i2 + . DISEASES Class I. 2. 5. 1. 



t 



ORDO II. 



Decreafed Irritation. 

 GENUS V. 

 Decreafed Aclion of the Organs of ' Senfe. 



SPECIES. 



I. SttJhika in irrii abulias. Folly from inirritability. Dulncfs 

 of perception. When the motions of the fibrous extremities 

 of the nerves of fenfe are too weak, to excite fenfation with fa 

 fkient quicknefs and vigour. The irritative ideas are neverthe- 

 lefs performed, though perhaps in a feeble manner, as fuch peo- 

 ple do not run againlt a peft, or walk into a well. There are 

 three other lands of folly ; that from deficient fenfation, from 

 deficient volition, and from deficient aiTociation, as will be men- 

 tioned in their places. In delirium, reverie, and fieep, the pow- 

 er of perception is abolifhed from other caufes, 



2. Vifusimminutus. Diminiflied virion. In our approach to 

 old age our viHon becomes imperfect, not only from the form of 

 the cornea, which becomes lefs convex, and from its decreafed 

 tranfparency mentioned in Clafs I. 1. 3. 14 % but alfb from the 

 decreafed irritability of the optic nerve. Thus, in the inirritative 

 or nervous fever, the pupil of the eye becomes dilated ; which in 

 this, as well as in the dropfy of the brain, is generally a fatal 

 fymptom. A part of the cornea as weli as a part of the alhugi- 

 rsea in ihefe fevers is frequently (cen during Seep •, which is ow- 

 ing to the inirritability of the .retina to light, or to the general 

 parens of mufcular action, and in conference to the lefs contrac- 

 tion of the fphincler of the eye, if it may be fo called, at that 

 time. 



In fome eves there is an inaptitude to adapt themfelves to 

 the perception of objects at different diftances, which I fuppofe 

 may be owing to thz inirritability of thofe mufcular fibres, which 

 conftitute the eiHary procefs, fc weli defcribed and explained by 

 Dr. Porterfield, and in the Scots Medical EfTays, and fo elegant- 

 ly feen in a diffecied eye. It was formerly believed, and has in- 

 deed lately been again pretended, that the focus of the cryftal- 

 line humour was adapted to objecls at different diflances by a 

 change of the fhape of the whole eye by the action of the exter- 

 nal mufcles, which are inferted into the tunica albuginea, and 

 give motion to it in every direction : but in anfwer to this may be 



obferved, 



