It is often desirable to keep up a discharge from the blistered surface for many days, or even weeks, in succession: for this purpose, the Ung. SabinAe is generally employed as a dressing; but there is reason to doubt the prudence of using this ointment, as Savin itself is a powerful irritant poison, and its use has been known to be followed by serious consequences, when thus applied. Some prefer dressing the surface with Cerat. Cantharid.; but the plan recommended by Sir B. Brodie is decidedly the best, viz., to apply a succession of blisters. After the second or third, they are productive of but little irritation. In employing any ointment with a view of keeping a blister open, it is necessary to vary the kind frequently, or the blister will heal in defiance of the remedies used. In many chronic diseases, issues or setons are preferable to perpetual blisters. (See Issues.)