ANIMAL HEAT. 389 



tity of heat such quantities of foods give rise to when completely 

 oxidized to carbonic acid and water. In the human body the carbo- 

 hydrates and the^fats, with the exception of the small portion which 

 escapes digestion, are reduced to carbon dioxid and water, and hence 

 practically liberate as much heat as they do when oxidized outside 

 the body. The proteids, however, are only reduced to the stage of 

 urea. As this compound is capable of further reduction in the calor- 

 imeter to carbon dioxid and water, with the liberation of heat, the 

 quantity of heat it contains must therefore be deducted from the 

 physical heat value of the proteid. According to Rubner, i gram 

 of urea will yield 2.523 kilogram calories. As about one-third of a 

 gram of urea results from tVi^jQftjdation of^i gram of proteid, the 

 amount ot heat to be deducted from the teat value of the proteid is 

 J of 2.523, or 0.841 calorie. It has also been shown by the same in- 

 vestigator that some of the ingested proteid is found in the feces, the 

 heat value of which must also be determined and deducted. This 

 having been done, the physiologic heat value becomes 4.124 calories. 

 The following estimates give approximately the number of kilo- 

 gram calories which should be liberated within the body when the 

 proteid is burned to the stage of urea, and the fat and carbohydrate 

 to the stage of carbon dioxid and water: 



i gram of proteid 4.124 calories 



i fat 9.353 



i carbohydrate 4.116 



The total number of kilogram calories yielded by the various diet 

 scales can be readily determined by multiplying the quantities of the 

 food principles consumed by the foregoing factors. The diet scale 

 of Vierordt, for example, yields the following: 



120 grams of proteid 494.88 calories 



90 " fat 841.77 " 



330 " starch 1358.28 " 



Total, _ 2694.93 " 



The total calories obtained from other diet scales would be as follows : 

 Ranke's, 2335; Voit's, 3387; Moleschott's, 2984; Atwater's, 3331; 

 Hultgren's, 3436. These numbers indicate theoretically the total 

 heat-production in the body daily/ 



2. Calorimetric Measurements. By this method the heat dissi- 

 pated from the body of an animal is directly collected and measured, 

 and the amount so obtained is taken as a measure of the heat evolved 

 by the oxidation of the food. A calorimeter is therefore an apparatus 

 for the direct estimation of the quantity of heat dissipated from the 

 body in a given time. The substance employed for collecting and 

 measuring the heat is either water or air. The calorimeters in 



