Description of the Gall. The punctures of the young twig of the tree by a hymenopterous insect, the diplolepis gallae tinctoriae, cause an astringent exudation, which concretes and produces the gall-nut; the eggs deposited by the insect become inclosed in the excrescence. Gall-nuts are more or less globular in form, tuberculated on the surface, about the size of a marble, varying from half-an-inch to three-fourths of an inch in diameter. There are two varieties, blue and white galls; the former, heavy, and of a bluish-green tinge, yellowish white within, with a small central cavity; the latter white, of a grayish colour, less astringent, and perforated with a small hole, the passage by which the insect escaped.

Prop. & Comp. Gall-nuts contain a very large amount, about 35 per cent., of tannic acid, and 5 per cent. of gallic acid, also another body named ellagic acid, with gummy and extractive matters, lignin, salts, etc.

Tannic Acid (C54 H22 O34) is prepared by percolating the powdered galls with a mixture of water and ether, the percolated fluid separates into two strata, the heavier of which, containing the tannic acid in solution, is separated and evaporated to dryness. Tannic acid occurs in the form of a light glistening spongy mass or powder, yellowish, or almost white; uncrystallizable, of a very astringent taste, freely soluble in water and spirit, but very sparingly soluble in ether; slightly acid in reaction; its solutions precipitate gelatine yellowish white, and the persalts of iron bluish-black.

According to the latest researches of Strecker, tannin has the formula (C54 H22 O34), and by the action of sulphuric acid is resolved into gallic acid and grape sugar. The same change is effected when a strong decoction of the galls is kept for a lengthened period at a temperature of about 70° or 80° Fah. The formula explaining this decomposition is thus represented by Strecker:

[(C54 H22 O34) + 8HO = 3 (C14H6 O10) + (C12 H10 O10)] or one equivalent of tannin and eight of water are resolved into three equivalents of gallic acid and one of grape sugar.

Gallic Acid (3 HO, C14 H3 O7 + 2HO) is prepared by making powdered galls into a thick paste with water, and keeping them in this state for six weeks at a temperature of between 60° and 70°. This paste is afterwards boiled with distilled water, and strained through calico; the solution is allowed to cool and the crystals which are deposited are collected on a filter and drained by pressure between folds of filtering paper. They are then re-dissolved in boiling water, the liquid allowed to cool to 80°, and the crystals which separate are washed with ice cold distilled water, and dried at a temperature not exceeding 212°.

Gallic acid occurs in white or pale, fawn coloured, silky, needles, very soluble in boiling water, rectified spirit and ether.

It differs from tannin in not precipitating gelatine, albumen, or the alkaloids, but it strikes bluish-black with the persalts of iron; its taste is acid and astringent, but much less so than that of tannin, perhaps owing to its slight solubility in the saliva. Gallic acid is decomposed by heat, with the formation of pyrogallic acid (C6 H3 O3) and metagallic acid (C6 H2 O2. The former acid strikes black with proto-salts of iron, and is a powerful deoxidizing agent.

Ellagic acid exists in gall-nuts in small quantities; it forms a white powder, differing from tannin and gallic acid in being almost insoluble in water, alcohol, or ether; it appears to be an isomeric modification of gallic acid. Probably ellagic acid is contained in many vegetables, as some of the intestinal concretions, called bezoars, found in the intestines of ruminants, are entirely composed of it.

Off. Prep. - Of Galls.

Tinctura Gallae. Tincture of Galls. (Galls, bruised, two and a half ounces; proof spirit, twenty fluid ounces. Prepared by maceration and percolation.)

Unguentum Gallae. Ointment of Galls. (Galls, eighty grains; simple ointment, one ounce.) [Nutgalls in very fine powder, a troy ounce; lard, seven troy ounces. U. S.]

Unguentum Gallae cum Opio. Ointment of Galls and Opium. [Not officinal in U. S. P.] (Ointment of galls, one ounce: opium in powder, thirty-two grains.)

Of Tannic Acid.

Suppositoria Acidi Tannici. Tannin Suppositories. [Not officinal in U. S. P.] (Tannic acid, twenty-four grains; glycerine, twenty minims; prepared lard and white wax, as much as is required.)

Trochisci Acidi Tannici. Tannin Lozenges. [Not officinal in U. S. P.] (Tannic acid made into lozenges, with tincture of tolu, sugar, gum arabic, mucilage of gum arabic and water.) One and a half grains of tannic acid are contained in each lozenge.

Therapeutics. Gall-nuts owe their efficacy to the tannic and gallic acids contained in them; and the description of the action of these acids applies not only to galls, but to all those vegetables which are made use of for their astringent effects.

Tannic Acid, when applied to a living part, acts as a most powerful astringent; if the surface of a mucous membrane is chosen, this effect is well seen in the contraction of the vessels, and consequent paleness produced. When the lips, or any part of the mouth, come in contact with this acid, the astringency becomes evident to the taste.

Taken internally, tannic acid sometimes causes a sensation of dryness of the mouth and fauces, thirst, and not unfrequently constipation; it soon becomes absorbed into the blood, and after some alteration in composition, is thrown out, or at least partly so, by the kidneys in the form of gallic and pyrogallic acids, and a brownish-black humus-like matter: sometimes the urine becomes quite dark-coloured, especially after it has been exposed to the air for a short time. The urine of patients taking tannic acid does not precipitate gelatine, showing the absence of tannic acid, but strikes black with persalts of iron, indicating the presence of gallic acid. Upon the alimentary canal, and also after absorption, the action of tannin is of the same character; and hence, not only topical but remote astringent effects are produced by its administration; and haemorrhages, as menorrhagia, haematuria, and haemoptysis, increased mucous and other discharges, hectic sweating, diarrhoea, and dysenteric affections, are quickly influenced by its administration.

Gallic acid appears to differ from tannin in its topical action, being less astringent, probably from its comparatively slight solubility; it however becomes absorbed, and the remote effects are identical with those of tannin. Probably as a remote astringent it is more powerful than an equal quantity of tannic acid, for the latter becomes converted in the blood into gallic acid and grape sugar, and hence part only is available. This was the conclusion at which the author arrived from some extensive trials made many years since, in the treatment of various forms of haemorrhages.

Externally, the decoction of gall-nuts, or solutions of tannic or gallic acid, may be employed to suppress haemorrhage from the gums, nose, or any part to which they can be applied; or to lessen discharges from mucous membranes, as in gleet, leucorrhoea, etc.

Dose. Of the tincture of galls (seldom used, except as a test), 1/2 fl. drm. to 1 1/2 fl. drm.; of tannic acid, 3 gr. to 20 gr.; of gallic acid, 3 gr. to 20 gr.; about 4 gr. of gallic acid can be dissolved in 1 fl. oz. of water. Both tannic and gallic acids are soluble to a considerable extent in glycerine.

Incompatibles. Salts of iron, especially the persalts, strike black with both tannic and gallic acids; infusions and decoctions of vegetable substances containing alkaloids; solution of gelatine, and many metallic substances, as salts of lead, etc. are precipitated by tannic acid.