THE GASEOUS EXCRETION. 381 



bohydrates the result is the same. For the fats, however, the 

 quotient is much smaller since 57 CO 2 is the carbon dioxide 

 volume excreted for an oxygen consumption of 81.5 O 2 . In 

 this case CO 2 /O 2 = 57/81.5 = 0.7. For the protein bodies 

 the factor cannot be as easily calculated, since we are not able 

 to assign a formula to these substances, and moreover we are 

 not familiar with all their oxidation products. But from the 

 percentage composition and the known facts regarding the 

 elimination of urea, uric acid, ammonia and creatine it is pos- 

 sible to calculate an approximate quotient. This is about 0.8, 

 which factor may be used in calculations. 



The use of these quotients is ordinarily based on the assump- 

 tion that the oxidation is a direct one and that corresponding 

 to the oxygen absorbed there is almost immediately a libera- 

 tion of carbon dioxide in the right proportion. But this as- 

 sumption does not hold absolutely true ; the breakdown of car- 

 bohydrate, for example, may yield at first, in part, products 

 with high oxygen content from which CO 2 separates later. 

 In other words, there may be an apparent temporary storing 

 up of oxygen, which would make the quotient appear low. 

 Later a compensating excessive liberation of carbon dioxide 

 would have the opposite result. However, in observations 

 carried out through a period of proper length these variations 

 would not affect the general mean. 



The Carbon and Nitrogen Balance. The body is in car- 

 bon equilibrium when just as much carbon is eliminated as is 

 consumed in the food, and a determination of this element in 

 the various excreted products and in the food is sufficient to 

 show whether there is gain, loss or equilibrium in body weight. 

 All the food stuffs are organic, it will be remembered, and 

 contain carbon as the fundamental element. 



A change in weight may result from gain or loss in fat or 

 gain or loss in protein. Nitrogen equilibrium exists when 

 income and outgo are equal; in this case all the proteins con- 

 sumed as foods are decomposed. A determination of nitrogen 

 in the urine and feces coupled with a knowledge of the food 



