70 T^esicating Principle of Cantharides. 



hour or two, or that the part to be blistered be covered rather more 

 perfectly with the oil ; this however will seldom be necessary, as blis- 

 ters are most frequently applied on parts which do not require this 

 particularity. It begins to draw in four, five or six hours, according 

 to the place where it is applied. 



In some cases, where the part is liable to get rubbed, it may be 

 advisable to cover it with a little soft paper or linen, but in general 

 no protection whatever is necessary. After the blister is cut and the 

 lymphatic water discharged, press the epidermis close to the skin, 

 and in most instances it heals in from twenty to forty eight hours. 



When a rubefacient is wanted, one drop dissolved in ten or fifteen 

 drops of sweet oil, or mixed with lard, will answer that purpose, and 

 for convenience and ready application, will be better adapted than 

 any preparation I am acquainted with. One ounce of this oil con- 

 tains the vesicating properties of nearly one pound of Cantharides. 



Preparation of the Oil of Cantharidin.^ 



The vesicating properties of the Cantharides, reside in a peculiar 

 crystalline principle, which has been denominated Cantharidin. It is 

 separated from the Cantharides by boiling them in sulphuric ether, 

 which takes up, with the Cantharidin, a greenish colored oil, some- 

 times combined with fatty matter. This may be separated from the 

 Cantharidin by washing the crystals in cold ether ; it is, however, 

 unnecessary to do this, as when it is thus combined, it produces the 

 epispastic effect equally well. Cantharidin, when thus washed, 

 presents beautiful prismatic crystals, entirely colorless. Combined 

 with an oil, it communicates to the latter, in a high degree, its vesi- 

 cating properties. It is well to dissolve the crystals in strong sul- 

 phuric ether, and mix the ether and oil together, which will make a 

 clear solution. They are with difficulty soluble in oil alone ; the 

 sulphuric ether is also an advantage, by its evaporating on the part 

 where it is applied, thus leaving the oil more circumscribed. 



I have tried this oil repeatedly on my own person, and found it in- 

 variably to produce a blister, in about the same time as the ordinary 

 blistering ointment, and it is so mild that it generally produces very 

 little sensanon, except on those places where muscles, nerves or ten- 

 dons, are in a state of compression. The experiments already made, 

 by several eminent members of the faculty in Philadelphia, have re- 

 sulted in the most satisfactory manner, and leave little doubt that this 

 preparation of Cantharides will prove a valuable acquisition. 



* Sold at 301, Market Street, Philadelphia. 



