134 ELECTRO-PHYSIOLOGY CHAP. 



ceeded in obtaining oscillations of great frequency by the use 

 of induction coils, produced by the rotation of a disc between the 

 free surface of the iron axis of a coil, and the opposite pole of a 

 powerful electro-magnet, the periphery of the disc consisting 

 alternately of iron and a non-magnetic substance (brass). Since 

 each iron tooth of the disc is magnetised as it passes over, a 

 corresponding change occurs in the magnetism of the iron axis of 

 the coil, and current is induced. The frequency of current- 

 oscillation is equal to the number of iron teeth which run 

 between the iron core and the pole of the magnet in a unit of 

 time. (A similar apparatus was constructed later by Griitzner.) 



Both, as well as v. Kries, showed that an upper limit of the 

 stimulation-frequency at which tetanus can still be called out 

 exists only relatively. " For each intensity of current given as 

 the amplitude of an oscillatory process, a frequency may be deter- 

 mined which need only be exceeded in order to produce disappear- 

 ance of excitation effects." In order, therefore, to maintain a 

 tetanus, intensity as well as frequency must be augmented, other- 

 wise the phenomenon of the initial twitch will ensue, which is 

 described by Eoth as a very brief tetanus, while Schoenlein (25) 

 regards it as a single twitch due to the summation of ineffective 

 stimuli. V. Kries (I.e.) also finds that the time-relations of the 

 initial twitch correspond throughout with simple induced twitches. 

 If the frequency in a given case remains constant, and current 

 intensity only diminishes, the effect remains approximately con- 

 stant (Kraft, 26). An appearance analogous to the "initial" and 

 " final " twitches was observed by Engelmann (6), during very 

 frequent rhythmical excitation, in the smooth muscle of the 

 rabbit's ureter, where " the close of a series of periodically recur- 

 ring, short stimuli acts like the break of a constant current, just 

 as the impact of a rapid succession of shocks acts like the closure 

 of a constant current." We have made similar observations on 

 the adductor muscle of Anodonta (27). And an effect corre- 

 sponding with the initial twitch may be observed in cardiac 

 muscle : " If a succession of stimuli (induction shocks) which 

 would produce a twitch after each pause of two or more seconds 

 with unfailing regularity, are sent into the excised ventricle at 

 intervals of less than a second, the first stimulus will be followed 

 by a systole, the later at most effect a weak local action " 

 (Engelmann, 22). 



