668 METABOLISM 



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

 bered (page 54.7), 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. 



