Principles of Feeding 59 
weak-boned because of the lack of mineral matter in the food. 
If to the corn ration some food rich in mineral matter, such 
as alfalfa, or even wood ashes, is added, no difficulty is ex- 
perienced. Hens always require more lime than is found in the 
food. This is strikingly illustrated when we compare the com- 
position of eggs and corn, for example, the former containing 
12.2 per cent ash, the latter only 1.5 per cent. The ash in the 
food of the milk cow also deserves special consideration on ac- 
count of phosphoric acid, lime, and potash so abundantly found in 
the milk which she secretes. 
111. Protein. — So far as known, the proteids of the food are 
the only source of the proteids of the body. In other words, 
the muscles, the connective tissues, the blood, the skin, the hair, 
the horn, the hoofs, and the larger part of the tissues of the secretive 
and excretive organs, owe their formation to the protein of the food. 
Since these are the tissues that largely determine the vigor and 
quality of the animal, and since they are formed rapidly in the 
early stages of growth, a normal and continuous development 
demands an abundant supply of protein food. In addition to 
this, protein is a source of fat and can serve as fuel, or as a source 
of energy. 
112. Carbohydrates. — Carbohydrates are used to maintain 
heat and to produce fat. Formerly it was thought that carbohy- 
drates were used for the former purpose only, but it is now well 
established that the animal fats may have their source in the 
carbohydrates. Again, experiments with milk cows show clearly 
that milk-fat may also be derived from carbohydrates. Because 
carbohydrates can be used as heat-producers and as fat-formers, 
and because of their ease of digestion and cheapness of production, 
this group of nutrients is very important. 
113. Fat. — Fat, like carbohydrates, serves as a source of 
heat and of animal fat. The differences are that the supply 
of carbohydrates is much larger, and the heat value of a simi- 
lar weight of fats much greater, —as we have already seen 
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