STUDIES OF THE NERVE IMPULSE

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Abstract
The electric responses from various points on a cat''s peroneal nerve were recorded by a method previously described, and the effect of alcohol vapor on the responses investigated. Careful control was employed to insure that approximately all fibers conducted the whole length of the nerve throughout the experiment, and therefore the observed response of the nerve at a given point represented the average response of the individual fibers. At the 3 points tested within the narcotized region the relative depressions of the electric responses were identical for a given degree of narcosis. (No point tested was less than 7 mm. from the chamber wall.) This result is in entire agreement with the recent work of Kato. It is concluded that the electric response does not suffer decrement as the impulse is conducted through such a region of narcosis. This is contrary to the classical theory of conduction with a decrement. The chief evidence supporting that theory and Kato''s further experiments and criticism of the old evidence are reviewed briefly. These results in relation to Adrian''s earlier work showing a constant although reduced velocity of conduction in a narcotized region, demonstrate a parallelism between the size of electric response and the velocity of conduction, even in narcotized nerve. This is the relationship predicted by the "membrane" theory of nerve conduction. It is further shown that, accepting this theory, the electric response may be used as a measure of the intensity of the nerve impulse. In view of these results Adrian''s proof of the all-or-none law is not valid, since he assumed decre-mental conduction in his method of measuring the intensity of the impulse. The present experiments, however, showing depression of electric response within the chamber but normal response beyond, are a direct proof of the all-or-none character of the electric response. If the electric response may be taken as an index of the intensity of the nerve impulse, then the impulse itself obeys the all-or-none law. The mechanism of conduction is considered from a general theoretical point of view, and it is concluded that transmission of the impulse from point to point must depend on a gradient of energy from the active to the as yet inactive region. Therefore, in passing into a narcotized region, the impulse must suffer a transitional decrement, extending as far into the depressed region as the gradient from the higher level of energy developed by the normal region is perceptible. The distance over which such decrement extends is undetermined as yet, except that it must be less than 7 mm.

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