A treatise on therapeutics : comprising materia medica and toxicology with especial reference to the application of the physiological action of drugs to clinical medicine / by H. C. Wood.

  • Wood, H. C., Jr. (Horatio C.), 1841-1920.
Date:
1880
Catalogue details

Licence: Public Domain Mark

Credit: A treatise on therapeutics : comprising materia medica and toxicology with especial reference to the application of the physiological action of drugs to clinical medicine / by H. C. Wood. Source: Wellcome Collection.

    31/740 (page 27)
    latter a gelatinous, inert substance. They ai-e further distinguished by the color of the precipitates which they yield with the perealts of iron; gdlo- tannic acid producing a blue-black, kino-tannic a green-black color. The officinal tannic acid—the gallo-tannic acid—is obtained by treating powdered galls with washed ether, which on standing separates into two strata, the upper of which is ethereal, and contains chiefly the coloring-matter and other impurities. The lower watery stratum contains the tannic acid, which is recovered by evaporation. Commercial tannic acid is a light, feathery, non-crystalline powder, of a yellowish-white color, a faint odor, and an astringent, somewhat bitter taste. When absolutely pure, it is colorless and free from odor or taste other than that of astringency. Its reaction is strongly acid, and it unites freely with both organic and inorganic bases. It is very freely soluble in water, even more so in glycerine, somewhat so in dilute alcohol, scarcely at all in absolute alcohol, and not at all in ether free from water. By a heat of from 180° C. to 215° C. it is changed into pyro-galUc acid, which crystallizes in white, shining plates, of a bitter taste and neutral reaction. With salts of the alka- loids it produces a whitish precipitate, very soluble in acetic acid; with per- salts of iron, a black (bluish or greenish) precipitate; with lime-water, a precipitate which is at first whitish, then gray, dingy greenish, and finally brownish ; with gelatine or albumen, a whitish coagulum. All of these sec- ondary products are tannates. Tannic acid also dissolves in concentrated sulphuric acid, with the production of a black color. By prolonged exposure in solution to the air, or by the action of dilute sulphuric acid, it is converted into gallic acid. Physiological Action.—Tannic acid is, so far as may be, a pure astrin- gent. As it coagulates albumen, it cannot be absorbed into the blood in any quantity, and its solution injected into the veins causes rapid death, with convulsions, or other nervous phenomena, due to the production of thrombi or emboli. Out of the body it is readily converted into gallic acid, and, when taken into the stomach, a pi-oportion of it undergoes a similar change. In the viscera of a rabbit poisoned with tannic acid, Schroff {Die Pflanzenstoffe, von Dr. Aug. und Dr. Theo. Husemann, p. 1005) found only gallic acid; and according to Clarus (titcZ.) the gi-eater part of ingested tannic acid can be recovered from the stools as tannate of albumen or as gallic acid. Wohler and Frerichs have found gallic acid with pyro-gallic acid iu the mine after the exhibition of tannic acid. Therapeutics.—As tannic acid must undergo conversion into gallic acid before absorption, it is evident that the latter is to be preferred to it when the part to be acted on can only be reached through the circulation. As a local application, tannic acid is much more powerful than gallic acid. Locally applied, it may be used to overcome relaxation, as in s])ongy gums, mercurial sore mouth, hemorrhoids, chronic sore throat. To check hemorrhage it may be used whenever the source of the flow can be reached directly, as in epis-