GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 63 



enters the nerve, and a physiological kathode at every point where it leaves the 

 nerve; therefore there is a physiological anode and kathode, or groups of 

 anodes and kathodes, for the part of the nerve beneath the positive electrode, 

 and another physiological anode and kathode, or collection of anodes and 

 kathodes, for the part of the nerve beneath the negative electrode. 



To understand the effect upon the normal human nerve of opening and 

 closing the battery current, it is necessary to bear in mind three facts, viz. : 



1. At the moment that a battery current is closed, an irritating process is 

 developed at the physiological kathode, and when it is opened, at the physio- 

 logical anode. 



2. The irritating process developed at the kathode on the closing of the 

 current is stronger than that developed at the anode on the opening of the 

 current. 



3. The effect of the current is greatest where its density is greatest. 



The amount of the irritation process developed in a motor nerve is esti- 

 mated from the amount of the contraction of the muscle. The contraction 

 which results from closing the current, the closing contraction as it is called, 

 represents the irritating change which occurs at the physiological kathode, while 

 the contraction which results from opening the current, the opening contrac- 

 tion, represents the irritating change developed at the physiological anode. 

 Since there are physiological anodes and kathodes under each of the two elec- 

 trodes the physical anode and physical kathode (see Fig. 26) four possible 

 cases may arise, namely: 



1. Anodic closing contraction i. e. the effect of the change developed at 

 the physiological kathode, beneath the physical anode (the positive pole). 



2. Anodic opening contraction i. e. the effect of the change developed at 

 the physiological anode, beneath the physical anode (the positive pole). 



FIG. 26.-Diagram showing physical and physiological anodes and kathodes: A, the physical anode, 

 or positive electrode ; K, the physical kathode, or negative electrode ; a, a, a, physic 

 physiological kathodes. 



3. Kathodic closing contraction i. e. the effect of the change developed at 

 the physiological kathode, beneath the physical kathode (the negative pole). 



4. Kathodic opening contraction i. e. the effect of the change developed i 

 the physiological anode, beneath the physical kathode (the negative pole). 



