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ON VESICATING INSECTS.
BY DR. FUMOUge, paris.
VESICATING insects live in all the countries of the globe, and more especially the hot and temperate climates; and there is perhaps not a people which is not acquainted with their properties and knows not how to utilise them. In Europe, one kind is more particularly employed; namely, officinal cantharides. It is pre-eminently the vesicating insect, or at least the one which holds the first rank in European pharmacopoeias. And yet it would be a mistake to conclude, from its place in the Materia Medica, that it possesses vesicating properties in the highest degree: it will be seen further that it is not so. Its vesicating properties are certainly quite sufficient for the wants of therapeutics, and this explains how its use has become so prevalent; but if it is so employed in preference to other more vesicating insects, it is most especially because it is more easily gathered. Cantharides, as is well known, alight in swarms upon certain trees; it is therefore possible to collect thousands of them in a few instants, whilst this is not the case with other vesicating insects. Sometimes, as with the meloës, it is even necessary to catch them one by one, and it follows that, being thus gathered, they are far more expensive than cantharides.
Such is, I believe, the cause of its almost exclusive, and I think I may say its quite exclusive, employment in pharmaceutical laboratories, as it has superseded the use of meloë and mylabris even in the countries where these were formerly employed; so that I am surprised to read, in the most recent treatises of Materia Medica, that the Mylabris and Meloë majalis
or Proscarabæus are employed, the former in Italy and the East, the latter in Spain. Already, several years ago, as I desired to study these insects, I asked for samples of them in Italy, Turkey, and Spain, on the strength of authors' statements; and the answer invariably was, that they no longer existed in commerce. It was with the greatest difficulty that I was enabled to procure a few pounds of Meloë.
There is, however, one mylabris, the Mylabris Sida, better known commercially by the name of China Mylabris, and which for several years has reached us from China in pretty large quantities, and may be procured in the London Docks. This insect affords on analysis as much cantharidine as cantharides; but as it is less abundant in fatty matter, it is not, I think, as suitable as cantharides for the preparation of vesicating plasters.
The richness in cantharidine of vesicating insects is certainly very variable, and it would be very interesting to classify them according to their degree of strength, as it would be easy to do if the chemists who have had occasion to analyse them had not generally contented themselves with asserting that such and such a kind was vesicating, without stating the richness in cantharidine. This blank in the history of vesicating insects, though it is to be regretted, is, however, of slight importance for the pharmaceutical chemist, who habitually in commerce only meets with the officinal cantharides, occasionally the China Mylabris, and scarcely ever the Meloë. These are, therefore, the only vesicating insects about which he cares to be informed, as regards their richness in cantharidine.
The Meloë majalis is perhaps, of all sorts, the one which contains the most cantharidine. According to my analyses, it contains 12 parts to 1,000. It is, therefore, not allowable to substitute it for cantharides in pharmaceutical preparations, as this latter insect only affords 4 parts of cantharides to 1,000, or only 5 at the maximum.
The China Mylabris affords, as I have said, as much cantharidine as cantharides do, but for reasons above stated it could not be used with advantage instead of cantharides in the preparation of vesicating plasters.
The pharmaceutical chemist should, therefore, not think of
using Meloë or Mylabris for his preparations, and should only employ cantharides, and even that with caution, as all cantharides do not contain the same quantity of cantharidine, and may be adulterated, as happens more often than is suspected. In order to make out their proportion of active principle and not be the dupe of cheats, he has only the resource of analysis.
Researches of this kind must be made with care and promptitude, and both these conditions are, I think, fulfilled by a method of analysis which M. Mortheux and myself made known some years ago.
Though this procedure has already been described in a former publication of mine, it may be of use to give an account of it here. First, we put into a displacing apparatus 100 or even 50 grammes of the cantharides, whose strength we wish to determine, and which have been previously triturated in a mortar; then we pour on the cantharides a sufficient quantity of chloroform to immerse them entirely; and after twenty-five hours the cock of the apparatus is opened so as to let the tincture of cantharides run out. In this way the cantharides are subjected to three successive macerations, and the tincture afforded by the three macerations is distilled in the bain-marie, so as to give out all its chloroform. The extract thus obtained is mixed with an equal quantity of sulphide of carbon, and then the liquid is agitated and poured on a filter. The filter retains the cantharidine, which must be washed with a little sulphide of carbon. When thus obtained it is not entirely pure, but it is sufficiently so to enable us to ascertain the therapeutical action and commercial value of cantharides.
By analysing with this procedure various specimens of cantharides, I have been able to find out that the French Codex has adopted too high a figure in fixing at 5 per cent. the minimum quantity of cantharidine contained in cantharides of good quality. It ought to have fixed upon 4 per cent., and perhaps even upon 3 per cent., as cantharides containing only this proportion have appeared to me to be quite strong enough.
I am also surprised to see that the commission of the French Codex and authors of the British Pharmacopoeia do not recommend to prepare tincture of cantharides with such a quantity
of cantharides as to cause this preparation to present invariably the same proportion of cantharidine.
If the following table of mine be consulted, it will be granted that the justness of my remark is obvious on noticing. that the proportion of cantharidine in cantharides may vary from 175 to 5 per cent.; and I have no need to insist on pointing out how untrustworthy a medicament is, prepared with a fixed quantity of a substance the active principle of which may vary in such a degree. This is a real danger when, as with tincture of cantharides, the preparation may be prescribed internally.
The British Pharmacopoeia ought also, I think, to have indicated the minimum quantity of active principle which cantharides, employed for the preparation of blisters or epispastic papers, ought to contain. It is obvious that, if need be, cantharides containing more or less cantharidine may be used for those preparations, but only within certain limits which should not be exceeded. The epispastic papers and blistering tissues which for years have been prepared in France according to my method and by the name of Albespeyres contain as nearly as possible 4 per cent. of cantharidine, and I think that this constitutes a valuable property and a real improvement in them.
Before concluding this paper it may be good to notice the trials which have lately been made with the object of replacing cantharides in the preparation of blistering plasters by cantharidine and cantharidate of potash.
The vesicating tissues prepared with cantharidine have until now been very unsatisfactory. The surface easily breaks, and
they soon lose their properties on account of the slow evaporation of the cantharidine, which as is well known, gives off vapours at the ordinary temperature. In order to prevent this last inconvenience, trials have been made of cantharidate of potash, which presents greater stability. Experience will show whether vesicating tissues prepared with the cantharidate are brittle or not; meanwhile it is quite obvious that if tissues thus prepared do not blister more quickly than those made with cantharides, there can be no advantage in using the cantharidate, which is so much dearer.
Vesicating tissues made with cantharides are at present the best agent we possess for producing vesication.