The vapour pressure of muscle

Abstract

In October, 1927, one of us (A. V. H.) noticed a curious phenomenon connected with the rate of resting heat production of a muscle suspended in pure nitrogen. The muscle, previously soaked for an hour or more in Ringer’s solution on a thermopile, in order ( a ) to quicken temperature equalisation in the chamber, and ( b ) to ensure its good condition,! showed a heat-rate in nitrogen, on removing the solution, which he believed, and which we still believe, to be a true measure of the resting anaerobic metabolism. When stimulated the muscle liberated heat; on the cessation of the stimulus this heat was dissipated and the galvanometer recording the temperature of the muscle returned towards, but not to, its original position. In hundreds of experiments, with no exception, the resting heat-rate in nitrogen after stimulation was greater than before. The phenomenon was obvious: it showed exact quantitative relations and was discussed in various papers (Hill, 1928 b , 1928 c , 1929 a , 1929 b ; Hartree and Hill, 1928). It seemed to be a sign of disintegrative chemical reactions, resulting from anaerobic activity. If oxygen, was admitted, after the completion of the usual recovery process the heat-rate in nitrogen, later reintroduced, returned towards, or to, its original level. This appeared to show that oxygen creates, or maintains, a barrier of some kind to disintegrative reactions which proceed in its absence. At an early stage the results were communicated to Prof. Meyerhof, then in Berlin, who attempted to confirm them by another technique, viz., by comparing the resting heat production of muscles in a closed calorimeter, before and after stimulation. The attempt was entirely unsuccessful—there was no sign of an increment in heat-rate, after anaerobic stimulation, comparable with that invariably observed with the thermopile. His results (Meyerhof, McCullagh and Schulz, 1930) have been published recently. This failure obviously demanded the most critical examination of the thermoelectric technique; no flaw, however, was found in it, and the phenomenon occurred unchanged when a sensitive resistance thermometer was substituted for the thermopile. In the meantime other characteristic properties of it were observed; the increment in heat-rate due to anaerobic stimulation had a temperature coefficient per 10°C. of about 2; it could be abolished not only by recovery in oxygen, but by prolonged soaking in Ringer’s solution (even oxygen-free); and finally in hydrogen it was 3 to 3 1/2 times as great as in nitrogen. This last astonishing effect supplied the clue to the explanation, which was given in a postscript to a paper (Hill, 1929 b ) published in September, 1929. The phenomenon is due entirely to a change of vapour pressure of the muscle, caused by the increase in the number of dissolved molecules (or ions) resulting from anaerobic stimulation.