72 ELECTRO-PHYSIOLOGY CHAP. 



indifferent at what interval the periodical excitations follow. A 

 maximal limit is only given in order that the stimuli should not 

 follow too slowly, if a " staircase " be required. This maximal 

 limit is about 60 sees, for the cardiac muscle of the frog accord- 

 ing to Bowditch, about 5 sees, for the striated skeletal muscles 



o 



of warm-blooded animals according to Eossbach. The minimal 

 limit is determined by that interval of stimulation at which the 

 series of twitches fuses into a tetanus. In regard to the form of 

 the staircase, it should be remarked that it is always, inde- 

 pendent of strength and frequency of excitation, an equilateral 

 hyperbola. 



When it is remembered that this manifestation is independent 

 of the nature of the stimulus (occurring equally with mechanical 

 excitation), as well as of the volume of blood in the muscle, 

 there can be no doubt that we are in presence of a process which 

 is intimately connected with the excitatory process, or contrac- 

 tion, in the muscle. We must reserve for a later point of the 

 discussion the probable cause of the above reaction, only re- 

 marking in conclusion that a similar, perhaps more permanent, 

 after-effect to that following each single twitch, also appears after 

 a tetanising excitation. Both Rossbach (I.e.) and Bohr (25) found 

 that the same excitation produced a greater effect (stronger con- 

 traction) after than before the tetanus. With maximal stimuli 

 this positive after-effect often continues for more than half an 

 hour. 



The latent period, as well as the height of muscular contrac- 

 tion, is partly dependent upon the strength of the excitation. 

 Helmholtz's estimation of the latent period as O'Ol sec. with 

 direct excitation of frog muscle (gastrocnemius) by single break 

 induction shocks, has been proved far too large by later investi- 

 gators ; the variously estimated values of Place, Kliinder, Lauter- 

 biich, Gad, Mendelssohn agree in showing that the latency period 

 of frog's muscle, directly excited with induction shocks, is only 

 from 0-005 to 0'006 sec. (cf. Tigerstedt, 26). Tigerstedt (I.e. 

 p. 152) also obtained the same result from his own extensive 

 observations. There is, moreover, the possibility that the latent 

 period of muscular contraction is even less in value, since 

 other significant data are included in the same computation. 

 Burdon- Sanderson (27) calculates the latent period of frog's 

 muscle at 0'0025 sec. only, and Eegeczy (28) even denies its 



