ON VESICATING APPLICATIONS. 
311 
paper. This liquid applied to the skin for twelve hours pro- 
duced no effect. 
Experiment 7. — Acetum Cantharidis was mixed with an 
equal quantity of ether. The mixture was frequently agitated 
and left to stand for twelve hours. The ether was then de» 
canted off, and allowed to evaporate spontaneously. A light 
yellow acid liquor remained, which on further evaporation 
afforded some appearance of crystallization. Two or three 
drops of oil being mixed with this, it was applied to the skin 
for twelve hours, but produced no effect. 
Acetum Cantharidis, obtained from Mr. Garden's, was sub- 
mitted to the same experiments as the foregoing; 100 grains 
required 198 grains of carbonate of soda for saturation. On 
evaporation, as in Experiment 1, it afforded a dirty brown 
residue, amongst which were perceived globules of green 
oil. When deprived of acid and applied to the skin, it 
caused slight irritation. Neutralized with soda and then 
digested in ether, as in Experiment 6, it yielded, on the evapo- 
ration of the ether, a bright green oil, which, applied to the 
skin for twenty hours, caused a slight redness on the part, but 
no blister. 
These experiments were repeated several times with the 
same result. They seem to indicate that acetic acid, of the 
strength ordered in the Pharmacopoeia, is not a solvent of 
Cantharidin. In order more completely to determine this 
point, some pure Cantharidin was prepared according to 
Robiquet's process. It was found to be insoluble in acetic 
acid. Again, the residue of the flies, after the preparation of 
Acetum Cantharidis was digested in ether, and the oil obtained 
on the evaporation of the etherial tincture, when applied to 
the skin, raised a blister in fifteen minutes. 
It is evident, therefore, that acetic acid is not a proper 
menstruum for exhibiting the acrid principle of the blistering 
fly. 
In referring to another preparation of the Cantharis, namely, 
the Unguentum Cantharidis, we shall, perhaps, be enabled to 
account for the difference of opinion which exists respecting 
