The division, then, of a number of small arteries, may cure inflammation in two ways; first, by inducing a different action; secondly, by possessing the general properties of bleeding, namely, a simple diminution of action. The first will operate chiefly, when we apply the leeches on part of the inflamed portion. The second will operate, when we detract only from the immediate vicinity; and, in this case, the quantity of blood which is taken away, must be greater; because the effect has to be extended some way, the vessels not being in the inflamed part. The quantity must likewise be greater, because the effect depends entirely upon this; whereas, in the other case, it depended, in part, upon the peculiarity of the action which was produced.
The number of leeches which it is necessary to apply, will depend upon the violence of the action, and the place on which they are set; for, the greater the distance from the inflamed part, the more numerous ought they to be. It is therefore impossible to give any particular rule for the extent of topical bleeding. It may, however, be proper to observe, that we ought not to be satisfied with one application, more than with one venesection, for a general disease, but ought to repeat the local bleeding, whenever it may be necessary, although it may be twice or thrice in a day, founding our indications upon the same principle on which we use general bleeding. It is by a too sparing application of leeches, and their not being repeated sufficiently frequently, that we so often fail in removing inflammations, which, by a more active treatment, we might resolve. In general, the leeches ought to be applied as near the affected part as possible, or upon it. If, however, the seat of the inflammation be chiefly in the cutis, as in erysipelas, it will perhaps be more prudent not to apply them upon the spot; because the subsequent irritation is apt to increase the action afterwards, on account of the great delicacy of the part. There may even be some doubt as to the propriety of applying leeches to the vicinity of the inflammation; for the irritation of the bites may produce erysipelas in the part, or cause the original disease to spread.