RESPIRATORY QUOTIENT. 831 



carbohydrates, and in the exclusive decomposition of carbohydrates in 

 the animal body the respiratory quotient must be approximately 1. In the 

 exclusive metabolism of proteins it is close to 0.80, and with the decom- 

 position of fat it is 0.7. In starvation, as the animal draws on its own 

 flesh and fat, the respiratory quotient must be a close approach to the 

 latter figure. The respiratory quotient, which is calculated with exclusive 

 combustion of carbohydrate, fat and protein, as respectively, 1, 0.707 and 

 0.809 and with alcohol is 0.667, also gives important information as to 

 the quality of material decomposed in the body, especially with the 

 supposition that the carbon dioxide elimination is not influenced by some 

 special condition such as a change in the respiratory mechanism. Another 

 supposition is that no incomplete oxidation step in combustion is elimi- 

 nated. 



Knowledge as to the extent of oxygen consumption is of special 

 importance in the calculation of the energy metabolism from the extent 

 of gas exchange, and one can under some circumstances approximately 

 calculate the energy exchange from the calorific value of the oxygen 

 alone with regard to the respiratory quotient (ZUNTZ and co-workers). 

 The calorific value of oxygen must be different for each of the three men- 

 tioned foodstuffs, as they require different quantities of oxygen for their 

 combustion. For fat and carbohydrate this calorific value can be readily 

 calculated, as bodies are completely burnt into carbon dioxide and 

 water. One gram of starch uses 828.8 cc. oxygen in its combustion, 

 and produces 828.8 cc. carbon dioxide, and 4183 calories of heat are 

 developed. For one liter (=1.43 gram) oxygen, 5047 calories are pro- 

 duced, therefore for every liter (=1.966 gram) carbon dioxide formed, 

 the same number, 5047 calories, are produced. In an analogous manner 

 the average calorific value of fat for 1 liter of oxygen, 4686 calories, and 

 for 1 liter carbon dioxide, 6629 calories, can be calculated. 



With proteins, because of the unequal composition of the different 

 proteins, the results are uncertain and variable, and the calculation is 

 much more complicated. As example we will give the following calcula- 

 tion of ZUNTZ 1 for the fat-free dry substance of meat. 



This substance consisted in 100 parts 



52.38g.C.; 7.27g.H.; 22.68g.O.; 16.65g.N.; 1.02g.S. 



Of which were found in the urine . . 9 . 406 2 . 663 14 . 099 16 . 28 1 . 02 

 Of which were found in the feces . . 1 . 471 . 212 . 889 . 37 



Retained 41.50; 4.40; 7.69; 0.0; 0.0. 



From this residue, with the taking up of 96.63 liters of oxygen, besides 39.6 

 grams water, 77.39 liters carbon dioxide were formed and the respiratory quotient 

 is therefore 0.801. Now 100 grams of such dry meat substance on complete 



1 Zuntz, Loewy, Miiller and Caspar!, Hohenklima und Bergwanderungen, Berlin, 

 1006, pages 102, 103 



