GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 53 



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. 28) — four possible 

 cases may arise, namely : 



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



Fig. 28.— Diagram showing physical and physiological anodes and kathodes: A, the physical anode, 

 or positive electrode ; K, the physical kathode, or negative electrode ; a, a, o, physiological anodes ; k, k, k, 

 physiological kathodes. 



the physiological kathode, the place where the current leaves the nerve, 

 beneath the physical anode (the positive pole). 



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

 the physiological anode, where the current enters the nerve, beneath the 

 physical anode (the positive pole). 



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

 the physiological kathode, where the current leaves the nerve, beneath the 

 physical kathode (the negative pole). 



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

 the physiological anode, where the current enters the nerve, beneath the 

 physical kathode (the negative pole). 



For convenience these four cases are represented by the abbreviations ACC, 

 AOC, KCC, and KOC. 



Since the irritation process developed at a physiological kathode In- 

 closing a current, is, other things being equal, stronger than that developed 

 at a physiological anode by opening the current, we should expect that the 

 two closing contractions, KCC and ACC, would be stronger than the two 

 opening contractions, KOC and AOC. This is the case, and as the current is 

 more dense in the region of the physiological kathode, beneath the physical 

 kathode, than at the physiological kathode, beneath the physical anode, KCC 

 is stronger than ACC. 



Of the two opening contractions, AOC is stronger than KOC because 

 of the greater density of the current in the region of the physiological anode, 



