172 THE CHEMISTRY OP THE FARM 



its milk, and assimilate at the same time 98 per cent, 

 of the lime, and 74 per cent, of the phosphoric acid. 

 During the first few weeks of a calf's life, 10 lbs. of 

 milk, containing 1"3 lbs. of dry matter, will yield 1 lb. 

 of live weight. A calf will sometimes gain in weight 

 as rapidly as a fattening ox ten times as heavy. These 

 extraordinary rates of increase are due to the very 

 large amount of food consumed in relation to the 

 weight of the body; to the watery nature of the 

 increase in a young animal, and the small formation 

 of fat. 



As the animal grows and takes more exercise, a 

 larger proportion of the food is applied to the pro- 

 duction of heat and mechanical work. The propor- 

 tion of nitrogenous matter in the food may therefore 

 gradually be diminished, carbohydrates 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 addi- 

 tion to its mother's milk. It is interesting to remark 

 that human milk, which forms the sole support of the 

 child for a far longer period than is the case with farm 

 animals, contains the smallest proportion of nitro- 

 genous matter. 



An animal when very young consumes more food in 

 relation to its body weight than in any later period of 

 its life. As growth proceeds, the quantity of food 

 eaten per day steadily increases, but the proportion of 

 food to body weight considerably diminishes, at the 

 same time the daily increase in live weight becomes 

 gradually less. The return in increase for food con- 

 sumed thus gets steadily less as the animal matures, 



