BASIC PRINCIPLES. 27 



quotient would be 0.722. 1 Under ordinary conditions, the respira- 

 tory quotient would lie between these two figures, and values above or 

 below these points might reasonably be considered as due to faulty 

 technique, to distinctly abnormal metabolism, or to a possible forma- 

 tion of fat from carbohydrate or carbohydrate from fat. 



It is thus clear that when the respiratory quotient is carefully deter- 

 mined, considerable light may be thrown upon the character of the 

 materials burned in the body. It should be considered , however, that to 

 determine accurately the respiratory quotient calls for an extraordi- 

 narily skilful technique, since any errors affecting either the determina- 

 tion of the carbon dioxide or the determination of the oxygen likewise 

 affect the respiratory quotient. 



The absolute values for the amounts of carbon dioxide exhaled and 

 oxygen absorbed in a given time, usually 1 minute, 1 hour, or 24 hours, 

 are also of importance in indicating the quantitative relations of the 

 total katabolism. For example, it is possible to strike a daily balance 

 from the amounts determined for 24 hours and show the adequacy or 

 inadequacy of the ration for maintenance by determining or computing 

 the carbon in the diet. 



INDIRECT CALORIMETRY. 



A number of physiologists have used the respiratory exchange to 

 compute the total calorimetry by the method of so-called "indirect 

 calorimetry," 2 and obtained results of still more importance. The total 

 katabolism may be apportioned between protein, fat, and carbohy- 

 drates by using the determination of nitrogen in the urine (protein 

 katabolism) and the respiratory exchange. Since in calculating the 

 materials katabolized in experiments with respiration calorimeters, it 

 is generally assumed that all of the food materials are first transformed 

 into similar substances found in the body, the calculation of the total 

 energy may with propriety be based upon the values of body-protein, 

 human fat, and glycogen. As each of these materials, when burned, 

 supplies definite amounts of heat, the total energy resulting from the 

 oxidation may be computed by multiplying the number of grams of each 

 katabolized material by certain factors, that customarily used for protein 

 being 5.65, or after deducting the potential energy in the urine, 4.4; for 

 fat, 9.54; and for carbohydrates, 4.19. 



Definite information regarding the calorific output of an infant is of 

 great importance in studying infant nutrition in order that a calculation 

 may be made of the amount of food required to provide a suitable quota 

 of calories for the day. The caloric losses from the body, therefore, 



Erroneously reported as 0.772 by Benedict, Am. Journ. Physiol., 1909, 24, p. 351. 



2 This method is not to be confused with the usage of certain French writers who consider "indi- 

 rect calorimetry" as indicating the computation of material consumed by noting the weights of 

 food eaten, excreta, and gain or loss of body-weight. 



