Electro-physiology (1896-98) Electro-physiology . electrophysiolog02bied Year: 1896-98 170 ELECTRO-PHYSIOLOGY CHAP. first effect is invariably a considerable increase in height of the closure twitches, without actual tetanus. Almost at the same time (usually after 2—4 minutes) a twitch, which is usually delayed, appears with the opening of the current also, provided the duration of closure is not too brief (Fig. 190). The duration of closure required, under the given conditions, to produce an excitation on opening the circuit, depends of course, apart from its intensity, upon the degree of al
Electro-physiology (1896-98) Electro-physiology . electrophysiolog02bied Year: 1896-98 170 ELECTRO-PHYSIOLOGY CHAP. first effect is invariably a considerable increase in height of the closure twitches, without actual tetanus. Almost at the same time (usually after 2—4 minutes) a twitch, which is usually delayed, appears with the opening of the current also, provided the duration of closure is not too brief (Fig. 190). The duration of closure required, under the given conditions, to produce an excitation on opening the circuit, depends of course, apart from its intensity, upon the degree of alcohol effect, strength of solution and length of application. The rise of excita- bility in the nerve usually occurs fairly soon, when it is treated with not excessively weak alcoholic saline, and the break twitch -7' JL JL JL JL JL FIG. 190.—Frog's nerve-muscle preparation. Excitation in the middle of the strip of nerve. Ascending direction of current. After the nerve has been bathed for thirty seconds in alcohol- ised saline (10 vols. %%%%%%%%) the current discharges delayed opening twitches (II) along with the closure twitch, preceded'after long treatment with alcohol by the opening twitch (I), which appears (according to duration of closure) alone, or partially or wholly fused with the opening twitch (II). also appears quickly, even with weak currents and brief closure. Here again it may be remarked that the opening of ascending- currents excites, as a rule, a little sooner than descending currents —which is no doubt related to the appearance of the so-called ' negative modification ' of katelectrotonus in the last case. The alcoholised nerve never sets up spontaneous tetanus, and isolated twitches of the muscle only appear occasionally with strongly alcoholised saline—up to 20 vols. c/o (Mommsen)—so that the dependence of the opening excitation upon the state of excita- bility of the nerve, as well as upon its special characteristics, may be studied here
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