SECT. XXXII. 2. DISEASES OF IRRITATION. 419 



^dually dying, the iris will, as ufual, contract it- 

 felf, as this motion is affociated with the ftimulus 

 of light ; {nit it is not fo in the laft ftages of ner- 

 vous fevers, where the pupil of the eye continues 

 expanded in the broad day-light: in the former 

 cafe there is, a want of voluntary power, in the lat- 

 ter a want of irritability. 



Hence alfo thofe conftitutions which are deficient 

 in quantity of irritability, and which poflefs too 

 great feniibility, as during the pain of hunger, of 

 hyfteric fpafms, or nervous headachs, are generally 

 fuppofed to have too much irritability ; and opium, 

 which in its due dofe is a moft powerful flimulant, 

 is erroneoufly called a fedative ; becaufe by increaf- 

 ing the irritative motions it decreafes the pains arif- 

 ing from defect of them, 



Why the pulfe fhould become quicker both from 

 an increafe of irritation, as in the fynocha irritativa, 

 or irritative fever with ftrong pulfe; and from the 

 decreafe of it, as in the typhus irritativus, or irri- 

 tative fever with weak pulfe ; feems paradoxical. 

 The former circumftance needs no illuftration ; 

 fmce if the ftimulus of the blood, or the irritability 

 of the fanguiferous fyftem be increafed, and the 

 Strength of the patient not diminifhed, it is plain 

 that the motions nmfl be performed quicker and 



In the latter circumtfance the weaknefs of the 

 mufcular power of the heart is foon overbalanced 

 by the elafticity of the coats of the arteries, which 

 they poffefs befides a mufcular power of contra6H- 

 bn ; and hence the arteries are diftended to lefs 

 than their ufual diameters. The heart being thus 

 flopped, when it is but half emptied, begins fooner 

 to dilate again ; and the arteries being dilated to 

 lefs than their ufual diameters, begin fo much 

 fooner to contract themfelves ; infomuch, that in the 

 dagcs of fevers with weaknefs the frequency of 



pulfation 



