BASIC PRINCIPLES. 



29 



With modern apparatus it is possible to arrive at an even more exact 

 knowledge of the energy output by determining both the oxygen con- 

 sumption and the carbon-dioxide production and calculating the respi- 

 ratory quotient. Zuntz, to whom we are especially indebted for the 

 introduction of this method for computing the heat output, has pains- 

 takingly computed the calorific value of oxygen with different respira- 

 tory quotients, and these figures may be considered to-day as the best 

 data that we have for the computation of the energy output from the 

 measurement of the gaseous exchange. In the Zuntz laboratory, where 

 practically all of the experiments carried out have been made upon 

 adults with a mouthpiece or upon animals with tracheal fistulas, the 



Table 15. — Calorific equivalents of carbon dioxide. 



determinations of the oxygen consumption are as accurate as are those 

 of the carbon-dioxide production; consequently Zuntz has utilized the 

 calorific values of oxygen, and these have been given in tabular form 

 in one of the publications from his laboratory. 1 Knowing the respira- 

 tory quotient, the calculation of the calorific value of carbon dioxide is 

 a simple one. Since, in our respiration apparatus, the carbon-dioxide 

 determinations for short periods are even more exact than are the deter- 

 minations of the oxygen, we give in table 15 the calorific equivalents of 

 carbon dioxide with the varying respiratory quotients, particularly as this 

 table will be used extensively in the computation of our own researches. 

 Since any form of indirect calorimetry must of necessity be somewhat 

 speculative, 2 one must always rely for fundamental values upon direct 

 heat measurements. Such measurements have been extensively made 



*Zuntz and Schumburg, Physiologie des Marsches, Berlin, 1901, p. 361. 



2 It will be noted that in this publication the computation of the energy derived from protein is 

 neglected and that the total energy output is computed only from the amounts of carbon dioxide 

 and oxygen. The possible error in neglecting the protein has been computed by Magnus-Levy to 

 be somewhat under 1 per cent, and as the determinations of nitrogen were not feasible in our studies, 

 we have used the method of simple computation from the gaseous exchange as recommended by 

 A. Loewy. (Loewy, Oppenheimer's Handbuch der Biochemie, Jena, 1911, 4, p. 281. See also, 

 Magnus-Levy, von Noordcn's Handbuch der Pathologie des Stoffwechsels, Berlin, 1896, 1 , p. 207.) 



