i84 PLANT PRODUCTS 



combination with food, is supplied in excess, an unnecessary 

 strain is placed upon the kidneys of the animals concerned. 

 Increased metabolism therefore takes place, and the water 

 actually passed has to be heated to the body temperature. 

 Waste of energy, and therefore food, is the result of supply- 

 ing unnecessary amounts of water. It is, of course, not 

 practical to cut the water supply down below the figure which 

 is necessary for the health and comfort of the beasts. They 

 themselves will be the first to make objection should they 

 be kept thirsty. 



The Fat in Foods. — The foods fed to beasts generally 

 contain fat in small quantities. The common anal3^ical 

 figures, which represent the total amount of material 

 extracted from the food by the use of ether, include other 

 substances than true oils and fats. Anything in the nature 

 of wax or resin will also be extracted by ether. In the case 

 of the oil seeds, the proportion of waxes and resins is relatively 

 small, but in such food materials as hay, the proportion 

 of ether extract which is not true fat is very considerable, 

 and may amount to one-half. In such cases, however, the 

 total percentage of oil is too small to make much difference, 

 whether it is considered or not in calculating rations. The 

 true fats are glycerine esters of some of the fatty acids (see 

 p. io8). When fed to stock, the fat undergoes hydrolysis 

 in the process of digestion with the production of the 

 corresponding fatty acids and glycerine, which are absorbed 

 and built up into the fatty tissues of the animal body. 

 Considerable portions of the breaking-down products of 

 the fats will be oxidized, for the purpose of producing heat, 

 in consequence of which the properties of the fat laid on 

 by the animal are more dependent upon the animal con- 

 suming the food than on the properties of the fat in the food 

 consumed: For rough purposes, the food value of fats is 

 about 2 J times the value of the same weight of carbo- 

 hydrates. 



The Nitrogenous Matter in Food. —The proteins in the 

 foods are similar to those described in Part III., p. 147. 

 So far as regards the more concentrated foods, the 'total 



