INFLUENCE OF VARIOUS CONDITIONS ON RESPIRATION. 715 



of the extent or character of the physiological oxidations in the body, 

 since any alteration in the depth or rapidity of the respiratory 

 movements may, by changing the ventilation of the alveoli, make 

 a difference in the output of CO 2 , a difference, however, which 

 would have no significance in regard to the nutritive changes of the 

 body. In longer experiments and in those during which the respira- 

 tory movements are not altered the determination of this ratio 

 throws light upon the nature of the material that is undergoing 

 oxidation in the body, as will be apparent from the following 

 considerations: Under ordinary conditions of rest and upon a 

 mixed diet the R. Q. varies between 0.65 and 0.95 (Loewy) or 

 between 0.75 and 0.89 (Magnus Levy). If, however, the material 

 oxidized in the body is entirely carbohydrate, the R. Q. should be 



f^(~\ 



equal to unity: -Q- 2 = 1. All the oxygen used in the combustion 

 might be considered as uniting with the C to form CC>2, since 

 enough O is present in the sugar to account for that used in oxidiz- 

 ing the H to H^O. Or, as expressed in a reaction, 



Dextrose. 



CeH 12 O 2 + 6O 2 = 6CO 2 + 6H 2 O. R. Q. = f = 1. 



The number of molecules of CO 2 formed in the oxidation is equal 

 to the number of molecules of O 2 used. If fats alone are oxidized 

 in the body the R. Q. should be low (0.7), since these substances 

 are poor in oxygen compared with the amount of C and H present 

 in the molecule. The combustion of palmitin may be represented 

 as follows : 



Palmitin, C 3 H 5 (C 16 H 31 O 2 ) 3 = C^H^A. 

 2(C H H fle 6 ) + 1450 2 = 102C0 2 + 98H 2 O. 

 R- Q. = ttt = 0.703. 



In estimating the respiratory quotient for proteins one must 

 bear in mind the fact that these substances vary somewhat in 

 composition and, moreover, that they are not completely 

 oxidized in the body. Calculations based upon the amount of 

 unoxidized carbon and hydrogen escaping in the urine and 

 feces give the average figure of 0.801 for the R. Q. of proteins. 

 It is evident from these statements that an increase in the 

 proportion of carbohydrate food will cause the R. Q. to approach 

 unity, while an increase in protein and especially in fat will 

 lower its value. In this way we can understand the actual 

 variation observed in the average respiratory quotient of different 

 classes of animals, as shown in the following brief table (Loewy) : 



Horse, herbivorous R.Q.= 0.960 

 Sheep, " =0.900 



Man, omnivorous " =0.800 

 Dog, carnivorous " =0.750. 



