Human Calorimetry

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Abstract
The temperature of the surface of the human body is 4° or 5° lower than the interior temperature, which is not reached until a depth of several centimeters. A calculation is made showing that about 50 per cent of the body is within an inch from the surface. Account must be taken of this cooler peripheral tissue in calculating the average temperature of the bodyespecially for the agreement of direct and indirect calorimetry. A theoretical estimate is made of how the rectal and surface temperatures should be combined to give the true average. From the results of forty hour periods with the respiration calorimeter upon a group of subjects in basal and absorptive conditionthe formula giving the least average discrepancy between direct and indirect heats is found experimentally. It agrees closely with that deduced theoretically, and is: average temperature equals 0.65 × rectal temperature plus 0.35 × average surface temperature. The latter temperature is found from measurements over the trunkthe lower leg and the forearm. The average error is reduced from 7½ per cent using rectal temperature alone to 5½ per cent using the formula. The changes occurring in surface temperature are on the average three or four times as great as those of the rectal temperatureand are poorly correlated with the latter when the changes are small. The measurement of surface temperatures is equally if not more important than the rectal in the calculation of the average. By using 0.6 times the change in surface temperature alonethe results in this group are slightly better than using rectal temperature alone. The average temperature from the body is from 1 to 2°C. lower than the rectal temperature in the basal state. In fever the two may be practically equal. Some discrepancies in the calculation of the Q10 for metabolism with temperature are explainedand the formula is applied to some experiments where subjects were heated by high frequency currents. The calculation of the average specific heat of the living human body is made possible for the first timebut the data can show only that it lies between 0.7 and 0.9.