As stated above, foods are articles of diet as found in the market. Foods are usually mixtures of foodstuffs. Bread, for example, represents all the foodstuffs. Milk is a food which contains sugar, fat, protein, salts, and water. The vegetables of the market usually represent mixtures of sugar or starch, or both, with a cellulose pulp. The fruits in a similar way are mixtures of sugar solutions with vegetable acids and salts, the whole contained in a cellulose pulp. The most convenient classification of foods is one which is based upon the chemical composition and the dietetic use of the several foods. Several such classifications have been suggested by different writers. The following classification has been used for several years by the writer in preference to others, because of its ready adaptability to the uses of practical dietetics:

Group I. Inorganic Foods: Water and salts.

Group II. Organic Foods:

Division A. Carbonaceous Foods:

Class 1. Sugars.

2. Starches.

3. Roots and tubers. " 4. Green vegetables. " 5. Fruits.

" 6. Fats.

Division B. Nitrogenous Foods:

Class 1. Lean meat. " 2. Eggs.

Division C. Carbo-nitrogenous Foods:

Class 1. Cereals. " 2. Legumes. " 3. Nuts. " 4. Milk.

At this point in the discussion of foods a most valuable help to the reader would be afforded by a series of chemical tests in which the experimenter could demonstrate for himself many of the statements made here. If the student has already had laboratory work in physiological chemistry, he will be familiar with many of the facts here stated. If he has not had such a course in chemistry, he will certainly be repaid for a few weeks at a well-equipped chemical desk, verifying for himself many of the statements here made.