Blistering is employed also for curbs, windgalls, spavins, &c.

Broken knees, unless skilfully treated, leave a callous swelling on the part; for the removal of which, blistering is employed. When blisters are properly made, and free from any caustic ingredients, such as sublimate, vitriolic acid, &c., there is no danger of destroying the hair; and if the first blistering does not prove effectual, it may be repeated until the desired effect is produced.

Before a blister is applied, the hair should be closely cut off, or even shaved off, if the situation of the diseased part will admit of its being done without wounding the skin; but good scissors, or shears, if skilfully used, will answer the purpose sufficiently. If the skin is scurfy it may be washed with flannel, soap, and warm water, and be made perfectly dry before the blister is applied. Blisters are generally employed in the form of ointment, but on some occasions they are preferred of a thinner consistence, or in the form of liniment, or even still thinner or more fluid, and are then named liquid blisters. Though a variety of ingredients are used in blisters, the cantharis or Spanish fly is the best; and if not injured by long keeping, or adulterated, is the only blistering ingredient required for common purposes.

The following formulæ are recommended by Mr. White.

BLISTER OINTMENT.
Hog’s lard4 oz.
Oil of turpentine1 oz.
Powdered cantharides1 oz.—Mix.

Melt the lard by a gradual heat; remove it from the fire, and stir in the turpentine, then add the cantharides, and continue stirring until it is cold.

Or,
Hog’s lard6 oz.
Oil of rosemary½ oz.
Oil of origanum2 dr.
Powdered cantharides6 dr.
Solution of sublimate in muriatic acid, one fluid drachm or sixty minims.
Mix as above.
Or,
Oil of turpentine2 oz.
Sulphuric acid, by weight1 oz.

Mix cautiously, under a chimney, or in the open air, and avoid the suffocating vapour which will arise. When perfectly united, add hog’s lard, from six to eight ounces, or more, according to the strength required. When a blister is wanted, take two ounces of this ointment, and rub up with it from two to three or four drachms of recently powdered cantharides. This ointment may be made still stronger by the addition of a little calomel or sublimate at the time it is wanted; but the latter must be used only in a small proportion, and with caution, as it is apt to ulcerate the skin, and cause sloughing and a permanent blemish. It should therefore be applied to a small surface only, as in bone spavin or splent. Neither the cantharides nor the calomel, or sublimate, should be kept ready mixed with the above ointment, as it is probable they would undergo some change, and be rendered inert after a little time. The above recipes may be varied by substituting mercurial ointment, oil of bay, or any other unctuous substance for hog’s lard, or oil of origanum, for oil of turpentine. And if a more solid form is desired, it may be obtained by the addition of a little bees-wax, suet, or resin.

BLISTERING LINIMENT.
Olive oil4 oz.
Oil of turpentine1½ oz.
Oil of origanum½ oz.
Recently powdered cantharides.1 oz.—Mix.
Or.
Olive oil4 oz.
Oil of turpentine1 oz.
Oil of rosemary, and oil of origanumof each½ oz.
Solution of sublimate1 dr.
Recently powdered cantharides1 oz.
Mix.
LIQUID BLISTER.
Boiling water6 oz. to 8 oz.
Powdered cantharides1 oz.

Macerate for twenty-four hours, and then add rectified spirit of wine, four ounces; solution of corrosive sublimate in muriatic acid, one drachm. To be kept well corked for two or three weeks before it is used: it may then be either strained through blotting paper, and used as a transparent tincture, or merely shaken up and employed as it is. The solution of sublimate should be added at the time the blister is used.