CANTHARIS VESICATORIA. 



true skin a yellowish serum is deposited. Sometimes fresh 

 blisters continue to rise round the first blister after the plaster 

 has been removed. Both the degree of excitement and the 

 character of the effused serum, and its quantity, are greatly 

 modified by circumstances connected with the general habits 

 of individuals, and the disease for which the blister is applied. 

 In many persons, the acrid principle of the insect is carried 

 into the circulation, and produces strangury ; especially when 

 the blister is applied to the scalp. In this case the hair should 

 be removed some hours before applying the blister, if the ne- 

 cessity of the case admit of delay. The usual time for per- 

 mitting a blistering plaster to remain applied is ten or twelve 

 hours, when it is usual to puncture the blister, and, after dis- 

 charging the fluid, again to apply the plaster. This practice 

 is to be reprobated, inasmuch as it does not answer any bene- 

 ficial purpose, and it favors the absorption of the cantharidin 

 and the consequent production of strangury. As soon as a 

 blister has risen, the plaster ought to be removed, and the fluid 

 discharged. In children, in particular, this rule should always 

 be attended to ; as, owing to great irritability of skin, they 

 are not only more easily blistered than adults, but when the 

 blistering plaster is permitted to remain too long applied, 

 spreading, irritable, sometimes gangrenous ulcers are apt to 

 supervene. When this happens, the strength of the patient 

 must be sustained by bark or other tonics, the irritability of 

 the part soothed by poultices made with a strong decoction 

 of poppies, and every method which can change the irritable 

 state of the habit into one of tone must be adopted. 



Blisters, by whatever means raised, should be applied as 

 near as possible to the affected part. They should also be as 

 large as the nature of the part will permit ; large blisters caus- 

 ing no more pain than small. In every instance, the blistering 

 plaster should be kept in close contact with the skin by a few 

 strips of adhesive plaster, or a bandage ; nevertheless, the pres- 

 sure ought not to be so great as to restrain the inflammation 

 of the capillaries, and prevent vesication. Strangury is best 

 prevented by interposing something between the blistering 

 plaster and the skin. Gauze or muslin, or thin paper, mois- 

 tened with oil, pressed down upon the blistering plaster, an- 

 swers the purpose effectually, does not prevent vesication, 

 and enables the plaster to be removed in a more cleanly man- 

 ner. When the tendency to strangury is great, the blistering 



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