560 JOHtf R. MURLIN 



sure and temperature, it would be found upon reduction to standard con- 

 ditions that the volume of CO 2 produced had just replaced the volume 

 of O 2 consumed. 



The same method may be employed, in fact has been repeatedly em- 

 ployed, especially by the French students of respiratory metabolism, to 

 examine the quality of combustion in the human body. For example, 

 Weiss sealed a child up in a closed box containing pure air, and at the 

 end of an hour drew off samples for analysis. The box had a capacity 

 of 60 liters and in this amount of atmospheric air the child could subsist 

 for several hours. Comparing then the composition of the air at the end 

 of an hour with the composition at-the beginning it was found that, in 

 certain instances, the carbon dioxid produced had exactly replaced the oxy- 

 gen utilized by the child. The observer correctly inferred that carbo- 

 hydrate had been the source of the energy liberated by the combustion; 

 for in carbohydrate there is nothing to unite with oxygen except carbon, 

 the hydrogen present being already cared for by the intramolecular oxygen. 

 In this instance the relation by volume of the carbon dioxid produced to 

 oxygen absorbed would be 1.0. This relationship in metabolism is the 

 respiratory quotient. 1 



The actual chemical reactions involved in the combustion of the sev- 

 eral organic foodstuffs will now be given and the respiratory quotients 

 typical of each deduced therefrom. 

 Glucose, the normal sugar of the blood is oxidized thus : 



C 6 H 12 O G + 6 O 2 = 6 CO 2 + 6 H 2 O 



f> 



The relation of CO 2 by volume to the O 2 is 2 = 1.0, or the rela- 



'*-. 6 U 2 



fi O 

 tion by weight of the O 2 in CO 2 to O 2 absorbed is 2 = 1.0. 



6 C/2 



The respiratory quotient is unity. When a simple fat like palmitine, 

 C 3 H 5 (C 16 H 31 2 ) 3 is burned, conditions are as follows: The fat may be 

 written thus: C 51 H 98 O G and its combustion would proceed according to 

 the equation : 



C 51 H 9S 6 + 72.5 2 = 51 C0 2 + 49 H 2 O 



51 



The relation of CO 2 by volume to the O 2 is f = 0.703, which is 



l2/*5 



the respiratory quotient. With a simpler fat such as the butyrate: C 3 H' 5 

 (C 4 H 7 O 2 ) 3 , the relationship would be quite different, owing to the rela- 

 tively larger quantity of O 2 already present in the molecule. Thus: 

 C 15 H 20 O 2 + 18.5 O 2 = 15CO 2 + 13H 2 O. The respiratory quotient 



15 



would be - 0.81. Food fats are for the most part composed of 

 18.5 



the glycerides of palmitic, stearic, and oleic acids, an average composition 

 on the percentage basis being 7G.5 per cent C; 11.9 per cent H; and 11.6 



