A plaster of the ointment of Spanish flies (cantharides), applied to draw a blister upon some part of the surface of the body. Such a remedy is only required for a rather severe case of internal inflammation, or for that of an eye or an ear ; in either instance, not during the first day or two of the attack. In serious inflammation of the brain, a blister to the back of the neck, or even over a large part of the shaven scalp is sometimes one of the best of remedies.
A blister is usually made by spreading a piece of buckskin, three or four inches square, with cantharides ointment, covering this with a piece of thin gauze, and laying it upon the part. After from two to five or six hours (according to age and delicacy of the skin) the skin will feel very sore, and on taking the plaster off, the outer skin will be found to be raised in a blister. This may be tapped with the points of a pair of scissors, and the part may then be covered with a rag spread thickly with simple cerate. It will heal in a few days.
For inflamed eyes, the back of the neck is the best place for a blister; for severe inflammation of an ear, just behind that ear; the plaster being cut to fit there.