202 On the Operation of Medicines. 



eafed parts. Thus, if we fuppofe cantharides 

 to be changed in form and texture, when 

 mixed with the chyle, the lymph, or blood, 

 yet in that form and texture they^ may be pecu- 

 liarly adapted to excite ftrangury in the urinary 

 paflages. Or, we may conceive that this new 

 modification of their corpufcles may again be 

 altered, and their original compofition reftored 

 by a fubfequent chemical change in the kidneysj 

 an event not more fingular than the feparation of 

 urine from the blood, than the revival of a 

 metal, or the precipitation of a folvend from its 

 menftruum by eledlive attraftion. The urinary 

 excretion feems to be defigned by nature to 

 carry off the recrementitious parts of the cir- 

 culating fluids. And it clearly fhews what 

 compofitions, and decompofitions take place in 

 the body. For it varies almofl: every hour both 

 in the ftate of health and of difeafc; and the 

 lateritious, pinky, mucous, and other appear- 

 ances it exhibits, are the refult of chemical 

 changes, either in itfelf, or in the fluids from 

 which it is derived. 



The fenfible qualities of any body are no cer- 

 tain criteria of its medicinal aftion. Peruvian 

 bark owes not its efficacy to bitternefs ; for 

 fl:ronger bitters are not poflfefTed of its febrifuge 

 powers. Antimony, though infipid, is violent 

 in its operation on the nerves of the fl:omach : 

 And yet, if applied to the eye, an organ 



endued 



