THE CARBON BALANCE 549 



Influence of Metabolism. Apart from diet, the respiratory quotient 

 may often be altered by changes in the metabolic habits of the animal. 

 These are most conspicuously exhibited in the case of hibernating 

 animals. In the autumn months, when the animal is eating voraciously 

 of all kinds of carbohydrate food and depositing large quantities of 

 adipose tissue in his body, the respiratory quotient may be considerably 

 greater than unity, indicating therefore either that relatively more 

 carbon dioxide is being discharged or less oxygen retained. As a matter 

 of fact, it can easily be shown that it is the former of the causes that 

 is responsible for the higher quotient, the explanation for the increased 

 production of C0 2 being that, as the carbohydrate changes into fat, the 

 relative excess of carbon in the former is got rid of as C0 2 , as indicated 

 in Equation 5. On the other hand, if the animal is examined while in 

 his winter sleep, it will be found that the respiratory quotient is now 

 extremely low, often not more than 0.3 to 0.4, which may be interpreted 

 as indicating either an excessive absorption of oxygen or a markedly 

 decreased excretion of carbon dioxide. As a matter of fact, there is a 

 great diminution in both the excretion of carbon dioxide and the intake 

 of 2 , because the whole metabolic activity of the animal is extremely 

 depressed, but this diminution affects the oxygen to a much less degree, 

 indicating therefore a relative increase in the oxygen retention. The 

 explanation is that the oxygen is being used in the chemical process in- 

 volved in the conversion of the- fat back into carbohydrate. 



Whatever may be the relationship between fat and carbohydrate in 

 the nonhibernating animal, there is no doubt that during hiberna- 

 tion, before the fat stores are burned, fat is converted into something 

 closely related to carbohydrates, the equation for the process being rep- 

 resented as given above (No. 4). 



In man and the higher mammalia, the only condition, apart from diet 

 which can affect the nature of the combustion process is disease; thus 

 in total diabetes (page 678) the organism loses, the power of burning 

 carbohydrate, so that whatever the diet may be, the respiratory quotient 

 is very low, never higher than that representing combustion of fat and 

 protein. It has been claimed by certain investigators that in diabetes 

 the respiratory quotient may fall considerably below 0.7, indicating, as 

 in hibernating animals, that fat is being converted into carbohydrate. 

 The most recent and carefully controlled observations, however, deny 

 this claim, and for the present we must assume that in the body of man 

 fat is not converted into carbohydrate (see page 664). In numerous other 

 diseases investigated by.Du Bois and others 6 no qualitative change in 

 the combustion processes in man has been brought to light. 



