276 Biological Chemistry. 



the same as that of the carbon dioxide produced. The 



,. C0 2 expired . , , . 



ratio = is known as the " respiratory quotient, 



O 2 inspired 



and in the case of carbohydrates is = 1. In fats, on the 

 other hand, the amount of oxygen in the molecule is rela- 

 tively much less than in the case of carbohydrates, and 

 more oxygen is required to be supplied to produce com- 

 plete combustion. The respiratory quotient is in this case 

 less than unity. The following are the respiratory quo- 

 tients of the chief foodstuffs 



Carbohydrates 1 (approximately). 



Animal fat 0711 



Protein 0'899 



If the respiratory quotient is determined after the inges- 

 tion of a meal of known chemical composition, it is 

 possible to determine at any given moment the nature of 

 the substances undergoing oxidation in the body. Large 

 numbers of determinations of respiratory quotients have 

 been made in the course of physiological and pathological 

 researches. It is, for example, of interest to ascertain the 

 respiratory quotient during severe muscular work with the 

 object of ascertaining which constituent of a diet forms 

 the chief source of muscular energy. Again, in such 

 a disease as diabetes, where the organism is not able 

 normally to utilize the sugar, which is excreted in the 

 urine in abnormally large quantity, it is of interest to 

 ascertain the methods of utilization of the constituents of 

 various experimental diets. 



(2) THE ANALYSIS OF THE FOODS. 



The constituents generally estimated are the fats, car- 

 bohydrates, and proteins. The fats may be roughly esti- 

 mated by determining the percentage of the material 



