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Besides caffein, both tea and coffee contain an astringent known as tannic acid. In coffee this substance is present only in small quantity, but in tea from four to twelve per cent occurs. Tannic acid is the substance found in oak bark, and has the property of making animal tissues hard—that is, makes leather of them. The habitual tea drinker subjects the delicate lining of the stomach and intestines to the action of this powerful drug.Share
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