ON VESICATING APPLICATIONS. 
317 
process was repeated with fresh boiling alcohol, and agitation 
as long as any color was afforded to the alcohol. The black 
residue was now found to be entirely destitute of vesicating 
power, while the alcoholic tincture possessed it in an eminent 
degree. The alcoholic extract was evaporated to dryness, and 
rectified ether added to the residue in a closed flask. After 
having been macerated some hours, with occasional agitation, 
a light yellow tincture was obtained, which, allowed to 
evaporate spontaneously, afforded small crystalline micacious 
plates. The yellow matter in which these crystals were formed, 
was removed by cold alcohol, and the crystals dried between 
folds of blotting paper. The yellow matter removed by the 
alcohol was found to be inert, but the crystals possessed 
powerful blistering properties. The l-100th part of a grain, 
placed on a slip of paper and applied to the edge of the lower 
lip, occasioned small blisters in about fifteen minutes. Some 
pommade being applied, served only to extend the action over 
a wider surface. Some atoms of the crystals dissolved in two 
or three drops of almond oil were rubbed over a small piece 
of paper and applied to the arm: in six hours a blister was 
formed the size of the paper. These crystals were insoluble 
in water, and in cold alcohol, but soluble in boiling alcohol, 
being again deposited in crystals, as the alcohol cooled. They 
were soluble also in ether, and very soluble in oils. The name 
of^Cantharidin has been given by Dr. T. Thomson to this 
crystalline substance, which imparts the peculiar value to 
Cantharides. 
Robiquet explains the difference between the result of his 
experiments and those which had previously been performed, 
by referring to the facts, that Thouvenel in treating the flies 
with wa^er, had merely made an infusion of them, by which 
means the Cantharidin had not been extracted by the water, 
but was afterwards obtained with the green concrete oil, in 
the alcoholic tincture ; but that Beaupoil, on the other hand, 
caused the flies to be boiled in the water, although not so as to 
remove the whole of their acrid principle, and he therefore 
had a portion of the Cantharidin in each of his products. 
