8 RESPIRATORY EXCHANGE OF ANIMALS AND MAN 



While the first condition can generally be taken as fulfilled in normal 

 higher animals fed on a normal diet, or fasting, the occurrence of syn- 

 thesis, especially of fat, is by no means rare. 



The formation of fat from carbohydrate is a process which takes 

 place regularly by the fattening of herbivorous animals. In this case 

 an oxygen rich substance (containing 53 per cent. O and 40 per cent. C) 

 is converted into another which is very poor in oxygen (i i'5 per cent. O 

 and 76-5 per cent C), and it is obvious that some oxygen must be 

 liberated by the conversion. This oxygen will replace the correspond- 

 ing amount of absorbed oxygen in the catabolic processes going on 

 simultaneously, and the quotient will rise. As a matter of fact the 

 quotient does often rise above unity as first observed by Bleibtreu on 

 geese (quotients up to 1*38) and since confirmed in a number of 

 similar cases. 1 



Low quotients may be produced, on the other hand, by the forma- 

 tion and storage of carbohydrate from protein as in diabetes. Magnus- 

 Levy [1894] nas calculated, however, that when carbohydrate is formed 

 from protein the respiratory quotient cannot become lower than 0*68. 

 When lower quotients are observed as in hibernating animals (p. 124) 

 they must, when not due to experimental errors, indicate either forma- 

 tion of carbohydrate from fat, incomplete oxidation by which organic 

 acids are formed to a certain extent instead of CO , or some other 

 metabolic process of an unknown nature. 



It is obvious that the processes mentioned may go on to a certain 

 extent even when the quotient remains within the limits 072 to 0-97, 

 and a certain caution is therefore necessary when the distribution of 

 the metabolism on the different food-stuffs is deduced from the respira- 

 tory quotient. 



Such caution appears doubly necessary when it is remembered 

 that the respiratory quotient, as determined from an experiment, de- 

 pends on the elimination of carbon dioxide and not directly on the 

 production of this gas in the animal economy. As will be shown 

 below (p. 1 6) carbon dioxide is very apt to become stored in the 

 tissues and the blood for some time, while on the other hand it may 

 under certain conditions be washed out by the ventilation of the lungs 

 in excess of the production. 



1 It should be borne in mind, however, that in herbivorous animals a considerable amount 

 of carbon dioxide is often produced by fermentation in the gut, thus producing an apparent 

 increase in the respiratory quotient, which has nothing to do with the metabolism of the 

 animal itself (see later, p. 53). 



