. Electro-physiology. Electrophysiology. 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—
. Electro-physiology. Electrophysiology. 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}. s os os os as os na OS usos t». FIG. 77.—Sartorius lixed 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
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