The second case, has generally been considered as a species of ulcer, and has been named the sinus ulcer; but, although the orifice may sometimes possess the diseased ulcerative action, yet the sinus itself still continues in the suppurative state, and, therefore, cannot heal. These sinuses depend, in different instances, upon very different causes, and, therefore, require a variation in the treatment. The most simple species of sinus may be called mechanical, and is produced by matter flowing from a neighbouring cavity, and which cannot be freely discharged: Thus, for instance, if a deep abscess open at the highest part, or at a point above the level of its bottom, the matter constantly oozes out, and keeps the canal open. This is most apt to occur, when abscesses are formed deep amongst muscular parts; in which case, although the matter point at the centre, yet an accumulation must take place below, and the matter must continue to be discharged by the aperture, when it becomes so abundant as to be raised to the level of the opening; or, being once raised, it continues to flow out. The cure of this may at first be attempted mechanically, by tight bandages, which press out the matter, and keep the sides in contact; but, if the disease have been of long duration, then, whatever may have been its nature at first, we find, that the suppurative action extends along the mechanical sinus, which then becomes affected with a chronic action; in which case, it becomes similar to the second species of sinus. We must, in this species, make an opening at the most dependent part, and employ the means which will be now mentioned in considering the second species, or that produced in consequence of the suppurative action becoming chronic or habitual, independent of any mechanical cause. This may take place, although the aperture have been originally in a proper place, and the matter, instead of being retained and keeping up the disease, shall have been regularly discharged. The case in which this is most likely to happen, is that in which the abscess has been very tedious in its progress, and the action has been, from the first, slow. The distinction betwixt this species, and those which remain to be mentioned, is founded upon the absence of the symptoms which they possess, and by our examination with the probe, which points out the cause and extent, and informs us whether we be near a bone. The orifice is flabby, and has the appearance of the indolent ulcer. The cure of these sinuses is to be attempted, by pressing out the matter by means of proper bandages, or by making a dependent opening, which is generally necessary, at the same time that we raise the action of the part to a proper degree, and render the suppurative action acute and vigorous; in which case, it naturally terminates in the ulcerative, and thus the part has its structure restored. This is most easily effected, by passing a seton, and applying a proper