ON THE VOLATILITY AND SOLUBILITY OF CANTHARIDIN. 303 
used as a vesicant in this country. Ether being a good solvent 
for cantharidin readily keeps that principle in solution. When 
applied to the skin, the escape of the ether leaves a coating of 
ethereal extract of cantharides, admixed with collodion. This pre- 
paration sometimes fails from a deficiency of cantharidin, at other 
times from want of a sufficient body in the collodion excipient, 
and it has been found mere advantageous to treat the cantharides 
with ether till exhausted, distill off the ether, and add the oily 
residue to collodion of the proper consistence. The addition of a 
little olive oil, and of Venice turpentine, as recommended by Mr. 
Rand, will give more activity to the preparation, especially if a 
piece of oiled silk or adhesive plaster be applied over the part. 
g. Besides these, many other epispastic preparations are made in 
France and other countries. The acetic alcoholic extract of can- 
tharides of Ferrari is made by digesting four parts of cantharides in 
sixteen parts of alcohol 36° B. mixed with one part of acetic acid 
10° B. In the opinion of the author, the acetic acid tends to pre- 
vent the crystallization of the cantharidin, a statement rendered 
doubtful by the above experiments, as that principle separates in 
crystals from an acetic solution of cantharides. The alcohol dis- 
solves the green oil which gives to the extract a butyraceous con- 
sistence. This is undoubtedly an efficient preparation, and is used 
by spreading it on paper with a brush, and applying to the skin. 
Nearly all the French preparations direct digestion of from 2 to 6 
hours, showing evidently that the experience of pharmaceutists is 
opposed to the opinion that cantharides is " a very volatile sub- 
stance, even at common temperatures." 
The vesicating tafetaof the Codex, is that proposed by Messrs- 
Henry & Guibourt, and is made by fusing together one part of 
the ethereal extract of cantharides and two of w 7 ax, and spreading 
it on waxed paper or linen in the manner of adhesive plaster. This 
preparation is said to lose its efficiency by exposure to the air. 
How can this occur in view of the results which have been detail- 
ed above ? admitting the fact, is it not probable that the change 
lies in the strong tendency of the cantharidin to separate in crys- 
tals ? a change easily observable in the ethereal extract. This is 
the chief objection to some otherwise excellent preparations of 
cantharides for vesication, and it is far more probably the true 
explanation, than that volatility should be the cause. 
