[Illustration: FIG. 1.——Composition of milk. 1. Whole milk. 2. Water. 3. Fat. 4. Protein. 5. Carbohydrate. 6. Mineral matter or ash. _Courtesy of President Gulliver, Rockford College._] You may then surmise from the sweet taste of milk that sugar is present; the chemist knows how to obtain it in pure form as “sugar of milk.” The chemist also finds certain mineral substances which remain behind when all the water is evaporated and the curds and sugar burned away. These mineral substances are spoken of by the chemist as “ash,” because this is what remains after burning the other portions of a food material, as ashes remain from a wood fire. Figure 1 shows you these substances in the amounts in which each occurs in a pint of milk. The sugar is one of a class of substances to which the chemist gives the name carbohydrate. To the substance in the curd that is different from all the other substances in the milk the name “protein” is given. We will now turn to the composition of beans, for in beans we find food stored up to nourish the young plant, which we, also, appropriate as food. The composition of both the milk and the beans is given in this table. Compare also Figures 35 and 41. Composition of Milk and Beans ================================================================= | WATER |PROTEIN | FAT |CARBOHYDRATE| ASH FOOD MATERIALS |PER CENT|PER CENT|PER CENT| PER CENT | PER CENT ---------------|--------|--------|--------|------------|--------- Milk | 87.0 | 3.3 | 4.0 | 5.0 | 0.7 Beans, dried | 12.6 | 22.5 | 1.8 | 59.6 | 3.5 ----------------------------------------------------------------- Notice that the substances in the beans are the same in general nature as those in the milk, although the amounts are different. The water that the young plant needs is, of course, supplied from the earth. There is another difference to note although this is not shown in the table; in the beans the carbohydrate is of two kinds, sugar and starch. FOODSTUFFS[1] All the varieties of food with which we are supplied will be found to contain some of these substances: protein, fat, carbohydrate, mineral matter, water; and to these we give the name _foodstuffs_. Some food materials (like the milk and beans just studied) contain all the foodstuffs, some only one, as in the case of sugar. We can now define food as something that contains one or more of the substances known as foodstuffs. But what are the foodstuffs themselves?