This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
1. For arresting morbid discharges they are employed in excessive secretion, resulting from advanced or chronic inflammation, or debility of the vessels, in the nostrils, conjunctiva, external auditory meatus, mouth and fauces, urethra and bladder, vagina and rectum. Hence their use in chronic coryza and ozaena, purulent ophthalmia, otirrhoea, stomatorrhoea, gonorrhoea and gleet, cystirrhoea, leucorrhoea, and mucous or purulent rectal discharges. Excessive sweating, and oedema of the limbs, may also be treated by them with advantage. They are the most effective remedies in hemorrhages from all these sources. The same caution should be observed, as in their internal use, not too hastily to arrest a discharge which is effecting some useful purpose. But they may sometimes be employed with propriety topically, where we might hesitate to administer them by the mouth, and almost always with much greater freedom. Any irritation they may excite in external parts is much less hazardous than an equal amount in the stomach or bowels. Besides, we can in this topical method precisely limit their application, if deemed advisable, and, should they act too powerfully, may remove; them. They may, moreover, be used much more effectively than by the stomach, because in a more concentrated state.
2. For obviating relaxation, not essentially connected with excessive discharge, they are employed in a great variety of affections, as in the different forms of venous distension, including varicocele, hemorrhoids, and varicose veins of the legs; in prolapsed anus, uvula, and uterus; in indolent, flabby, and fungous ulcers; and in various other conditions of local debility, attending or following advanced and chronic inflammation of the different surfaces mentioned in the preceding paragraph, and additionally in that of the larynx.
3. In the forming or early stage of inflammation, with the view of contracting the capillaries, the astringents are much and most usefully employed. When, however, that process is in full vigour, and sustained by a plethoric: state of the blood, or some cause acting strongly through the constitution; when, too, exudation has taken place in the tissue;, and blood may have coagulated in some of the vessels, astringents will often fail to produce their characteristic effect, and may even increase the inflammation by acting as irritants. But, even under such circumstances, after the activity of the inflammation has been subdued by depletion, they may again be resorted to, and will now not unfrequently succeed when; they had before failed, Hence, astringents are used locally in inflammalion of the conjunctiva, of the mouth and fauces, of the recturn, of the mucous membrane of the genito-urinary passages, and of the skin. It is upon this principle, in part, that they operate so usefully in various cutaneous eruptions. But, in the choice of astringents for these purposes, there is great occasion for the exercise of judgment. From their diversified powers, some are applicable where others might prove injurious. It is obvious that those which possess other antiphlogistic powers, besides astringency, must be more efficient in answering the indication than the pure astringents. Hence, the mineral are generally more efficacious than the vegetable substances belonging to the class.