=Fruits= are chiefly used as adjuncts to other foods; but the vegetable salts and the cellulose and sugar which they contain, make them very valuable. =Cucurbitaceous= fruits are used as vegetables rather than as fruits. Vegetable marrow is wholesome and agreeable, but not very nutritive. Cucumber is most digestible when rapidly grown and freshly gathered.
=Stone-fruits= or drupes, such as the peach, nectarine, plum, cherry, are rather luxuries than foods, like many other fruits. Before ripening they are unfit for food; when ripening is complete, the acids and astringent matter largely disappear. The _date_ contains chiefly sugar, and forms an important food in the East.
=Pomaceous Fruits=, as the apple, pear, and quince, are more digestible when cooked; and, speaking generally, all fruit not perfectly ripe should be cooked before eating. The presence of vegetable acids in fruit soon converts the sucrose of cane sugar into dextrose, a less sweet variety of sugar. It is therefore more economical to sweeten after than before cooking.
The chief =Berries= are the grape, currant, gooseberry, cranberry, and elderberry. The grape is the most important, and 1,500 varieties of it have been described. Its juice contains a large amount of grape sugar (dextrose), and small quantities of glutinous material, bitartrate of potash, tartrate of lime, malic acid, etc.
Besides the above fruits, we have strawberries, mulberries, figs, plantains, melons, etc., which are all refreshing and anti-scorbutic. The orange family furnishes us with the orange, lemon, citron, lime, shaddock, and pomelo, of which the orange is by far the most important, and possesses most valuable refreshing qualities.
=Sugar= exists in two chief forms, viz. sucroses and glucoses. =Sucroses=, known chemically as disaccharids (Sucrose = C_12H_22O_11; compare starch = C_12H_20O_10) are exemplified in cane, beet, maple, malt (maltose), and milk sugar (lactose). Cane sugar has been gradually displaced by beet sugar. The two are chemically identical, and equally nutritious. Maltose is given in malt extract as a food, and because of the digestive action of the ferment also contained in the extract on starchy food. Thus:—