CALCULATION OF THE CALORIC VALUE. 889 



The figures for the oxygen vary less than those for the carbon dioxide, 

 and this is a reason why the oxygen values are better suited than the 

 C02 values for calculating the energy production from the extent of gas 

 exchange. Other investigators have obtained results which correspond 

 more or less with the above values for the heat value of oxygen, and E. 

 VOIT and KuMMACHER, 1 who have made calculations in another way, 

 have obtained still smaller differences for the relative oxygen value. 



From what was said above we can calculate the extent of protein 

 metabolism, the corresponding development of energy and the correspond- 

 ing absorption of oxygen and carbon dioxide formation, from the quantity 

 of nitrogen in the urine. If we subtract the oxygen and carbon dioxide 

 values from the total, directly determined gas exchange, the result repre- 

 sents the fats and carbohydrates used. According to ZUNTZ from this 

 residue we can calculate the heat value of the oxygen used as well as the 

 division of the decomposition of the fat and carbohydrate by consider- 

 ing the respiratory quotient. For this purpose ZUNTZ and SCHUMBURG 

 have constructed a table, an abstract of which we give below, taken 

 from the work of MAGNUS-LEVY. 2 



R. Q. Calories value Division in per cent. 



per 1 liter O. Carbohydrate. Fat. 



1.000 5.047 100 



0.950 4.986 83 17 



0.900 4.924 66 34 



0.850 4.863 49 51 



0.800 4.801 32 68 



0.750 4.740 15 85 



0.707 4.686 100 



As the calorific oxygen values in the combustion of protein, fat 

 and carbohydrate show no great differences among themselves, in those 

 cases where, as in starvation, the part taken by the proteins in the total 

 metabolism is relatively small, one can calculate the total energy exchange, 

 without any striking error, from the respiratory quotient and the oxygen 

 used. This is especially important in experiments of short duration 

 where the protein metabolism cannot be directly determined, but is 

 calculated from the nitrogen elimination occurring during a longer time. 

 The method of ZUNTZ and GEPPERT, mentioned on page 869, has shown 

 itself especially useful in the study of the material and force exchange 

 in these experiments of short duration, while the respiration apparatus 

 constructed on PETTENKOFER'S or the REGNAULT-REISET principle are 

 only useful in experiments over a longer period. 



KAUFMANN 3 incloses the individual to be experimented upon in a capacious 

 sheet-iron room, which serves both as a respiration-chamber and a calorimeter, 



1 Voit, Zeitschr. f. Biol., 44; Kummacher, ibid. 



2 A. Magnus-Levy in v. Noorden's Handb. d. Pathol. des Stoffwecheels, Bd. 1. (1906). 

 * Arch. d. Physiologic (5), 8. 



