RELATION OF FOOD TO ANIMAL REQUIREMENTS. 97 



from 1 : 2'3 to 1 : 4-1, and the latter proportion is seldom 

 much exceeded in any sample of milk. In supplying very 

 young animals with artificial food the above facts must be 

 borne in mind ; the food should clearly be of an easily 

 digestible character, and contain a considerable proportion 

 of albuminoids and fat. Instead of this, foods rich in 

 starch are too often employed. Linseed is perhaps, of 

 ordinary foods, the one most similar to milk in composition. 

 As the animal grows the quantity of food it requires 

 increases, at the same time a larger proportion of the food 

 is applied to the production of heat and mechanical work ; 

 the proportion of nitrogenous matter in the food may 

 therefore gradually be diminished, carbo-hydrates and fat 

 being quite as fit as albuminoids for producing heat and 

 work. Under natural conditions this diminution in the 

 nitrogenous character of the diet soon takes place, the 

 animal daily taking more and more grass in addition to 

 its mother's milk. The albuminoid ratio * of the diet of 

 rapidly growing animals may vary from 1 : 5 to 1 : 7, the 

 more nitrogenous diet being most suitable for younger 

 animals, or for the production of more rapid increase. 



The adult Animal. — Food, we have already seen, is 

 primarily employed for the renovation of the animal 

 tissues, and for the production of heat and mechanical 

 work ; by far the greater portion of the food is applied to 

 the latter purposes. 



Much of the work performed by an animal is internal, 

 and consists in the muscular movements which produce 



* The albuminoid ratios henceforward given will represent, as far as pos- 

 sible, the proportion of true albuminoids present in the food. 



I H 



