_The treatment of a chronic encapsuled abscess, wherever situated._ In attempting to evacuate a chronic encapsuled abscess, both the trocar and cannula and the evacuator merely impinge against, and tend to push aside, the dense enclosing wall of the abscess cavity. When such obstruction is suspected, a director should be introduced in the direction of the abscess, and the brain explored till the resistance of the abscess-wall is encountered. With the aid of two narrow spatulæ, or other suitable instrument, the passage through the brain is gently enlarged till the wall of the abscess becomes visible. The margins of the passage through the brain are gently retracted and the abscess-wall freely incised with the knife. After the evacuation of the pus, a drainage tube can be introduced, but, as such a method seldom permits of a permanent cure--the abscess filling up again as soon as the tube is withdrawn--it is generally advisable to attempt the entire removal of the abscess-wall. The cut edges of the capsular incision are seized with narrow-bladed forceps, gentle traction applied, and the surrounding brain substance carefully peeled away. As a rule, there is no great difficulty attendant on this process and the hæmorrhage is seldom severe. The cavity that remains in the brain substance is _lightly_ packed with gauze, this packing being allowed to remain for twenty-four to thirty-six hours, after which it is withdrawn and a little fresh gauze introduced, if necessary. The cavity fills up with extraordinary rapidity, mainly as a result of the expansion and falling together of the surrounding brain (see Figs. 86 and 86a). 2. The one-stage operation. _Preliminary exploration of the mastoid operation, followed by an investigation of the middle and posterior fossæ of the skull._ To expose the mastoid antrum, the incision commences immediately above and behind the ear, and, carried down to the bone throughout, terminates near the tip of the mastoid process. The soft tissues are peeled away in the forward direction and the cartilaginous ear detached from the posterior and upper boundaries of the bony auditory meatus. Macewen’s suprameatal triangle and the supramastoid crest are identified, the former landmark being taken as a guide to the communication between the mastoid antrum and the middle ear, the latter representing the uppermost limit of the field of operation. [Illustration: FIG. 80. THE ‘RADICAL’ MASTOID OPERATION. To show removal of the ‘bridge’ from above. The seeker, inserted into the aditus, acts as a protector to the underlying external semicircular canal and facial nerve. (After Hunter Tod.)] With the aid of the hammer and chisel the bone is chipped away till the antrum is exposed--on an average this will be situated about three-fifths of an inch deep from the surface. The opening necessarily becomes funnel-shaped, but it should be made as complete as circumstances permit.