OBSERVATIONS ON BLISTERING PLASTER. 305 
ready means of getting rid of it after it has performed that 
function. The proportion of olive oil is rather greater than 
in the Phafmacopoeia > but it is believed to be properly 
increased. 
Vesication, has been produced in several instances in two 
hours, and from that to six has been the period found necessary 
for its complete action. 
Since writing the above, my attention has been turned to 
some observations on Cantharides by Joseph Scattergood, 
(Jour. Phil. Col. Pharm.^ vol. iii. p. 212,) which go to confirm 
the above conclusions respecting the action of heat on Cantha- 
rides. He proposes an ointment made by decocting blistering 
flies in olive oil, straining and then adding sufficient wax to 
render it of the proper consistence; This preparation, though 
an elegant one, would be weaker than that now proposed; 
and besides, by removing the flies more space is left for the 
ill effects of careless manipulation. 
Notwithstanding various substitutes for cerate of Cantharides 
have been proposed, such as a decoction in olive oil, a solution 
in acetic acid, &c, yet it is hardly probable that that prepara- 
tion will be superseded, and hence the importance of im- 
proving it. 
The attention of pharmaceutists has hardly been sufficiently 
attracted toward the influence of the material upon which the 
cerate is spread. The article usually employed is sheep skin, 
which, from its porous character, absorbs much of the vehicle, 
and sometimes leaves the surface of the plaster so dry as to 
prevent its adherence and activity. The material should, 
therefore, be soft and yielding, at the same time that it should 
not absorb the oil from the cerate. Oiled silk, which possesses 
all these requisites, is now proposed as a substitute for sheep 
skin. The small difference in the cost of the two should not 
counterbalance the employment of the former, when accom- 
panied by such great advantages. 
yol. vn. — no. iv. 39 
