The term blister is applied to any substance that has the power to raise the outer skin into bladders or pustules. There are several varieties of blisters—animal, vegetable, and mineral, the principal being cantharides or Spanish flies, mustard, euphorbium, mezereon, savin, antimony, silver, vinegar, potassa, and ammonia. Blistering and counter-irritation is a mode of treatment by which it is sought to cure one disease by establishing another of the same type, but less severe than the first; bearing this in mind, the general utility of all external stimulants, especially that of blisters, will be better understood and more fully appreciated. Blisters are used in medicine as a means of depletion, either to carry off from the body a certain amount of blood in the form of serum, and thus act as a local bleeding, or in addition to this effect, to cause, by the inflammation they produce on the surface, a larger amount of blood to circulate through the adjacent cuticle, and thus relieve some deeper organ or part from the excess of blood that disease causes to be attracted to it. With this view only, and when no depletion is required, medical men are in the habit of using a milder form of blistering than that effected by raising the epidermis in bladders, and to this they give the name of rubifacients, or, in simple English, substances that “make red.” From the benefit they afford, the ease of application, and the safety of their employment, blisters have become of universal use, and may be considered as an established domestic remedy. Yet there are certain points in connection with them that require explaining, both for protection and guidance. When the blister has sufficiently risen, remove the plaster, and nipping the blister where it bags most, gently press out the water, taking great care not to break the skin as it collapses; immediately place over the whole a warm bread poultice, the bread confined within a fold of muslin, and allow it to remain for one or two hours; then carefully remove the poultice, and sprinkle the blistered part with a thick layer of violet powder, cover this with a piece of linen, and, by a bandage or handkerchief, keep the whole in its place; every four hours add more violet powder, especially over the moist part, taking care not to remove the cake or crust that forms till the cuticle is sufficiently healed to permit of its being taken away, when the place is to be lightly dusted with the powder from time to time, to avoid cracking the new cuticle. It is seldom if ever necessary to interpose gauze or tissue paper between the blister and the skin, and, except in very rare and singular cases, should never be done, nor is there any time that can be fixed as the duration a blister should remain on; this must depend on the rising, which will take from eight to sixteen hours to effect; though in infancy and childhood, from the extreme delicacy of the cuticle, the time required is infinitely shorter. But this is