The effect of temperature upon the absolute refractory period in nerve

IN the course of a study of the electric response of nerve to two stimuli, Downing and I(1) found that the duration of the absolute refractory period in nerve can be determined with good accuracy by the observation of the stimulus interval at which an increase occurs in the maximal deflection of a sensitive Downing moving-magnet galvanometer, over and above that previously given when the two stimuli were sent in at shorter intervals. The appearance of a second action potential wave is indicated by this increase in electric response, which comes in suddenly as the stimulus interval is gradually increased. The technique used for this determination is fully described in our paper. As an extension of this study I became interested in the effect of temperature upon the duration of the absolute refractory period, concerning which relationship the literature yielded rather meagre and incomplete information. I therefore carried out a group of determinations on the sciatic nerves of large R. esculenta, between 90 and 270 C., with results which were so regular and consistent that it seems wise to put them on record. The data here submitted are in good agreement with values published by a number of other workers, where comparison is possible; their chief advantage lies in the fact that they cover a wider temperature range than has previously been studied by any one investigator, and are more consistent than any to be found in the older literature. Previous measurements of the duration of the absolute refractory period in nerve have followed either the method of Helmholtz(2), in which determination is made of the least interval between two stimuli applied to the nerve which just produces a summated contraction in muscle, or the method of Got ch and Bu r c h (3) which measures the least interval required for the appearance of a second electrical response in