On the operation of Medicines. 199 



fifts in all the operations of nature, that a medi- 

 cine is only the cauje of a caufe, -to adopt a phrafe 

 of the logicians j and that its proper aflion is 

 confined to the nerves or fibres to which it is 

 immediately applied. When received into the 

 ilomach, after the firft impreffion on the very 

 fenfible coats of that organ, the nature of it is 

 gradually changed, by the folvent powers of the 

 gaftric juices : Or, if incapable of being digefted 

 into a mild and nutritious chyle, it is carried 

 through the inteftinal canal, and ejedled as ufelefs 

 and noxious to the body. 



Error may be built on the bafis of acknow- 

 ledged, if only partial, truth j and is then mod 

 fpecious in its form, and moft authoritative in 

 its influence on the underftanding. But the 

 impofition ceafes when we extend our , views. 

 And I {hall endeavour to fhew, that the operation 

 of medicines is to be meafured by a more en- 

 larged fcale than the foregoing hypothefis ap- 

 plies to it, or any other which now occurs to 

 my recolleflion. 



I. Medicines may a(5t on the human body by 

 an immediate and peculiar impreffion on the 

 ftomach and bowels, either in their proper form; 

 in a (late of decompofition ; or by new powers 

 acquired from combination, or a change in 

 the arrangement of their parts. The fympathy 

 of the ftomach v/ith the whole animated fyftem 

 is fo obvious to our daily experience, that 'it 

 O 4 cannot 



