THE VOLATILITY AND SOLUBILITY OF CANTHARIDIN. 49 
402° F. and 410° F. it fused, and rapidly sublimed at a few 
degrees higher. Cantharidin at this temperature volatilizes 
with great ease, and condenses in beautiful well-defined 
crystals like salicylic acid. 
“The specific gravity of cantharidin is considerable, as it 
sinks in nitric acid, sp. gr. T38 ; it is exceedingly acrid ; its 
powder applied to the skin with a little oil produces speedy 
vesication, and taken internally it is an irritant poison of the 
most virulent kind. 
“ From these experiments it must be admitted that cantha- 
ridin is less volatile than has been asserted. The effect pro- 
duced on the eye of the pupil of Robiquet who was watching 
the crystallisation of cantharidin during the evaporation of 
an ethereal solution, may be accounted for by the mechanical 
action of the dense ethereal vapour escaping near his eye, 
as he watched the process with a lens, carrying off some par- 
ticles of catharidin ; and the readiness with which this prin- 
ciple may be brought mechanically in contact with the skin 
of the face, during a series of experiments, by want of care, 
will easily account for the occasional testimony of writers in 
favour of its volatility at low temperatures based on that kind 
of evidence. During the whole of the experiments detailed 
in this paper, the author has not experienced any inconve- 
nience to his eyes or face except in two instances, once when 
decomposing cantharides by destructive distillation, during 
which some of the vapours escaped near his person, and again 
where a small capsule containing aqueous extract of cantha- 
rides was accidentally exposed to high temperature over a 
lamp so as to partially decompose it ; he suffered slight pain 
for a few hours in the conjunctiva of both eyes. 
“ Having now studied the effects of the ordinary solvents on 
cantharidin in a free state, and in the condition in which it 
exists in the insect, we are prepared to consider with some 
clearness, the pharmaceutical preparations of the Spanish fly, 
and their action as vesicants. 
“ ct. If one thirtieth of a grain of pure cantharidin, in fine 
powder, be placed on the skin of the arm, and covered with 
a piece of warmed adhesive plaster, active vesication occurs 
in eight hours, with pain. If the same quantity of cantha- 
ridin be put on the other arm, a small piece of paper be 
laid over it, and then a piece of adhesive plaster with a cir- 
cular hole in it be applied, so as to hold on the paper, no 
vesication occurs in sixteen hours, the powder remaining 
dry. If then a large piece of plaster be put over the whole, 
xxvi. 7 
