In cases of sloughing chancre, of phagedaena, of hospital gangrene, etc., when it is necessary to destroy portions of diseased tissue, and to stimulate to healthy action, strong nitric acid is one of the best caustics in use. The affected part should be cleansed and dried, so that the acid be not too diluted by secretion, the neighboring parts should be protected by oil or ointment, and the caustic then thoroughly applied with a glass brush, splinter of wood, or pledget of lint, until a firm dry yellowish mass is formed; the pain is at first severe, but soon subsides under cold water dressings, the eschar formed is not very deep, and usually separates in one or two days; the application may sometimes require to be repeated.