208 ELECTRO-PHYSIOLOGY CHAP. 



Each contraction, however small, was then defined by a more or 

 less considerable reduction in one or more of the cross-bands or 

 the coloured spaces between them. Within the passively partici- 

 pating muscle tracts, on the other hand, the coloured cross-bands 

 are much contorted, but do not appear to get smaller. In very 

 widely extended tracts they grow considerably broader, as will 

 appear below (22). 



In a tracing conformably with direct observation the 

 persistent closure contraction only appears in the curve correspond- 

 ing with the kathodic half of the muscle, but if the currents 

 employed are not too strong (Figs. 77 and 78) the closure twitch 

 is seen on both sides equally. It is only with the weakest minimal 

 currents that the twitch appears higher on the kathodic than on the 

 anodic side, where it is sometimes no more than a little hump. 

 This marked difference, which is plain with the application of the 

 weakest currents, occasionally persists for a considerable period, 

 disappearing, however, as a rule (provided the excitability and 

 conductivity of the muscle have not otherwise suffered), at an 

 intensity of current which may still be termed low, giving place to 

 complete uniformity of twitch on either half of the muscle. The 

 assumption that the mechanical conditions of shortening are less 

 favourable in the one half than in the other is easily shown by 

 control experiments to be inadequate, so that the behaviour of the 

 sartorius towards the weakest minimal closure stimuli, as described, 

 is no less calculated to confirm v. Bezold's theory of the seat of 

 direct excitation by the current, than, with application of stronger 

 currents, the fact of localisation of the persistent closure con- 

 traction. These experiments show further that the waves of 

 excitation, i.e. contraction, may die out on passage through the 

 intrapolar tract if the discharging stimulus is very weak, and 

 that with somewhat stronger stimuli they are propagated in 

 a diminishing degree (with a decrement) in the anodic or, at the 

 opening excitation, kathodic half of the muscle. This is quite 

 evident in a prolonged series of twitches obtained by repeated 

 closure at uniform strength and direction of current. Here the 

 height of the curve of the twitches decreases more rapidly than the 

 magnitude of the sustained contraction, which still appears at each 

 new closure, even when the make twitch has completely died out 

 on the kathodic side. On the other hand, the unequal decrease 

 in the height of the closure twitch on the kathodic and anodic 



