Active Ingredients. - The principal active ingredients contained in oak bark are tannic acid, gallic acid, and pectin, all of which are yielded both to water and to spirit. The amount of tannic acid varies with the age of the branch from which the bark is taken, also with the age of the bark itself, and with the season of the year at which it is removed from the tree. For pharmaceutical purposes these two acids are prepared from the galls of the Quercus infectoria, under which head it will be more convenient to speak of their composition.

Physiological Action. - Oak bark is powerfully astringent, and similar in its operation to other vegetable astringents containing tannin.

Therapeutic Action. - Powdered oak bark is valuable in cases of passive haemorrhage, and in diarrhoea. The infusion or decoction may be employed with advantage as an astringent gargle. Injections and fomentations of a powerfully astringent character may also be conveniently prepared from oak bark.

Preparations And Dose. - Decoctum: Quercus Albae,

Corylaceae The Oak Quercus Alba 50

ij. (15. - 60.).