416 
VESICATING COLLODIONS. 
The cantharides, coarsely powdered, are placed loosely 
into a displacement apparatus, the flow of which can be regu¬ 
lated by a tap; upon this is poured the ether and acetic 
acid, previously mixed together; after the whole has passed 
through, it will be found that the debris has retained by ab¬ 
sorption seven fluid ounces, which must be displaced by the 
gradual addition of an equal bulk of methylated spirits. If 
properly done, there is not the least danger of the admixture 
of the spirits with the percolated menstruum, as the animal 
substance of the flies swells considerably under the prolonged 
influence of the spirits of wine, so that the same bulk will 
be insufficient to quite displace the ether. The ethereal so¬ 
lution should then be made to measure exactly f^xv, by the 
addition of a little spirit, and may then be converted into 
collodion by the addition of the gun-cotton. Mylabris 
cichorii, treated in the same manner, gives even a more 
powerful vesicant than the cantharides. Those flies, which 
constituted the blister of the ancients, are, I believe, to be 
procured in great profusion in India. The percentage of 
cantharidin is larger in the flies than in the cantharides, but 
they resemble them in all respects excepting their physical 
appearance. 
The most effectual method of using the collodion is as 
follows :—The part upon which the vesicle is to be raised 
should be painted with the vesicant to the desired extent, 
bearing in mind that the blister produced always extends to 
about one tenth of an inch beyond the margin of the space 
covered by the collodion. Care should also be taken that 
there is a considerable thickness of collodion upon the sur¬ 
face, To ensure this the brush should be passed over and 
and over again, until about 5ss has been used to the square 
inch, or less when operating upon a tender epidermis. It is 
desirable to place a piece of oil silk, or what is still better, a 
piece of sheet gutta percha two or three inches larger than 
the surface of the intended blister; the gutta percha is not 
spoiled, whilst it hastens considerably the action of the 
collodion.* 
In ten minutes or a quarter of an hour, if the cuticle is 
hard, the collodion should be wiped off with a little cotton¬ 
wool moistened with ether, when the blister will almost 
instantly rise. The principles which advocate the use of the 
collodion may be enumerated as follows:—Cleanliness, ease 
•/ * 
* The action of the gutta percha is easily explained, by its stopping the 
evaporation of the exhalations of the skin ; in this manner the scarf-skin is 
rendered moist and permeable, the ordinary dry and harsh texture of the 
skin militating greatly against the production of a vesicle. 
