364 INHIBITION BY EXCITATION. 



the nature of the changes effected by the current is in fact to be 

 attained only by the combination of both methods of investigation. 

 In this connection it should be distinctly noticed, that a direct proof 

 of the presence of an antagonistic process following or preceding 

 excitation, and indicated by corresponding changes in form of the 

 muscle, is obviously only possible in the course of a persistent 

 contraction of the muscle which has already come into existence ; 

 without this, it could only be inferred in a most indirect way, 

 by observations of the changes of excitability. On the other 

 hand, the investigation of secondary electromotive phenomena serves 

 to demonstrate with complete certainty, the existence of polar 

 antagonistic processes in muscle when in a state of repose. 



Positive anodic polarisation coupled with negative kathodic on 

 the one hand, positive kathodic polarisation coupled with negative 

 anodic on the other, owe their origin to polar antagonistic 

 alterations of the muscular substance : one set of these alterations 

 produces negativity and the other set produces positivity of the 

 affected spots. The closing and opening contraction represent the 

 mechanical excitatory effect of the former, and the opening and 

 closing relaxation the inhibitory effect of the latter (when a tonic 

 condition of contraction is present). Both contraction and relaxa- 

 tion are no doubt conditioned by chemical changes of the excitable 

 muscle substance, evoked by the influence of the current, though 

 nothing definite can be said at present as to the nature of these 

 changes. But while the changes which take place on closing the 

 current are directly produced by it, the effects of opening it are 

 essentially reaction phenomena, which have their origin in the 

 altered muscular substance ; a statement which applies not only to 

 the anodic opening excitation, but also to the kathodic opening 

 inhibition. 



