FOODS: THEIR CLASSIFICATION 387 



foods it cannot be sharply adhered to for the simple reason that 

 some foods may function either as repair materials or for yielding 

 energy. 



The substances we take into our Bodies belong in one or the 

 other of the two great chemical groups : they are either organic or 

 inorganic. The inorganic foods are included without exception, 

 in the class of maintenance foods. They are taken into the Body 

 to replace materials which are essential to it, but which are neces- 

 sarily lost from it in the course of its functioning. Of the various 

 organic foods a great number form what are commonly known as 

 accessory articles of diet. By imparting flavor to the food they aid 

 the digestive process, or they may exert influence upon other 

 bodily processes, as tea and coffee do upon nervous activity; they 

 are therefore to be included as maintenance foods. 



The organic constituents of our food not included among the 

 group of accessory articles of diet belong chemically to one or 

 other of three great subdivisions. They are either carbohydrates, 

 fats, or proteins. The entire supply of energy for the Body, and 

 its repair and maintenance to great extent are derived from these 

 three classes of food-stuffs. Because of their prime importance 

 they are usually set apart from the other foods as nutrients proper. 



Occurrence of Nutrients in Food. The articles which in com- 

 mon language we call foods are, in most cases, mixtures of several 

 nutrients with inorganic and accessory substances and with sub- 

 stances which are not foods at all. Bread, for example, contains 

 water, salts, gluten (a protein) , some fats, much starch, and a little 

 sugar; all true food-stuffs: but mixed with these is a quantity of 

 cellulose (the chief chemical constituent of the walls which sur- 

 round vegetable cells) , and this is not a food since it is incapable of 

 digestion. Chemical examination of all the common articles of 

 diet shows that the actual number of important food-stuffs is but 

 small: they are repeated in various proportions in the different 

 things we eat, mixed with small quantities of different flavoring 

 substances, and so give us a pleasing variety in our meals; but the 

 essential substances are much the same in the fare of the workman 

 and in the " delicacies of the season." These primary food-stuffs, 

 which are found repeated in so many different foods, belong to one 

 or the other of the classes of nutrients mentioned above; and the 

 food value of any article of diet depends on them far more than on 



