There is no bone within the skin of the belly; but fistulas in that part are extremely dangerous; insomuch that Sostratus believed them incurable. That they are not always so, experience has shewn. And indeed, which may seem very wonderful, a fistula opposite to the liver and spleen, and stomach, is more safe than one opposite to the intestines: not that the thing is of its own nature more pernicious there, but because it exposes to a danger of another kind. The reason of which fact some authors have but little understood, though their experience convinced them of this difficulty. For the belly itself is often wounded by a weapon, and the intestines, that have fallen out, are replaced, and the wound united by sutures: the manner of doing which I shall point out presently. Therefore, when a small fistula has even penetrated the abdomen, it may be cut out, and the lips of it joined by a suture. But if the fistula spreads wider within, upon its being cut out, it must necessarily leave a pretty large vacuity, which cannot be sewed up without great violence; especially on the internal side, where there is a kind of membrane, which the Greeks call peritonaeum, that surrounds the abdomen. Therefore, as soon as a person begins to walk or move, the suture breaks, and the intestines are let loose, so that the patient must perish. But the case is not always desperate; and therefore, we must attempt the cure of smaller fistulas there. [Sidenote: _Of fistulas in the anus._] Fistulas in the anus require a particular treatment. A probe being put into them, an incision must be made in the skin at its further end: then the probe must be drawn out at the new orifice with a thread following it, which was put through an eye made in the other end for the purpose. There the thread must be taken hold of, and tied to the other end, that it may gently take hold of the skin above the fistula: and the thread should be made of crude lint(6), double or triple, and so twisted as to make one string. In the mean time the patient may go about his business, walk, bathe, and eat, just as if he were in the most perfect health. Only loosing this knot(7) twice a day, the string must be drawn in such a manner, that the part, which was above, may then be within the fistula. And the thread must not be suffered to rot, but every third day, the knot must be untied, and at its one end must be fixed a fresh ligature, which when the old one is drawn out, must be left in the fistula with a like knot. For thus it gradually cuts the skin that is above the fistula: and, at the same time, the part that has been eat through by the thread, heals; whilst the remainder, which is pinched by the thread, continues to be cut by it. This method of cure is long, but is attended with no pain.