degree of pressure, diminishing the size of the seton gradually, and in proportion to the vigour of the action and the approximation toward health. When, from the situation of the sinus, we cannot pass a seton (which rarely happens in this species of sinus), injections of wine may be used frequently, and pressure applied during the intervals. When these means fail, which is seldom the case, the part should, if its structure permit, be laid open. If this sinus have remained long open, its surface, like that of the chronic abscess, becomes changed, and a coat is formed, like the cyst of a tumour. When this is thick and hard, the sinus has been called a fistula, and it has been deemed necessary to dissect out the tube; but it is in general sufficient to use the remedies which increase the vigour of the action, and make it run its natural progress; such as the seton, or a free incision, if the parts be superficial, or no considerable vessel or nerve runs the risk of being wounded. The third species of sinus is that in which the suppurative action is kept up by the operation of some adventitious cause; such as a caries bone, diseased cartilage, or the lodgement of a foreign body; as, for instance, a ball, a splinter of wood, bit of cloth, &c. This species is distinguished by our feeling the extraneous body, or diseased bone, with the probe, and by the fungous protuberance, or papilla, which shoots out from the orifice. In addition to the method of curing other sinuses, we must here endeavour to remove the adventitious cause, which is generally very difficult to be done. If the foreign body be deep, or if the diseased bone lie deep, and the sinus be narrow, we can do little in this way; sometimes, indeed, by enlarging the external part, we can come at the foreign body with a pair of small forceps, and may extract it, or may accelerate the exfoliation of the diseased bone; but we can have no certainty of success. If, however, the sinus be superficial, which sometimes happens in caries of the tibia, &c. it ought, in every instance, to be fully laid open, and the bone exposed, and treated in the way immediately to be mentioned. When this cannot be done, we may sometimes, by conveying the proper remedies through a tube down to the bone, procure exfoliation; or may, by setons, injections, and pressure, procure a temporary cure; but, as long as the adventitious cause remains, we cannot expect a permanent recovery. It is observed, that sinuses, when they can be healed in these circumstances, break out again upon very trifling exertions, and very frequently are renewed, after a short interval, in spite of all our precautions; such as rest, warmth, &c.