BREEDS OF HORSES 53 



in a general way are quite easily understood. The chief constitu- 

 ents are: Protein, Fats, Carbohydrates, Mineral Matter. 



Protein is a name given to a group of food constituents that 

 contain nitrogen or nitrogenous compounds. This group is made 

 up of true proteids and albumens, such as the gluten of wheat, 

 white of egg, etc. 



Fat includes the true vegetable fats and oils, like the oil of 

 cotton seed as well as vegetable wax, etc. In brief, it may be stated 

 that it includes, as it is used in this connection, all those substances 

 that are dissolved out of the food by ether and is known as an ether 

 extract. 



Carbohydrates include starches, sugars, crude or woody fibre, 

 etc. Carbohydrates are sometimes divided by chemists into groups, 

 as nitrogen free extract and crude fibre. 



Mineral matter includes the inorganic bodies present in the 

 form of salts in the juices and tissues of different feeding stuffs, 

 some of the principal elements of which are sodium, potassium, cal- 

 cium, sulphur, etc. The term ash is often and very appropriately 

 used to express this matter; since the mineral matter represents that 

 which is left when the food in question is burned. 



Functions of Food. 1. To supply material to build up the 

 animal body, and to repair waste of the body through work, exer- 

 cise, etc. 2. To yield energy. 



The chemical composition of foods serves as a basis for much 

 of their value for building and repairing the various tissues of the 

 body. The value of energy, however, must be learned in another 

 way. The most usual way of measuring energy is in terms of heat, 

 a calorie being taken as a unit. This is the amount of heat which 

 would be required to raise the temperature of one kilogram (about 

 2 1-5 pounds) of water one degree C., or about 1.8 degrees F. In- 

 stead of this, the unit of mechanical energy, the "foot-ton" (the 

 force which would lift one ton one foot) may be used, but it is not 

 as convenient. One calorie corresponds very nearly to 1.54 foot- 

 tons. In compounding a feeding ration the relation between the 

 quantities of nitrogen compounds in the food and the nitrogen free 

 compounds is called the "nutritive ration." In calculating this 

 ratio one pound of fat is taken as equivalent to 2.25 pounds of 

 carbohydrates; this being approximately the ratio of their fuel 

 values. So that the nutritive ratio is actually that of the protein 

 to the carbohydrates plus 2.25 times the feed. All the organs and 

 tissues of the body contain nitrogen. Protein is the only constitu- 

 ent of the food which supplies this element, and is therefore essen- 

 tial for building and repairing bodily tissues. Protein, however, 

 and carbohydrates may be burned within the body, and therefore 

 serve as a source of energy. The mineral matter in food is required 

 for a number of different purposes; a considerable amount being 

 needed in the growing animal for the formation of the bony skele- 

 ton, teeth, nails, hoofs, etc. ; some is also present in the various organs 

 and tissues. The mineral matter cannot be regarded as a source of 

 energy, since it cannot be burned within the body. The water 



