This section is from the book "An Experimental History Of The Materia Medica", by William Lewis.
Cantharides Pharm. Lond. & Edinh. Cantharides or Spanish flies: an infect of the beetle kind, (Meloe vesicatorius Linn.) generally about half an inch in length; on the upper side, of a shining green colour, variegated with more or less of a blue and a gold yellow; on the lower side, brownish. These infects are frequent in Spain, Italy, and the southern parts of France: they are collected from herbs and bushes, killed by the steam of strong vinegar, and afterwards dried in the fun. The largest and best are said to come from Italy. They should be chosen fresh coloured, entire, and free from dust: on long keeping, they are apt to lose of their colour, and become powdery, and in this state are to be rejected.
Cantharides have little or no smell, unless the quantity is large; in which case they yield a faint disagreeable one. Cautiously tailed, they impress a slight sense of acrimony: those who describe. the taste as highly acrimonious and caustic, have probably judged, not from the direct sensation of taste, but from the con-sequential effects. Applied to the skin, they first inflame, and afterwards excoriate the part; raising a more perfect blister, and producing a more plentiful discharge of serum, than any of the vegetable acrids. Hence their common use as a vesicatory.
(a) Ray, Hist. plant. p. 156.
Vesicatories are employed, either as a general stimulus, for raising the pulse and quickening the circulation, in low fevers, and in lethargic, disorders; or for resolving topical obstructions. fixt pains, whether external or internal, as in the rheumatism, sciatica, dysentery, pleurisies and peripneumonies, are frequently observed to yield to a blister upon the part; though frequently also the matter is lodged so deep, as to be beyond the reach of this as well as of other external medicines. Blisters are likewise applied to the head in epileptic and maniacal disorders, inveterate and periodic head-achs, and obstinate defluxions on the eyes, in which cases they are not to be considered merely as topical remedies: Hoffman relates, that in defluxions on the eyes, he has known a blister, applied to the nape of the neck, increase the pain; whilst one laid on the foles of the feet has procured relief as soon as the discharge from its operation began to take place. Blisters on the head give the least pain; on the legs the mod,
The blistering applications are generally com-posed of cantharides reduced into fine powder and mixed with plasters or other compositions of a due consistence. Three ounces of the powder are stirred into three ounces each of hogs lard, yellow wax, and white resin, melted together †; or into six ounces of the drawing plas-ter with the addition of an ounce and a half of hogs lard ‡. Vinegar is supposed to promote or facilitate the action of the cantharides: for in some cases, where the plaster without vinegar has failed of taking effect, on removing it and washing the part with vinegar, the same plaster, applied again, has blistered freely: it is probable, however, that this was owing, not so much to any peculiar quality of the vinegar, as to its soften-ing and deterging the skin; an effect which is not to be expected from it when mixed with the other ingredients of the plaster. Other stimulating ingredients are sometimes added, as pepper, mustard-seed, and verdigris; but it does not appear that these kinds of substances give any material assistance to the action of cantharides. The powdered flies spread on the surface of a common plaster operate as effectually as any of the compositions, and in this form they are often used.
Empl. veficatorium + Ph. Ed.
Empl. can-tharidis ‡ Ph. Lond.
In some cases, as in variolous eruptions or other inequalities of the skin, compositions of a softer consistence than plasters are required, that they may apply themselves to the depressed parts: for these purposes, equal quantities of finely powdered cantharides and wheat flour are mixed with vinegar into a paste. Where blisters are intended to be made perpetual, or continued, as a constant drain of serous humours, for a considerable time, some cantharides are added occasionally in the dressings, to keep the ulcers open: an ointment for this intention is prepared by melting seven parts of yellow bafilicon, and then adding one part of powdered cantharides.
Cantharides are applied also, in smaller quantity, sufficient to warm and stimulate the part considerably, but not to raise a blister, against some rheumatic pains, chilblains, and paralytic affections. In this intention, the blistering compositions are diluted with other plasters, in such proportion, that the quantity of the fly may be about one twenty-sixth part of the whole compound.
Ung. epifpaf. e pulvere Cantharidum Ph. Ed.
Emp. cali-dum Nosocam. Ed.
The external use of cantharides, if the quantity be considerable, is often followed by a stran-gury and heat of urine; this infect being peculiarly disposed to affect the urinary organs, though applied to the remotest parts. This inconvenience is prevented or remedied, by emulsions or mucilaginous liquors plentifully drank.
Small doses of cantharides are given internally in suppressions of urine, and for deterging ulcerations of the bladder. They have like-wife been found remarkably serviceable in semi-nal weaknesses and old gleets; in which the balsamic medicines, generally recommended, are often ineffectual (a). In leprous cases also they have frequently had excellent effects, in virtue perhaps of their diuretic power; for so great is the consent of the kidneys with the skin, that the humours accumulated in the cutaneous glands may be discharged by urine; as the urinary liquor, when the kidneys fail in their office, sometimes transpires through the skin (b).
Great caution is requisite in the use of this highly stimulating medicine; a small excess in the dose producing not only a strangury, but a discharge of blood, with intense pains about the neck of the bladder: a grain, and even a quarter of a grain (c), has in some cases had this effect. The remedy for these symptoms, in good habits, and where the cantharides have not been greatly overdosed, consists in plentiful dilution with emollient liquors in which some nitre has been dissolved, with the interposition of moderate doses of opium. It is commonly supposed that camphor, given along with the fly, corrects in some degree its irritating power.
(a) Mead, Monita & praecepta, p. 256.
(b) Idem, Medica sacra, p. 24.
(c) Hermann, Cynosura, m. m. pars ii. edit. Boecler p. 56.
Cantharides, digested in rectified spirit, impart to it a bright yellow tincture, and have their own colour improved: boiling water receives from them a muddy yellowish or brown-ish hue, and considerably impairs the colour of the fly. The active matter of the cantharides is completely taken up by both menstrua, and does not rise with either in distillation or evaporation: the substance of the fly remaining after digestion either in water or in spirit, does not in the least blister or inflame the skin; whereas both the watery and spirituous extracts blister freely.
The safest and mod commodious form for taking cantharides internally, is the spirituous tincture; which, dropt into watery or vinous liquors, mingles uniformly, without precipitation or turbidness. Two drams of the cantharides, bruised a little, are commonly digested two or four days in a pint and a half or two pints of proof spirit, with or without the addition of half a dram or more of cochineal as a colouring ingredient. These tinctures are usually given from fifteen to thirty or more drops twice a day: the most certain method of obtaining, without danger, the full effect of the cantharides, is, to begin with the smaller dose, and increase it by two or three drops at a time, till a little uneasiness is perceived in making water; after which, the medicine being intermitted for a day or two, the dose is to be diminished a little, and continued just below the quantity which produced that effect.
Tinct. canth. Ph. Lond. Ph. Ed.
A soft extract of cantharides is in many cases preferable, for external purposes, to the ointments and plasters made with the powdered fly, particularly for the dressing of perpetual blisters; as it acts more uniformly than the compositions containing the fly in substance, and occasions less pain in the dressing. Hoffman's mild blister which gives little pain, mentioned now. and then in his works, seems to have been, or to have had for its basis, a preparation of this kind; and probably the empyrical perpetual blister is no other. The colleges of Edinburgh and London have received a composition on the same principle: the former direct an ounce of cantharides to be infused for a night in four ounces of boiling water, the liquor to be strongly pressed and strained out, and boiled with two ounces of hogs lard till the humidity is wasted; after which, an ounce of white resin, an ounce of yellow wax, and two ounces of Venice turpentine, are to be added, and the whole well mixed so as to form a smooth ointment: the latter order two ounces of the powder of cantharides to be boiled in eight ounces of water to the consumption of half the liquor, which is then to be drained, and added to eight ounces of the yellow resin ointment, and the mixture evaporated in a brine bath to a due consistence.