NUTRIENTS 171 
various organs, arid also form a protecting layer under the skin, 
giving it a plump, full appearance. The proportion of fat in the 
bird’s body varies from 15 to 34 per cent, being lowest in the adult 
bird which is emaciated from disease or improper feeding, and 
highest in birds which are well fattened. 
Glycogen.—Another material called glycogen, very similar to 
starch, is stored in relatively small amounts in the organs of a 
healthy animal. This substance resembles fat in that it contains 
neither nitrogen nor sulphur, but is composed entirely of hydrogen, 
oxygen, and carbon, in the same proportion as in starch. It may 
be called animal starch. 
Nutrition is the process by which life is maintained and indi- 
vidual growth is promated. It controls the wearing away and 
the building up of the body tissues, converts feed into heat and 
energy, and supplies the material for products which are essential 
to normal life. The chief processes of nutrition are digestion, ab- 
sorption, circulation, assimilation, and respiration. 
Nutrients.—Materials in feeds, as seen in their raw state, are 
not transformed directly into living tissue, but they are first broken 
up into simple compounds, called nutrients, which go toward the 
formation of the solids and fluids of the body. Their classification 
is the same as that of the components of the body already consid- 
~ ered, with an added group (carbohydrates), making five in all,— 
namely, (1) protein, (2) fat, (3) carbohydrates, (4) mineral mat- 
ter (or ash), and (5) water. 
Protein.—The groupof nutrients classed as protein includes com- 
pounds which contain those elements that are found in the tissues of 
all plants and animals used in feeds. The classes of materials which 
provide protein are always necessary, are the most expensive to buy, 
and are the hardest to produce at home; hence, in purchasing feed 
stuffs for the various rations, the proportion of protein they con- 
tain is usually the factor which determines the price to be paid. 
Fat.—In the form of oils, in seeds, in vegetable products, and 
in animal tissues, fat is familiar to all. Most feed stuffs, especially 
if from vegetable sources, are relatively poor in oil content. Some 
vegetables, as flax and cotton, store up oil instead of starch and 
are at the same time rich in protein; but, as a rule, the materials 
commonly available for poultry feeding though poor in fat are 
rich in carbohydrates. 
Carbohydrates.—This third class of nutrients includes the 
starches, sugars, and fibres which are chiefly valuable for producing 
