182 ELECTRO-PHYSIOLOGY CHAP. 



completely abolished, while it was fully maintained and even 

 heightened for the constant current. Neumann observed similar 

 changes in fatigued or moribund conditions. 



Along with these changes there is the gradual development 

 of a much more sluggish process of contraction, so that here too 

 contractile substances with a slow reaction require a longer 

 period of excitation than those which react quickly. This is 

 developed to such an extreme degree in many smooth muscles, 

 that one is justified in saying that moribund striated muscle, 

 especially at the beginning of degeneration, approximates to a 

 certain extent, in its physiological properties, to smooth muscle. 

 The differences described are most marked in a series of observa- 

 tions (not yet published), by T. Krehl (Jena), on frogs, in which 

 one sciatic nerve had been divided at the thigh. After J- year 

 the comparison of the two gastrocnemii still exhibited marked 

 differences on excitation with tetanising, or single, induction cur- 

 rents, or, on the other hand, with the constant current. In the 

 first case the coil had almost to be pushed home before the 

 slightest effect could be produced in the paralysed muscle ; in 

 the second an excessively marked, persistent contraction was 

 exhibited during closure. The muscle of the uninjured side 

 reacted normally. 



A. Tick (7) was the first to show by unexceptionable experi- 

 ments, that the make excitation is a function of duration of current 

 in this case also. In order to regulate the duration of a single 

 " impact of current " as required, Tick used a spring-contact, which 

 conducted a metal point rapidly over a metallic plate of varying 

 breadth (spiral rheotome). From this it appeared that, with excita- 

 tion of a normal striated frog's muscle, the magnitude (height) of 

 twitch produced by closure of the constant current depended 

 not merely on strength of current, but on the time during 

 which, at constant density, it was passing through the muscle. 

 The limit below which the duration of closure must not fall, 

 if the height of twitch is to remain maximal, corresponds 

 according to Tick with about O'OOl sec. Even if this value 

 is only approximate it shows that the difference between the 

 duration of closure required to produce an effective make 

 excitation in smooth muscle, and in striated frog's muscle, is 

 enormous. We shall see later that a similarly graduated differ- 

 ence also occurs between striated muscle and medullated nerve, 



