Relations between Factors of Metabolism. 



211 



If, therefore, the body were to burn pure carbohydrate, the volume of oxygen 

 absorbed would equal exactly the volume of carbon dioxide eliminated. On the 

 contrary, if the body burned pure fat, for every liter of oxygen absorbed there 

 would be 710 c. c. of carbon dioxide expired, the remainder of the oxygen 

 uniting with the organic hydrogen of the fat and appearing in the form of 

 water. Similarly, if protein alone is burned, for every liter of oxygen absorbed 

 there would be about 800 c. c. of carbon dioxide eliminated. 



It is thus seen that we are able to approximate the nature of the material 

 burned, if we know the relation between the carbon dioxide eliminated and the 

 oxygen absorbed. If during an experiment it is found that the ratio of carbon 

 dioxide to oxygen is 0.94, it is evident that the metabolism during this period 

 must have been largely of a carbohydrate nature. If, on the contrary, as is fre- 

 quently found in fasting experiments, the ratio of carbon dioxide to oxygen is 

 0.74, it is clear that the metabolized material must have been in large part fat. 

 The relationship, then, between the carbon dioxide produced and the oxygen 

 absorbed furnishes very valuable evidence as to the nature of the material katab- 

 olized, and if we know simultaneously the nitrogen excreted in the urine, the 

 carbon dioxide eliminated and the oxygen consumed, we can apportion the total 

 katabolism between the protein, fat, and carbohydrate. 



It is unnecessary here to enter into an extended discussion as to the merits 

 and accuracy of this method of apportioning the katabolism between the three 

 principal body-constituents. For experiments of long duration, it seems clearly 

 proved that a knowledge of the excretion of nitrogen in the urine, the carbon- 

 dioxide elimination and oxygen consumption, and of the complete elementary 

 analyses of the food and feces enables us to calculate the metabolism with very 

 great accuracy and to apportion it between the protein, fat, and carbohydrate. 

 While this may be true of long experiments, it is not, however, at present defi- 

 nitely proved with regard to short experiments. The assumption that the dis- 

 integration of protein is accompanied by an immediate excretion of nitrogen in 

 the urine, and the oxidation of carbohydrate by an immediate absorption of an 

 equivalent amount of oxygen is not definitely proved. There are many inter- 



