Concerning the carbolic acid treatment Allingham says: “Since the publication of my last edition I have cured many patients by dilitation of the sphincters and the use of the bone stud and carbolic acid. One practical point I would mention. The further the external aperture is from the sphincter the more likelihood is there that the sinus will heal. This is shown as well in the cases of spontaneous cure as in my own successes. You must always enjoin rest after a strong application, and watch that not too much inflammation be set up.” The fistulatome shown in fig. 16, is a contrivance which is perhaps destined to take the lead in the treatment of fistula generally. It is so constructed that the fine cutting blades close on themselves, while the instrument, which is probe pointed, is being introduced, but immediately open on withdrawal, and thus catch up and cut through the fistulous membrane. [Illustration: FIG. 16.—Fistulatome with blades extended.] Who the inventor of this clever device is, I have been unable to ascertain, having seen it claimed by three different physicians, one of whom speaks of curing 76 per cent. of all cases treated by one operation. That is by drawing the fistulatome through the tract once. Cases of long standing require that the instrument should be turned at right angles and drawn through the second time and possibly repeated later on, or a tenotome employed to scarify any remaining indolent sinus. It will be readily seen, however, that a fistula with a side pocket, branch or diverticulum, would hardly be reached by this method; although the blades are so formed that they draw the membrane of a dilatable pouch to them from the sides. In such cases a little ingenuity would be required in finding these diverticula, for the purpose of scarifying them with a tenotome. The preparation of the sinus and the after-treatment are the same as already mentioned. Also evacuation of the bowels and constipation by the use of an opium suppository, even to the dilitation of the sphincters, if thought necessary to bring about a cure. In rare instances, where divulsion has been practiced and while yet under the influence of anæsthesia, it might be advisable to lay open the cavity by cutting _from_ the sphincters, pockets traced, scarified and partitions divided. [Illustration: FIG. 17.—Flexible Silver Canula.] In relation to treatment, Andrews says: “The truth is, that anal fistulæ have a natural tendency to recovery, and are held back from it mainly by two things. 1. “The unfavorable effect of the undrained septic fluids within the sac. 2. “The tightness of the external opening, which prevents free drainage, and keeps the sac distended with this putrid pus.