iv GENEEAL PHYSIOLOGY OF NERVOUS SYSTEM 251 



with an ascending polarising current, and depends upon excitation 

 at the former anode, as is also proved by the fact that division of 

 the nerve in the intrapolar tract during tetanus is not enough to 

 abolish it. 



The closing contraction of a polarising current may also, 

 under special conditions of exaggerated local excitability of 

 nerve, be transformed into a closure tetanus when the direction 

 of the current is descending. This phenomenon evidently 

 depends on persistence of kathodal excitation. 



Waller and De Watteville (1882) devoted much time to 

 verifying Pfliiger's law for man. The study of the polar 

 phenomena on man presents special complications, owing to the 

 presence of the tissues by which the nerve is surrounded. In the 

 frog's nerve the polarising current is applied directly, the poles 

 being set far enough apart to keep the kathodal and anodal 



r+S 



PIG. 161. Diagrams to show the spread, or concentration, of a polarising current that enters or 

 leaves the skin by a series of points above a nerve, over which the anode (A) or kathode (/<) of 

 a battery is applied. (Waller.) 



influences distinct. In man, on the contrary, the current must 

 be sent in through the skin, and before reaching the nerve it has 

 to pass through all the tissues which lie above it. Peripolar 

 regions are thus formed more or less extensively round the poles, 

 which make it futile to apply the two electrodes to the same 

 nerve, since the kathodal and anodal regions cannot be kept 

 distinct, nor can the direction of current strictly speaking be 

 called ascending or descending. It is, therefore, necessary to 

 employ Chauveau's method of unipolar stimulation, in which 

 one electrode is placed upon the skin above the nerve and the 

 other applied to a distant point of the body. When the anode 

 is applied to the nerve, the current enters by a series of points, 

 over a considerable length of the nerve, and leaves by another no 

 less extensive series of points (Fig. 161 A). The former constitute 

 the anodal polar region, the latter the kathodal peripolar region. 

 When, on the contrary, the kathode is applied to the skin over 

 the nerve, the opposite phenomena occur (Fig. 161 K). The 

 current which is widely diffused in the body is thus concentrated 

 at the points of exit from the body which form the kathode. Its 



