HEAT PRODUCTION OF THE HUMAN BODY 



275 



If we substitute a heavier task such as 

 stone working (400 Calories per hour) under 

 the eight-hour work period, the total would 

 be increased to 4660 Calories per 24 hours. 

 The daily extremes for various forms of 

 normal human activity will vary between 

 2000 and 5000 Calories. 



TABLE III 

 Total Heat Production of a 24-Hour Period 

 Assuming a Routine of Work and Rest 



Influence of Environmental Temperature upon 

 Metabolism 



Within a range of atmospheric conditions, 

 within and slightly above the comfort range, 

 metabolism remains unaffected by environ- 

 mental temperature. Beyond this range, 

 metabolism rates tend to increase on each 

 side for quite different reasons. The initial 

 stages of this phenomenon are illustrated by 

 an analysis of the following data obtained 

 at the Pierce Foundation. 



In one series of experiments by Winslow, 

 Herrington, and Gagge (42) 35 tests were 

 made on each of two nude subjects, at 

 varying operative temperatures from 18°C 

 up to 41°C. (The operative temperature 

 represents the combined effect of air and 

 wall temperatures, and will be discussed 

 later.) Air and walls were nearly identical; 

 under these circumstances operative temper- 

 ature is, of course, the same as the air 

 temperature. 



In another study by Gagge, Winslow, and 

 Herrington (17), 44 experiments were made 

 on clothed and on nude subjects, with a 



somewhat similar variation in air tempera- 

 tures, and, again, with walls at the same 

 temperature as the air. In Table IV we 

 have averaged the observed metabolic 

 rate (per square meter of body surface) as 

 observed in three major ranges of environ- 

 mental temperature. 



Very few experiments were performed 

 with the nude subjects below 20°C. In the 

 case of Subject No. 1 in Study A, the value 

 of 42 under cold conditions may be unre- 

 hable, since there were only two experiments 

 in this temperature range and one of them 

 showed a quite abnormally low metabolism. 

 However, this subject was obese and hence 

 well insulated. Subject No. 2 in Study A, 

 and the clothed subjects in Study B, showed 



TABLE IV 

 Effect of Temperature on the Heat Produc- 

 tion OF Subjects Seated at Rest 



a marked and significant rise in metabohc 

 rate under the cold conditions, and all of 

 these latter subjects were of normal body 

 build. On the other hand, the hot condi- 

 tions in all cases but that of the clothed 

 subjects of Study B show a slight but 

 appreciable increase in metabolism. It 

 appears that, in general, the minimum 

 metabolism is observed at 20°-25°C, and 

 that below 20° and above 25°C there is a 

 tendency to increase metabolic rate. The 

 increase under cold conditions is clearly a 

 useful adaptive reaction. This increase is 

 related to muscular tension and shivering. 

 No significant reductions in metabolism 

 under warm conditions have been reported 



