21'2 ELECTRO-PHYSIOLOGY CHAP. 



the passage of the current, which remained at uniform strength 

 throughout the experiment, exceeded a certain value. If the 

 experiment was then continued with increasing" duration of 

 current, the twitches reappeared and rose to a second maximum, 

 from which point they remained constant with further extension 

 of stimulation. The same effect appears when the strength of 

 the shock is varied with unaltered duration of current ; further, 

 with diminishing values of current duration the diminution 

 and disappearance of the twitches implies increasing strength 

 of current (Tigerstedt, 54, p. 4). Tick subsequently deter- 

 mined the same effect with ascending induction currents, since 

 here too, with increasing intensity, there is a " breach " after 

 the first maximum, followed by renewed twitches with further 

 increase of current intensity, which soon become " supramaximal." 

 The existence of the breach was confirmed by Tiegel (55), 

 and again by Griitzner (55). Tiegel claims to have seen it 

 with both ascending and descending currents. Griitzner, like 

 Tigerstedt, on the other hand, failed to discover it with descend- 

 ing induction currents. The effect is quite regular with ascending 

 induction currents. The twitches beginning at a given, and 

 under uniform conditions of experiment fairly constant, strength 

 of current (distance of coil) diminish rapidly, and then 

 gradually rise again. The diminution in height with increasing 

 strength of current occasionally fails to reach the zero, so that 

 here the breach is, as it were, imperfect. As regards its interpre- 

 tation, the breach must, according to Tick, be viewed as a result 

 of inhibition at the positive pole, which at a certain strength 

 (duration) of current is sufficient to neutralise the excitation 

 proceeding from the negative pole. The character of the twitches 

 appearing after the breach will be discussed later. The diminution 

 and abolition of the twitches with an ascending shock, or 

 induction current, would thus be perfectly analogous with the 

 corresponding phenomena of the ascending constant current 

 (Fick, 55). Griitzner's theory, according to which the breach is to 

 be referred to a sort of interference between pre-existing differ- 

 ences of potential between nerve current and exciting current, 

 was finally disproved by Tigerstedt. The strongest evidence in 

 favour of Fick's view is the fact that the breach only appears 

 with ascending direction of current ; if the inhibition at the 

 kathode is not strong enough to neutralise the kathodic excita- 



