CALCULATION OF THE EXCHANGE OF MATERIAL. 827 



On the other hand, the phosphorized protein substances, lecithins and 

 phosphatides, are also decomposed within the body, and their phosphorus 

 is chiefly eliminated as phosphoric acid and also in part as organic phos- 

 phorus (see page 718). For these reasons the phosphorus is of great 

 importance in certain investigations on metabolism. 



If it is found, on comparing the nitrogen of the food with that of the 

 urine and feces, that there is an excess of the first, this means that the 

 body has increased its stock of nitrogenous substances proteins. If, on 

 the contrary, the urine and feces contain more nitrogen than the food 

 taken at the same time, this denotes that the body is giving up part of its 

 nitrogen that is, part of its own proteins has been decomposed. 



S])( 



proteins, but as decomposed muscle-substance or flesh. Lean meat contains on 

 an average about 3.4 per cent nitrogen; hence each gram of nitrogen of the urine 

 corresponds in round numbers to about 30 grams of flesh. The assumption that 

 lean meat contains 3.4 per cent nitrogen is arbitrary, and the relation of N : C 

 in the proteins of dried meat, which is of great importance in certain experiments 

 on metabolism, is given differently by various experimenters, namely, 1:3.22- 

 1 :3.68. ARGUTINSKY found in beef, after complete removal of fat and subtrac- 

 tion of glycogen, that the relation was 1 :3.24 (see Chapter XI). 



The carbon leaves the body chiefly as carbon dioxide, which is elimi- 

 nated by the lungs and skin. The remainder of the carbon is excreted in 

 the urine and feces in the form of organic compounds, in which the quan- 

 tity of carbon can be determined by elementary analysis. It was formerly 

 considered sufficient to calculate the quantity of carbon in the urine from 

 the quantity of nitrogen according to the relation N:C= 1:0.67. This 

 does not seem to be trustworthy, as this relation varies and depends, 

 according to TANGL and PFLUGER, LANGSTEIN, and STEiNiTz, 2 upon the 

 kind of food. TANGL has shown that the richer the food is in carbohydrates 

 the more carbon and hence the more heat of combustion per gram of 

 nitrogen does the urine contain. He found the following for 1 gram of 

 nitrogen in the urine: With diet rich in fab 0.747 gram C and 9.22 calories; 

 for carbohydrate-rich diet he found 0.936 gram C and 11.67 calories. 



The extent of the gas exchange can be determined by any of the methods 

 given on pages 819, 820. By multiplying the quantity of carbon dioxide 

 found by 0.273 one obtains the quantity of carbon eliminated as CC>2. 



: 





metabolism can be found in Albu and Neuberg, Physiol. u. Pathol. des Mineralstoff- 

 rechsels, Berlin, 1906. 



1 In calculating the protein catabohsm from the nitrogen of the urine it must not 

 forgotten that the food often contains nitrogenous extractives whose nitrogen cannot 

 be calculated as protein and for which a special correction must be made, if necessary. 

 2 Tangl, Arch. f. (Anat. u.) Physiol., 1899, Supplbd.; Pfliiger in Pfliiger's Arch., 79; 

 Langstein and Steinitz, Centralbl. f. Physiol., 19. 



