IX.] MINERAL CONSTITUENTS OF FOODS 175 



ruminant animals they can become converted into 

 proteins by the action of the bacteria in the intestinal 

 tract. Little need be said about the mineral constitu- 

 ents of the food — the ash — though it is essential to build 

 up the bones of the animal, and to supply the salts 

 circulating in the blood. As with the other constituents, 

 some of the contents of the ash are digested and excreted 

 in the urine, some are excreted unchanged in the dung. 

 Salt is one of the most important food constituents, 

 since from it has to be made the hydrochloric acid 

 which is secreted in the stomach, and is required for the 

 digesting processes there proceeding. Phosphate of 

 lime is also absolutely necessary; from it is built up 

 the framework of the bones as well as the phosphorus 

 compounds which occur in all parts of the body. 

 Young animals soon become diseased if fed upon foods 

 in which this constituent is deficient. Of course, besides 

 these main constituents which run the machinery of the 

 body — the fat, carbohydrates, proteins — foods contain a 

 variety of other bodies which give flavour, and affect 

 the disposition of the animal towards its food, although, 

 as far as is known, they do not actually alter its digesti- 

 bility. The question of flavour is as yet beyond 

 scientific treatment, its influence must be left to the 

 observation and judgment of the skilled feeder of 

 cattle. 



When the value of different foods comes to be 

 considered, especially with the object of compounding 

 rations for feeding stock, it is not sufficient to know the 

 percentage of fat, proteins, etc., which the food contains, 

 we must also know how much of each is digestible. 

 For example, pure fat is completely digestible by the 

 animal so that it is wholly burnt up within the body, yet 

 the same fat when disseminated through the mass of a 

 hard seed may, to a greater or less degree, escape the 



