(Quasi fusula, from fundo, to pour out). So the Latins called a catheter. See Catheterus; and also a clyster pipe. See Enema.

Fistula. A Pipe. In surgery it is a kind of ulcer which resembles a pipe; named also eligii morbus. It is narrower than a sinus; generally continues further; hath its internal surface and its orifice usually callous; and is generally the consequence of abscesses. The seat of a fistula is in the cellular membrane. It is known to be present when there is an aperture on the surface of the body from which any matter either flows or may be pressed out: its depth and direction are discovered by a probe; or, if the directions are various, warm water may be injected into it; and, if near the skin, these will be ascertained by the elevation occasioned by the water; if otherwise, the quantity of water retained will determine the size of the cavity. The probe often discovers whether the fistula runs upon an adjacent bone, or whether the bone be carious. The parts in which these ulcers are seated, and their various circumstances, constitute the chief differences betwixt fistulae. A fistula is more dangerous in proportion to the depth of the cellular membrane, and the thickness of the muscles. While it is simple, and extends no further than it can be reached with a knife, it may be generally cured: when so situated as to open into the neck of the bladder, or when attended with a caries in the adjacent bone, particularly the os sacrum or the coccyx, the cure is difficult, and often impossible.

Mr. Bell includes the fistula in his species of sinous ulcer; by which he means that kind of sore which hath one or more openings running into it from the same or different directions, and generally seated in the cellular membrane. A sinus, as thus described, he says, is the most simple state of the disorder, and is, by long continuance, or by the use of drying astringent applications, liable to become hard and callous in its internal surface, and in such a state, from its supposed resemblance to a pipe, is termed a fistula. The most frequent cause of sinuses in ulcers and abscesses, is the want of vent or a sufficient opening for the discharge, which easily insinuates itself into the yielding substance of the cellular membrane, and proceeds gradually till it finds an opening either externally or into some of the neighbouring cavities. An improper application of bandages on ulcers is often the cause of a sinus.

When fistulas, not yet become callous,' are complicated with ulcers, the most expeditious relief is from an incision to the bottom, if it can be done without danger: after which the wound is to be cleaned and healed. Another method is, to compress the fundus of the sinus; for which purpose a narrow compress, or a slip of plaster wrapped up in that form, is to be applied externally over the bottom, and secured, as in other ulcers, with a plaster and bandage, that the peccant matter may be propelled from the bottom to the mouth of the fistula, that the former may be soonest healed. This happens most frequently when the fistula is in the arms or legs, or when its orifice is lower than its fundus. Belloste, and some other surgeons, reject all tents and injections; but when fistulas lie deep, detergent injections must be used. These are a decoction of birthwort, mixed with honey of roses, or with the tincture of myrrh and aloes: they must be injected warm at every dressing, and retained for a short time; the bottom and mouth of the fistula are gently pressed, that the matter may more effectually be washed off. This method must be continued until the bottom of the fistula begins to heal. It may then be dressed with some soft digestive, of which the balsamum Peruv. or balsamum capivi are ingredients. When this method fails, the operation must be attempted; but it is not to be depended on, except when the opening can be carried to the bottom of the ulcer. The incision is made with most ease to the patient with a knife; and whatever instrument be used, the incision must be so deep as will be sufficient to answer the end; for when the bottom is laid open, the matter is not only discharged, but medicines more com-modiously applied. If, upon making the incision, a large quantity of blood is discharged, fill the wound with dry lint, and proceed as is usual in recent wounds. Mr. Bell advises almost universally to avoid the practice of laying the different sinuses open from one end to the other, and cutting out all the hardened parts, so as to convert the whole into one common ulcer. This method he owns will frequently effect a cure; but independent of the great pain, and very large unseemly cicatrix occasioned, it cannot, in every case, be safely practised. When sinuses, for instance, run far up the rectum, it cannot ever be conveniently done; they penetrate deep, and run below either large blood vessels or nerves: in these cases such treatment cannot be advised. The object in every case of sinus, is to produce a coalescence of its sides, so as to destroy any vacuity that may have occurred; and the most effectual means of accomplishing it is, to make a depending orifice for a free exit to the matter; or by a gentle irritation, to induce, on its internal surface, a slight degree of adhesive inflammation; so that a firm union of the sides of the sinus may be obtained. To answer both these intentions, Mr. Bell thinks that the introduction of a seton is sufficient. The seton must pass from the orifice in the ulcer along the course of the sinus to its other extremity, where an opening, large enough for the discharge, should be made, as in cases of abscess. The cord of cotton, or of silk, should at first be large in proportion to the capacity of the sinus, and diminished gradually as the cure advances. When the discharge is greatly lessened, by the diminution of the vacuity, the seton should be totally withdrawn; abandage somewhat tight applied over the part, and continued till a complete cure is effected. In this process the first step is, to discover the direction of the sinus, or sinuses; which may commonly be done either by introducing a probe, observing where the matter points, or allowing the matter to collect, and remarking from whence it comes when the parts are pressed: then into every sinus which opens into the ulcer a seton should be introduced. This method of curing sinuses, by the use of a seton, is free from all danger, and may be employed in all cases of this kind; for a seton, by means of a director, may always be used with safety. The sinuses being removed by the setons, the ulcers connected with them are to be cured in the way appropriated to each kind. This practice rarely fails in any case of simple sinus; in general it answers in real fistula; and for a fistula in the perinaeum this practice is peculiarly advantageous, as it does not produce that troublesome cicatrix which follows the use of the knife. The only objection to the use of the seton in cases of fistula in ano, is the irritation it would occasion in the gut; but of these we must next speak. See Cel-sus, lib. vi. c. iv. Boerhaave's Aphorisms, the English translation, pp. 102, 103. Pott's Treatise on Fistulas. Bell's Treatise on Ulcers, edit. 3, p. 244, etc.