Fruits can conveniently be classified as those that are eaten as a relish or to afford variety, and those that have food value. Their value as food is small, however. They are pre-eminently carbohydrates for their chief nutritive constituents are sugars, mostly levulose, or fruit-sugar, and cane-sugar. Many of them contain varying small amounts of a jelly-producing substance called pentose, the chemical nature and utility of which are not well understood. They contain numerous salts formed of potassium and sometimes of sodium, and magnesium, with the fruit acids, such as citric and malic. The flavors of fruits are due to oils and ethers. Very few fruits contain enough sugar to make them of much value as food. The most nutritious of the raw fruits is the banana. Many others become more so when they are concentrated by drying. For instance, fresh apples contain 12 per cent, of carbohydrate, but when dried, almost 50 per cent.; dates and figs, more than 60 per cent.; raisins, 74 per cent., but fresh grapes, only from 10 to 20 per cent.

Fruit is eaten, first, because it is appetizing and palatable; second, because it is refreshing, lessening thirst by its large amount of water; third, because of its nutritive properties; fourth, because of its salts and acids which make fruit an important antiscorbutic; fifth, because some kinds possess diuretic properties, and sixth, because most of them possess laxative properties.

Unripe fruit contains a relatively large amount of cellulose and of solid matter and a small amount of sugar. It is, therefore, usually hard, sour, and indigestible. It lacks the flavor of ripe fruit. When fruit ripens it becomes juicier, and the starch in it is converted into soluble sugars. The acids that it contains are more dilute. The cellulose framework of fruit as it fills during the stage of ripening becomes thin, relatively soft, and easily broken by mastication and agitation.

Cooking usually makes fruit more digestible, because it softens the cellulose and converts the gums (pectin) into a gelatinous mass. Nevertheless if stewed or cooked with water, fruits lose part of their nutritive ingredients. Apples lose 4 per cent, of carbodydrates, pears about the same, and peaches 7 or 8 per cent.

Fruit is often cooked to preserve it, and cane-sugar is added to make it keep better. It is usually stewed, but is also often dried, which concentrates it by raising its percentage of sugar. Partial desiccation prevents its spoiling. Jellies are made from many fruits. They are useful condiments for invalids. Jams and marmalades are fruit sweetened and partly converted into jelly. Occasionally fruits are spiced and preserved in an acidified (vinegar) syrup. In Germany fruit soups are often eaten. In the United States they are almost unknown. Fruit-juices and syrups are sometimes employed to flavor iced drinks, and are often grateful to invalids, and, if not drunk in too large quantities, are wholesome. All these preparations are used because of their agreeable flavors rather than for their nutritive value. From the banana, a meal is made by drying and grinding it. In nutritive power it is quite equal to the same quantity of rice. It is agreeable, easy to digest, and very thoroughly absorbed. Those who have digestive disorders that make the stomach and bowels intolerant can use it because it is so bland. It is, therefore, a useful addition to the list of bland foods, such as sago and arrow-root. Banana flour contains little or no starch but an abundance of sugar. It is not used so much as it might well be.

Ripe fruits, stewed fruits, and jellies are usually very digestible. If taken in too large quantities, they often ferment in the alimentary canal and produce colic and gastro-enteric disorders. Unripe or overripe and spoiled fruit is especially prone to cause these disturbances. The time during which fruit remains in the stomach and its absorbability by the intestine have not been thoroughly studied. A large apple does not pass out of the stomach for more than three hours. Many fruits are marketed before they are ripe, and are allowed to ripen partly afterward. These are much less digestible than they would be if eaten when ripe. The acids of many fruits make them indigestible to those who suffer from acid fermentation in the stomach. Occasionally a person is met with who possesses an idiosyncrasy, and who, after eating certain fruits, will have gastroenteric troubles, hives, or other evidence of poisoning. The seeds of berries often irritate the intestines.

Apples, pears, and even more often figs, dates, and prunes, are employed as laxatives. The laxative effect is most noticeable when these fruits are eaten the last thing at night or the first thing in the morning, at a time when the stomach contains little or no food. They are least effective when they are eaten at the end of a meal or with a full meal. The very acid fruits, such as lemons, grape-fruit, and oranges, are least laxative. Most berries must be classed as intermediate between these two groups, so far as laxative properties are concerned.

When the 'grape cure' is taken in Germany, from one to eight pounds of grapes are eaten daily, and little or no other food for a time. At first, a small quantity is eaten, but day by day it is increased. Those who take this 'cure' are expected to pick the grapes for themselves, which insures outdoor life and gentle exercise. It is a mode of treatment chiefly adapted to the obese and to those who lead a sedentary life.