208 ELECTRO-PHYSIOLOGY CHAP. 



certain range of strength of current the same is undoubtedly 

 true of indirect excitation of the muscle also. On the other 

 hand, we know that stronger induction currents, acting upon 

 curarised muscle, produce changes at the point of entrance 

 (anode) also, which, if not invariably expressed in visible changes 

 of form, cannot be interpreted otherwise than as the consequences 

 of a break excitation. To this category belong more especially 

 the positive anodic polarisation currents which appear as the 

 after-effect of excitation by single induction shocks. In nerve, 

 as in muscle, it may be shown by any of the above methods 

 for proving the polar action of the constant current, that 

 both impacts of current and single induction shocks excite within 

 a certain range of intensity at the kathode only, i.e. that 

 the twitches thus discharged must be defined as closure 

 twitches. At Tick's suggestion, Lamansky (50) undertook ex- 

 periments to determine (by v. Bezold's method, as applied to the 

 constant current) the difference of latent period, with ascending 

 and descending induction currents, at the seat of stimulation. 

 The latent period was found longer for the ascending than for 

 the descending direction of current. V. Vintschgau (51) next 

 ascertained that with maximal, or nearly maximal, induction 

 currents this difference of latent period is considerably greater 

 than on exciting with weak currents. He is inclined to refer this 

 to differences of spatial extension, and relative intensity of the 

 electrotonic changes in the nerve produced by current. 



The polar action of induced currents is also manifested in 

 the different effects of excitation, according to the direction of 

 current, in medullated nerve, excitability being depressed in 

 the region of the central electrode (Biedermann, 30). The 

 facts relating to this point were already known to Hai'less, who 

 found, on applying ammonia to a portion of tire intrapolar 

 region of the nerve, "that even the intrinsically stronger break 

 shock had no effect after the action of ammonia, if applied to 

 the nerve, at its former strength, in the ascending direction," 

 while the make shock sent through the nerve in the opposite 

 direction is effective. With uniform distance of coil there is 

 never excitation when, with ascending direction of current, the 

 kathodic section ?.- is rendered inexcitable by ammonia or any 

 similar reagent, i.e. the excitatory process can only proceed from 

 the kathode. We learn from the same fact that kathodic 



