In suppuration of the cellular substance in the neighbourhood of the anus, the matter may present itself externally, whilst it is making extensive progress internally; and if a free opening is not made, fistula ani is the result. The propriety of an early evacuation of purulent matter in important, or very sensible, organs, such as the eye and testicle, is very evident. The larger arterial and venous trunks appear not to suffer from suppuration, for in purulent depôts we find them entire, and much thickened by copious effusion of lymph into their outer cellular coat and sheath; the nerves, however, are not so much protected, or do not appear to resist the pressure and insinuation of pus, and suffer along with the other tissues. [Illustration] The most convenient and effectual mode of opening an abscess is with a sharp-pointed bistoury, and the incision should vary in extent according to the circumstances of the case. The straight instrument, used as described and represented in the “Practical Surgery,” p. 5[6], will be found to answer best in deep-seated collections; in the more superficial it may be slightly curved. It is used as here shown, only that the edge of the knife should be turned more downwards before the integument is divided by withdrawing it. The aperture must always be made at the most dependent part, which is also, generally, the thinnest; thereby a free exit is allowed to the matter. If the incision be not made in a dependent part, a considerable quantity of the matter will be retained within the abscess, and can only be evacuated at the time by squeezing the parts—at all times a very cruel and improper practice—applying compresses, &c., which produce much irritation and unnecessary inconvenience to the patient. The cavity of the abscess inflames, the discharge becomes bloody and putrid, and great constitutional disturbance is apt to follow. When, again, the opening is sufficiently large, properly placed, and the matter flows out through the elasticity of the coverings, no air enters, the cyst gradually contracts, and the cure is soon completed.