x ELECTROMOTIVE ACTION IN NERVE 277 



(which is closed by altering the position of the slider on the 

 rheotome at any given moment between the closure and opening, 

 or after the opening of the polarising current) at most occupies 

 10 1 00 sec. Under these circumstances the electrotonic incre- 

 mental current does not make a clean entrance, either when the 

 galvanometer electrodes are applied to the nerve under isoelectric 

 conditions, or on leading off from longitudinal and transverse 

 sections; the contacts always interfere with either the phasic 

 current of action or the negative variation. The diminution of 

 the nerve current observed in the last case, even without the 

 rheotome, on tetanising with descending currents, must always 

 with adequate approximation of the leading-off and exciting tract 

 be due to the negative variation and the katelectrotonic 

 incremental current. The rheotome, as it were, analyses this total 

 effect into its single components, and determines the time-relations 

 between the arrival of the excitatory wave, and of the electrotonic 

 current, in each single stimulation. If the latter is already present 

 at its full strength at the moment of closing the polarising 

 current, the galvanometer deflection must obviously begin from 

 that point, and increase steadily in proportion with the shifting of 

 the rheotome from zero (i.e. the position at which the opening of 

 the galvanometer circuit occurs simultaneously with the closure 

 of the constant current) to that position at which closure of the 

 polarising current coincides with that of the nerve circuit. This 

 never occurred in Bernstein's experiment ; on the contrary, after 

 closure of the polarising current, there was a definite and 

 measurable period before any effects appeared on the galvanometer. 

 Let SO (Fig. 211) be the time-abscissa, S the closure, the 

 opening of the battery current, Sy the height of the " resting 

 nerve current," then the entire process of katelectrotonic alteration 

 that accompanies each single stimulus in the tract led off, is 

 expressed by the curve ngskte. The galvanic expression of 

 the excitation, which would otherwise produce a closure twitch, 

 is first a fugitive negative variation, temporarily of the opposite 

 sign (absolutely negative) to the nerve current in the given case. 

 It is only much later, at Jc, that the negative variation due to 

 the slowly rising katelectrotonic current commences. It occasion- 

 ally outlasts the opening of the polarising current, and then 

 disappears rapidly. The end of the kathodic closure wave (as 

 Bernstein terms the initial negative variation due to the closing 



