334 



PHYSIOLOGICAL CHEMISTRY. 



just intimated, examinations of the urine give us information 

 as to the nitrogen excretion, and the extent of oxidation of fats 

 and carbohydrates may be measured by respiration experi- 

 ments. In a fasting animal at rest the respiratory quotient 

 sinks to a value but little above 0.7, showing that the substance 

 metabolized is mainly fat; as some proteins are also used up 

 the quotient cannot absolutely reach 0.7. If work is done by 

 the fasting animal, the carbohydrate bodies of the muscular 

 juices, glycogen essentially, are called upon and their effect is 

 added to that of the proteins in raising the respiratory quotient. 

 On the other hand, it has been found that a well-fed animal 

 at rest, with abundance of carbohydrates in the ration, will 

 excrete a volume of carbon dioxide nearly as great as that of 

 the oxygen absorbed. In this case the ratio CO 2 /O 2 shows 

 that essentially carbohydrates are burned and that fat is al- 

 lowed to accumulate. When very hard work is done by the 

 well-nourished animal the quotient sinks to an intermediate 

 value, showing that fats are now consumed as well. This 

 would be evident also from observations continued over a long 

 period in which no accumulation of fat could be recorded. 

 With moderate work there is not much change. 



Some of these results are illustrated by the figures in the 

 following table taken from observations published by Chau- 

 veau and Laulanie, in which dogs were the subjects of experi- 

 ment. These figures show very clearly alteration in the res- 

 piratory quotient with work, and also by diet. 



