OBSERVATIONS ON BLISTERING PLASTER. 
303 
of the melted ingredients at the temperature that they usually 
are when removed from the fire. On the contrary, it is highly 
probable that a cerate made by adding the flies, just when the 
other substances are removed from the fire, would be more 
active, than one made by adding them after the melted ingre- 
dients begin to thicken. 
Cantharidin, as stated by Thenard (Traite de Chimie, &c, 
tome iv. p. 592,) fuses at 210° C, (410° F.) and heated more 
strongly, it is sublimed in brilliant needles, but a small part 
being decomposed. 
To ascertain if it was really true that oil at the high tempe- 
rature above stated, exercised no injurious effect on the active 
principle of Cantharides, a solution composed of one part of 
Cantharidin to 100 parts of olive oil was heated until the oil 
began to vaporize. A portion of this solution, after cooling, 
w r as applied to the writer's arm, and in eight hours the surface 
to which it had been applied was in a state of vesication. 
Thinking that possibly the matter associated with Canthari- 
din in the flies might exercise an injurious influence on that 
principle, when exposed together to a high temperature, a 
portion of the cerate was heated to 325° Fahr., when its whole 
surface was in a state of ebullition, extricating offensive va- 
pors, which were probably some substonce in the fly, volatile 
at that heat. It was then suffered to cool, and a portion ap- 
plied as before, to the writer's arm for three hours, when par- 
tial vesication had taken place, followed in a few hours 
by a copious secretion of serum. Was any further evidence 
necessary, the preparation called "decoction of Cantharides," 
made by subjecting the Cantharides in powder to long con- 
tinued heat in oil of turpentine, at a temperature considera- 
bly above that of boiling water, might be adduced. 
It is hardly probable that under any ordinary circumstances, 
the vehicle would be heated as high as 300° Fahr., and 
consequently the active matter of the flies would remain 
uninjured. 
The fluidity of the vehicle for the application of Cantharides 
is a subject of much importance, as on it depends in a great 
