Tea has been used by Europeans for about three hundred years. It is employed in the United States extensively, but not so much as in England, in the British colonies, and in Russia.

Many varieties of tea can be purchased. These depend for their peculiarities upon the plant from which they are obtained, upon the season of the year when the leaves are gathered, and upon the age, tenderness, and juiciness of the leaf. Tea-leaves were primarily culled from two species of plants, Thea chinensis and Thea assamica. Now, however, there are numerous hybrids. Teas grown in China, Japan, India, and Ceylon vary somewhat in flavor. The finest tea is made from the small tender leaves at the end of new shoots, each succeeding pair of leaves upon the branch furnishing a different and less valuable grade. Three or four pairs of leaves or grades are gathered. The various kinds and grades of tea are classified as green or black, according to the method adopted for curing them. Black tea is made by 'withering' the freshly picked leaves in the sun. They are then mashed and rolled in order to break the fiber and cells of the leaf and liberate their constituents. After this the leaves are gathered together and fermented, during which process a part of the tannic acid in them is made less soluble and the essential oils are modified in character. They are again exposed to the sun, and finally ' fired' or dried in an oven. Green teas are withered in pans that are at a temperature of 1600 F.; in Japan they are steamed. They are then rolled, withered again, sweated in bags, and finally slowly roasted. These processes of manufacture modify the composition of the product. The following table shows these changes:

The nutritive ingredients of tea are insignificantly small. Thein, chemically the same as caffein, and tannic acid are the ingredients that are physiologically active. The aroma and its variations are produced by volatile oils.

In the process of manufacture of green tea the quantity of water and of caffein in it is lessened, and the tannic acid is much increased in amount. In general it may be said that teas contain fron 2 to 4 per cent, of thein or caffein and from 10 to 25 per cent, of tannic acid. Caffein is responsible for the feeling of nervous stimulation that tea-drinkers experience. Tannic acid affects digestion chiefly in a detrimental manner. It is, therefore, important so to prepare tea as a beverage that it will contain a maximum quantity of caffein and a minimum quantity of tannic acid. To accomplish this more depends upon the manner of brewing than upon the variety of tea. Caffein is extracted from the leaves at once when boiling water is poured upon them, but tannic acid is extracted much more slowly. Almost one-third more tannic acid is obtained in the beverage if the leaves stand in hot water thirty minutes than if they are in it only five. The difference in the percentage of eaffein in the two infusions is slight. As ordinarily made, a cup of tea contains about one-tenth as much thein or eaffein as a cup of coffee.

The beverage tea, is made by pouring boiling water upon tea-leaves. The mixture should stand where it can be kept hot, but not boiling, for from three to five minutes. The water should be fresh, not very hard, and just brought to a boil. Stale water, very hard water, and water that has been subjected to prolonged boiling and from which, in consequence, all air has been driven does not make so agreeable a beverage. Some inveterate tea-drinkers keep the tea-pot with water and tea-leaves in it upon the stove constantly and frequently drink the beverage that is thus made. It contains a large amount of tannic acid and is most unwholesome. The tannic acid in concentrated solution precipitates the pepsin of the gastric juice and prevents digestion. In weaker solution it often makes digestion slow. When taken upon an empty stomach, it acts as an astringent, lessening the secretions from the mucous membranes. In the intestines it is an astringent and often causes or aggravates constipation.

Tea should not be used by dyspeptics or by those who are constipated. When taken in too large amounts, it will produce wakefulness, nervousness, excitability, and even muscular unsteadiness or twitching. The digestive disorders due to its tannic acid are much more pronounced when tea is drunk to excess than its stimulating effects. Flatulence, gastric distress, constipation, often cardiac irregularity, pleurodynia, and sleeplessness are the predominant symptoms of excessive tea-drinking.

Tea is not disposed of by the stomach so rapidly as water. It is estimated that a pint of the latter is evacuated into the intestine within an hour. Half as much tea remains in the stomach for from one to two hours.