. Electro-physiology . FIG. 192.—Frog's nerve-muscle preparation. Ascending direction of current, otherwise the same experimental conditions as in the previous Figs. Effect of commencing desiccation on the result of breaking a battery current of medium strength. The opening twitch (I) appears as the initial phase of the delayed opening tetanus (II). must be regarded as transitional forms between the simple opening- twitch and persistent tetanic shortening of the muscle. This agrees with the fact that the appearance of closure tetanus in weak electrical excitation of alcoholised nerve must be r
. Electro-physiology . FIG. 192.—Frog's nerve-muscle preparation. Ascending direction of current, otherwise the same experimental conditions as in the previous Figs. Effect of commencing desiccation on the result of breaking a battery current of medium strength. The opening twitch (I) appears as the initial phase of the delayed opening tetanus (II). must be regarded as transitional forms between the simple opening- twitch and persistent tetanic shortening of the muscle. This agrees with the fact that the appearance of closure tetanus in weak electrical excitation of alcoholised nerve must be regarded as exceptional, although the curves of both closing and opening twitches are distinguished by their rounded tops from such as are obtained on exciting normal nerve by instantaneous stimuli (single induction shocks), or by the closure of a battery current. These experiments show conclusively that while in normal, uninjured nerve it is never possible to obtain an opening excitation from weak currents, this may result when excitability is artificially raised : thus seeming to justify the view that the appearance of the break twitch on applying a cross-section to the nerve is due to the consequent rise of excitability. Yet (in addition to the objections already cited) the bare comparison of the opening effects of excitation in the two cases
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