CANTHARIS VESICATORIA. 197 



acrimony, to the attacks of mites, which gradually reduce them to 

 dust. It appears, however, that these little animals feed on the 

 inactive part only, and that the powder still possesses its vesicating 

 powers. The largest and best are imported from Astracan and 

 Sicily, where they are packed in chests. They should be chosen 

 dry, entire, of a small size, free from mould and dust, of a strong 

 nauseous odour, brilliant colour, and not mixed with the Cetonia 

 aurata, and other beetles, which is frequently the case to a great 

 extent. 



Blistering-flies, when reduced to powder, have a greyish-green 

 colour, mingled with brilliant green points. They have a very 

 nauseous odour, and a very acrid burning taste. Their active prin- 

 ciple is extracted both by water and by alcohol ; and from the 

 analysis of M. Robiquet it appears to reside partly in a crystalline 

 matter and partly in a greenish volatile oil. If the inspissated 

 decoction of these insects be treated with pure alcohol, a solution 

 of resinous matter is obtained, which is separated by gentle evapo- 

 ration to dryness, and submitted for some time to the action of 

 sulphuric ether, forms a yellow solution. By spontaneous evapo- 

 ration small crystalline micaceous plates are obtained, insoluble in 

 water and in cold alcohol, but soluble in boiling alcohol and in 

 ether, and very soluble in oils ; on the presence of which the vesi- 

 cating property of the flies depend. The smallest quantity of this 

 matter dissolved in oil forms a liquor, which, applied to the skin 

 quickly raises a blister. Dr. Thompson has named it cantharadin. 

 Besides this peculiar substance, Cantharides contain, according to 

 Robiquet, a green bland oil, insoluble in water, soluble in alcohol, 

 which is the source of their disagreeable odour ; a black matter, 

 soluble in water, insoluble in alcohol, without blistering properties; 

 a yellow viscid matter, mild, soluble in water and alcohol ; the 

 crystalline plates ; a fatty bland matter ; phosphates of lime and 

 magnesia ; a little acetic acid, and much lithic or uric acid. 



The common Blister-Fly taken into the stomach in the dose of 

 a few grains is an active poison both to man and animals. The 

 symptoms produced by this insect in man are a sense of burning 

 heat in the throat and stomach, and sometimes vomiting and 

 diarrhoea, acute pain in the lower belly, tenesmus, great heat and 



