Technically speaking, fruits include all plant products which bear or contain a seed. They are valuable for their acids and organic salts—citrates, malates, or tartrates of potassium, sodium, magnesium, and calcium. They are composed for the most part of starch, sugar, water, and various organic acids, cellulose, and pectin. (Pectin is the substance which jellies under heat.) Fruits which do not contain pectin must be combined with others which do, or with gelatin, if jelly from them is desired. The organic acids in fruits are readily split up in the body, and form alkalis. For this reason acid fruits are useful in certain acid conditions of the stomach, because they combine with the stomach acids, liberating substances which cause an alkaline reaction. The citrus fruits—oranges, lemons, grapefruit and limes—are rich in citric acid. Malic acid is found in gooseberries, peaches, pears, apples, currants, and apricots. Tartaric acid is prominent in grapes. The value of fruits as a food depends largely on the amount of starch and sugar they contain, though their agreeable odor and taste, by furnishing variety in the diet, render them, also, of great value as appetizers. As a rule they contain too much water to be of great food value if eaten alone. The organic acids and salts contained in fruits are of value as they stimulate the activity of the kidneys and lessen the acidity of the urine. The urine may even be rendered alkaline by them; hence, when a test shows evidence of too much uric acid, acid fruits are used to neutralize the acids in the tissues, particularly the acids of the citrus fruits. The fruit juices are readily absorbed and the potassium calcium, sodium, and magnesium they contain are liberated with the formation of alkaline carbonates. These alkalis are largely eliminated through the kidneys, which accounts for the diuretic effect of fruits, their acids and salts stimulating the activity of the kidneys. The seeds in the small fruits are not digested, but they serve the purpose of increasing intestinal peristalsis and of assisting the movement of the contents of the intestines. The skin and the fiber of fruits also assist the intestines in this way, just as the fiber in vegetables does. All acid fruits—particularly lemons, limes, grapefruit, and oranges—stimulate the action of the skin as well as the kidneys and whenever the kidneys and skin are not sufficiently active, these fruits should be eaten freely. In case of an excess of hydrochloric acid in the stomach, lemon juice or citrus fruits are valuable about half an hour _before_ a meal, as when taken on an empty stomach they decrease the secretion of hydrochloric acid. When the secretion of hydrochloric acid is limited, acids are given _after_ a meal to supplement the deficiency, or stimulate the glands to activity.