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



lus becomes gradually diminimed. Thus if two 

 grains of opium be fwallowed by a perfon unufed 

 to ib ftrong a ftimulus, all the vafcular fyftems in 

 the body act with greater energy, ali the fecretions 

 and the abforption from thofe fecreted fluids are 

 increafed in quantity ; and pleafure or plain are in- 

 troduced into the fyftem, which adds an additional 

 ftimulus to that already to6 great. After fome 

 Jiours the fenforial power becomes diminifhed in 

 quantity, expended by the great activity of, the 

 iyftern ; and thence, when the ftimulus of the 

 opium is withdrawn, the fibres will not obey their 

 ufual degree of natural (limulus, and a confequent 

 torpor or quiefcence fucceeds, as is experienced by 

 drunkards, who on the day after a great excefs of 

 fpirituous potation feel indigeftion, head-ach, and 

 general debility. 



In this fit of torpor or quiefcence of a part or of the 

 whole of the fyftem, an accumulation of the fen- 

 forial power in the affected fibres is formed, and 

 occaiions a fecond paroxyfm of exertion by the ap- 

 plication only of the natural ftimulus, and thus a 

 libration of the fenforial exertion between one ex- 

 cefs and the other continues for two or three days, 

 where the ftimulus was violent in degree ; and for 

 weeks in fome fevers, from the ftimulus of conta- 

 gious matter. ^'< 



But if a fecond dofe of opium be exhibited be- 

 fore the fibres have regained their natural quantity 

 of fenforial power, its effect will be much lefs than 

 the former, becaufe the fpirit of animation or fen- 

 forial power is in part exhaufted by the previous 

 excefs of exertion. Hence all medicines repeated 

 too frequently gradually lofe their effect, as opium 

 and wine. Many things of difagreeable tafte at 

 firft ceafe to be difagreeable by frequent repetition, 

 as- tobacco ; grief and pain gradually diminifh, and 



at 



