An excrescence on the young twigs Quer'cus infectoria and other species of Quercus produced by the punctures and deposited ova of Cynips gallae tinctoriae (Fig. 59) Olivier (class, Insecta; order, Hymenoptera). Not more than 5 per cent. of Galls float in water.)
BOTANICAL CHARACTERISTICS.—A shrub or small tree 6 to 8 feet high. Leaves short-petiolate, obovate-oblong, obtusely toothed, oblique at base. Acorn solitary, obtuse, two or three times the length of the cup.
DESCRIPTION OF DRUG.—Hard, heavy, subglobular, from the size of a pea to that of a large cherry, contracted below into a short stipe and covered above with a few or many prominent warts (tuberculated) between which the surface is smooth. Heavy, sinking in water, except the smaller ones which should not be present to a greater extent than 5 per cent. Externally dark bluish or lead color, frequently with a greenish tinge, often with a circular hole near the middle upper part, communicating with the central cavity. They break with a flinty fracture, showing a whitish or brownish interior, with often a central cavity, lined with a thin, hard shell, which contains the insect in all stages of development, or the pulverulent remains of the developed insect mixed with partly eaten fragments of the starchy parenchyma. Odorless; very astringent.
STRUCTURE.—The tissue is chiefly parenchyma, loaded with tannin and chlorophyll; the cavity lining is composed of stone cells containing calcium oxalate crystals, within this cavity, if not eaten out, is a starchy parenchyma.
VARIETIES.—Most of the oaks are occasionally affected as the above species, the resulting excrescence, known as galls, developing a tannin which may be employed for various practical purposes. The Aleppo or Syrian, dark colored and heavy (although the designation Aleppo is not wholly applicable to the official galls—"Galla"), are the products of different parts of Asiatic Turkey; still the name is applied to this variety. Smyrna galls, grayish-olive color, intermixed with white galls. Sorian, size of a pea, blackish. Japanese and Chinese from Rhus simulata, 1/2 to 2 inches long, ovate, very irregular, tubercular, grayish downy, inclosing the remnants of numerous insects. The Chinese make use of this product in dyeing and as a medicine.
Powder.—Gray. The microscopic elements consist of: See Part iv, Chap. I, B.
CONSTITUENTS.—Tannin 65 to 77 percent. (Acidum Tannicum, gallotannic acid 105a), chemically known as digallic acid, C14H10O9. It is a yellowish-white amorphous substance, insoluble in absolute ether, chloroform, benzol, benzin, and carbon disulphide, soluble in glycerine, alcohol, and water; precipitated blue-black by ferric salts, and white by gelatin. It appears to exist, in part at least, as a glucoside and digallic acid. Digallic acid may be considered as an anhydride of gallic acid, C7H6O5. formed from two molecules of the latter by elimination of one molecule of water. Gallic acid also exists in galls. It is precipitated blue-black by ferric salts, the color disappearing on boiling, and is not affected by gelatin when gum is absent.
Preparation of Tannic Acid.—Powdered nutgall is exposed to damp atmosphere for twenty-four hours, then made into paste with washed ether. Allow to stand six hours, then express in canvas cloth between tinned plates. After powdering the pressed cake, again make into paste with washed ether. Repeat the former process and allow the mixed liquid to evaporate spontaneously.
ACTION AND THERAPEUTIC PROPERTIES.—When taken into the digestive tract some of it is changed into gallic acid and absorbed as such; while some may be taken up as a soluble alkaline tannate.
Because of its power and lack of toxicity, tannic acid is one of the most widely used of all the astringents, either in the form of the tannic acid itself or of one of the various vegetables containing it.
Locally applied it may be used to overcome relaxation, as in spongy gums, mercurial sore mouth, hemorrhoids, and chronic sore throat.
To check hemorrhage it may be used whenever the source of flow can be reached directly, as in epistaxis, hematemesis, hemorrhage from the bowels, etc.
Tannic is useful as an antidote against a number of poisons including most of the irritant metallic salts, especially those of antimony and iron. Dose: 8 gr. (0.6 Gm.).
- Preparations commonly employed:
- Unguentum Gallae (20 per cent.),
- Acidum Tannicum, Dose: 10 to 20 gr. (0.6 to 1.2 Gm.).
- Trochisci Acidi Tannici, Each 1 gr. (0.06 Gm.).
- Glyceritum Acidi Tannici (20 per cent.), Local use.
- Unguentum Acidi Tannici (20 per cent.), Local use.
- Collodium Stypticum (2 per cent.), Local use.
A Manual of Organic Materia Medica and Pharmacognosy, 1917, was written by Lucius E. Sayre, B.S. Ph. M.