_Chronic abscesses_, besides recent wounds, are treated with carbolic acid. The surface to be punctured is covered with a piece of thin muslin soaked in carbolic oil, and the knife to be used is dipped in the oil also. Then, a second piece of muslin being ready, the surgeon opens the abscess through the muslin, and as he withdraws the knife an assistant lays on the second piece of muslin over the wound. The matter drains away from under this curtain, and the access of atmospheric air is prevented. When the matter ceases to flow, the lac plaster is laid on, and the oily cloth outside, which can be changed as often as is requisite. Abscesses so treated usually soon cease to secrete matter, shrink, and fill up without delay. If the abscess has burst or had communication with the external air, the interior must be filled with watery solution 1 to 20 before it is dressed, that fermentation in the cavity may be prevented; the further treatment is the same as for a recent wound. [Illustration: Fig. 114.—Irrigating a wound.] =Irrigation.=—The continual flow of ice-cold water is used to prevent inflammation of certain wounds. In using cold, it is particularly necessary that the temperature of the water remain steady, for alterations of temperature cause alterations in the capacity of the blood vessels, and promote congestion rather than diminish it; hence irrigation, badly attended to, becomes an evil instead of a benefit. The simplest way (see fig. 114) of contriving irrigation is to lay the limb in an easy position on pillows, protected by a sheet of india-rubber cloth, weighted at one corner to draw the cloth into a channel, down which the water trickles into a receiver under the bed; over the limb a jar, wrapped in blanket, is suspended. This is filled with water from time to time, and kept charged with lumps of ice. A syphon is made by a few feet of fine india-rubber tubing reaching from the bottom of the jar to the wound, the escape of water through the tube being moderated by drawing the end more or less tightly through a bit of cleft stick. It is sufficient that the wound should be kept constantly and thoroughly wetted; more than that is waste of cooling power. _Esmarch’s Irrigator._—This is a simple contrivance for washing out wounds and sinuses with a stream of water. It consists of a tall can of block tin (see fig. 115), with an orifice at the lower end, to which a couple of feet of india-rubber tubing are attached. The tube is fitted with an ivory nozzle and a hook, so that when the stream is not wanted the flow of water is stopped by hanging the nozzle on the upper edge of the can. The stream can be made more or less forcible by raising or lowering the can above the wound. [Illustration: Fig. 115.—Esmarch’s Irrigator.]