IMPROVED. 143 



in the fame Place, is plain to any who has the lead 

 Notion of Opticks ; for, unlefs the Eye be kept 

 truly fteady and fixed in the fame Pofition, it is 

 not poffible a perfon fhould obferve the Mote or 

 Speck always the fime. 



Some will have it, that the Reprefentations I am 

 fpeaking of are not occafioned by the difeafed Cry- 

 Jialliney and pretend to prove from Experiments in 

 Opticks, that no Objefts fixed upon the Cornea or 

 Cryftalline can be reprefented upon the Retina, for- 

 afmuch as thofe Parts are fo near the Retina, and 

 of fuch Convexity, that the Pencil of Rays, pafTmg 

 from Objedls thro' them, cannot fall upon the Re- 

 tinn, fo as to be diflinguifh^'d ; and therefore con- 

 clude, that the Parts of the Retina (in the Diftem- 

 per I am treating of) are too much comprefs'd by 

 a Dillention or Stretching of the Arteries, and that 

 fuch Diftention is often the Caufe of a Gutta 

 'Serena. 



Thefe may feem plaufible Arguments, but I mufl: 

 ov/n I could never obferve any Part of the Eye dif- 

 order'd in Cafe of a Cafara^, befides the Cryftal- 

 line Humour, altho' I have differed feveral Eyes 

 which were troubled with fuch Malady. Indeed The Caufa 

 I cannot help thinking, but that the Gutta Serena of a ^ v.ua 

 may proceed from fuch DiHention or ftretching of •^^''^'"*' 

 the Coats of the Arteries upon the Retina, I mean 

 when fuch Diforder proceeds from a Bruife, or the 

 like, and then it is moftly confined to one Eye only : 

 But if both Eyes be affefted with a Gutta Serena^ 

 and that the Diftemper came without much Pain, I 

 am apt to believe the Seat or Caufe is an Obftruc- 

 tion of the Optick Ner^ve : But whether it be occa- 

 fionM from a Diftention of the Blood-VefTels which 

 ccmprefs and fqueefe the Retina, fo that Objefts 

 cannot be reprefented to the Brain, or whether it is 

 an Obftrudlian, Convulfion, or Paralytick Indifpo- 

 fition of the Op ick Nern)e, I think is not much to 

 my prefent Purpofe, feeing I am fatisfied they are 

 equally incurable by Art. 



I had 



