Class I. 2. 1. OF IRRITATION. . 51 



ORDO II. 



Decreafed Irritation. 



GENUS I. 

 With decreafed Aclicn of the Sanguift-rdus Syjem, 



The reader (liould be here apprized, that the words (treiigtlt 

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

 prefs the quantity of refiftance fuch motions may overcome ; but 

 that, when they are applied to mean the fufceptibility or infui- 

 ceptihiiity of animal fibres to motion, they become metaphorical 

 terms ; as in Seel. XII. 2. 1. and would be better expreifed by 

 the words activity and inactivity. 



There are three fources of animal inactivity ; fit-ft, the defect 

 of the natural quantity of ftimulus on thofe fibres, which have 

 been accuftomed to perpetual (limulus ; 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 that at 

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

 cites the vefiels of the (kin into violent action. We mull ob- 

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

 not fubject to perpetual ftimulus, as the locomotive mufcles, 

 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 thefyftem has been previoufly ex- 

 fraufted 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 powd- 

 er. See Sect. XII. 2. 1. 



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 no 

 accumulation of fenforial power produced ; as in the inactivity 

 owing to defect of ftimulus j 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 ; which are therefore in general to be remedied by 



fucft 



