On the Operation of Medicines. 201 



efficacy of emetics in flopping haemorrhages. 

 The head, when difordered with vertigo, fome- 

 tlmes derives fudden relief from a tea-fpoonful 

 or two of asther, adminiftered in a glafs of water. 

 And I have known an inceffant cough to attack 

 the lungs, in confequence of the flimulus of 

 a pin, which had been unwarily fwallowed. Of 

 the adtion of medicines on the ftomach, under 

 decompofition or recompofition, we have an 

 example, familiar to every one, in magnefia. 

 For this abforbent earth by neutralizing the 

 acid in the prima via, acquires a purgative 

 quality, and at the fame time yields a gas of 

 great falubrity, as an anti-emetic, tonic, and 

 antifeptic. 



II. Medicines may pafs into the courfe of 

 circulation in one or other of the dates above 

 defcribedj and, being conveyed to different and 

 diflant parts, may exert certain appropriate 

 energies. Chemiflry furnifhes numberlefs cafes 

 wherein fubflances undergo changes, and put 

 on new forms more remarkable than can be 

 effedled by the digeftion of the flomach, retain- 

 ing flill the materia prima, and being capable 

 of refuming the original arrangement of their 

 particles, and confequently their original qua- 

 lities. Now, a body altered in its texture, by 

 the digeflive organs, and carried into the fyflem 

 with the aliment, may by fuch alteration ac- 

 quire fpecific powers on particular found or dif- 



eafed 



