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.) 



K'oth, 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 Roth as a very brief tetanus, while Schoenlein (25) 

 regards it as a sinylc 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 Engehnann (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). 



