With regard to fistulas, if they penetrate pretty deep, so that a collyrium cannot reach the bottom of them, if they are tortuous, or consist of several sinuses, operations are more useful than medicines; and those, that run in a transverse direction below the skin, give less trouble than such as go directly inward. Therefore, if the fistula be transverse under the skin, a probe ought to be introduced, and an incision made upon that. If it be tortuous, its windings are to be followed by the probe and knife. And the same course must be taken, if several of them appear like rivulets uniting their streams. When we have reached to the end of the fistula, all the callosity must be cut out, and fibulae applied to it with medicines to agglutinate. But if it points directly inward, when its direction is found by a probe, that sinus must be cut out: then a fibula put upon the lips of the skin, and agglutinating medicines laid over it; or if the ulcer be very foul (which sometimes happens from a carious bone) when that also is cured, medicines to promote a digestion.

It is common for fistulas to extend beneath the ribs. When this case occurs, the rib in that part must be cut through on both sides, and taken out, lest any thing corrupt be left within. It is usual for them also, when they have got through the ribs, to penetrate the transverse septum, that divides the intestines from the superior viscera. Which circumstance may be known, both from the situation, and from the violence of the pain, and because sometimes the air comes out with the matter, as it were bubbling, and particularly when the patient keeps in his breath. For this case there is no remedy. In the other kinds about the ribs, which are curable, greasy medicines are hurtful, and therefore we should use such as are adapted to wounds: but the best application is dry lint, or if any thing requires to be cleansed, the same dipped in honey.

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.

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.

Those, that are for making quick dispatch, ought to tie the skin tight with the string, that it may be the sooner cut; and at night to introduce some small slips of a penecillum, that the skin may be made thin by the same means that it is distended; however this occasions pain. The dispatch, as well as the pain, is increased, if both the string and the penecillum be turned with some one of those medicines, which I mentioned, for consuming a callosity. It may happen, however, that the use of the knife may be necessary, even in this part, if the fistula points inward, or consists of several sinuses. Wherefore in these kinds, the probe must be introduced, and the skin must be cut in two lines, so that betwixt them a very small habenula may be cut out(8), to prevent the lips from uniting presently; and that room may be left for pledgits of lint, as few of which as possible ought to be laid on; and the same course must be pursued as was directed in abscesses. But if, from one orifice, there shall be several sinuses, that sinus, that runs straight, must be opened with a knife, and the others, that branch from it, which will then appear, must be tied with a ligature. If any one penetrate so deeply, that an instrument cannot be safely used, a collyrium must be put in.

The food, in all these cases, whether the treatment be by an operation, or by medicines, ought to be moist; the quantity of drink pretty liberal, and for a long time water. And when the flesh begins to sprout up, then indeed the bath may be used, but sparingly, and such food as plumps the body.