Celsus treats of fistulæ with more than his wonted minuteness. This is his definition: “Id nomen est ulceri alto, angusto, calloso.” He has described all the complications of it with great accuracy. He directs us to commence by making an inspection with a probe or sound, so as to ascertain the state of the parts and of the discharge. If a soft body is felt at the bottom, we conclude that the fistula terminates in the flesh, but if a hard one is felt, we know that it ends with a bone. If the probe slide readily over the bone, it is free from caries, but if it does not so, and yet no inequalities are felt on it, caries has taken place, but it is still smooth: if it feel unequal and rough, the bone is eaten with caries. For a simple and recent fistula, not deep-seated or in a joint, the plaster for recent wounds will be sufficient, provided salt, or alum, or the scales of copper, or verdigris, or any of the other metals, be added to it. The application is to be made upon a piece of linen, and a sponge soaked in vinegar is to be put over it, and is to be removed on the fifth day. The patient must live upon nutritious food. If the fistula is at a distance from the præcordia, emetics with radishes are said by him to be proper. When the fistula is old it becomes callous, and requires stronger applications, containing such ingredients as calamine, atramentum sutorium, verdigris, galls, lime, orpiment, or realgur. He mentions as a very ready application a solution of ammoniac in vinegar, with some verdigris added to it. However, he remarks, any other caustic will accomplish the same purpose. If the fistula is long and transverse, an incision is to be made at its commencement, after which the collyrium may be applied. When the fistula is double, or consists of still more passages, he recommends us to blow in with a writing pen the medicines in the form of powder, or to apply them dissolved in wine, mulse, or vinegar. But whatever the internal dressing be, he recommends us to apply on the outside of it something of a refrigerant and repressing nature, as the parts around are generally affected with inflammation. When the dressings are removed the fistula is to be syringed with wine if the discharge of the pus is copious, with vinegar if its edges are callous, but with mulse, or a decoction of tares, if the passage be clean. By the means we have been describing it will generally happen, he says, that the inner coat of the fistula will slough off, and leave the ulcer in a clean state. Agglutinants are then to be applied, especially a sponge smeared with boiled honey. When the sides of the fistula are clean there need be no apprehension lest they do not adhere, since, he remarks, we often see in ulcerations of the fingers that without great care one finger is apt to adhere to another.