The leaves of the tea plant, grown in China, contain theine, the active principle; tannic acid, and a volatile oil.

Tea is stimulating and refreshing. Used to excess it weakens the digestive system and causes constipation, depresses the heart and vaso-motor nerves, producing neuralgic pains. In cases of poisoning, when tannin is needed, it may sometimes be most quickly procured in the form of strong, rank tea. By boiling it hard and squeezing dry the leaves, the tannin is extracted as thoroughly as possible, and the tea is given, without sugar or milk, in large quantities.