664 



PHYSIOLOGY. 



The above are the excitants of the sensory and motor nerve. 

 However, it must not be forgotten that in the normal being it is not 

 these forces which come into play to stimulate to activity the motor 







Fig. 266. Method of Studying Physiological Electrotonus. 

 ( LAHOUSSE. ) 



P, Five Daniell cells. R, Rheocord. D, Pohl's commutator to make either 

 ascending or descending current, e, e, Unpolarizable electrodes. N, Motor 

 nerves. M, Muscle, to be attached to a myographic lever. C, Induction current 

 which can be sent to A or B by the commutator W with the cross bars removed. 



Supposing we have a descending constant current passing through the nerve, 

 then an induced current will not make the muscle contract when it is applied 

 at A in the extra polar anelectrotonic region of the nerve. Before the passage 

 of the constant current the induction current of the same strength as before 

 caused a minimal contraction. On the contrary, an induced current when sent 

 to B, that is, in the katelectrotonic region of the nerve, causes a maximal con- 

 traction instead of the minimal contraction previous to the passage of the con- 

 stant current. 





