Quercus. Oak Bark. The dried bark of the small branches and stems of Quercus Pedunculata, the Common Oak; Lin. Syst., Moncecia polyandria; indigenous. The bark should be collected in spring from plants growing in Britain.

Description. The bark, when dry, occurs in long pieces generally covered with a greyish-white epidermis, of a fibrous consistence, brittle, internally cinnamon coloured, as also is the outer surface, when denuded of the epidermis; the taste is very astringent.

Prop. & Comp. Oak bark yields to water and spirit its active principles, viz., tannic acid and gallic acid; it also contains pectin. The amount of tannic acid varies very much with the age of the branches from which the bark is taken; season, and other circumstances, likewise have an influence upon the amount of astringent matter present in the bark.

Off. Prep. Decoctum Quercus. Decoction of Oak Bark. (Bruised oak bark, one ounce and a half; distilled water, twenty fluid ounces.)

Therapeutics. Seldom used except as an external astringent, in the form of the decoction, which forms a useful and economical lotion, gargle, or injection, in relaxed sore throat, leucorrhcea, etc. It may be given internally in the cases in which tannin acid is useful.

Dose. Of decoction, 1 fl. oz. to 2 fl. oz., when internally administered.

Galla. Galls. Excrescences occurring on the small twigs of Quercus Infectoria, the Gall or Dyer's Oak, caused by the punctures and deposited ova of Diplolepis Gallae tinctoriae. Lin. Syst., Monoecia polyandria; growing chiefly in Asia Minor.