180 



MUSCLE AND NERVE 



may be accepted then that the rise of irritability of the nerve 

 at the kathode when the stimulating current is closed, and at 

 the anode when the current is opened, indicate the generation 

 of nerve impulses. 



Closing excitations arise at the kathode, while opening excita- 

 tions arise at the anode. Moreover, during electrotonus the 

 conductivity is increased slightly at the kathode and decreased 

 greatly at the anode. When the current ceases to flow, the 

 conductivity is greatly lowered at the kathode and is raised 



FIG. 10 



Muscle-nerve preparations: With the nerve exposed in A to a descend- 

 ing and in B to an ascending constant current. (Foster.) In each, a is the 

 anode, k the kathode of the constant current; x represents the spot where 

 the induction shocks, used to test the irritability of the nerve, are sent in. 



at the anode. Reflection will make clear that with an ascend- 

 ing current the closing contraction fails to appear because the 

 conductivity is so lowered at the region of the anode that the 

 excitation which arises at the kathode cannot reach the muscle. 

 With a descending current the opening contraction fails to 

 appear because the conductivity is so lowered at the kathode 

 that the nerve impulse generated at the anode cannot reach 

 the muscle. The impulses that originate at the electrode 

 nearest the muscle are the only ones that are effective. At 



