668 METABOLISM 



an examination of the respiratory quotient, which, it will be remem- 

 bered (page 547), varies according to the nature of the foodstuff or body 

 constituent that is undergoing metabolism at the time, being about 1 

 with carbohydrate and about 0.7 with protein. If the quotient is 

 observed during starvation, it will often be found to fall below 0.7, a 

 figure which can be explained only by assuming that oxygen has been 

 retained in the body beyond the quantity which is necessary for imme- 

 diate purposes of oxidation (cf. equations on page 548). 



Since it is known that this retained oxygen can not exist in the body 

 in a free state it must be concluded that it has become incorporated 

 into substances having a high oxygen content. Such would be the case 

 if protein or fat, which contains only from 12 to 20 per cent of oxygen, 

 were converted to carbohydrate, which contains about 53 per cent. 

 Utilization of inhaled oxygen for this purpose, as we have seen, becomes 

 very striking in the case of hibernating animals during the winter sleep. 



