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.
The indications for the use of astringents are such as might be inferred from their physiological effects. They are three in number; 1. to check morbid discharges, 2. to obviate morbid relaxation, and 3. to check inflammation in its earliest stage. For the first two purposes they may be used either generally or locally; for the third, they must be applied directly to the seat of the inflammation. It will be most convenient to treat first of their internal, and afterwards of their external use; including under the former head only what has reference to their entrance into the Stomach, under the latter all their direct local applications from without.
It must not, however, be forgotten that, in their operation upon the mucous membrane of the alimentary canal when taken into the stomach, they act as directly as upon the external surfaces; the only difference being that they cannot be applied so freely to the former, in consequence of its greater sensitiveness, the greater danger of any excess of action, and the impossibility of limiting the extent of their application, or readily removing them if found to be injurious.