The heat production of nerve

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Abstract
It has proved possible to measure the heat produced by an isolated frog''s nerve undergoing a faradic stimulus located at a point distant from the temperature-recording apparatus. Controls have shown that, with suitable precautions, no error is introduced by the heat liberated by the stimulus itself. A detailed account is given of the methods used. The essential features are (a) the employment of a thermopile with a large number of junctions, (b) the use of thermal amplification of the galvanometer''s movements, (c) adequate electrical insulation, (d) prolonged thermal equalization, (e) calibration of the apparatus in absolute units, (f) the study of the heat after, as well as during, the stimulus. About 90% of the total heat is liberated after the stimulus is over. A rough analysis of the results indicates a small initial heat production, followed by a prolonged phase of heat production lasting 9-11 minutes. The heat liberated in the initial phase averages about 7.6 X 10-6 cal. per gm. of nerve per second of stimulation; the total heat about 6.9 X 10-5 cal. per gm. of nerve per second of stimulation. Previous experiments tended to indicate that the heat-production, if any, was much smaller than this. The reasons for the discrepancy are (a) the absence of a direct calibration in the earlier experiments, and (b) the lack of realization that a large fraction of the heat might appear in a recovery phase. The absolute values obtained are compared with the results of other observers on the O2 consumed and the CO2 liberated owing to nervous activity. In particular, the observations of Parker on the extra CO2 output agree well with the total heat observed, on the hypothesis of the oxidation of some ordinary foodstuff. The possibility of measuring the heat-production of stimulated nerve obviously opens up new avenues for the study of nerve function. The matter is being pursued, and only a few deductions from the absolute values are given here.

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