EXPLANATION OF WEDENSKY INHIBITION

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Abstract
I. Six kinds of experiments were made to determine the point in the narcotized nerve at which the series of subnormal impulses vanishes. All gave the same result, viz., that the subnormal impulses are extinguished, not by decrement as supposed by Lucas, but at the beginning of the narcotized area, about 3-5 mm. inside the upper wall of the narcotizing chamber.[long dash]II. It was shown that the recovery curve of the narcotized part approached, as narcosis deepened, a horizontal line, indicating prolonged absolute refractory period and heightened threshold in the relative refractory period. To know the depth of narcosis necessary to produce complete inhibition, the least intervals were determined at A (normal part outside) as well as at B (narcotized part) through the whole course of narcosis. In the early stage of narcosis the least interval at A increased more slowly than that at B, and from certain stages the former increased more rapidly and overtook the latter. Therefore the curves A and B cross. Complete inhibition could never be produced until this stage of narcosis at which the curves cross, however frequent the tetanic stimuli might be. Curves A and B cross because the 2nd impulse started from A vanishes in the narcotized area by falling into the relative refractory period left by the 1st impulse. For the production of complete inhibition such a depth of narcosis is necessary that the 2nd impulse shall be extinguished on account of the heightened threshold in the relative refractory period due to the 1st impulse. This 2nd impulse, although itself extinguished, leaves behind an "after-effect" which lasts long enough to inhibit the 3rd, and so on. The duration of the inhibitory "after-effect" left by the 2nd (extinguished) impulse was measured. Similar experiments were made to measure the inhibitory "after-effect" left by the 3rd (extinguished) impulse. Furthermore, experiments are described in which the narcotized part was directly stimulated during the relative refractory period, with a stimulus which was below the threshold at the moment. The inhibitory "after-effect" left by such an apparently ineffective stimulus falling actually in the relative refractory period was measured. It was sufficiently long, in an advanced stage of narcosis, to account for the "after-effect" left by the extinguished impulse. The conditions necessary to produce complete inhibition are that curves A and B cross and that the 2nd impulse falls in the shaded area between AA and BB.

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