828 METABOLISM. 



If the total quantity of carbon eliminated in various ways is compared 

 with the carbon contained in the food some idea can be obtained as to 

 the transformation of the carbon compounds. If the quantity of carbon 

 in the food is greater than in the excreta, then the excess is deposited; 

 while if the reverse be the case it shows a coriesponding loss of body 

 substance. 



The nature of the substances here deposited or lost, whether they consist 

 of proteins, fats, or carbodydrates, is learned from the total quantity of the nitrogen 

 of the excretions. The corresponding quantity of proteins may be calculated from 

 the quantity of nitrogen, and, as the average quantity of carbon in the proteins 

 is known, the quantity of carbon which corresponds to the decomposed proteins 

 may be easily ascertained. If the quantity of carbon thus found is smaller than 

 the quantity of the total carbon in the excreta, it is then obvious that some other 

 nitrogen-free substance has been consumed besides the proteins. If the quantity 

 of carbon in the proteins is considered in round numbers as 52.5 per cent, then the 

 relation between carbon (52.5) and nitrogen (16) is 3.28, or in round numbers 

 3.3 : 1. If the total quantity of nitrogen eliminated is multiplied by 3.3, the excess 

 of carbon in the eliminations over the product found represents the carbon of the 

 decomposed non-nitrogenous compounds. For instance, in the case of a person 

 experimented upon, 10 grams of nitrogen and 200 grams of carbon were eliminated 

 in the course of twenty-four hours; then these 62.5 grams of protein correspond 

 to 33 grams of carbon, and the difference, 200 (3.3 X 10) = 167, represents the 

 quantity of carbon in the decomposed non-nitrogenous 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 carbohydrates as compared with the fats 

 of the body is extremely small, in such cases in order to avoid mistakes the assump- 

 tion must be made that the person experimented upon has used only fat and pro- 

 teins. As animal fat contains on an average 76.5 per cent carbon, the quantity 



100 



of transformed fat may be calculated by multiplying the carbon by =^ = 1.3. 



t o.o 



In the case of the above example, the person experimented upon would have used 

 62.5 grams of proteins and 167 X 1.3 = 217 grams of fat of his own body in the course 

 of the twenty-four hours. 



Starting from the nitrogen balance, it can be calculated in the same way 

 whether an excess of carbon in the food as compared with the quantity of carbon 

 in the excreta is retained by the body as proteins or fat or as both. On the other 

 hand, with an excess of carbon in the excreta one can determine how much of the 

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

 one side and of non-nitrogenous bodies on the other side. How to especially 

 calculate the part taken by the fats and carbohydrate will be shown in connection 

 with the calculation of the energy metabolism. 



The quantity of water and mineral bodies voided with the urine and 

 feces can easily be determined. The quantity of water eliminated by 

 the skin and lungs may be directly estimated by means of the large 

 respiration apparatus. 



The organic constituents of the body as well as the foodstuffs intro- 

 duced, represent a sum of chemical energy which the body can use for force. 

 The exchange of material is also an exchange of force, and the first 

 stands in such close relation to the second that the study of one cannot 

 be separated from the other. The energy theory of metabolism has 



