THE BALANCE OF NUTRITION 2O$ 



in the body and since not all the animal proteins contain 

 exactly 16.67 P er cent f nitrogen, but the error involved is 

 insignificant in most cases so far as it relates to the question of 

 the balance between income and outgo. 



On this basis, the steer in the foregoing example was losing 

 daily 17.37 X 6.0 = 104.22 grams of body protein. Evidently 

 the results of an experiment in which a gain of nitrogen occurs 

 can be computed in precisely the same way. 



The gain or loss of fat and glycogen 



292. The carbon balance. By a method quite similar in 

 principle to that just described for protein, it is possible to com- 

 pute approximately the gain or loss of body fat from the com- 

 bined income and outgo of nitrogen and carbon, while if the 

 balance of hydrogen and of oxygen can also be determined the 

 computation may be made considerably more exact and may 

 include glycogen also. The experimental methods, however, 

 are necessarily much more elaborate than those required for a 

 simple determination of the nitrogen balance, since it is evident 

 that, in addition to the carbon of the feed and of the visible 

 excreta, it is necessary to determine the amount of this element 

 contained in the gaseous excreta, viz., carbon dioxid and 

 methane, while if the balance of hydrogen and oxygen is to be 

 included, the hydrogen of the feed, the water excreted and the 

 amount of oxygen taken up from the air must also be ascertained. 

 An outline of the experimental methods employed for these 

 purposes is given in a succeeding paragraph (297), but at the 

 outset it seems desirable to confine attention to the principles 

 involved. 



293. Computation of gain or loss of fat. According to the 

 conception of the schematic body (280) on which the whole 

 scheme of the balance experiment is based, substantially all the 

 carbon of the body is regarded as existing in the two forms of 

 protein and fat. Evidently if a comparison of the income and 

 outgo of carbon shows a gain of that element it can, according 

 to the fundamental assumption, have been only in one or the 

 other or both of these two forms. The nitrogen balance, how- 

 ever, shows the amount of protein gained and the carbon con- 

 tent of protein is known. If the carbon of the protein gained 



