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CHAPTER XIII. 

 FOODS AND FEEDING. 



IN previous chapters many references have been made to 

 the chief constituents of the food of animals. 



In this chapter will be given a summary of some of the 

 chief facts relating to the composition, digestibility, and other 

 properties of foods, and to the principles upon which the con- 

 struction of rations or diets for special purposes is based. 



The Composition of Foods. This subject has already been 

 discussed (Chap. IX.). The useful constituents of foods are 

 classed as 



( Carbohydrates, 



1. Non-nitrogenous J Fat, 



^Minerals ; 



fAmides, 



2. Nxtrogenous -..{ Albuminoids . 



while in a third class are placed the portions which are 

 thought to be indigestible and comparatively useless the 

 so-called "crude fibre." Though this method of classification 

 is not entirely satisfactory, it is convenient, especially as the 

 larger number of published analyses are expressed according 

 to it. The more satisfactory plan (possible because of recent 

 improved methods of analysis), in which the carbohydrates are 

 differentiated, has been already alluded to. Unfortunately 

 only a limited number of food stuffs have hitherto been 

 examined by these later methods. 



Another improvement in food analysis, not, however, of such 

 recent introduction, is the differentiation of the nitrogenous 

 constituents into amides and albuminoids. In older analyses 

 the total nitrogen of the food was determined, and, multiplied 

 by 6*25, was taken as a measure of the albuminoids. 



As already stated, many vegetable products contain a con- 

 siderable proportion of their nitrogen in the form of amides 



