732 ELEMENTS OF MATERIA MEDICA.

bark is then removed by the peeling-irons, the separation being P r ^ gmoted, when necessary, by beating the bark with the square end omallet. It is then carefully dried in the air, by setting it on wh a tcalled lofts or ranges, and is afterwards stacked ( Loudon’s Encyclof-Agricult., 3rd ed. p. 658, 9). . pj

Description.— Oak bark ( cortex quercus) consists of pieces of &one to two feet long, which vary in their appearance according j,

age of the stem or branch from which they have been taken. The a

of young stems is thin, moderately smooth, covered externally j jrsilvery or ash-gray cuticle, and is frequently beset with lichens-ternally it is, in the fresh state, whitish; but, when dried, brokenrough, and fibrous. The bark of old stems is thick, very rough eXnally, cracked, and wrinkled, and is of inferior quality. ,-

Composition. —According to Braconnot {Ann. de Chim. et de “t. 50, p. 381), oak bark contains— Tannic acid, t annates of lime, rtia(f iepotash, &c., gallic acid, uncrystallizable sugar, pectin, and lignin.

1. Tannic acid .—The quantity of tannin [impure tannic acid] obtained by ^(Elem. of AgriculU Chem. p. 83, 4th ed.) from oak bark is as follows:—

Tannin

480 lbs. of atf»r deU -

Entire bark of middle-sized oak, cut in spring. ... ^

,, coppice oak. S'”

„ oak cut in autumn .

White interior cortical layers of oak bark .

■ fr«

Biggins (Pfaff, Syst. d. Mat. Med. Bd. ii. S. 207) obtained 30 parts of tanni* 1 jjjJthe bark of an oak felled in winter, while the same weight of the bark of an oakin spring yielded him 108 parts. , „jcr

2. Gallic acid .—This contributes to the astringency of oak bark. It is form ebably by the action of the air on the tannic acid.

Chemical Characteristics.— Decoction of oak bark reddensand becomes dark blue or purple ( tannate of iron) on the additi °, gsesquicliloride of iron. A solution of gelatin causes a precipitateof gelatin) with it. It is somewhat remarkable, however, that a soWj ^of emetic tartar causes no precipitate with the decoction. [If alcoh°‘ j tadded to the decoction, concentrated to the consistence of a syr u P’ 9causes the precipitation of pectin. A decoction, rendered alkalin® •' g {fixed alkali, deposits a gelatinous matter ( pectic acid) on the addinacetic acid. Braconnot.'] , gS e

Physiological Effects. —The effects of oak bark are similar toof other vegetable astringents containing tannic acid, and havealready described (pp. 79, 80). its

Uses. —The principal value of oak bark, in medicine, arises w° jpastringent property. Thus we employ a decoction of it as a 8^ t j 0 ji srelaxed conditions of the uvula, and in chronic inflammatory affe cof the throat (Cullen, Mat. Med. vol. ii. p. 45); as a wash, in flab ^’ a pdconditioned, or bleeding ulcers; as an injection in leucorrhcea, in V.’ 0 ldin prolapsus of the uterus or rectum; as an internal astringent i ^, c .diarrhoeas, in the last stage of dysentery, in alvine haemorrhagedPoultices made of powdered oak bark have been applied with ^).mortified parts (Barton, Collect, towards a Mat. Med. of the U- ~ jjpSMr. Lizars {Ed. Med. and Surg. Journ., July 1822) states that 1