OF THE NERVE CELL. 135 



possibly also an important intercellular nervous structure that 

 may play an important role in the functions of the nerve centers. 

 This view is represented schematically in Fig. 64. According to 

 others, this network around and outside the cells is a supporting 

 tissue simply that takes no part in the activity of the nerve units. 



Fig. 64. Bethe's schema to indicate the connections of the pericellular network; 

 Rz, A sensory cell in the posterior root ganglion ; the fibrils in the branch that runs to the 

 cord are indicated as connecting directly with the pericellular network of the motor cells, 

 Gz. 



General Physiology of the Nerve Cell. Modern physiologists 

 have considered the cell body of the neuron, including the den- 

 drites, as the source of the energy displayed by the nervous system, 

 and it has been assumed that this energy arises from chemical 

 changes in the nerve cell, as the energy liberated by the muscle 

 arises from or is dependent upon the chemical changes in its sub- 

 stance. It would follow from this standpoint that evidences of 

 chemical activity should be obtained from the cells and that these 

 elements should exhibit the phenomenon of fatigue. Regarding 

 this latter point, it is believed in physiology that the nerve' cells do 

 show fatigue. The nerve centers fatigue as the result of continuous 

 activity, as is evident from our personal experience in prolonged in- 

 tellectual or emotional activity and as is implied in the necessity of 

 sleep for recuperation and by the rapidity with which functional 

 activity is lost on withdrawal of the blood supply. Objectively, 

 also, it has been shown in the ergographic experiments (see p. 50) 

 that the well-known fatigue of the neuromuscular apparatus pos- 

 sibly affects the nerve centers as well as the muscle. Assuming that 

 the nerve cells are the effective agent in the nerve centers, such facts 

 indicate that they are susceptible to fatigue under what may be des- 

 ignated as the normal conditions of activity. But we have no very 



