x ELECTROMOTIVE ACTION IN NERVE 275 



earlier minimal strength of excitation still produces a perceptible 

 twitch, the interval between this excitation and the closure of 

 the polarising current is lengthened, and the experiment repeated. 

 This is continued until the minimal excitation remains without 

 effect." " The interval between the two closures gives the time 

 occupied by transmission of the decreased excitability from 

 the intrapolar tract to the excited point. If this distance were 

 taken, the required rate of transmission could be deduced from it." 

 In order to determine the appearance of the galvanic alterations 

 of electrotonus at a point of the nerve beyond the polarised part, 

 two points symmetrical to the electromotive equator are in the 

 first place uninterruptedly led off, and existing differences of 

 potential compensated. This circuit, which included a sensitive 

 galvanometer, could be opened by means of a spring myograph, 

 at different times after brief closures of a battery current, that 

 traversed the nerve in an ascending or descending direction at a 

 given distance from the leading-off tract. The interval between 

 closure of the polarising current in the nerve, and the opening of 

 the galvanometer circuit, could thus be varied at pleasure. It 

 is clear that the determination of the time required between this 

 last and the closure of the polarising current, in order to detect 

 the first trace of electrotonic variation of current on the galvano- 

 meter, must also determine the time required by the latter in 

 every case, for its transmission from the polarised to the led- 

 off tract. Both series of Tschirjew's experiments were severely 

 criticised by Hermann (36), who emphasised the fact (as regards 

 Tschirjew's galvanic measurements) that, as will presently be 

 shown, the electrotonus at any given point of nerve does not reach 

 its full intensity at the first minute, but increases gradually. " And 

 if the electrotonus immediately after its origin is weaker by 

 only a quarter of its total amount, the results of Tschirjew 

 are quite compatible (as Hermann points out) with an instan- 

 taneous appearance." The same of course holds good of the 

 experiments in which the time to be determined is that which 

 must elapse after closure of the polarising current, in order to 

 produce anelectrotonus at a distant point of the nerve sufficient 

 to suppress the twitch called out here by a test stimulus. 

 " This interval is not, however, identical with that which must 

 elapse before the commencement of anelectrotonus at that point 

 of the nerve," but probably shorter. Consequently, as Hermann 



