Ulcers vary much in disposition and appearance, follow wounds, abscesses, sloughing, eruptions, &c., and often occur without any previous læsion of the surface. Those most generally met with are comprehended in the following classes:—1. The simple purulent ulcer, or healthy or healing sore. 2. The weak or sluggish ulcer,—a sore with undermined integuments and an unhealthy state of the cellular tissue. 3. The indolent ulcer,—a sore with hard elevated edges, and presenting little or no appearance of reparation. 4. The irritable ulcer,—a sore with over-action, and generally affecting only the mere surface of the true skin. Besides these, there are sores connected with diseases of the bones, and others arising from specific action; some are complicated with a varicose state of the veins: the former have been already treated of; the latter are reserved for consideration. Ulcers change their characters, as from simple to irritable, and from indolent to inflamed; the change depends on situation, on the state of the constitution, and on the treatment which they receive. I. The appearances of the first class were described when the healing of wounds by granulations was considered, p. 173. They heal more readily on the upper extremities, on the face, neck, and trunk, than on the lower limbs; for in the former parts the circulation is more vigorous, the natural processes of cure proceed more easily, and are less liable to interruption. The sore only requires rest, a clean condition of the surrounding parts, mild and light dressings, and moderate support; dry lint or lotions are preferable to ointments, since the latter are apt to irritate by their rancidity. When the sore is of considerable size, and there is a tendency in the granulations to rise above the level of the surrounding skin or cicatrix, the edges may be protected by very narrow slips of fine old linen or cambric, spread with fresh spermaceti ointment or cold cream; a pledget of dry lint is then laid on, and retained by a roller. The dressings thus arranged do not adhere, and the tender cicatrix is not ruffled and disturbed; or a piece of pierced linen spread thinly with unirritating ointment may be placed over the sore, and above that dry lint. When the sore has contracted to a small size, and some powder, as starch or calamine stone, or a piece of dry lint, may be applied, so as to allow a scab to form for the protection of the subjacent surface; but this will, in most cases, be better accomplished by touching the surface lightly with lunar caustic or blue stone; the fluids on the part are thereby immediately coagulated, a crust is quickly formed, and by covering it with charpie, it is retained in its situation, whilst the process of cicatrisation proceeds beneath it: if a small quantity of matter should be secreted, it readily escapes by the sides of the crust, without disturbing either it or its covering; the limb should be raised above the level of the trunk.