605. Cantharis.—Cantharides.

Fig. 257. Spanish fly. The beetle, Can'tharis vesicato'ria De Geer. (Fam. Coleoptera.) Thoroughly dried at a temperature not exceeding 40°C. (104°F.). Should not contain more than 10 per cent. moisture, and should contain not less than 0.6 per cent. of cantharidin.

HABITAT.—Southern and Central Europe and Northwestern Asia, feeding on plants of the families Oleaceae and Caprifoliaceae.

COLLECTION.—By shaking or beating the food-plants; the insects are then killed by heat (hot water) and rapidly dried.

DESCRIPTION.—A bronze-green beetle, with long (about 1 in. or 25 mm.) and narrow (¼ to ⅓ in., about 7 mm.), subcylindrical body. The vertical, rather triangular, head is constricted behind so as to form a conspicuous neck. Odor strong and disagreeable, caused, in the living insect, by a secreted fluid containing uric acid, according to Maquetti. The crushing of the dried insect yields a grayish-brown powder containing green shining particles (the bits of the green wing-covers and the body-wall). Chap. I, B

The dried insects or the powder is subject to the attacks of several Dermestid beetles and of several mites (Glyciphigus). The addition of a little chloroform, oil of turpentine, or naphthalene balls in a tightly closed vessel will help to keep out these cantharid-eating pests; or, if they have established themselves in the vessels, they may be killed by the use of carbon disulphide. (See Part III.)

OTHER SPECIES.—Besides Cantharis vesicatoria, several other beetles of the family Meloidae, especially species of Mylabris, Epicauta, and Macrobasis, are used to obtain vesicatory agents, and give a larger percentage of cantharidin than the officially recognized insect.

Fig. 258. Old-fashioned Potato Beetle. Epicauta vittata.—The Old-fashioned Potato Beetle. (This "Potato Beetle" should not be confused with the well-known Colorado Potato Beetle (Doryphora decemlineala, Say), belonging to the family Crysomelidae, a short, oval, yellow-and-black insect with ten longitudinal stripes on its wing-covers. This latter beetle probably possesses no vesicatory principle.) Found, often abundantly, in the United States; feeds largely on leaves of potato-plants. This insect was formerly official.

Mylabris cichorii Fab., and M. phalerata Pallas.—Chinese Blister Beetles. Habitat: Southern and Eastern Asia. Cichorii has its black wing-covers crossed by three broad orange-yellow bands; one band is terminal, thus rendering the apices of the wing-covers yellow.

Mylabris bifasciata.—The Two-striped Blister Beetle. Habitat: Northern Africa. The body is black, the wing-covers presenting two undulating narrow yellowish stripes. All these species of Mylabris yield about 1 per cent. of cantharidin.

ADULTERATION.—Spanish flies exhausted of their vesicating principle have been met with as substitutions. Powdered euphorbium has been spoken of as one of the adulterants, but adulteration is not common in this drug. The assay of the drug is accomplished by treating the powder with a mixture of benzine (2 vols.) and petroleum ether (1 vol.), acidulated with HCl; digesting the mixture; decanting the clear liquid, after cooling; evaporating and purifying the residue. For details, see U.S.P. IX.

CONSTITUENTS.—The chief constituents are: (1) cantharidin, the active principle, a fatty crystallizable body forming shiny, colorless plates, soluble in alcohol, ether, acetic ether, glacial acetic acid, chloroform, and oils; volatilizable by heat (100°C., 212°F.) without decomposition, the vapor condensing in acicular crystals; (2) a volatile oil, giving the odor of cantharides, and said to have vesicatory properties; and (3) a green oil, the coloring principle, closely allied to chlorophyll.

Preparation of Cantharidin.—Obtained by percolating the powder with chloroform, distilling off the liquid, and purifying the resulting crystals by washing them with CS2 to remove fat. Colorless prisms; soluble in alcohol, ether, fats, etc.

Cantharidin is associated with certain alkalies and alkaline earths in the drug, and seems to exist partly in combination with them. The principle itself has been found to combine with salifiable bases like an acid.

ACTION AND USES.—Internally cantharides acts as a powerful irritant, and has a peculiar effect on the urinary and genital organs. Large doses produce violent strangury, attended with excruciating pain and a discharge of bloody urine. The principle use of cantharides is the application, externally, of the cerate as a blistering plaster. It is seldom used as a rubefacient, but as an epispastic or vesicant it is to be preferred of all substances of this class. Its blistering action terminates in a copious secretion of serum under the cuticle. Dose: ½ gr. (0.03 Gm.).

Ceratum Cantharidis (32 per cent.).
Collodium Cantharidatum (60 per cent.).
Tinctura Cantharidis (10 percent.) Dose: 1 to 5 drops (0.065 to 0.3 mil)

A Manual of Organic Materia Medica and Pharmacognosy, 1917, was written by Lucius E. Sayre, B.S. Ph. M.