and 



CLASS I. 2. 1. OF IRRITATION. 



ORDO II. 



Decreased Irritation. 

 GENUS I. 



With decreased Action of the Sanguiferous System. 



THE reader should be here apprized, that the words strength 

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

 press the quantity of resistance such motions may overcome; but 

 that, when they are applied to mean the susceptibility or insus- 

 ceptibility of animal fibres to motion, they become metaphorical 

 terms; as in Sect. XII. 2. 1. and would be better expressed by 

 the words activity and inactivity. 



There are three sources of animal inactivity; first, the defect 

 of the natural quantity of stimulus on those fibres, which have 

 been accustomed to perpetual stimulus; as the arterial and se- 

 cerning systems. When their accustomed stimulus is for a 

 while intermitted, as when snow is applied to the skin of the 

 hands, an accumulation of sensorial power is produced; and then 

 a degree of stimulus, as of heat, somewhat greater than that at 

 present applied, though much less than the natural quantity, ex- 

 cites the vessels of the skin into violent action. We must ob- 

 serve, that a deficiency of stimulus in those fibres, which are not 

 subject to perpetual stimulus, as the locomotive muscles, is not 

 succeeded by accumulation of sensorial power; these therefore 

 are more liable to become permanently inactive after a diminution 

 of stimulus; as in strokes of the palsy, this may be called inac- 

 tivity from defect of stimulus. 



2. A second source of animal inactivity exists, when the sen- 

 sorial power in any part of the system has been previously ex- 

 hausted by violent stimuli; as the eyes after long exposure to 

 great light; or the stomach, to repeated spirituous potation; this 

 may be termed inactivity from exhaustion of sensorial power. See 

 Sect. XII. 2. 1. 



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

 cient production of sensorial power in the brain; and hence 

 stimuli stronger than natural are required to produce the accus- 

 tomed motions of the arterial system; in this case there is no 

 accumulation of sensorial power produced; as in the inactivity 

 owing to defect of stimulus; nor any previous exhaustion of it, 

 as in the inactivity ow T ing to excess of stimulus. 



This third kind of inactivity causes many of the diseases of 

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



