These are drugs which tend to shrink mucous membranes or raw tissues. Astringents produce their effects: (1) by constriction of arterioles, as epinephrine and cocaine; (2) by abstraction of water, as glycerin and alcohol; and (3) by chemic precipitation of the superficial layers of protein, as the metallic and vegetable astringents.

The most employed metallic astringents are: Alum, silver nitrate, ferric chloride, ferric subsulphate (Monsell's salt), zinc sulphate, and copper sulphate. (See Metals.)

Potassium chlorate in saturated aqueous solution (1: 16) is employed in relaxed sore throat and in stomatitis, especially that from mercury; but where there is ulceration its solutions are quite irritant. Taken internally it is believed by some to be a specific in ulcerative stomatitis, Holt, for instance, recommending 2 grains (0.13 gm.), every hour the first day, then every 2 hours. Bachem (1912) gave 1 ounce (30 gm.) daily for six weeks to pups, and there was no effect on growth rate, kidneys, stomach, or blood. The drug was rapidly eliminated in the urine, and acted as any other indifferent salt. Loevenhart in his Harvey Society Lecture, 1914, stated that it does not give up its oxygen in the body and is excreted unchanged in the urine, yet it is capable of causing severe irritation of the gastro-intestinal tract, methemoglobinemia, and albuminuria. Buri states that this takes very large doses. Fifteen grains (1 gm.) have caused death in a child; 1 ounce (30 gm.) has been taken without symptoms. Mercier (1902) reports death in a child of three years eighteen hours after taking "a pinch or two" of the chlorate. At autopsy the blood and bone-marrow had a prune-juice appearance and contained methemoglobin; the bladder was filled with dark brown urine. The treatment for poisoning is lavage, transfusion, and measures to overcome shock.

Potassium chlorate mixed dry with sulphur, hypophosphites, and oxidizable organic matters is likely to explode. In the form of tablets it has frequently caused fire on contact with sulphur matches.

The vegetable astringents contain either resins or tannic acid. The resinous astringents are myrrh, a tincture of which, diluted with water, is used for soft and bleeding gums, and Hydrastis, whose tincture, diluted with water, is used locally in vaginitis and urethritis.

The tannic acid astringents are: blackberry root (rubus), catechu, galls, gambir, kino, rosa gallica, sumac fruit (rhus glabra), and witch-hazel bark (hamamelis). They have dropped largely out of use and their only official preparations are the tincture of kino, 5 per cent., and the compound tincture of gambir, dose of each, 30 minims (2 c.c.). A blackberry brandy or cordial is employed by the laity in diarrhea.