. Electro-physiology. Electrophysiology. 102 ELECTRO-PHYSIOLOGY CHAP. usually remains unaltered, or at most undergoes some insignificant changes. With stronger excitation the result is otherwise. There will then be, along with the relaxation of the muscle and conse- quent fall of the curve, a perceptible and often considerable diminution in the height of the individual contractions, which does not necessarily entail an alteration in rhythm. This may be carried so far as to render the changes of form in the muscle quite imperceptible at the time of greatest relaxation, or at most in- dicated as
. Electro-physiology. Electrophysiology. 102 ELECTRO-PHYSIOLOGY CHAP. usually remains unaltered, or at most undergoes some insignificant changes. With stronger excitation the result is otherwise. There will then be, along with the relaxation of the muscle and conse- quent fall of the curve, a perceptible and often considerable diminution in the height of the individual contractions, which does not necessarily entail an alteration in rhythm. This may be carried so far as to render the changes of form in the muscle quite imperceptible at the time of greatest relaxation, or at most in- dicated as slight undulations in the curve (Fig. 168). The tracings obtained from such inhibitory effects not infrequently exhibit a superficial resemblance to kymographic curves, which show the inhibitory action of the excited vagus upon cardiac FIG. 168.—Inhibition of artificial contractions of adductor muscle of crayfish claw owing to stimulation of the nerve. The contractions were evoked by direct, rhythmic tetanisatious of the muscle. FIG. 169.—As in Fig. 168. Predominant diminution of single contractions. From these observations we learn that diminution of the artificial rhythmical contractions proceeds pari passu with the relaxation of the muscle, and the same fact is even more evident in cases where the muscle has time to relax completely between two consecutive stimuli. The active inhibitory action then betrays itself only by a more or less considerable diminution of the single twitches, or (more correctly) short tetani (Fig. 169). Such a series of curves reminds us directly of the demonstrations of Heidenhain and Lowit, on the effect of minimal vagus-excitation on the rhythmical contractions of the frog's heart, where the first effect of inhibition is a diminution of the single beats. The reaction thus described in the muscles of the crayfish claw (which can hardly be explained otherwise than by the antagonistic working of two opposite kinds of fibres passing by
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