586 COMPARATIVE ELECTRO-PHYSIOLOGY 



medical application of electricity, since the failure to recog- 

 nise that reversal of effects which is to be expected under a 

 feeble E.M.F. might here lead to a result the very opposite 

 of that intended. 



It has thus been shown that Pfliiger's Law of the Polar 

 Variation of Excitability is not universally applicable. It 

 fails when the E.M.F. is either too high or too low, the 

 effects observed under these circumstances being precisely 

 the opposite of those enunciated by Pfliiger. Under a low 

 E.M.F. then, it is the anode which enhances the excitability, 

 depression being induced by the kathode. This important 

 fact, and the further fact that with low E.M F. conductivity 

 is increased in the direction of the rising electrical potential, 

 and depressed in that of the falling potential, will be found 

 to explain all the varied electrotonic phenomena of nerves 

 described in the previous chapter. 



