QUANTITY OF HEAT PRODUCED BY THE BODY. 445 



degree C. = 422-25 kilogrammetres. One kilo.-degree C. = 3,057 foot- 

 pounds. 



Two methods have been employed in arriving at estimates of the actual 

 quantity of heat produced by the body in a definite time : 



1. The direct method consists in placing an animal in a calorimeter and 

 measuring the heat produced, making all necessary corrections. This has 

 been repeatedly done, but the results obtained have been very variable and 

 not entirely satisfactory. 



The observations of Senator (1872) seemed to fulfill the necessary experi- 

 mental conditions ; and as an average of five observations made on dogs at 

 rest and fasting, he found a production of about 4-21 heat-units per hour 

 per pound weight of the body (2-34 kilo.-degree C. per kilo.). 



J. C. Draper (1872) estimated the heat-production in his own person by 

 immersing the body in water. In this observation, many errors must have 

 escaped correction ; but the results agreed remarkably with those obtained 

 by Senator. Deducting 1 Fahr. of heat lost by the body, as shown by a 

 reduction in the general temperature, and imparted to the water a correc- 

 tion not made by Draper about 4 heat-units were produced per hour per 

 pound weight of the body (2-22 kilo.-degrees C. per kilo.). According to 

 the estimate of Draper, a man weighing 140 pounds (63-5 kilos.) would pro- 

 duce 13,440 heat-units (3-383 kilo.-degrees C.) in twenty-four hours of repose. 

 This would be equal to 10,375,680 foot-pounds, or about 1,430,000 kilogram- 

 metres. 



An important element of inaccuracy in all direct observations and one, 

 indeed, which it seems impossible to correct absolutely, is due to the great 

 variations in heat-production with digestion, conditions of muscular repose 

 or exercise, external temperature etc. Another source of error is the diffi- 

 culty in estimating the heat lost by the body and not actually produced dur- 

 ing the time of the observation. These possible inaccuracies are so impor- 

 tant and so evident, that the results of direct observations have not been 

 generally accepted by physiologists. 



2. The indirect method consists in estimating the heat represented by 

 oxidation, calculated from the quantity of oxygen consumed in the various 

 processes which result in the production and discharge of carbon dioxide, 

 water, urea etc. These estimates have been compared with the calculated 

 heat- value of the food consumed, and the results very nearly correspond. 



According to the estimates of Helmholtz, Ranke and others, by the in- 

 direct method, the heat-production is equal to about 2*5 heat-units per hour 

 per pound weight of the body (1'39 kilo.-degree C. per kilo.) In a man weigh- 

 ing 180-4 pounds (82 kilos.) the heat-production in twenty-four hours 

 (Helmholtz) was 10,818 heat-units (2,732 kilo.-degrees C.). According to 

 this estimate, a man weighing 140 pounds (63-5 kilos.) would produce 8,400 

 heat-units (2,118 kilo.-degrees C.) in twenty-four hours. This would be 

 equal to 6,484,800 foot pounds, or about 894,500 kilogrammetres. 



Comparing the results of direct observations, showing a production of 

 about four heat-units per pound per hour (2*22 kilo.-degrees C. per kilo.), 



30 



