METABOLISM 197 



If we express these results in the form of a ratio between the 

 carbon dioxide produced and the oxygen used, we have : 



Vol. CO2 r u u ^ 4. 6 vol. i.o 

 ,, , ^ = for carbohydrates = — =1.0 



Vol. O2 6 vol. 1.0 



= for fats lMJ^=9:l=o,7 



163 vol. 1.0 



Now in the animal body the oxidation of the food products or 

 body substance is brought about in the muscle cell by the oxygen 

 of the inhaled air and the carbon dioxide gas produced by the 

 reaction is then exhaled by the lungs. The two gases then are 

 involved in the process of respiration and this quotient, be- 

 tween the carbon dioxide and oxygen, in the oxidation of car- 

 bohydrates or fats, may be determined by accurately measur- 

 ing the oxygen inhaled and used and comparing it with the 

 carbon dioxide produced and exhaled. This quotient is there- 

 fore known as the respiratory quotient. 



When now an animal that is fasting and in which all reserve 

 carbohydrate food has been used up is examined, by a deter- 

 mination of this quotient it is found that the quotient approxi- 

 mates 0.7, the value for the oxidation of fats. This must mean 

 that the animal is using up body fat as fuel for the energy pro- 

 duction of the body. 



In a similar way if the animal body is supplied with a suffi- 

 cient supply of carbohydrate food, but not an excess, the respi- 

 ratory quotient approximates i.o, the value for the oxidation of 

 carbohydrates. This means that under these conditions the 

 animal is using, as fuel for its energy production, only carbo- 

 hydrate food. When the carbohydrate food supply is less than 

 sufficient to furnish the necessary energy of the body, it is found 

 that the respiratory quotient lies between 0.7 and 1.0, which 

 means that the body is oxidizing both carbohydrates and fat. 



If, however, the animal is fed a large excess of carbohydrate 

 food, so that both liver glycogen and muscle glycogen are stored 

 to their maxima, it is found that a determination of the 

 respiratory quotient gives a value greater than 1.0. This can 



