Eelatioxs between Factors of Metabolism. 219 



heat produced was likewise calculated. In previous publications these relation- 

 ships have been designated as the " carbon-dioxide and oxygen thermal quo- 

 tients," these terms indicating the number of grams of carbon dioxide or oxygen 

 accompanying the production of 100 calories of heat. In this report the more 

 explicit designation of " calorific equivalent " has been applied to the ratio 

 between the amount of carbon dioxide and heat produced, and oxygen absorbed 

 and heat produced. 



A consideration of the chemical composition and the heat of combustion of 

 many of the typical food materials shows that when protein is oxidized, for 

 every gram of carbon dioxide produced, there are 2.90 calories of heat liberated, 

 assuming the usual fragment of the protein molecule leaving the body in a 

 partially-oxidized form. When fats are burned, for every gram of carbon 

 dioxide produced there is a corresponding production of 3.42 calories of heat. 

 When the carbohydrate glucose is oxidized, for every gram of carbon dioxide 

 2.5G calories are liberated, with cane sugar 2.5G calories, and with starch 2.58 

 calories. In general, the disintegration of sufficient carbohydrate to produce 

 1 gram of carbon dioxide results in a liberation of 2.57 calories of heat, with 

 fat 3.42 calories, and for every gram of carbon dioxide produced when protein is 

 oxidized we have a heat liberation of 2.90 calories. 



The relationship between the carbon-dioxide elimination and the heat pro- 

 duction depends in a large measure upon the nature of the material burned, and 

 the absolute amount of carbon dioxide can not of itself indicate accurately the 

 heat production, particularly when there are material changes in the nature of 

 the diet or of the drafts upon body material. It may be assumed, however, that 

 with an average mixed diet in which the proportions of carbohydrate and fat 

 are relatively constant, the carbon dioxide can be taken as a reasonably accurate 

 index of the total heat production, but if diets are consumed in which there is a 

 marked preponderance of either fat or carbohydrate, the variations may be so 

 great as to make the carbon-dioxide measurement of little or no value as an 

 index of the heat-production. Obviously, in very few diets would the amount 

 of protein be so large as to play an important role. 



The marked difference in the chemical composition of carbohydrate and fat, 

 more especially with regard to the proportion of oxygen in the molecule, account 

 for the differences in the number of calories of heat liberated per gram of carbon 

 dioxide produced, but if we examine the number of calories accompanying the 

 absorption of 1 gram of oxygen, as given in table 87, we find that the differences 

 are by no means as great. While there are wide differences in the amount of 

 heat resulting from the disintegration of sufficient protein, fat, or carbohydrate 

 to produce 1 gram of carbon dioxide, the calorific value of 1 gram of oxygen is 

 much the same whether the oxygen is utilized in the combustion of protein, fat, 

 or carbohydrate. The carbon-dioxide production may be taken as only an 

 approximate index of the total energy transformation, but an exact knowledge 

 of the oxygen consumption in an experimental period should give us a reason- 



