258 



VETERINARY PHYSIOLOGY 



fats alone. When food is taken, the determination of the 

 extent to which each of them is being oxidised depends upon 

 the fact that carbohydrates are rich in oxygen, while fats are 

 poor in oxygen. Hence, to oxidise a given weight of fat to 

 CO2 requires more oxygen than to oxidise the same weight 

 of carbohydrates. 



For this reason the amount of oxygen required to 

 produce say 100 c.c. of COg is greater when fats are being 



Fat 

 100 



Protein 

 100 



A B 



Fig. 132. — Output of Nitrogen and Carbon in a fasting animal to show how the 

 combustion of Proteins and Fats is calculated from it. A, the Protein 

 and Fat metabolised. B, the Nitrogen and Carbon excreted, derived 

 from A. 



consumed than when carbohydrates are being used, and 

 hence, if the CO2 output and the O2 intake are determined 

 and their proportion expressed as — 

 CO2 



0. 



^ the Respiratory Quotient, 



This is found to be, in the case of Fats, 0-7, and in the 

 case of Carbohydrates, 1"0. 



In the case of proteins, in which the amount of oxygen 

 is intermediate between that in fats and carbohydrates, the 

 respiratory quotient is about 0'8. 



Knowing the amount of carbon coming from proteins 

 we can calculate the O2 necessary for their combustion, 

 and any excess of CO2 and of O2 over this is due to com- 



