66 OF STIMULUS SECT. XII. 5. 4 , 



As the pains, which riginate from defect of ftirrmlus, only 

 occur in thofe parts of the fyftem, which have been previoufly 

 fubje&ed to perpetual ftimulus ; and as an accumulation of fen- 

 forial power is produced in the quiefcent organ along with the 

 pain, as in cold or hunger, there is reafon to believe, that the 

 pain is owing to the accumulation of fenforial power. For, in 

 the locomotive mufcles, in the retina of the eye, and other or- 

 gans of fenfe, no pain occurs from the abfence of ftimulus, nor 

 any great accumulation of fenforial power beyond their natural 

 quantity, fince thefe organs have not been ufed to a perpetual 

 (upply of it. There is indeed a greater accumulation occurs in 

 the organ of vifion after its quiefcence, becaufe it is fubje6t to 

 more conftant ftimulus. 



4. A certain quantity of ftimulus lefs than natural induces 

 the moving organ into feebler and more frequent contractions, 

 as mentioned in No. I. 4. of this Section. For each contraction 

 moving through a lefs fpace, or with lei's force, that is, with lefs 

 expenditure of the fpirit of animation, is fooner relaxed, and the 

 fpirit of animation derived at each interval into the acting fibres 

 being lefs, thefe intervals likewife become fhorter. Hence the 

 tremors of the hands of people accuftomed to vinous fpirit, till 

 they take their ufual ftimulus ; hence the quick pulfe in fevers 

 attended with debility, which is greater than in fevers attended 

 with ftrength -, in the latter the puife feldom beats above 120 

 times in a minute, in the former it frequently exceeds 140. 



It muft be obferved that in this and the two following arti- 

 cles the decreafed action of the fyftem is probably more fre- 

 quently occafioned by deficiency in the quantity of fenforial 

 power, than in the quantity of ftimulus. Thus thofe feeble 

 conftitutions which have large pupils of their eyes, and all who 

 labour under nervous fevers, feem to owe their want of natural 

 quantity of activity in the fyftem to the deficiency of fenforiai 

 power ; fince, as far as can be feen, they frequently poiTefs the 

 natural quantity of ftimulus. 



5. A certain quantity of ftimulus lefs than that above men- 

 tioned, inverts the order of tucceflive fibrous contractions ; as 

 in vomiting the vermicular motions of the ftomach and duode- 

 num are inverted, and their contents ejecled, which is probably 

 owing to the exhauftion of the fpirit of animation in the acting 

 mufcles by a previous exceilive ftimulus, as by the root of ipecac- 

 uanha, and the confequent defect of feniorial power. The 

 lame retrograde motions afreet the whole inteftinal canal in 

 ileus; and the cefophagus in globus hyftericus. See this fur- 

 ther explained in Sedt. XXIX. No 1 1. on Retrograde Motions. 



I muft obferve, alfo, that fomething fimilar happens in the 



production 



