But sometimes from abscesses of this kind and other ulcers, arise fistulas. That is the name of a deep, narrow and callous ulcer. It occurs almost in every part of the body; and it has some peculiarities in each place. I shall first treat of the general properties. There are then several kinds of fistulas; for some are short, others deeper; some point inward in a straight line; others, and by far the greatest part, are transverse; some are simple, others are double, or triple, which beginning from one orifice, branch out within, into three or more sinuses; some straight, others bent and tortuous; some end in the flesh, others penetrate to bones or a cartilage; or where neither of these lies beyond them, reach to the more internal parts; some again are easily cured, others with difficulty, and some are even found incurable. The cure of a simple and recent fistula in the flesh is easy. It is an advantage to it, if the person be young, and the constitution firm: the contrary are very unfavourable circumstances; as also if the fistula has injured a bone, or cartilage, or nerve, or muscles; if it have seized upon a joint, or has penetrated either to the bladder, or the lungs, or to the womb, or to the large veins or arteries, or to the jaw-bones, throat, stomach, or thorax. When it points towards the intestines too, it is always dangerous, and often mortal. In these cases it greatly increases the malady, if the patient be either sick, or old, or of a bad habit. First of all, it is proper to put a probe into the fistula, that we may find its direction and depth: and at the same time whether it be altogether moist, or drier than it should be, which appears upon drawing out the probe. It may also be determined, whether the bone be affected or not; and if the fistula has penetrated there, how far it has injured it. For if that part is soft, which is touched by the end of the probe, the disorder is confined to the flesh; if it resists more, it has made way to the bone. And again, if the probe slides, there is no caries begun: if it does not slip out(88) of the point where it is placed, the caries is begun, but is slight yet: if it feels unequal also, and rough, the bone is very much corroded. The situation itself shews when there is a cartilage below; and that the fistula has reached it, appears by its resistance.