When the cerate is withdrawn, the subsequent treatment depends on the object aimed at. if the intention be that the blister shall heal as quickly as possible, the cuticle should be cut in the most dependent part, and at as few points, and with as small incisions, as may answer for the evacuation of the serum. This is done, in order that the epidermis may be kept as nearly as possible entire, and serve as a dressing to exclude the air. if it be wished to keep the blister open for a short time, the epidermis should be cut very freely, and at various places, particularly all around the edges of the blistered part, so that it may come away with the first dressings, and a denuded surface be left to the action of the air, and of irritant applications. The best dressing, when the blister is to be healed, is simple cerate, which should be free from all rancidity. Fresh suet will also answer very well. To maintain a moderate degree of inflammation, but one which will subside, after a short time, even under the continued application of the dressing, and allow the surface to heal, the resin cerate or common basilicon ointment may be used. Should it be wished to keep the blister long open, and to maintain a running purulent discharge, it may be dressed with the ointment of cantharides, Savine cerate, or ointment of mezereon.

Should strangury supervene, the cerate, if still in contact with the skin, should be instantly removed, and its place supplied with an emollient poultice. At the same time, from forty to sixty drops of laudanum may be thrown up the rectum in a wineglassful of thin starch or mucilage, and the patient should drink freely of mucilaginous liquids, or water impregnated with sweet spirit of nitre. Camphor has been recommended, but I have found it of little use. The anodyne enema almost always affords prompt relief. if not, it should be repeated. in some rare instances, it is necessary to draw off the urine by a catheter.

In persons known to be liable to strangury, the cerate should be removed before vesication has fairly commenced, and before strangury has made its appearance, but after the occurrence of complete rubefac-tion; generally at some period between four and eight hours. if a poultice be now applied, vesication will often take place; though the inflammation may be less than in other cases.

Should the blister be much inflamed, red, swollen, and very painful, dressings with cold water, or with solution of acetate of lead in cold water, in the proportion of a drachm to the pint, may be used. if it refuse to heal, and remain obstinately open, I know no remedy equal to Goulard's cerate, or cerate of Subacetate of lead, which will almost always cause it to heal quickly. At least such has been my nearly uniform experience.

Should ulceration and gangrene have taken place, measures must be employed, with the removal of all irritating substances from the diseased parts, and the application of emollients, to support the strength of the patient; as by quinia, the mineral acids, opium, the fermented liquors, and a good diet.

Contraindications

Excessive excitement in a part of feeble vitality endangers the life of the part, and gangrene is apt to follow. This law was inculcated by John Hunter, and, whatever explanation of it may be given, is a truth which cannot be gainsayed. Hence, the inflammation from blisters is not unfrequently destructive to the blistered tissue, when at the time greatly enfeebled. There is no condition which so badly resists this effect of blisters, as that in which debility is owing to a depraved state of the blood. Blisters are, therefore, generally contraindicated in affections of this kind; at least they require to be used with great caution. The advanced stages of typhus and typhoid fevers, and of malignant diseases generally, are of this kind. Certain exanthematous fevers, in which it may be supposed that the blood suffers under the influence of a poison in the system, are other examples. Thus, blisters often cause sloughing in scarlatina, and in low states of erysipelas. When the excitant and revulsive influence of cantharides is wanted in such affections, it is often better to allow the plaster to remain only during the rubefactive stage, and to remove it before vesication begins. it has been stated, in the preliminary remarks on the class of epispastics, that it is safer, under these circumstances, to apply the blister to the trunk than to one of the extremities, because there is greater vital power of resistance in the vicinity of the heart than in the more remote parts; and, for the same reason, if applied to a limb, that it should be put upon the thigh or arm, preferably to the leg or forearm. Other diseases in which the blood is depraved, and blisters are usually contraindicated, are scurvy and purpura, and, it may be added, passive hemorrhages in general. in the distended limbs of dropsical patients, the vital powers are so much reduced, that a slight irritation is often sufficient to cause sloughing, and blisters of course are hazardous.

Under the name of Cerate of Extract of Cantharides (Ceratum Ex-tracti Cantharidis, U. S.) a modification of the above cerate has been introduced into the present Pharmacopoeia, consisting in the substitution for the powdered flies of an alcoholic extract prepared with stronger alcohol. (See 12th ed. of the U. S. Dispensatory.) if well made, it should be at least equal in efficiency with the common cerate.