CANTHARIDES, or SPANISH FLIES, the common blister beetles (Cantharis vesicatoria) of European pharmacy, are bright, iridescent, golden-green or bluish-coloured beetles (see COLEOP TERA), from half-an-inch to an inch in length, found in the south of Europe.
Cantharides owe their value to the presence of a chemical prin ciple (cantharidin). Cantharidin constitutes from I- to 1% of cantharides. It has the formula and on hydrolysis is converted into cantharinic acid, It crystallizes in colour less plates and is readily soluble in alcohol, ether, etc., but not in water.
The external action of cantharides or cantharidin is character istic. When it is applied to the skin there are no obvious conse quences for some hours, then the part becomes warm and painful. Soon afterwards there is an accumulation under the epidermis of a serum derived from the dilated blood-vessels. The numerous small blisters or vesicles thus derived coalesce, forming a large sac full of "blister-fluid." Taken internally in any but minute doses the drug causes the most severe gastrointestinal irritation, the vomited and evacuated matters containing blood, and the patient suffering agonizing pain and extreme depression. The further characteristic symptoms are displayed in the genitourinary tract. The effect of large doses is to cause great pain in the renal region and urgent wish to mictu rate. The urine is nevertheless small in amount and contains albumen and blood owing to the local inflammation produced in the kidney by the passage of the poison through that organ. The drug often has a marked aphrodisiac action, producing priapism, or in the female sex the onset of the catamenia or abortion. Its criminal employment is usually intended to heighten sexual desire, and has frequently led to death.
A very large number of other insects belonging to the same family possess blistering properties owing to their containing cantharidin. Of these the most remarkable is the Telini "fly" of India (Mylabris cichorii), the range of which extends from Italy and Greece through Egypt and central Asia as far as China. It is very rich in cantharidin, yielding fully twice as much as ordi nary cantharides. Several green beetles are, on account of their colour, used as adulterants to cantharides, but are easily detected by examination with the eye, or, when they have been powdered, under the microscope.