in ELECTRICAL EXCITATION OF MUSCLE 209 



sides respectively is very apparent during the process of " fatigue"; 

 both curves are almost equal in height at the beginning. The 

 anodic twitch is later only half as high as on the kathodic side, 

 and finally disappears altogether, while the latter is still twitching 

 visibly (Fig. 77). If the intensity of current exceeds a certain 

 limit there is regularly an apparent invasion of the persistent 

 closure contraction, which starts at first from the kathodic 

 end only, and spreads over the fixed centre of the muscle. 

 This phenomenon is most conspicuous with currents that are 

 inadequate to produce an effective break excitation at the usual 

 period of closure. It is very remarkable that the degree of 

 persistent shortening, is not, as might a priori be expected, 

 under all conditions higher on the kathodic side than on that of 

 the anode, but with currents of a certain strength the ratio is usually 

 augmented. Aeby (20) drew attention to an analogous relation 

 for the closure twitch, when he found that the ratio of height of 

 twitch in either half of the muscle was inverted with stronger 

 currents, and under the influence of progressive fatigue the 

 twitches of the anodic half, which at the beginning were equal 

 with or smaller than those of the kathodic half, gradually becom- 

 ing larger than the latter. Indeed it may happen that con- 

 versely to the case of currents of medium intensity the kathodic 

 half will exhibit only a weak sustained contraction, while the 

 anodic half still twitches plainly at each new closure. 



The asymmetry of the sartorius is very disturbing in all 

 these experiments, since, as we shall see, it produces an a 

 priori inequality of excitation effects in the two halves of the 

 muscle with alternating direction of currents. This agrees with 

 the fact that the diffusion of the persistent closure contraction 

 over both halves of the muscle already referred to always shows 

 itself earlier, and is much more marked, with an ascending 

 direction of current (i.e. from knee end to pelvic end), than 

 with a descending current. This is the more remarkable since, 

 in consequence of the increasing density at the small, tapering, 

 lower end of the muscle, and the more pronounced make excita- 

 tion produced by it with a descending direction of current, the 

 opposite might rather have been expected if with increase of 

 current the magnitude of the make twitch and the degree of 

 diffusion of the persistent closure contraction really depend 

 essentially upon the strength of excitation at the kathode. 



P 



