CLASS I. 2. i. OF IRRITATION. 5 1 



ORDO II. 

 Decreafed Irritation* 



GENUS I. 



With decreafed AB'wn -of the Sangitiferous SyJIem. 



THE reader mould be here apprized, that the words flrength 

 and debility, when applied to animal motions, may properly cx- 

 prefs the quantity of refiftance fuch motions may overcome ; but 

 that, when they are applied to mean the fiifecptibility or i: 

 reptibility of animal fibres to motion, they become metaphorical 

 terms ; as in Sect. XII. 2- i. and would be better expreiled by 

 the words activity and inactivity. 



There are three fources of animal inactivity ; firft, the d 

 of the natural quantity of ftimulus on thofc fibres, which . 

 been accuftomed to perpetual ftimulus ; as the arterial and fe- 

 cerning fyftems. When their accuftomed ftimulus is for a 

 while intermitted, as when fnow is applied to the ikin of the 

 hands, an accumulation : of fenforial power is produced \ and then 

 a degree of ftimulus, as of heat, fomewhat greater than th 

 prefent applied, though much lefs than the natural quantity, ex- 

 cites the vefTels of the fkin into violent action. We muft ob- 

 ferve, that a deficiency of ftimulus in thofe fibres, which arc 

 not fubject to perpetual ftimulus, as the locomotive mufcllk 

 is not fucceeded by accumulation of fenforial power -, thefe 

 therefore are more liable to become permanently inactive after 

 a diminution of ftimulus ; as in ftrokes of the palfy, this may 

 be called inactivity from defect: of ftimulus. 



2. A fecond fource of animal inactivity exifts, when the fen- 

 forial power in any part of the fyftem has been previouily ex- 

 haufted by violent ftimuli ; as the eyes after long expofure to 

 great light ; or the ftomach, to repeated fpirituous potation ; 

 this may be termed inactivity from exhauftion of fenforial pow- 

 er. See Sed. XII. 2. i. 



3. But there is a third fource of inactivity owing to the defi- 

 cient production of fenforial power in the brain ; and hence 

 ftimuli ftronger than natural are required to produce the accuf- 

 tomed motions of the arterial fyftem ; in this cafe there is 1,10 

 accumulation of fenforial power produced ; as in the inactivity 

 owing to defect of ftimulus ; nor any previous exhauftion of it, 

 as in the inactivity owing to excefs of ftimulus. 



This third kind of inactivity caufes many of the difeafes of 

 this genus j which are therefore in general to be remedied by 



fucl> 



