504 
PHYSIOLOGY OE THE EYE OF THE HORSE. 
a blow, or that some foreign matter has been lodged in the eye 
in the course of the night; and, indeed, the eye itself betrays 
appearances externally that would lead to this fallacy of opinion, 
for the upper lid droops, giving the organ a weak and gloomy 
aspect, the haw projects, and tears flow over the under lid, and 
trickle the cheek. When, however, we inspect the interior of 
the organ, we find the cornea so dull that the iris can scarcely 
be seen; and the eye so impatient of strong light, that consider¬ 
able efforts are made by the lids and haw to oppose every 
attempt to open the eye. The most effectual mode of obtaining 
a full view of it, is to turn the head from any direct or strong 
light, and then the animal will voluntarily open the eye, at least 
sufficiently to admit of inspection. 
The pupil will now be seen more or less contracted, and pre¬ 
senting a hazy appearance through the dull filmy cornea ; the 
iris will also have suffered in brilliancy, and, perhaps, will shew 
some partial or general discolouration. As the disease proceeds, 
the cornea continues to lose its pellucid lustre, until we can no 
longer see through it, and which may be caused by its increased 
vascularity, or some interstitial effusion. The aqueous humour 
also becomes generally turbid. The corpora nigra, after a time, 
lose their jetty blackness, and the pupil becomes so contracted 
that we can hardly see through it at all. These internal marks 
of disease are a tended with conjunctival inflammation. In some 
cases the membrane becomes intensely red, and vessels cover 
the opaque cornea, across which they multiply in serpentine lines. 
It must not be inferred that this disease proceeds rapidly and 
without intermission to the total destruction of the organ; on the 
contrary, it is comparatively tardy in its progress, and effects 
the final destruction of the part by obstinately relapsing after 
considerable intervals of apparently restored healthy action. 
The paroxysm usually continues about six weeks, and then 
subsides altogether, leaving the eye (should it have been the 
first and not a very violent attack) to all appearance unim¬ 
paired, except that it may evince rather more susceptibility of 
light than the sound eye, shedding, perhaps, a few tears, and 
twinkling a little when suddenly exposed, and having its haw 
more irritable and prominent than that of the eye which had 
escaped attack. The disease is seldom seen in both eyes at 
the same time; but it will seemingly run through its course 
in one eye, and then, a month or two afterwards, suddenly 
appear in the other eye, leaving the organ after the first attack 
more or less injured in both structure and function. Its ordi¬ 
nary mode of proceeding is to attack, alternately, first one and 
then the other eye, until the structure or function of both have 
