Syn. Spanish Flies.

Origin

The Spanish Fly, or Cantharis vesicatoria, is a coleopterous insect, inhabiting the southern and middle portions of Europe, and abundant in Spain, Italy, Sicily, the South of France, and the southern provinces of Russia. The insects are collected by beating with poles, or shaking the trees which they frequent, and receiving them, as they fall, in a large cloth spread upon the ground beneath. They are killed either by exposing them to the vapour of boiling vinegar, water, or other liquid, or by immersing them, contained in bags, in hot vinegar and water. They are then dried, and packed in casks or boxes lined with paper. They are imported from Spain and other parts of the Mediterranean, and directly or indirectly from St.Petersburg. Those from the latter source are larger, and more highly esteemed than the Mediterranean flies, and are distinguished by their coppery hue.

Properties

The insect is about two-thirds of an inch long, and from a sixth to a quarter of an inch in breadth, and is of a beautiful golden green, or brilliant coppery hue. The powder is of a dark-gray colour, diversified by shining green or copper-coloured particles, which are minute fragments of the wing-cases, head, and feet. Cantharides has a characteristic odour, and an acrid, burning, disagreeable taste, said to resemble that of urine. it yields its virtues to water, alcohol, ether, and officinal acetic acid, especially with the aid of heat. These virtues have been ascertained to reside chiefly, if not exclusively, in a peculiar proximate principle denominated cantharidin.

Cantharidin. This may be obtained by exhausting cantharides with ether, distilling off the ether from the solution thus obtained, dissolving the residue in boiling alcohol, decolorizing with animal charcoal, filtering, and allowing the liquid to cool. Cantharidin is deposited in the form of white, shining, crystalline scales, which are insoluble in water, scarcely soluble in cold alcohol, but readily dissolved by ether, chloroform, the oils at ordinary temperatures, and by hot alcohol and acetic acid, which let most of it fall on cooling. it is melted by heat, and, at a still higher temperature, rises in white vapours, which form acicular crystals upon condensing. it is not injured by any temperature below 300° F. Besides this constituent, cantharides contains a peculiar yellow matter, which has a strong affinity for cantharidin, and through the influence of which, this principle, as it exists in the flies, is rendered soluble in water and cold alcohol, though insoluble in these menstrua, or nearly so, when pure.

Cantharides is apt to be attacked by worms, which, though they do not entirely destroy its virtues, impair them very considerably. The addition of camphor has been recommended as a preservative; but a few drops of strong acetic acid, in a bottle of the flies, are more effectual. A good method is to immerse the bottle containing them in boiling-hot water, which destroys the eggs of the insect without injuring the flies. With this precaution, and that of keeping them in bottles well stopped, they may be preserved, whether whole or in powder, for a long time without injury.

Effects on the System

The effects of cantharides upon the system, when internally administered, have been already fully described. (See page 642.) in the preliminary remarks upon the class of epispastics, its remedial effects as an external agent, and the principles which should govern its therapeutic use, have been sufficiently considered. it remains here to treat of the mode of applying the medicine externally, and of the particular effects attendant on, or following, the several methods of application. This brings us to the consideration of its preparations; for the flies are almost never used in an unprepared state.

The use of blistering insects was familiar to the ancients; but it is quite uncertain, from any accounts which have come down to us, whether they used the particular species now under consideration.