x ELECTROMOTIVE ACTION IN NERVE 289 



from the exciting tract, there will be absence of an- and katelectro- 

 tonic reaction, corresponding essentially with the electrotonic 

 manifestations throughout the entire extrapolar tract of non- 

 medullated molluscan nerve, and characterised above all by failure 

 of genuine katelectrotonus. 



If the sciatic nerve of a cold frog is prepared, together 

 with the leg connected with it, and led off from two points as 

 near as possible to the muscle (the exciting electrodes being as 

 before at the central end), then if there is no marked difference of 

 potential the closure of a descending current will have no percep- 

 tible effect, even when it is of considerable intensity. This is 

 also the case when the intermediate tract is shortened by shifting 

 the galvanometer electrodes up to the bifurcation of the branch 

 to the muscles of the thigh. 



These statements imply that there is no considerable difference 

 of potential within the unbranched part of the nerve. If the 

 distance between the galvanometer and exciting tracts is reduced 

 beyond a certain point, there will of course be katelectrotonic 

 action here as in all medullated nerve, which will increase rapidly 

 on shortening the intermediate tract, and essentially depends 

 upon the intensity of the current. We shall return later to the 

 character of the anelectrotonic manifestations in uninjured nerve, 

 and need only state here that they can be demonstrated at 

 maximal distance from the exciting tract (with ascending currents), 

 and increase steadily on shortening the intermediate portion. 



This is illustrated by Tables II. and III., which relate to highly 

 excitable preparations of R. escnlenta. The indications are the 

 same as in the previous series. 



If we first consider the electromotive alterations on the side 

 of the kathode only, the extrapolar tract of the nerve is 

 seen to fall, with sufficient length, into two sections, in which 

 the electromotive effects that appear at and during the closure 

 of a constant current originate (notwithstanding their similarity 

 of direction) in fundamentally different causes. At maximal 

 distance from the effective pole, distinct effects of katelectrotonus 

 appear only when a current of rest is present, and occur more 

 especially in nerves that are predisposed to tetanus. These effects 

 diminish irrespective of the shortening of the intermediate 

 tract with the diminution of P.D., when the galvanometer 

 electrodes are shifted back from the cross-section, while much 



VOL. II U 



