IX 



ELECTRICAL EXCITATION OF NERVE 



171 



less pronounced but always perceptible delay in the entrance of 

 the twitch ; (b) the dependence of the magnitude and form of 

 the curve of the twitch upon duration of closure. Both are 

 clearly seen in the graphic tracing of the opening twitch, as 

 discharged with weak currents from the alcoholised nerve. 



The extent of the delay varies within a considerable range. 

 At times it is hardly perceptible ; in other cases the shortening 

 of the muscle is much retarded. The determining factors 

 are here duration and intensity of current the " latent period " 

 being usually reduced as these increase. 



The " latent period of the opening excitation " is also 



affected, in alcoholised nerve, by the 



degree 



of increase of 



JL. 



FIG. 191. Alcohol treatment of nerve. Method of experiment as in Fig. 190. Effect of duration 

 of closure upon height of break twitch (II). Break twitch (I) appears quite independent of 

 the same. 



excitability, so that it usually appears much greater at the 

 beginning of a series of experiments than during their course, even 

 if in this case the influence of the single stimuli following at short 

 pauses (with constant duration of closure) is of more importance. 

 As Pfliiger pointed out, " the phenomenon (of delay) alters after 

 repeated closures, since the break twitch follows more and 

 more closely upon opening, until finally no perceptible interval 

 remains." 



A glance at the opening twitches marked II in Fig. 191 

 shows the striking dependence of the break excitation upon 

 duration of exciting current under the given conditions 

 of experiment comparatively slight modifications of current 

 sufficing, on the one hand, to suppress the twitches altogether, 

 on the other to discharge maximal contractions. So far the effect 

 of electrical stimulation upon alcoholised nerve, and upon nerves 

 of which the excitability has been heightened by partial loss of 



