IKRITABILITY AND CONDUCTIVITY 177 



ductorium in action (binding posts 2 and 3), 

 and stimulate the nerve with weak induction 

 currents. 



The leg will be flexed. 



Use stronger induction shocks. 



As the intensity increases extension as well as 

 flexion is seen. A still further increase causes 

 extension only. 



The gradations of intensity necessary to show 

 these results are sometimes difficult to secure. 

 The phenomenon of relative excitability is not lim- 

 ited to the case just cited. Weak stimulation of 

 the vagus causes adduction of the vocal bands ; 

 stronger stimulation, abduction. Weak stimula- 

 tion causes opening of the claw of the lobster, while 

 stronger stimulation of the same nerve causes clo- 

 sure. Weak stimulation of the hypoglossal nerve 

 in the dog and rabbit causes the tongue to be thrust 

 from the mouth, while with strong stimulation the 

 tongue is withdrawn into the mouth. It must not 

 be forgotten that the anatomical nerves stimulated 

 in these experiments are composed of many axis 

 cylinders, each of which is a physiological nerve. 

 That they should vary in excitability is to be 

 expected. 



A second and probably better explanation of 

 the Ritter-Rollett phenomena is found in the dif- 

 ference in structure of the flexors and extensors. 



12 



