Quercus Cortex-Oak Bark.-The dried bark of the small branches and young stems of Quercus pedunculata. Collected in spring, from trees growing in Great Britain.

Characters.-Covered with a greyish shining epidermis, cinnamon-coloured on the inner surface, fibrous, brittle, and strongly astringent.

Substance resembling Oak Bark: Pale Cinchona Bark, which is bitter.

Composition.-Oak bark contains 4 to 20 per cent of tannic and gallic acids, pectin, and other constituents of plants.

Incompatibles.-Those of tannic and gallic acids.

Preparation.

Decoctum Quercus.-1 in 16. Dose, 1 in 2 fl.oz. Seldom given internally.

Galla-Galls.-Excrescences on Quercus infec-toria, caused by the punctures and deposited ova of Diplolepis Gallae tinctoriae.

Characters.-Hard heavy globular bodies, varying in size from half an inch to three-fourths of an inch in diameter, tuberculated on the surface, the tubercles and intervening spaces smooth; of a bluish-green colour on the surface, yellowish-white within, with a small central cavity; intensely astringent.

Composition.-Galls contain from 15 to 65 per cent. of tannic acid, about 5 per cent. of gallic acid, and other less important constituents.

Preparations.

1. Tinctura Gallae

Tinctura Gallae. 1 in 8. Dose, 1/2 to 2 fl.dr. Seldom used except as a test.

2. Unguentum Gallae

Unguentum Gallae. 1 in 6 1/2.

From Unguentum Galloe is prepared:

Unguentum Galloe cum Opio.-1 of Opium to 14 2/3 of Oint-ment of Galls.

From Galla are also made:

1. Acidum Tannicum

Acidum Tannicum. Tannic Acid. Tannin. C27H12017. An acid extracted from galls.

Source.-Made by exposing powdered galls to a damp atmosphere; macerating with ether; pressing; and partially evaporating and drying the liquid portion.

Characters.-Pale yellow vesicular masses, or thin glistening scales, with a strong astringent taste, and acid reaction. Solubility: 10 in 8 of water or spirit; sparingly in ether; 1 in 3 of glycerine.

Incompatibles.-Gelatine (which it precipitates, distinguishing it from gallic acid), mineral acids, alkalies; salts of antimony, lead, silver; persalts of iron, alkaloids, vegetable emulsions. Dose.-2 to 10 gr.

Preparations.

a. Glycerinum Acidi Tannici.-1 to 4. Dose, 10 to 40 min.

b. Suppositoria Acidi Tannici,-3 gr. in each.

e. Suppositoria Acidi Tannici cum Sapone.-3 gr. in each. d. Trochisci Acidi Tannici.-1/2 gr. in each. Dose, 1 to 6.

2. Acidum Gallicum.-Gallic Acid. H3c7h3 05.H10

A crystalline acid prepared from galls.

Source.-Made by fermenting a paste of powdered galls and water, boiling with water, straining, and purifying the crystalline product.

Characters.-White or pale fawn silky needles, with an acid taste. Solubility: 1 in 100 of cold water, 1 in 3 of boiling water, 1 in 8 of spirit, 1 in 20 of glycerine. It may be combined with the proto-salts of iron. Resembles Tannic Acid, but has no astringent taste, and does not precipitate solutions of gelatine.

Incompatibles.-Spiritus Aetheris Nitrosi; metallic salts, including per-salts of iron.

Dose.-3 to 10 gr.

Preparation,

Glycerinum Acidi Gallici.-1 to 4. Dose, 10 to 60 min.

Action And Uses. 1. Immediate Local Action And Uses

Externally.-The action of tannic acid, and of the many officinal substances which contain it, including oak-bark and galls, depends upon its property of precipitating albumen and gelatine. When applied to the skin or exposed mucous surfaces, it condenses or constringes the albuminous and connective tissues, and coagulates the fluids pervading the solid elements (an action which in the dead skin converts the whole into leather). At the same time the sensibility of the nerves is reduced. The vessels are compressed by the constringed tissues to such a degree that their size is indirectly reduced, the circulation through them diminished, and haemorrhage from them arrested by pressure and by coagulation of the blood by the acid. If a "passive" discharge of plasma and leucocytes is escaping from their walls, as in chronic inflammation, the exudation is stopped. Thus tannic acid is a powerful indirect styptic and astringent. Broken surfaces, such as ulcers, have their superficial layers of cells condensed, and the discharge disinfected and coagulated, thus promoting healing. It is a remarkable fact that tannic acid does not actively contract blood-vessels, like lead and silver; on the contrary, it dilates them; but the indirect or constringent influence more than neutralises this.

There is hardly a limit to the application of tannic acid, and preparations containing it, as astringents and styptics. Superficial haemorrhage from small wounds, the nose, gums, throat, etc., and chronic or subacute inflammatory discharges from the skin, eyes, nose, urethra, vagina, womb, or rectum, may all be treated with it. The acid may be used solid, being dusted or insufflated on the part; in solution as injection, lotion, etc.; or inserted into canals or cavities as bougies or suppositories. The two ointments of galls are favourite applications to haemorrhoids.

Internally.-In the mouth, tannic acid produces its peculiar " taste," with a sensation of astringency, dryness, roughness, stiffness of the tongue and throat, and thirst; the parts being constringed and partially anaesthetised, and the other effects produced, as described, externally. Preparations containing this drug are in much request in chronic sore throat with a relaxed condition of the uvula, pharynx, and larynx, slight catarrh, cough, and occasional slight bleeding. The trochisci, gargles, sprays, or the glycerine applied with a brush, may be used in different cases.

In the stomach, tannin precipitates the pepsin with the albumens of the gastric juice; and if in quantity, will interfere with digestion by this means, as well as by constringing the mucosa, reducing the circulation, and diminishing the secretion. On the contrary, if a chronic gastric catarrh be present, causing dyspepsia, tannin will give relief by arresting the morbid process, on the principles already discussed. Haemorrhage from ulcer of the stomach is often successfully treated by free (1 dr.) doses of the acid, which acts as a direct styptic. In the stomach another highly important use is made of the drug, viz. as an antidote to antimony, and such alkaloids as morphia, nicotin, strychnia, etc.; a strong infusion of tea being given if no other tannate is at hand. An emetic or purgative should be afterwards given in alkaloidal poisoning, as the compounds with tannic acid are not perfectly insoluble.

The astringent effect of tannin is continued in the intestines, where it and its compounds are the most popular remedies for diarrhoea, whether alone or combined with other astringents, antacids such as chalk, or anodynes such as opium. Intestinal haemorrhage may sometimes be arrested by the same means. During its passage along the alimentary canal, part of the tannin is converted into gallic acid, which enters the blood; the rest is excreted in the faeces.

Tannic acid + water = gallic acid + glucose. C27H12O17 + 4H10 = 3H3C7H305 + C6H1206. Gallic acid possesses no local astringent or antiseptic properties, and is therefore seldom if ever given for immediate local purposes.

2. Action On The Blood, And Its Uses

Entering the circulation as gallic acid, the preparations of tannin are not certainly known to have any further astringent effect on the vessels, any antiseptic action, or coagulating influence on the blood. If injected directly into the veins, tannic acid would prove rapidly fatal by clotting and embolism.

3. Specific Action And Uses

The action of these substances on the tissues must depend entirely on the gallic acid. In full doses gallic acid causes circulatory depression, by weakening the heart and dilating the vessels; and it also causes dyspnoea. But besides these effects determined by experiment, it is almost universally regarded to be a specific astringent and haemostatic, and thus to arrest chronic discharges from internal and distant parts, such as the uterus and rectum, and to check bleeding, especially haemoptysis. Gallic acid is much used for these purposes, and should be given in full doses-even up to one drachm at a time if haemorrhage be urgent. It must be confessed that some authorities do not believe in this action or use of the drug.

4. Remote Local Action And Uses

Tannic and gallic acids are rapidly excreted, chiefly as gallic acid, partly also as pyrogallic acid, in the urine, which is darkened in tint. No remote disinfectant effect is to be obtained in the kidneys or bladder; nor is gallic acid now believed to diminish the albuminuria of Bright's disease. Some hold that it arrests renal haemorrhage; but in this, and in all kinds of haemorrhage, there is a constant possible source of error, from the fact that the spontaneous arrest of bleeding is extremely common.

Gallic acid has also been used in night-sweats, with doubtful success.