THE CHEMICAL COMPOSITION OF FOODS 9 



derives its supply of carbon ; in other words, the plant's 

 elaboration of carbon has raised it to a form in which 

 it is available as food for one of the higher animals. 



Just as the carbon required by an animal is largely 

 taken in as carbo-hydrate, so the other elements are 

 found to occur in plants in certain combinations suitable 

 for assimilation by animals. On analysis plants can be 

 resolved into these various compounds ; and since this 

 resolution is something far short of ultimate separation 

 of the elements, the resulting compounds are termed 

 the proximate principles of the plant. They are : 

 water, nitrogenous substances, fats, carbo-hydrates, 

 crude fibre, and salts, and all the foods to be considered 

 later can be resolved into these proximate principles. 



Water is present in all foodstuffs, varying in amount 

 from some 12 per cent, in cereal grains to over 90 per 

 cent, in turnips. It is of great importance in the 

 nutrition of an animal that it shall be plentifully sup- 

 plied with water, but a small amount of water in the 

 food can be made good by a larger quantity of drinking 

 water ; and for many purposes concentrated foods, con- 

 taining little water, are of greater value than the watery, 

 and therefore bulky, green foods or roots. Especially 

 is this so in the case of the working horse, with his small 

 stomach and at the same time large requirements of 

 energy. 



The Nitrogenous Substances are of two classes, 

 known as proteins and amides, the latter being a stage 

 in the building up, and conversely in the decomposition, 

 of proteins. Proteins, albuminoids, or flesh-formers, are 

 composed of the elements carbon, hydrogen, oxygen and 

 nitrogen, with small traces of sulphur and phosphorus, 

 and they are found in protoplasm, the essential vital 



