x ELECTROMOTIVE ACTION" IN NERVE 285 



both of the pronounced effects that obtain near the exciting tract, 

 and also of the weaker and weakest effects at more remote 

 parts. Seeing that the alterations of the nerve, fundamental 

 to the homodromous incremental current below the ascending 

 exciting current, require an incomparably longer period for their 

 development than the initiation and transmission of excitation, 

 the duration of closure of the constant current is an indispensable 

 factor in the positive effect in question. Immediately after 

 making the ascending current, or at the close of the negative 

 variation, the scale passes beyond the zero-point in the positive 

 direction, and moves towards the acme of the deflection, at first 

 slowly and then more rapidly, until it reaches its limits 

 after a closure of 56 sec. The nearer the galvanometer 

 electrodes are brought to the exciting tract, the greater will be 

 the positive effects, and the more marked this gradual swelling of 

 the incremental current (homodromous with the exciting current), 

 its strength remaining constant during further extension of 

 closure. When as is usual on leading off from the transverse 

 end of the nerve the variation is diphasic, i.e. first negative and 

 then positive, the first phase nearly always predominates where 

 the intermediate tract is of any length, and a moderate ascending 

 current is employed. In this case, owing to the slow decline of 

 the negative phase, a much longer closure is required before the 

 gradually appearing and weak positive effect can be detected, than 

 in a nerve with less distance between the o-alvanometer and 



O 



exciting tracts, where the positive effect, as a rule, far outweighs 

 the negative, or alone makes its appearance. In order to deter- 

 mine with certainty to what distance from the anode the effect 

 extends, it is advisable to exclude the interference of the negative 

 deflection, either by using very strong currents ab initio, or by 

 killing the upper part of the exciting tract, and thus making 

 closure excitation from the kathode impossible. In such a case, 

 both with transverse leading off, and along the continuity of the 

 nerve, there will only be a monophasic positive deflection, while, 

 if the limit to which the alteration from the anode extends be 

 exceeded, all perceptible effects upon the galvanometer will fail, at 

 and during the closure of an ascending current. The rapid 

 increment of effect on bringing the galvanometer electrodes 

 nearer the exciting tract may thus be demonstrated with great 

 distinctness. 



