184 ELECTRO-PHYSIOLOGY CHAP. 



Wundt (8) was the first to observe that the muscle does 

 not recover its normal length immediately after the closure twitch 

 has subsided, but exhibits a greater or less degree of shortening, 

 which only relaxes suddenly and sharply when the circuit is 

 opened, provided this break does not in itself excite the muscle 

 and produce a vigorous second contraction (opening twitch). The 

 magnitude of the persistent closure contraction increases in this 

 case also, up to a certain point, with the strength of the exciting- 

 current ; it is at any rate under the given conditions (re- 

 cording the changes of form with Bering's double myograph) im- 

 perceptible with weak currents, but expresses itself plainly later 

 on in a specific section of the curve, inasmuch as the descending 

 shoulder of the curve does not reach the abscissa, but runs along 

 more or less above it, so long as the current remains closed 

 (Fig. 77, K). 



FIG. 77. Sartorius fixed in the middle (double myograph). Successive excitations at closure with 

 uniform strength and direction of current. Effect of (local) fatigue at the kathode. 



With the application of very strong currents, the make 

 twitch eventually appears only like a hook, since the muscle 

 relaxes very little after reaching its maximum of shortening, 

 thus approximating to the normal reaction of smooth molluscan 

 muscle. This seems to appear earlier, and to be more marked, 

 in preparations that are already fatigued, and less capable of 

 reacting. The persistent closure contraction is in general capable 

 of much greater resistance than the closure twitch, as appears 

 inter alia from the fact that when a muscle is fatigued by 

 repeated closure with unaltered direction of current, the initial 

 twitch rapidly diminishes in size, and at last ceases to appear 

 altogether, while the persistent contraction decreases only very 

 slowly with progressive fatigue of the muscle. The initial 

 twitch has long disappeared, when each new closure still excites 

 the muscle to persistent shortening in almost the same degree 

 as at the beginning of the experiment (Fig. 77, K}\ it is not 



