_Blistering, or Spanish Flies._
This beautiful insect of the beetle tribe is exceedingly abundant in the
southern parts of Europe, and particularly in Spain. They are collected
from the leaves of the different trees on which they delight to dwell,
in June and July, and are afterwards destroyed, as recommended by
Dioscorides, by the fumes of strong vinegar, and dried in the sun. The
chemical history of Cantharides is still involved in some obscurity; the
blistering principle has been obtained by Robiquet in a separate state,
when it assumes the form of small crystalline plates, having a micaceous
lustre, not unlike spermaceti; Dr. Thomson has given to it the name of
_Cantharidin_;[441] when pure, it is insoluble in water and in cold
alcohol; boiling alcohol, however, dissolves it, but precipitates it
again on being cooled. Æther and the oils dissolve it readily. Although
not soluble in water it is rendered so by the presence of a yellow
matter which exists in native combination with it. A very minute portion
of this substance dissolved in sweet oil, and applied to the skin with a
piece of paper, produces vesication in five or six hours. In addition to
this active principle, Cantharides contain a green concrete oil; a
yellow fluid oil; a peculiar black substance soluble in water and proof
spirit, but not in pure alcohol; a saponaceous or yellow substance,
soluble both in water and alcohol; Uric acid; Acetic acid; Phosphate of
Magnesia, and a parenchymatous substance.[442] MEDICINAL USES.
Cantharides, when administered internally, are powerfully stimulant and
diuretic;[443] and whether applied as a vesicatory to the skin, or taken
into the stomach, they have a peculiar tendency to act upon the urinary
organs, and especially to irritate and inflame the neck of the bladder,
and occasion strangury. On this account they have been very successfully
employed both for the cure of incontinence of urine, and suppression of
this discharge, from torpor or paralysis of the bladder; they have also
been used in gleet and leucorrhæa, and in cases of seminal weakness and
impotence. In consulting the works of Dioscorides, Galen, and Pliny, we
shall find they entertained a notion, that the _virus_ existed only in
the body of the fly, and that the head, feet and wings, contained its
antidote! Hippocrates prescribed them internally in Dropsy, Jaundice,
and Amenorrhœa; and yet in the end of the sixteenth century, Dr.
Groenvelt was charged and sued[444] for giving them inwardly, in
substance, for the cure of the stone. DOSE, in substance, not exceeding
gr. i, combined with opium or hyoscyamus. See _Tinctura: Cantharid_. A
strong decoction of the Cantharides in Oil of Turpentine furnishes a
most powerful Epispastic, and may be easily applied by means of dossils
of lint. As the general belief, which exists with respect to the
aphrodisiac powers of this substance, may induce persons to try its
efficacy in large doses, either for goading the exertions of exhausted
nature, or for incensing the passions of females whose seduction is
meditated, it behoves the medical practitioner to become acquainted with
the symptoms which it may produce, and of which the following may be
considered as the most prominent;—violent retching; copious alvine
evacuations, frequently bloody; very severe colics; active inflammation
of the stomach and intestines; sometimes universal convulsions, attended
with a horror of liquids, resembling that which occurs in hydrophobia;
furious delirium, &c. But the affections of the urinary passages, and
organs of generation, may be regarded κατεξοχην, as the peculiar
symptoms of poisoning by Cantharides; such as heat in the bladder,
bloody micturition, horrible strangury, painful and obstinate priapism,
_satyriasis_, &c. The method of treatment to be pursued on such
occasions will consist in copious bleeding, warm bath, local
fomentations, mild and mucilaginous drinks; and opium, especially in the
form of clyster or suppository. OFFICINAL PREP. _Tinct: Cantharid:_ L.
_Emplast: Cantharid:_ L. _Ceratum Cantharid:_ L. _Unguent: Infusi
Cantharid: Vesicat:_ E. _Unguent: Cantharid:_ D. The flies do not lose
their virtues by being kept; it is, however, curious that even those
acrid insects are soon reduced to dust by others feeding upon them; but
since the inert parenchymatous portion is alone selected by them, the
residue is extremely active.[445]