328 DISEASES SECT. XXXIV. i 2. 



tions, or motions in confequence of avevfion, though in common 

 language they are called involuntary ones. Thofe fenfitivc un- 

 reftrainable actions, which contribute to remove the caufe of 

 pain are uniformly and invariably exerted, as in coughing or 

 freezing ; but thofe motions which are exerted in confequence 

 of averfion without contributing to remove the painful caufe, but 

 only to prevent the fenfation of it, as in epileptic or cataleptic 

 fits, are not uniformly and invariably exerted, but change from 

 one fet of mufcles to another, as will be further explained ; 

 and may by this criterion alfo be diftinguifhed from the former. 



At the fame time thofe motions, which are excited by per- 

 petual ftimuius, or by affociation with each other, or immedi- 

 ately by pleafurable or painful fenfation, may properly be term- 

 ed involuntary motions, as thofe of the heart and arteries ; as 

 the faculty of volition feldom affects thofe, except when it exifts 

 in unnatural quantity, as in maniacal people, 



2. It was obferved in Section XIV. on the Production of 

 Ideas, that thofe parts of the fyftem, which are ufually termed 

 the organs of fenfe, are liable to be excited into pain by the ex- 

 cefs of the ftimuius of thofe objects, which are by nature adapt- 

 ed to effect them ; as of too great light, found, or preffure. But 

 that thefe organs receive no pain from the defect or abfence of 

 thefe ftimuli, as in darknefs or filence. But that our other or- 

 gans of perception, which have generally been called appetites, 

 as of hunger, third, want of heat, x want of frefh air, are liable to 

 be affected with pain by the defect, as well as by the excefs of 

 their appropriated (Hmuli. 



This excefs or defect of ftimuius is however to be confidered 

 only as the remote caufe of the pain, the immediate caufe being 

 the excels or defect of the natural action of the affected part, 

 according to Sect. IV. 5. Hence ail the pains of the body may 

 be divided into thofe from excels of motion, and thofe from de- 

 fect of motion, which diftinction is of great importance in the 

 knowledge and the cure of many difeafes. For as the pains 

 from the excefs of motion either gradually fubfide, or are in 

 general fucceeded by inflammation ; fo thofe from defect of 

 motion either gradually fubfide, or are in general fucceeded by 

 convulfion, or madnefs. Thefe pains are eafily diftinguifhable 

 from each other by this circumftance, that the former are attend- 

 ed with heat of the pained part, or of the whole body ; where- 

 as the latter exid without increafe of heat in the pained part, 

 and are generally attended with coldnefs of the extremities of 

 the body , which is the true criterion of what have been called 

 nervous pains. 



Tims when any acrid material, as fnuff or lime falls into the 



eye, 



