outlet, sinuses were formed, and the vitality of the integument impaired, rendering it necessary to lay the several openings into one, or to destroy the tissues by potassa fusa; and the same results would follow opening an abscess elsewhere, if the like plan were adopted.

In gangrenous abscess free incision is absolutely requisite, that the sloughs may readily be discharged; this form so far resembling carbuncle in character, in there being a considerable destruction of the cellular tissue.

After the evacuation of the contents of an abscess, a warm poultice must be applied; the horizontal position must still be preserved, and the bowels kept easy by laxatives. The diet allowed may be better than when resolution was being attempted, but it must not be stimulating or heating; beer, wine, and spirits should be prohibited, except in the gangrenous form of abscess, when they will probably be requisite, from the debilitated condition of the patient.

As there is greater disposition in the integument to heal than in the cellular tissue, care must be taken to prevent the closure of the external opening before the cavity has healed from the bottom: this is to be done by inserting a slip of lint between the lips of the wound, but the whole cavity is not to be crammed,

as was once the custom, and is still frequently practised on the Continent.

After opening a traumatic abscess, if the presence of ball, splinter of bone, portion of the dress, or any other foreign substance, can be detected, it must of course be removed.

CHAPTER XIII.

FISTULA IN ANO.

AN abscess formed in the ischio-rectal fossa, although opened early by free incision, and before the cavity becomes greatly distended with pus, frequently will not heal; it may fill up and contract to a certain extent, but it does not become entirely obliterated, a narrow tract remaining indisposed, from various causes, to yield further to reparative action without surgical interference. It is this sinus which constitutes the affection designated fistula in ano.

The disturbance to which the part is subject whenever the bowels are moved, and the action of the sphincter, are assigned by most surgeons as the reason why the healing process is arrested; but may it not be attributed, with more reason, to the nature of and the several disadvantageous circumstances attending on an abscess in this locality, such as the depending position, the numerous veins that exist there, and their liability to congestion, all of which tend to

retard the process of granulation and cicatrization? Moreover, when these phenomena are slow in their progress, the surface of the internal cavity assumes a peculiar organization, which, save that it is destitute of villi, somewhat resembles mucous membrane in structure, function, and in the inaptitude of the opposed surfaces to unite. It is not alone in the neighbourhood of the rectum, but in other situations also, that we find sinuses form, when the healing process is tardy. In complete fistula in ano, the passage of particles of the less solid feculent matter, and the gases generated in the intestinal canal, also prevent the healing process. Those who maintain the opinion that the action of the sphincter is the chief cause in preventing reparation, argue, à posteriori, that division of the muscle, whereby it is set at rest for a time, effects a cure; may not the successful result rather depend upon laying the sinus freely open, as when we have recourse to the same plan of proceeding in the treatment of sinuses occurring in other situations?

Fistulæ in ano are described by most writers as perfect, fistula ani completa,-and imperfect, fistula ani incomplete; the former are those which have both an opening into the intestine and one externally; the latter have but one opening, which may either be internally in the mucous membrane of the intestine,

or externally in the integument. When a fistula has no communication with the cavity of the bowel, it is called a blind external fistula; and when the opening exists only within the anus, and there is no external communication, it is known as a blind internal fistula. Blind external fistula is very rare, an internal opening almost always existing if the abscess has degenerated into that state to which the term fistulous may properly be applied. The opening into the intestine may be very small, or, from the sinuosity of the fistula, we may be unable to detect it on a first examination; yet on a second or third exploration, conducted with care and a due consideration of the position it is most likely to occupy, and the employment of a suitable probe, it will probably be discovered.

A difference of opinion exists between several eminent surgeons as to the formation of the internal opening in complete fistula. Sir Benjamin Brodie says: "I believe that this is the way in which fistula in ano are always formed, namely, the disease is originally an ulcer of the mucous membrane of the bowel, extending through the muscular tunic into the cellular membrane external to the intestine; and I will state my reasons for entertaining that opinion. The matter is of great importance as a question of pathology, but it is one of great importance, as I shall