PROPERTIES OF THE NERVE CELL. 129 



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 the chemical changes in its substance. 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 fatigue readily. The nerve 

 centers show fatigue as the result of continuous activity, as is evident 

 from our personal experience in prolonged intellectual or emo- 

 tional activity and as is implied in the necessity of sleep for re- 



Fig. 59. 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. 



cuperation and 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. 45) that the well- 

 known fatigue of the neuromuscular apparatus possibly 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. But we have no very direct 

 proof that this property is possessed universally by the nerve cells 

 nor any indication of the probable differences in this regard shown 

 by nerve cells in different parts of the central nervous system. 

 It seems probable that under normal conditions that is, under 

 the influence of what we may call minimal stimuli some portions 

 of the nerve centers remain in more or less constant activity during 



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