The depolarization of crustacean nerve by stimulation or oxygen want

IN 1927, at the time of his sudden untimely death, Levin, working with crustacean nerve, was investigating a remarkable characteristic of the action current, which he termed the "retention of action current," and the extreme fatigability of the nerve in question(). His chief resuIts may be summarized as follows: 1. The galvanometer deflection (the " negative variation of the injury current ") due to a continued tetanus through a single pair of stimulating electrodes increased with the time, reached a maximum in about 20 sec., and then gradually declined. The galvanometer leads were monophasic, non-polarizable electrodes were used, and the nerve was in moist air. 2. If stimulation were stopped within two minutes the galvanometer moved quickly back to a certain position and then returned only slowly towards its original place. The size of the rapid swing back decreased as the duration of the stimulus increased: no back swing at all was observed after two minutes of continuous tetanization. The time required for the galvanometer to return to its original position after the end of a stimulus depended upon the duration of that stimulus, being from 1 to 10 min. or more. Levin described this phase of slow return by the term "retention of action current." 3. The maximum displacement of the galvanometer from its earliest unstimulated position was the same in a succession of tetanic stimuli (the "ceiling effect"), whatever the position of the galvanometer at the beginning of any particular stimulus, provided that the nerve was not over-stimulated by too strong a faradic current, or unduly fatigued by too long a stimulus. In other words, the sum of (a) the "retention," and (b) the action current produced by a stimulus, was constant. 4. Fatigue set in particularly quickly in the neighbourhood of the stimulating electrodes. L evin suggested that the disappearance of his "retention" was due to some kind of restitution process following activity.