BLISTERS. 125 



economy, that two great operations could not go on in one 

 system at the same time ; in confirmation of which we have 

 only to refer to our daily practice. Do we not find that 

 inflammation of the lungs very much abates or entirely sub- 

 sides when fever in the feet supervenes ? And that inflamed 

 lungs will supersede a common catarrh ? On this principle 

 of one disease curing another, we proceed when counter- 

 irritation is employed. The counter-irritants we commonly 

 resort to, are blisters, rowels, setons, and filling. 



BLISTERS. 



For general use we possess no counter-irritant equal to a 

 blister. While it inflames the skin, and thereby causes a 

 sort of revulsion from the diseased part, it induces an efi*usion 

 of serous fluid from the true skin to collect under the 

 cuticle. 



Blisters exert more influence than other counter-irritants ; 

 their operation is superficial ; and the discharge they create 

 is abundant. There are a variety of substances which, 

 applied to the skin, act as excitants; we can trace these 

 agents from the simple rubefacient to the powerful caustic ; 

 some of them will blister, while others will only bring forth 

 pimples : many have no other eff'ect than producing angry 

 inflammation. For the purpose of blistering the skin, there 

 are few substances equal to canthay^ides or Spanish flies ; 

 the same that forms the base of our common blister : though 

 I believe euphorbium and cheaper drugs to be often sub- 

 stituted by the shops. 



Portions of the flies should never be left in blisters de- 

 signed for the horse ; because these irritate the true skin 

 after the cuticle has been removed, and often provoke the 

 animal to gnaw the part. When the blister does not take 

 efi'ect, another should not be applied, but a little simple oil 

 may be rubbed into the part. Oil is a solvent for the 

 cantharidine or active principle of the flies. Fresh oil, 

 therefore, redissolves the blister, and this will frequently 

 occasion sufficient vesication, whereas a fresh blister might 

 produce sloughing of the cutis. 



