ON CANTHARIS VESICATORIA. 85 
to be cantharidin, in small crystalline scales, mixed with a 
yellow substance which is readily dissolved by alcohol, 
taking up this coloring principle, but which does not affect 
the cantharidin. These crystals are then to be dried be- 
tween the folds of bibulous paper. Cantharidin, when pure, 
is insoluble in water or cold alcohol, but it is soluble in 
boiling alcohol, (which precipitates on cooling,) ether, 
and the oils. It is capable of being fused and volatilized 
by heat without decomposition, the condensed vapor being 
composed ofacicular crystals. 
A small quantity of cantharidin prepared by the writer, 
by the above process, and dissolved in olive oil, produced 
vesication in about two hours. An aqueous extract, made 
by boiling the flies in water for a few hours, filtering and 
evaporating over a water bath, caused the same effect in 
x six hours. 
A quantity of cantharides was digested in spirits turpen- 
tine for twenty-hours, and prepared in the same manner as 
above, to produce an extract. This extract was applied to 
the writer's arm, and in less than three hours the surface to 
which it was applied was in a complete state of vesication, 
attended with much pain, and which did not entirely heal 
for the space of ten days. 
A tincture of cantharides made with ether, and also one 
with spirits of turpentine, when suffered to evaporate sponta- 
neously, will leave a crystalline mass, which is no doubt 
cantharadin, as this will vesicate in about the same time 
as that of cantharidin with oil. 
Passing from the general history of the Cantharis vest- 
catoria, its natural history, &c., I purpose making a few 
remarks principally on a few pharmaceutical preparations 
of it, with some observations upon the blistering cerate of 
the shops. 
It is the generally received opinion, that cantharides are 
injured, as regards their vesicating properties, by a high or 
protracted heat in the preparation of the Cerat. Cantharidis* 
8* 
