442 PHYSIOLOGICAL CHEMISTRY. 



they consist of proteids, fats, or carbohydrates, is learned from the 

 total quantity of nitrogen of the excretions. The corresponding 

 quantity of proteids may be calculated from the quantity of nitro- 

 gen, and as the average quantity of carbon in the proteids is known, 

 the quantity of carbon which corresponds to the decomposed pro- 

 teid may be easily ascertained. If the quantity of carbon found is 

 smaller than the quantity of the total carbon in the excretions, it is 

 then obvious that some other nitrogen-free substance has been con- 

 sumed besides the proteids. If the amount of carbon in the pro- 

 teids is considered in round numbers as 54$, then the relation 

 between carbon (54) and nitrogen (16) is as 3.4:1. Multiply the 

 total quantity of nitrogen eliminated by 3.4, and the excess of 

 carbon in the eliminations over the product found represents the 

 carbon of the transformed non-nitrogenized compounds. For 

 instance, in the case of a person experimented upon, 10 grms. nitro- 

 gen and 200 grms. carbon were eliminated in the course of 24 hours; 

 then these 62.5 grms. proteid correspond to 34 grms. carbon, and 

 the difference 200 (3.4x10) = 166, which represents the quantity 

 of carbon in the decomposed non-nitrogenized compounds. If we 

 start from the simplest case, starvation, where the body lives at the 

 expense of its own substance, then, since the quantity of carbohy- 

 drates as compared to the fats of the body is extremely small, in 

 such cases in order to avoid mistakes the assumption must be made 

 that the person experimented upon has only taken fat and proteids. 

 As animal fat contains on an average 76. 5$ carbon, the quantity of 

 transformed fat may be calculated by multiplying the carbon by 



-i r\r\ 



j = 1.3. In the case of the above example the person 

 7o.o 



experimented upon would have used 62.5 grms. proteids and 

 166 x 1.3 = 216 grms. fat of his own bodily weight in the course 

 of the 24 hours. 



Starting from the balance of the nitrogen, we can calculate in 

 the same way whether an excess of carbon in the food as compared 

 with the quantity of carbon in the excretions is retained by the 

 body as proteids or fat or as both. On the other hand, with an 

 excess of carbon in the excretions we can calculate how much of the 

 loss of the substance of the body is due to a consumption of the 

 proteid or of fat or of both. 



