Medical properties and uses. - Blistering flies, internally exhibited, are powerfully stimulant and diuretic; and, externally applied, rubefacient and epispastic. Notwithstanding their acrimony, they appear to have been given as an internal remedy by Hippocrates, who prescribed them chiefly in cases of dropsy and amenorrhcea.3 They have a considerable effect on the urinary organs, even when externally applied; and unless the dose be moderate, and their internal exhibition be conducted with great caution, they act with so much violence on the kidneys, bladder, and small intestines, as to produce bloody urine, purulent stools, insupportable pains of the abdomen, vomiting, and other symptoms of intestinal inflammation; convulsions, delirium, syncope, and death. They have, however, been successfully employed in dropsy, obstinate gleet4, yellow matter, 1-2; green matter, 1-8; parenchyma, 4-36; phosphate of lime, 12 grains; carbonate of lime, 2 grains; sulphate and muriate of lime, 4 grains; oxide of iron, 2 grains; and an acid, the quantity of which was not ascertained.

Annales de Chymie, xlviii. 33.

1 Vide System of Chemistry, 5th edit. iv. p. 436.; and Ann. de Chym. lxxvi. p. 308. Thierry's method of procuring the principle is to macerate the bruised beetle in ether for several days, in an apparatus for filtering by displacement; adding, after the liquid ceases to flow out, fresh portions of ether, till the soluble matter is exhausted. Then pour water on the mass to displace the ether. The etherial tincture is next to be distilled, and the deposit from the residue, when cold, is to be treated with boiling alcohol and animal charcoal. The cantharidin is thus obtained pure in crystals : 1,000 parts of cantharides yield four parts of pure cantharidin.

2 Dioscorides and Galen imagined that the active principle of the fly was contained in its body, and that the head, wings, and feet contained its antidote.

3 Dr. Groenvelt was prosecuted for using them internally, and published his tract, "De tuto Cantharidum usu interna," as his vindication; but although it proved to his prosecutors the safety of his practice, yet (says Quincy, Pharm p. 152.) it ruined the unhappy doctor.

4 Probably gleets were included in the term gonorrhoea by the old writers, who frequently mention cantharides as a remedy for gonorrhoea. Thus Boccone(Mu-seo di Fisica, 1699,) says, they were much used by the Sicilians in gonorrhoea.

leucorrhoea, and incontinence of urine arising from paralysis of the sphincter vesicae. The free use of diluents, as milk, almond emulsion, and mucilaginous solutions, is absolutely necessary during their employment to moderate their action. The tincture is the most proper form for internal use; or, if given in substance, the dose should not exceed one grain of the powdered flies, formed into a pill with opium or extract of henbane. They require to be used for a considerable length of time, in order to prove beneficial.

Blistering flies, when applied to the skin, act as a local stimulant, first reddening and inflaming the part, and then producing from the exhalents a copious discharge of serum under the cuticle. These effects they produce more certainly and completely than any vegetable acrid, and therefore they may be employed either as rubefacients or to raise blisters.

It is uncertain whether blisters were used by the ancients; but modern practitioners daily and successfully employ them. Although their first operation is local, yet, under certain circumstances, the stimulus is sufficient to rouse the whole nervous energy, and excite the general system, so as to render their application useful in diseases of diminished excitement; on which account, in deep-seated local affections, when the inflammatory diathesis is considerable, the force of the circulation must be diminished by bleeding, purging, or other evacuants, before blisters can be advantageously applied. The diseases of debility in which they are useful, are low nervous fever, when accompanied with delirium, pale urine, frequent sighing, great anxiety, deafness, a fixed stare and glistening eyes. In palsy, and gutta serena, they are applied to the forehead over the supra-orbital nerve. They are found efficacious also in spasmodic and convulsive affections, from the irritation they produce overcoming the morbid irritation which induced the spasm.

Blisters, by their local action, relieve internal inflammatory diseases, by altering the balance of the circulation; partly, also, by diverting the attention from the prior seat of pain, contrary to the opinions of the ancient physicians, who attributed much of their efficacy to the serous effusion which they induce. Hence, their utility in ophthalmia, applied behind the ears, on the temples, or the forehead; in phrenitis, over the head; in cynanche tonsillaris, and in small-pox, when the swelling of the fauces affects respiration, upon or near the neck; and in phthisis, catarrh, hepatitis, pneumonia, gastritis, and other intestinal inflammations, immediately over the seat of pain. In acute rheumatism, particularly that variety of it named sciatica, they have been found very useful. On the same principle, caries in the bones and joints, or a disposition to it, is often cured by the repeated application of blisters. "Under their application the enlargements obviously subside; the crepitation between the bones, the consequence of the abrasion of the cartilages, ceases to be felt when the blister begins to operate, the use of the joint is effectually recovered, and anchylosis prevented."1 A succession of blisters, also, to the vicinity of an inflamed organ, is more beneficial than a protracted discharge from one; and a second blister often relieves after the first has failed.

Blisters are contra-indicated in diseases of great debility, where there is a tendency to mortification; as in the low stages of petechial fevers, cynanche maligna, confluent smallpox, and malignant measles; and in dropsy, in which they are apt to occasion a very painful, dangerous erysipelas, and gangrene. Peculiar idiosyncrasies forbid their use in some persons, as they irritate, heat produce thirst, pain, tremors, and sometimes convulsions. In those of irritable temperament, their application is often attended with strangury and bloody urine; and this effect is much increased, if the blister-plaster be applied over a newly-shaved part, or if it be allowed to remain too long on after the blister has risen. To prevent strangury from the application of blisters, camphor has been erroneously regarded as a specific. It is more effectually prevented and relieved by copious dilution with milk, and mucilaginous fluids, by fomentations of warm milk and water to the blistered part after the removal of the plaster, by the introduction of an opium suppository into the rectum; and by interposing between the vesicatory and the skin a piece of gauze, wetted with vinegar, and applied smooth and close over the plaster2; or a piece of silver paper moistened with oil.

The internal dose of cantharides is from gr. j. to grs. iij.

Officinal preparations. - Tinctura Cantharidis, L. D. Emplas-trum Cantharidis, L. D. Emplastrum Cantharidis vesicatorice, E. Ceratum Cantharidis, L. Unguentum infusi Cantharidis vesica-toriae, E. Unguentum Cantharidis, L. Unguentum Pulveris Can-tharidis vesicatoria, E.