302 
ON THE VOLATILITY AND SOLUBILITY OF CANTHARIDIN. 
advocated digestion in making this cerate, (a recommendation also 
made by Mr. Donovan, of Dublin, about the same time,) and also 
the use of a portion of the oil of turpentine to facilitate the solu- 
tion of the cantharidin, but the foregoing experiments prove that 
fatty matter is quite as good, if not a better solvent alone than 
with turpentine. 
c. It has been asserted long ago by Beaupoil, Robiquet and others, 
that water will perfectly extract the active matter from Spanish 
flies, which these experiments corroborate. Hence it is easy to 
understand how the condensed perspiration may facilitate the 
action of a blister, especially when, as was formerly much the 
case, its surface is coated with the dust of the flies, and the 
skin moistened. 
It is also clear why the Unguentum Cantharidis of the U.S. Phar- 
macopoeia is active although made with a decoction of flies, yet, 
in this preparation, care should be observed not to evaporate all 
the water, as on the existence of the aqueous extract in a soft 
state depends much of the efficiency of the preparation as an irri- 
tant dressing. 
d. In the Linimentum Cantharidis, U. S. Pharm., in which an 
ounce of flies is digested in eight fluid ounces of oil of turpentine, 
the cantharidin is to the menstruum as 1 to 1500, a proportion 
probably quite sufficient to retain it in solution. The importance 
of the officinal direction to digest is evident. It is quite doubtful 
whether this liniment, as made by the process of Dr. Jos. Harts- 
horne, one part of flies to three parts of oil, will retain all the can- 
tharidin after standing awhile. 
e. The Acetum Cantharidis, (Lond. Ph.) made by macerating an 
ounce of flies in ten fluid ounces of acetic acid, 1.48, has been 
criticised by Mr. Redwood, (Pharm. Journal, Oct. 1841,) who ar- 
rived at the conclusion that it owed its vesicating power almost 
solely to the acid, he not being able to discover cantharidin in it. 
The inefficiency of cold acetic acid as a solvent for pure cantharidin 
has been proven by the above experiments, and its efficiency when 
hot equally shown. There can be little doubt that the London 
preparation wou ] d be much improved by digesting the flies in the 
acid for an hour in a close glass vessel at the temperature of 
boiling water. 
f. The cantharidal collodion of M. Uisch has been considerably 
