Computing Rations for Farm Animals 1565 



understanding of the relation of the food to the body the dry matter may 

 be divided into four groups of substances, namely, ash, nitrogenous sub- 

 stances, carbohydrates, and fats. The dry matter of the body is so 

 grouped because this is the usual grouping of the chemical compounds 

 that make up plants, and it is desired to study the relation of the groups 

 in plants with the same groups in the body. 



Ash. — The ash is the mineral part of the body. In determining the 

 mineral part of any substance in the chemical laboratory the substance 

 is completely burned and all the organic matter goes off in the form of 

 gas, leaving behind the mineral matter in the form of ash. The ash of 

 the body constitutes two to five per cent of the live weight. This mineral 

 matter occurs mostly in the bones, but some is found in all the tissues. 



Nitrogenous substances. — The nitrogenous parts of the body are known 

 by various names, which are also applied to the nitrogenous substances 

 in foods. Some of these names are protein, proteids, albuminoids. The 

 term protein will here be used to designate all the nitrogenous substances 

 of the body, the body products, and the food. Examples of the nitrog- 

 enous parts of the body are lean meat, skin, hoofs, horns, and hair; of 

 the body products, wool, feathers, the albumen of eggs, and the curd of 

 milk. In food, good examples of protein as such cannot be given, since 

 the protein does not exist in any part of the plant in so nearly pure a state 

 as it does in the hair, hoofs, or horns of the animal. The protein of the 

 body is built up entirely from the protein of the food. The distinguishing 

 characteristic of protein is that it contains nitrogen. 



Carbohydrates. — The carbohydrates of the body and of the food are 

 made up of carbon, hydrogen, and oxygen. Examples of common carbo- 

 hydrates are sugar and starch. 



Very few carbohydrate substances exist in the body, except in the 

 blood. These substances are taken from the blood to furnish the energy 

 of the muscles and part of the heat of the body. The liver acts as a 

 storehouse of carbohydrates and regulates the supply to the blood so 

 that the amount of carbohydrates in the blood is kept constant for prop- 

 erly supplying the muscles. It is also thought that the liver has the power 

 to make carbohydrates from the fats and the protein of the food if the 

 supply of carbohydrates is limited. 



Fats. — The fats in the body are used to supply energy to the animal 

 for work, and to furnish fuel for heating the body. The fats serve also 

 as the storehouse of heat and energy; they are added to when the food 

 supply is in excess of that needed by the animal for its work or pro- 

 duction, and they are drawn upon when the food supply is short. Fats 

 have the same function that carbohydrates have except that they are 

 more concentrated, supplying about 2j times as much energy to the 



