If the internal opening is more than an inch from the anus, a probe-pointed bistoury (Figs. 28, 30, p. 61) should be introduced into the fistula upon a director, and its point made to impinge upon a finger in the rectum. As the finger and the instrument are withdrawn, the necessary incision is made. Or the director can be passed through the sinus, and a wooden gorget (Fig. 35) inserted into the bowel, after which the track can be divided with an ordinary bistoury. The gorget prevents the opposite side of the bowel from being injured should the knife slip. (Fig. 36). [Illustration: Fig. 35—Gorget.] [Illustration: Fig. 36—Operation for Fistula with Gorget (Bernard and Huette).] When the track of the fistula is much indurated, and considerable force is therefore required to make the incision, it will be better to perform the operation by means of Mr. Allingham's spring-scissors and special director (Fig. 37). With this instrument, fistulæ running high up in the bowel may be divided, no matter how dense they may be. The director is made with a deep groove, the transverse section of which is more than three-quarters of a circle; in this the globe-shaped probe-point of one blade of the scissors runs. When placed in the groove the blade cannot slip out; so, the director having been passed through the sinus, the forefinger of the left hand is introduced into the bowel, and then the probe-pointed blade of the scissors is inserted into the groove of the instrument, and run along it, cutting its way through the diseased tissue as it goes, the finger in the bowel preventing the healthy structure from being wounded. [Illustration: Fig. 37—Allingham's Spring-Scissors and Director.] A frequent error in operating on fistulous cases consists in not keeping to the sinus, the director being pushed through the track-wall, and then being free to roam about in the cellular tissue of the part, at the operator's will. In this manner a portion of the fistulous channel is left, and an unnecessary amount of the tissues (skin and subcutaneous structures) is divided. Such a mistake can always be avoided by taking plenty of time in performing the operation, and by careful sponging of the sinus as it is laid open, in order to follow the track of the granulation-tissue lining it, which by this simple means is freely exposed to view. The method of treating EXTERNAL RECTAL FISTULÆ must vary according to the direction and extent of the track. If the mucous membrane alone intervenes between the finger introduced into the bowel and a probe passed along the sinus, the channel should be transformed into a complete fistula by perforating the mucous membrane with the probe, or with a director, at the uppermost limits of the fistulous channel. The regular operation for complete fistula is then to be performed by dividing the intervening septum between the fistula and the bowel.