432 TEXT-BOOK OF PHYSIOLOGY. 



orimeter, the heat evolved by the oxidation of the food within, and dissipated 

 from, the body daily. 



i. Direct Oxidation. The amount of heat which any given food prin- 

 ciple will yield can be determined by burning a definite amount e.g., i 

 gram to carbon dioxid and water and ascertaining the extent to which 

 the heat thus liberated will raise the temperature of a given amount of water, 

 e.g., i kilogram. The amount of heat may be expressed in gram or kilo- 

 gram degrees or calories; a gram calorie or kilogram Calorie being the amount 

 of heat required to raise the temperature of a gram or a kilogram (1000 

 grams) of water i C. The apparatus employed for this purpose is termed 

 a calorimeter, which consists essentially of a closed chamber, in which the 

 oxidation takes place, surrounded by a water-jacket. The rise in tempera- 

 ture of the water indicates the amount of heat produced. 



The results obtained by investigators employing different calorimeters 

 and different food principles of the same class vary, though within narrow 

 limits: e.g., i gram casein yields 5.867 kilogram Calories; i gram of lean 

 beef, 5.656; i gram of fat, 9.353, 9.423, 9.686 Calories; i gram of starch or 

 sugar, 4.116, 4.182, 4.479, etc -j Calories. These results are, however, 

 physical values, and indicate the quantity of heat such quantities of foods 

 give rise to when completely oxidized to carbonic acid and water. In the 

 human body the carbohydrates 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 proteins, however, are only reduced to the stage of urea. As 

 this compound is capable of further reduction in the calorimeter 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 protein. 

 According to Rubner, i gram of urea will yield 2.523 kilogram Calories. 

 As about one-fhird of a gram of urea results from the oxidation of i gram 

 of protein, the amount of heat to be deducted from the heat value of the 

 protein is J of 2.523, or 0.841 Calories. It has also been shown by the same 

 investigator that some of the ingested protein 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 kilogram 

 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 protein 4.124 Calories 



i gram of fat 9-353 Calories 



i gram of carbohydrate 4.116 Calories 



The total number of kilogram calories yielded by the various diet scales 

 can be readily determined by multiplying the quantities of the food prin- 

 ciples consumed by the foregoing factors. The diet scale of Vierordt, for 

 example, yields the following: 



120 grams of proteid 494.88 Calories 



90 grams of fat 841.77 Calories 



330 grams of starch 1358.28 Calories 



Total 2694.93 Calories 



