The Initial Heat Production of Stimulated Nerve

Non-medullated nerve. In a single impulse at 0 °C the heat production occurs in two phases, positive and negative. Records were made of the heat during repetitive stimulation at various frequencies. With 5 shocks/s the diphasic character of the heat was evident, with 10 shocks/s the instruments were too slow to show it, as they are above about 12 °C at any frequency. But the two phases probably occur under all conditions. Medullated nerve. No indication was obtained that the heat production in medullated nerve is diphasic : but this may well be due to the instruments being too slow to separate the phases. During a short tetanus at 0 °C the rate of heat production rises apparently abruptly at the start, and falls equally suddenly at the end, of the stimulus. This is the most probable interpretation of the records, but it remains possible that a short delay (0.02 to 0.04 s) may occur between an impulse and the corresponding heat production: at room temperature this could not be more than about 0.01 s. The magnitude of the heat production is considered in relation to the possibility that activity during an impulse occurs only in the nodal region.