304 OBSERVATIONS ON BLISTERING PLASTER. 
measure, their effects. Hog's lard is frequently employed, 
and in many respects it is an excellent material. Its fusing 
point is about that of the temperature of the human body; it 
is economical, and when olive oil cannot be obtained, it is a 
proper substitute. 
Olive oil possesses all the requisites, and is the correct 
menstruum. 
Oil of turpentine, so far as regards its being a good solvent 
for Cantharidin, is very suitable, and makes an active prepara- 
tion, as has been ascertained by experiment, but its volatility 
precludes its use per se in this preparation, because it gradually 
evaporates and leaves the cerate too stiff. The sequel will 
demonstrate that a combination of the two last substances, 
affords the most eligible menstruum for extracting the activity 
of Cantharides, as relates to the preparation under considera- 
tion. 
The following formula is proposed, and the numerous in- 
stances, in which the activity of the Cerate which it yields, 
has been tested, gives confidence to the writer in thus making 
it public — 
Take of Cantharides in fine powder, ^vj. 
Olive oil, §vj. 
Oil of turpentine, §iij. 
Yellow wax, Resin, of each, giv. 
Mix the Cantharides with the olive oil and oil of turpentine 
in a suitable vessel, place the mixture on a water bath, and 
continue the heat until the turpentine has nearly all evaporated, 
which requires six or eight hours, and stir it occasionally 
during that period. Then add the wax and resin, previously 
melted together; and continue the heat until they are tho- 
roughly incorporated, and finally remove the vessel from the 
bath and stir them constantly until cool. 
The object of adding the oil of turpentine is to increase 
the quantity of the vehicle, and thus sooner and more effec- 
tually to dissolve the Cantharidin; and its volatility affords a 
