NUTRITION OF POULTRY 179 



according to the kind and condition of the article. Fiber is largely 

 indigestible. Water is the necessary solvent for food solids. It is 

 present in sufficient quantities for this purpose only in succulent 

 vegetables and fruits and in fresh meats. As its function is mechan- 

 ical, it is not considered in discussing and calculating nutritive 

 values, but in feeding practice the quantity of water in the food 

 may have an important bearing on results. Fiber also seems to 

 have a mechanical function. 



Protein is the common name for the nitrogenous substances 

 which supply material for the structure of the body. The white 

 (albumin) of an egg is protein, supplying the materials for a fully 

 developed chick. 



Carbohydrates are principally starches and sugars supplying 

 fuel (for heat and energy) and fat (reserve fuel for the same 

 purposes). 



Fats (as food) "are considered highly concentrated carbohydrates. 



Minerals in animal nutrition are chiefly calcium and phosphate 

 compounds. In poultry feeding, lime in available form is of special 

 importance. 



The common grains contain these food elements in snch propor- 

 tions that, so far as actual nutrients are concerned, any of them 

 will make a good gi'ain ratioti for ponltiy sufficiently supplied with 

 greeti food and animal food, and so able to balance their own 

 ration, as they do in the natural state. The differences in the 

 composition of the whole grains are in some cases considerable, 

 yet not so great that they cannot be equalized by variation in the 

 quantities of other foods and by the power of organisms to utilize 

 an excess of one kind of nutrients to supply a deficiency of an- 

 other, or to conserve available supplies of another. Thus an excess 

 of protein is converted into fat and stored in the body, and an 

 excess of carbohydrates or fat, though not convertible into protein, 

 is also stored up as fat in the body, furnishing a reserve of heat and 

 energy. The by-products of articles manufactured for human beings 

 often have nutrient elements in quite different proportions from 

 the articles of which they are made. Usually the by-product is less 

 valuable as a food, but in some cases it contains a larger propor- 

 tion of some valuable element (see descriptions of foodstuffs in 

 the next chapter). 



