SECT. XII. 3. OF STIMULUS AND EXERTION. 85 



at length ceafe altogether, and hence life itfelf be- 

 comes tolerable. 



Be (ides the temporary diminution of the fpirit of 

 animation or fen ferial power, which is naturally 

 ftationary or refident in every living f-bre, by a 

 ilngle exhibition of a powerful ftimulus, the contrac- 

 tile fibres themfeives, by the perpetual application 

 of a new quantity of ftimulus, before they have re- 

 gained their natural quantity of fenforial power, 

 appear to fuffer in their capability of receiving fo 

 much as the natural quantity of (enibrial power ; 

 and hence a permanent deficiency of fpirit of ani- 

 mation take* place, however long the ftimulus 

 may have been withdrawn. On this caufe depends 

 the permanent debility of thofe, who have been 

 addicled to intoxication, the general weaknefs of 

 old age, and the natural debility or inirritability 

 of thofe, who have pale {kins and large pupils of 

 their eyes. 



There is a curious phenomenon belongs to this 

 place, which has always appeared difficult of folu- 

 tion j and that is, that opium or aloes may be ex* 

 hibited in fmall dofes at firft, and gradually in- 

 creafed to very large ones without producing ftu- 

 por or diarrhoea. In this cafe, though the opium 

 and aloes are given in fuch fmall doles as not to 

 produce intoxicatioij or cathariis, yet they are ex* 

 hibited in quantities fuilicient in fame degree to 

 exhauft the fenforial power, and hence a ftronger 

 and a ilronger dofe is required ; otherwife- the me- 

 dicine would foon ceafe to act at all. 



On the contrary, if the opium or aloes be exhi- 

 bited in a large dofe at firft, fo as to produce in- 

 toxication or diarrhoea; after a few repetitions the 

 quantity of either of them may be diminifhed, and 

 they will ftill produce this effect, For the mor e 

 powerful ftimulus dhTevers the progreffive catena- 

 tions of animal motions, defcribed in Sect XVjj. 



a nd 



