In this variety of fistula the feces are coated more or less with pus or blood, and a boggy swelling is noted at some portion of the circumference of the anus. A peculiar feature of this swelling is often noted—viz., its presence one day and its disappearance in a day or two, followed by an increased discharge of pus from the bowel. This fact is explainable by the closure of the outlet of the fistula, caused either by a plug of feces or as a result of inflammatory swelling, which allows the collection of a quantity of pus and the consequent formation of a boggy tumor. The swelling disappears upon the reëstablishment of the communication between the bowel and the sinus, and is attended by the profuse discharge of matter previously mentioned. This phenomenon is repeated over and over again, and indicates the nature of the disease. In other cases of blind internal fistula, if the orifice can be felt, or if it can be seen through a speculum, a bent probe may be introduced into it and made to protrude near to the cutaneous surface of the body, where its point can be felt. DIAGNOSIS.—The method of diagnosing fistula has already been sufficiently detailed. A few words, however, as to differential diagnosis may prove useful. Fistulæ frequently coexist with other rectal diseases; it is therefore important that an examination should be carefully made, so as to exclude such lesions—for instance, the presence of stricture, malignant disease, hemorrhoids and other tumors, etc. A thorough physical examination of the chest should also be made, to ascertain the presence or absence of phthisis, which so frequently complicates fistula in ano. Serious kidney disease should be excluded before recommending operation, for obvious reasons. In cases of caries of the vertebræ, of the sacrum, or of the pelvis, fistulous tracks may form and simulate anal fistula. In such instances a careful investigation will reveal the true origin of the trouble, and will show that the case is not one of ordinary fistula in ano. COURSE AND PROGNOSIS.—This disease untreated has a tendency to increase. The longer its duration the more tortuous and complicated does it become. Hence the earlier the patient submits to treatment the more favorable will be the prognosis, and the time and extent of the treatment necessary to effect a permanent cure will be correspondingly diminished. ----- Footnote 44: _Op. cit._, p. 77. Footnote 45: _Op. cit._, p. 21. CHAPTER III. THE PALLIATIVE TREATMENT OF FISTULA IN ANO. TREATMENT OF ABSCESS.—Preliminary to a consideration of the treatment for the disease when the fistulous track has been formed, some attention must be devoted to the importance of dealing promptly with the inflammatory and suppurative process which leads to abscess, and which usually forms the first stage of the affection known as fistula in ano.