PROPERTIES OF THE NERVE CELL. 135 



the existence of an extracellular nervous network. Most recent 

 histologists agree in the belief that there is a delicate network 

 surrounding the cells and their protoplasmic processes. This 

 pericellular net or Golgi's net is claimed by some to be a ner- 

 vous structure connecting with the neurofibrils inside the cell 

 and forming not only a bond of union between the neurons, but 

 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: 

 fiz, 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 



