CX024) 
enough to oblige me, to grant back again this Preeminence to 
the Retind. 
Youfay,inyouryrr/?Obje(aion,thatif thtScUrotis and the 
Choroeides be taken away from an Eye that is very frefti, and 
that the Retina be left diftended on the Vitreous Hnmor, one 
ftiall not be able to fee well through this membrane: whence 
you conclude, that it^ is TOt tranfparent enough , to let fo 
much light , as is fufficient for vifion, pafs upon the ch$^ 
roeides. > -^ r 
In my opinion, there is good reafon to doubt of this confe- 
quence, feeing there may be a great deal of difference between 
the Retina of a dead Animal, after it hath been expofed to the 
Ayre , and that of a living Animal^, while it is exactly fhut up 
between the Vitreous humour and the Chomides, Different dif- 
pofitions do ordinarily change the qualities of things Fat, 
which is tranfparent when it is melted, grows opacous after it is 
cold again 5 and th^Tunica cornea of an Eye being held fome 
hours in ones hand, in a hot Ayre grows thick, and a little after 
entirely opacous. But to the end you may be perfwaded, that 
the Chomides is fufficiently enlightned in a living Animal, you 
muft take the Eye of an Ox (newly kill'd) while it is hor,^ and 
cut it in two, in fuch manner that a good part of the vitreous hu- 
mour may remain extended upon the Retina 5 then you fhall fee 
diftindly the colours of tht choroeides^ the bafis of theOptick 
nerve,the trunck of the little vcffels which proceed from thence, 
and their difperfion through the thicknefs of the Retina, with 
fa much perfpicuity that you cannot even difcern , whether 
there be a Retina beyond the Vitreous humour or no. Hence 
youmay judge, that the light, which the Objeds fend to the 
choroeides^ is more than fufficient for vifion, feing that being 
much weakned by the reflexion and by a fecond paflage through 
the Retina and the Vitreous humour, it is yet ftrong enough to 
form a clear and diftindl vifionof the Choroeides m our Eyes. 
Not that Ideny the Retina to have fome whitenefs in a living 
Animal, and that it is a little lefs; tranfparent than the other 
Humours, chiefly in that part which is contiguous to the Cho- 
roeides 5 and Nature may have made it fo on purpofe to tem- 
per the brightnefs of great Hghts, and to hinder dazeling 5 In 
like 
