in materia medica, substances distinguished by a rough austere taste, and changing solutions of iron, especially those made in the vitriolic acid, into a dark purple or black colour; such are galls, tormentil root, bistort root, baoulines, terra japonica, acacia, &c. Astringents yield their virtues by infusion both to water and vinous spirits, but generally in greatest perfection to the former. The medical effects of astringents are, to constringe the fibres, and incrassate or lightly thicken the juices. Their more experienced use is in disorders proceeding from a debility or flaccid state of the solids; in hemorrhages from a thinness of the blood, laxity, or rupture of the vessels; in preternatural discharges of other kinds, after the offending matter has been duly corrected or evacuated; and in external relaxations.