ON VESICATING APPLICATIONS. 
319 
soluble in boiling nitric and muriatic acids, without changing 
color, and is again deposited on cooling. It is dissolved by 
potash and soda; but when concentrated acetic acid is added 
to the solution, the Cantharidin is precipitated. Ammonia 
is without action on it. According to Regnaud, it consists of 
carbon, 61.6S ; hydrogen, 6.04, and oxygen, 32.28. 
Thus we have the active principle of Cantharides eliminat- 
ed from those inert or useless matters, with which it is asso- 
ciated in its natural state ; the character and properties of 
this principle, Cantharidin, are described ; and the best 
means are pointed out, for effecting its solution, whether it be 
in an isolated or combined form. Upon these data may, per- 
haps, be founded improvements in the preparation of our vesi- 
cating applications. Having alluded to objections which at- 
tach to some of the preparations in usej it has been my object 
to adduce the result of such investigations, as far as they 
have hitherto been carried, as may tend to elucidate the sub- 
ject, by explaining the cause of those imperfections that are 
met with, and suggesting the means for their remedy. 
The Chairman inquired whether the pain which usually 
accompanies a blister, is essential to its etficacy ; he had heard 
it stated by a physician, that this was the case.* 
Mr. Ure remarked that the pain and irritation were mere- 
ly symptoms of vesicating action. In acute cases it is often 
necessary to produce immediate vesication, and then boiling 
water or essential oil of mustard would be most effectual. In 
more chronic cases, the slow and regular action of a blister is 
preferable. 
* The following is Dr. Pereira's statement : " It was formerly suppos- 
ed that the efficacy of blisters was in proportion to the "quantity of fluid 
discharged. But the truth is, that the therapeutic influence is in propor- 
tion to the local irritation, and has no more relation to the quantity of 
fluid discharged, than that the latter is frequently (not invariably) in the 
ratio of the former. Stroll's axiom is therefore correct, Non suppuratio sed 
stimulus prodest" — Materia Medica, Part II., page 1372. 
