NERVE 



597 



tivity here, too, begins to diminish, until at last the anode is 

 also blocked ; but this is to be looked upon as merely an 

 extension of the defect of conductivity which has been creep- 

 ing along the intrapolar area from the kathode. After 

 the opening of the current, the relation between kathodic 

 and anodic conductivity is reversed, for now the post- 

 kathodic region conducts the nerve-impulse relatively better 

 than the post-anodic. 



FIG. 184. KATELECTROTONUS. 

 Weak tetanus of muscle (the right-hand 

 elevation), greatly intensified in katelec- 

 Irotonus of the motor nerve (the left-hand 

 elevation). 



FIG. 185. ANELECTROTONUS. 



Strong tetanus of muscle (left-hand 

 elevation), lessened in strength by an- 

 electrotonic condition of the motor nerve 

 (right-hand elevation). 



The above facts serve to explain the manner in which 

 the effects of stimulation of a nerve with the constant 

 current vary with the strength and direction of the stream. 

 These effects, so far as the contraction of the muscles 

 supplied by the nerve is concerned, have been formulated 

 in what has been somewhat loosely termed the law of con- 

 traction. In this formula the direction of the current in the 

 nerve is commonly distinguished by a thoroughly bad but 

 now ingrained phraseology, as ascending when the anode is 

 next the muscle, and descending when the kathode is next 



the muscle. 



Law of Contraction, 



Here M means ' make,' B, ' break,' of the current ; C means 'contraction follows.' 



