POODS AND FEEDING 649 



Proteids consist} of carbon, hydrogen, oxygen, nitrogen, and 

 sulphur, united in different proportions. Carbohydrates are 

 composed of carbon, hydrogen and oxygen. Fat is similar 

 in composition to carbohydrates, but in its combustion out- 

 side the body yields approximately two and a half times as 

 much heat as that produced by an equal weight of carbo- 

 hydrate. Fat as a nutrient, is therefore empirically regarded 

 as equivalent to two and a half times the same weight of 

 carbohydrate material. The percentage of digestibility of 

 the common food stuffs has been determined experimentally 

 and is pretty uniform in all healthy animals. In 100 lbs. of 

 hay there are approximately : 



Per cent. Lbs. 



Lbs. digested. digested. 



Protein 9.7 .56 5..4 



Carbohydrates 67.3 .60 40.4 



Fat ; 2.5 .48 1.2 



If we multiply the 1.2 lbs. of digestible fat by 2.5 to 

 reduce it to the same terms as carbohydrates according to 

 the empirical premises stated above, we have 3 lbs. of carbo- 

 hydrates. The total amounts of carbohydrates digestible in 

 100 lbs. of hay is therefore 40.4 lbs. + 3 lbs. = 43.4 lbs. of 

 jion-nitrogenous matter. The nitrogenous nutrient consists of 

 >5.4 lbs. of digestible protein, and the proportion of the latter 

 to the digestible non-nitrogenous material is as 1 to 8. This 

 .proportion in any given fodder is called the nutritive ratio, or 

 the relation of the nitrogenous to the non-nitrogenous nutri- 

 ents. The nutritive ratio is of the greatest importance, as it 

 enables us to compose a proper ration with almost any kinds 

 <^f fodder at hand, by so adjusting them that we secure the 

 right proportion of nutrients. The proper nutritive ratio is 

 indeed that proportion of nutrients which. has been found to 

 be most economically and physiiologically valuable in any 

 ^iven class of animals and for any given purpose. The 

 nutritive ratio varies accordingly for different animals and 

 f PI" the same animals under different conditions. Such ratios 



