208 NUTRITION OF FARM ANIMALS 



0.7 liter of carbon dioxid. Similarly, it may be computed that 

 if protein of average composition be oxidized to urea, carbon 

 dioxid and water, the respiratory quotient will be approxi- 

 mately 0.8, although in reality the quotient for protein varies 

 according to the nature of the nitrogenous products formed and 

 the amount of carbon thereby withdrawn from oxidation to 

 carbon dioxid. Ordinarily, however, the proportion of the 

 gaseous exchange of the body due to the katabolism of protein 

 is comparatively small, so that if, for example, the respiratory 

 quotient closely approaches i.o, it is clear that the katabolism 

 must be chiefly that of carbohydrates, while if, on the other 

 hand, its value approaches 0.7, it is equally evident that the 

 katabolism must be chiefly that of fat. Values for the respira- 

 tory quotient intermediate between these extremes imply that 

 the katabolism is in part that of fats (or proteins) and in part 

 that of carbohydrates. 



The respiratory quotient of course affords no information 

 regarding the balance between income and outgo but its deter- 

 mination gives valuable information as to the nature of the 

 material which is being katabolized in the body, particularly 

 in short periods. 



297. The respiration apparatus. A determination of the 

 gaseous exchange of an animal, such as is necessary in order to 

 formulate the complete balance of matter, requires the use of 

 some form of special apparatus known as a respiration apparatus. 



In its simplest and earliest form the respiration apparatus 

 consisted of a closed chamber of known capacity, such as was 

 used by Crawford, Mayow, Black, Priestly, Lavoisier and 

 others in their early experiments. The animal was placed in 

 the hermetically sealed apparatus and the changes in the com- 

 position of the enclosed air which were brought about by its 

 respiration were determined. Evidently, however, the method, 

 while charmingly simple, is open to objections. The oxygen 

 of the air is gradually consumed, while the carbon dioxid and 

 other products of respiration accumulate. Even if the experi- 

 ment be broken off before fatal results to the animal ensue, it 

 is made under varying and increasingly abnormal conditions, 

 while no very long trials are possible. 



Two obvious methods of avoiding this difficulty at once 

 suggest themselves; either to absorb the products of respira- 



