450 Influence of Inanition on Metabolism. 



The computation of the theoretical respiratory quotient from the combustion 

 of carbohydrate or fat is relatively simple, but the nature of the cleavage of 

 the protein molecule and the excretion of partially oxidized material in the 

 urine complicates the computation of the quotient resulting from the oxidation 

 of protein. The value commonly accepted for protein is 0.809. 



For further discussion of the theoretical factors involved in the computation 

 of the theoretical respiratory quotients resulting from the combustion of 

 protein see Magnus-Levy. 141 



While the theoretical consideration of the respiratory quotients to be derived 

 from the combustion of the various nutrients in the body is capable of mathe- 

 matical expression, considerable difficulty is experienced in interpreting the 

 respiratory quotients actually determined on man. For, instead of the com- 

 bustion of any given one of these ingredients of the body, protein, fat, or 

 carbohydrate, there is in practically all cases a simultaneous combustion of the 

 three. It has commonly been believed that in fasting experiments of short 

 duration, the combustion is chiefly that of fat with a small amount of protein, 

 and it has been maintained that the combustion of protein is relatively con- 

 stant from hour to hour. Hence, in the studies made by Zuntz, Loewy, 

 Magnus-Levy, and their associates, the quotient obtained during fasting has 

 been taken as a measure of the respiratory quotient derived from the com- 

 bustion of fat with a constant amount of protein. The various factors 

 influencing the quotients, such as the ingestion of food, muscular exercise, etc., 

 have been studied in the majority of the experiments made by these investi- 

 gators, and the results obtained are, for the specific purpose for which they 

 were designed, all that could be desired. 



On the other hand, when the respiratory quotient is determined not only for 

 the total 24 hours, but also for 2-hour periods, there may be, during the 

 periods, a lack of uniformity in the amount and rapidity of the disintegration, 

 not only of protein but likewise of carbohydrate, and, therefore, it is readily 

 seen that the interpretation of quotients for 2-hour periods, even when cor- 

 rectly determined, is a matter of considerable complexity. Indeed, the use 

 commonly made of the respiratory quotient is of but little value in complete 

 metabolism experiments, and recourse must be had to the more complete 

 apportionment of the oxidation among the three principal ingredients of the 

 body protein, fat, and carbohydrate according to the method elaborated 

 and discussed in connection with the statistical data of experiment No. 59 

 (p. 36). 



The respiratory quotients for each day, as determined in these experiments, 

 are of decided general interest judged from the standpoint of the observations 

 of other investigators, and accordingly they are here presented in table 225. 



141 Physiologie des Stoffwechsels (1905), p. 217; also Zeit. f. klin. med. (1906), 

 60, Heft. 3, p. 1. 



