1104 ANIMAL HEAT 



quently, the heat Uberated by the proteins in the body is less than that 

 obtained when they are burned in the bomb-calorimeter. The 

 carbohydrates and fats, on the other hand, are reduced to carbon 

 dioxid and water and produce, therefore, practically as much heat 

 in the body as when oxidized in the bomb. In the latter case, the 

 discrepancy amounts to only 3 per cent, and is dependent upon the 

 fact that some portions of these substances escape unutilized into the 

 feces. In the case of the proteins, on the other hand, this loss 

 amounts to 20 or 25 per cent, which is caused in part by their entrance 

 into the feces (1.0 to 1.3 per cent.) and in part by their incomplete 

 reduction into urea. But as this compound may be further split 

 up in the bomb to carbon dioxid and water under liberation of heat, 

 it becomes necessary to deduct this amount of heat from that obtained 

 during their physical combustion. According to Rubner, 1 grm. of 

 urea yields 2.523 calories; moreover, since this amount of urea re- 

 quires the oxidation of 3 grm. of protein, the amount of heat to be 

 deducted from the heat-value of protein substance is 0.841 calorie. 

 This loss, together with that incurred by the escape of protein into the 

 feces, reduces the physiologic heat-value of this foodstuff to about 

 4.124 calories.^ 



The experiments of Voit and Rubner upon dogs have shown a very 

 close correspondence between the heat values of the different foodstuffs 

 calculated in the above manner and those obtained in the calorimeter. 

 These results are fully upheld by the determinations of the heat-pro- 

 duction in normal men under different conditions of life. Thus, it 

 has been found that the basal value in an adult weighing 70 kilos (156 

 pounds), is 70 calories in 1 hour or 1 .680 calories in 24 hours. This term 

 of basal heat-production, however, signifies that the person has received 

 no nounshme nt during the preceding 15 hours and lias continued to 

 r est m beTafter a night of sleep. If any food has been taken during 

 this period, about 168 calories should be added to this total, which 

 makes 1.848 calories in all. Exercise increases this value very materi- 

 ally, and naturally, this increase must be compensated for by a larger 

 intake of food. According to the experiments of Atwater and Bene- 

 dict, ^ the efforts connected with arising and sitting in a chair increases 

 the basal heat-production by 8 per cent, and the ordinary movements 

 performed by us in the course of a day, by 20 per cent., thus: 



Night 616 calories 



Day 1 .552 calories 



Total 2.168 calories 



A man of medium weight, leading a sedentary life, requires 320 calories 

 in addition to these 2.168, or 2.500 calories in all, in order to supply him 



^ Rubner, Die Gesetzedes Energieverbrauchs., 1902, also: Calorim. Methodik, 

 Marburg, 1891. 



2 Ergebn. der Physiol., iii, 1904. 



