290 DOMESTIC ANIMALS, DAIRYING, ETC. 



pound of intestinal fat showed considerable variation. It was highest 

 as a rule with the silage fed cattle. WMle the greater weight of the 

 intestinal fat may be attributed in a measure to the succulent food, 

 it is also influenced by individuality and is not a factor of sufficient 

 importance to have any marked influence on the investigation. 

 (Tenn. No. 3, Vol. XV.) 



RATIONS AND ENERGY VALUES. 



Components of the Animal Body. The essential working parts 

 of the body contain a great variety of substances, but these may, for 

 our present purpose, be grouped under three heads water, ash, and 

 protein. The bones, constituting the framework of the body ; the liga- 

 ments, muscles and tendons which bind together and move the bones ; 

 the skin and hair, or wool, which cover and protect the body; the 

 internal organs of circulation, respiration, digestion, excretion, and 

 reproduction ; the brain and nerves in short, the whole mechanism 

 of the body can be regarded as being composed substantially of 

 these three classes of substances 



Water. Rarely less than half and sometimes as much as three- 

 fourths of the weight of the live animal consists of water. The pro- 

 portion of water is greatest in young and lean animals and decreases 

 as they become more mature or fatter. 



Ash. The ash or mineral matter is the portion left after com- 

 plete burning. Its presence is most familiar in the bones, but it is 

 found in all parts of the body and is just as essential as water or pro- 

 tein. It amounts to from 2 to 5 per cent of the weight of the body. 



Protein. Protein is the name given to a highly important group 

 of substances, of which the white of egg, washed lean meat, the casein 

 of milk, the gluten of wheat flour, etc., are familiar examples. They 

 are composed of the chemical elements carbon, hydrogen, oxygen, 

 nitrogen, and sulphur. They are what are commonly called organic 

 substances, which simply means that they may be burned completely 

 in air or oxygen. They differ from the other groups of substances 

 found in the animal body in containing sulphur and especially nitro- 

 gen, the latter element constituting from 15 to 18 or 19 per cent of 

 their weight. 



Protein is the basis of the living tissues of the body the so-called 

 protoplasm and is the substance through which life especially mani- 

 fests itself. In the body it is always associated with water and ash. 



Fat. Besides its working parts, the body contains a store of 

 reserve material in the form of fat. While the fat deposits in the 

 body are of use mechanically as cushions between the various organs 

 and as a protecting layer under the skin, nevertheless fat represents 

 essentially a storage of material derived from food consumed in ex- 

 cess of the body's immediate needs. When the food is insufficient or 

 entirely lacking, this store of surplus material is drawn upon, and 

 the animal gradually becomes lean. The percentage of fat in the 

 bodies of agricultural animals may vary greatly, but seldom falls 

 below 6 or rises above 30 per cent. 



Glycogen. Besides fat there are stored up in the muscles, liver, 

 and other organs of a healthy animal rather small amounts of a sub- 



