Page:Philosophical Transactions - Volume 002.djvu/212



ong the many defects and distempers in the Eyes, the Eyes of Horses are peculiarly affected with one, which no Animal besides is troubled withall (as far as I have observed) neither do I remember any Author hitherto to have taken notice of it; and that is a Spungy Excrescence (commonly of a dark musk colour) which grows out of the edge of that Coat of the Eye called the Uvea; which Spunge, if it grow large, or increase in number (as it frequently happens) it depraves the sight very much, or totally intercepts it. But that you may more easily conceive the manner how 'tis done, you may remember, that the Uvea is a musculous part, the use of it being chiefly to contract and dilate itself for the admission of the Objects with as much light as the Eye can conveniently bear; so that the brighter and more refulgent the light is, to which the Eye is expos'd, that Membrane contracts it self into a narrower compass; and the more dark the place is, it dilates it self the more, as you may see in a Cats Eye more readily perform'd, than in any other Animal I have yet observ'd': So that if that spungy substance, which grows out of the edge of the Uvea, be so great, or the number of them such, as that they grow in several places about the pupil of the Eye, where it contracts it self, the pupil or sight is very much (if not totally) obstructed, and consequently the Horse sees very little or nothing at all: As I have many times taken exact notice in some Horses, which being brought into the Sun-shine, could not see at all but suffer'd me to touch the sight of their Eye with my finger without the least winking; which Horses being led back into the Stable, the Uvea in that obscure place dilating it self, they could see very well again, and would not suffer me to shew my finger near to the Eye without frequent closing their Eye-lids and tossing their Heads. The same Horses I understood by the Rh