THE BALANCE OF NUTRITION 207 



computation can, of course, be applied when there is a loss of nitro- 

 gen or carbon or both. 1 



295. Gain or loss of glycogen. The only non-nitrogenous organic 

 substance other than fat present in the body in sufficient amounts to 

 affect the foregoing computations is glycogen. It is generally assumed 

 that under reasonably normal conditions of feeding the glycogen con- 

 tent of the body does not fluctuate materially, so that any consider- 

 able or long continued gain of carbon, other than that contained in 

 protein, is in the form of fat. Probably this is not equally true in 

 the case of a loss of carbon, and in any case the results of computations 

 like that of the preceding paragraph are evidently subject to a degree 

 of uncertainty as regards a possible gain or loss of glycogen by the 

 body. While this is probably not serious in reasonably long periods 

 it may be relatively important in short experiments. If, however, 

 there can be added to the determination of the nitrogen and carbon 

 balance that of the balances of hydrogen and oxygen the means are 

 afforded for a more accurate calculation, since it is evident that the 

 amounts of the latter two elements, especially of oxygen, retained in 

 the body would be greater in the case of a storage of glycogen than in 

 that of a storage of fat containing the same amount of carbon. The 

 method of computation is, however, somewhat complicated and need 

 not be gone into here. 2 



296. The respiratory quotient. The respiratory quotient is 

 the ratio of the volume of carbon dioxid excreted by an 

 animal to the volume of oxygen taken up during the same time, 



i.e., it is ' The respiratory quotient will obviously 



Vol. G 



vary according to the kind of material which is being katabo- 

 lized in the body. Thus in the oxidation of carbohydrates each 

 liter of oxygen consumed gives rise to the production of one 

 liter of carbon dioxid and the respiratory quotient therefore 

 is i.o. On the other hand, when fat is oxidized, a portion of the 

 oxygen unites with the hydrogen of the fat and only the re- 

 mainder is available for the production of carbon dioxid. It 

 is easy to compute, therefore, that each liter of oxygen con- 

 sumed in the oxidation of fat will give rise to the production of 



1 To avoid errors in computation it is convenient to regard losses in such compu- 

 tations as negative gains and to carry through the computation exactly as in the 

 above experiment, using the algebraic sum or difference in every instance. 



2 See Atwater and Benedict, A Respiration Calorimeter, etc., Carnegie Institu- 

 tion of Washington, Publication No. 42 (1905). 



