This is another of the remedies that operate indirectly on the protective principle. Though a powerful irritant itself, it often proves useful in ulcerative affections. When applied undiluted to a surface of this kind, it coagulates the albumen, and thus gives a white coating, which protects the parts beneath. it should be used only in the indolent and flabby ulcers, the phagedenic, or the gangrenous ulcers following burns; and never in those already in a highly inflamed state. Mixed with about four parts of lard, and applied every two hours, it has been recommended as having specific powers in the cure of erysipelas. On a former occasion, I spoke of the efficacy of creasote in toothache, and ascribed it in part to the insoluble coating it gives to the carious surface.

Besides the Protectives heretofore considered, we may rank in the class certain insoluble substances which are supposed, when swallowed, to act mainly by adhering to the surface of the mucous membrane of the stomach and bowels, thereby sheathing them against the influence of irritating agents. it is to inflammatory or irritated conditions of this membrane that they are considered applicable; and hence they have been employed in gastritis, diarrhoea, dysentery, and cholera, and in neuralgic conditions of the stomach and bowels. These medicines have been or will be individually considered elsewhere, with their uses and modes of action; and they are mentioned here only to collect in one view all the remedies which may be supposed to have the characteristic properties of the class. To this set of Protectives belong calomel, subnitrate of bismuth, and probably subcarbonate of iron, all given in very large doses; and chalk may be considered as belonging to the same category, when taken in quantities beyond the solvent powers of the gastric and intestinal acids. it is not only when taken internally that these medicines act usefully on the principle of protection. in the form of powder, or rubbed up with mucilage, they have been applied, with supposed advantage, to external ulcers and inflamed mucous surfaces, as in gonorrhoea, leucorrhoea, and inflammation of the rectum. Remarkable virtues have been ascribed to anthracite coal, by Dr. A. Dyes, who was led to the discovery of its virtues by observing that it was greedily devoured by pigs, in which animals it was thought to promote digestion. He used it in intestinal worms, catarrhal disease of the stomach, chlorosis, enlargement of the spleen, scurvy, etc. The probability, however, is that, when productive of any benefit, it acts simply on the principle of the Protectives above explained; by guarding, namely, the mucous surfaces from the effects of irritating substances. (B. and F. Medico-chir. Rev., Jan. 1866, p. 237; from Schmidt's Jahrbuch, Feb. 1865.)

Carbonate of lead is used externally for the same purpose; and, rubbed up with flaxseed oil, in the form of white paint, has been recently strongly recommended by Mr. Alfred Freer, in erysipelas, eczema, herpes, furuncles and carbuncles, burns, and painful ulcers of the leg. The affected part, and a little of the surface beyond, are painted with it, by means of a feather, and a fresh layer applied every two hours, until a sufficient coating is procured, the integrity of which must afterwards be maintained. {Lancet, June, 1859, p. 610.)

The sulphate of lead produced when the acetate of lead and sulphate of zinc are mixed, is probably a material agent in the cure of gonorrhoea, treated by that mixture. Through its insolubility and weight, it adheres to the mucous surface, and may thus guard it against irritation.

Clay reduced to the state of an impalpable powder, and rubbed with water to a soft semiliquid consistence, has proved, in the hands of Dr. Schreber, of Leipzic, one of the best applications to surfaces yielding foul discharges; and, in the form of poultices, has been tried by others with advantage in local inflammatory affections. {Braithwaite's Retrospect, No. xlxxx. p. 120.)