We use mustard-plasters not to blister, but only strongly to warm and stimulate the skin. For raising a blister, cantharides is mostly resorted to. The oldest way is to spread the ointment of cantharides on a piece of buckskin, three or four or five inches square ; cover this with a piece of gauze, and lay it on the part. This will draw a blister upon a grown person in four, five, or six hours ; with a child, in two hours or less. Then nip (do not remove) the raised scarfskin with the point of a pair of scissors, and lay upon it a soft muslin rag thickly spread with simple cerate, as a healing dressing.

Once in a while strangury (difficulty in passing water) will follow the application of a blister, from some of the cantharides being absorbed into the blood, and so getting through the kidneys into the bladder. Flannel wrung but of hot water applied to the bladder and perineum (crotch, just between the thighs at the pelvis) ; spirits of camphor, taken in twenty-drop doses ; and, if the difficulty lingers, a laudanum injection into the bowels,' are remedies for strangury. Blue Pill, or blue mass. This is a preparation of mercury, one-third of the Strength of calomel. It is a soft solid, easily made into pills. Apothecaries usually keep on hand three-grain blue pills.

The best established usefulness of blue mass is in the relief of what is called "biliousness," when there is a bitter taste in the mouth, especially on awaking in the morning; with some degree of nausea (sick feeling at the stomach), and more or less yellowness of the tongue and of the whites of the eyes; perhaps of the face or the skin generally; the bowels also being constipated, or the stools slate-colored instead of brown or yellowish-brown, as is natural. One or two grains of blue pill at bedtime, and the same again in the morning or the next evening, taking in all from two to four grains, will do well, without any risk of salivation, at least in all but one case or so in a thousand.

Calomel is better for a similar purpose as a baby's medicine. Indigestion and commencing diarrhoea in infants are often much helped by small doses of calomel; powders, each of which contains one-twelfth of a grain of the medicine, with a grain or two of soda (sodium bicarbonate) or magnesia, or only sugar; the last for taste, and to give substance to the small dose of the drug.