670 CANTHARIDES 



(C 10 H 12 4 ), which is confined to the soft parts of the body, 

 and is present particularly in the blood and female sexual 

 organs. It is slowly deposited, when an alcoholic solution 

 of cantharides is concentrated. When pure, it crystallises 

 in colourless scales or prisms, melts at 482 Fahr., is insoluble 

 in water, but soluble in alcohol, acetic acid, ether, chloro- 

 form, and oils ; T ^ of a grain suffices to blister. 



IMPURITIES. As the powdered cantharides sold in the 

 shops sometimes contains euphorbium and various cheap 

 irritants, it is advised that the flies be purchased entire. 

 Other insects are sometimes mixed with them. The species 

 of mylabris sold as Chinese blistering flies have two orange- 

 coloured bands and spots on the wing-covers. Activity 

 is sometimes impaired by damp, long-keeping, and attacks 

 of mites, moths, and beetles parasitic attacks which are 

 prevented by keeping the fresh flies in closely-stoppered 

 bottles, with a few drops of acetic acid, or a few grains of 

 camphor or ammonium carbonate. 



ACTIONS AND USES. Cantharides is an irritant, and pro- 

 duces its effects on any part with which the free cantharidin 

 is brought into contact. Applied externally, it stimulates 

 and vesicates, and is used as a counter-irritant. When 

 swallowed it irritates the digestive mucous membrane ; 

 large doses produce gastro-enteritis. The active cantharidin 

 is absorbed, and in the blood forms a non-irritant albu- 

 minoid, but in the kidneys is again liberated, developing 

 its characteristic irritation small doses stimulating the 

 urino-genital tract, causing diuresis ; and in some animals 

 increased sexual desire ; full doses inducing nephritis, 

 cystitis, strangury, and haematuria. 



GENERAL ACTIONS. According to the strength of the 

 preparation, or the period during which it is applied, 

 cantharides produces redness, vesication, or sloughing of 

 the skin or mucous surfaces. An ordinary vesicant dressing 

 causes congestion, elevation of local temperature, and, 

 usually within three to twelve hours, formation of blisters, 

 which, after a variable but generally short time, burst, 

 and discharge a yellow, serous fluid, which dries into 

 scurfy cicatrices. When freely or continuously used, the 

 deeper-seated skin tissues are inflamed, and ulceration, 



