384 
ON PERIODICAL OPHTHALMIA. 
“ Iii proof of the stable malaria,” says the Professor, “ it would 
be a phenomenon to see ophthalmia in a horse that had been kept 
wholly at grass ; and it would be equally rare to find a horse, 
five or six years old, that had been so kept, and whose services 
had been exacted in the usual way, that had not had ophthalmia.” 
Notwithstanding this assertion, however, we do see it occur at 
grass too often to be a phenomenon, or require confinement in a 
stable for its production. It is frequently seen in the pony em¬ 
ployed by the farmer, and who knows but little of the comforts 
of the stable; the field in which to cater for himself being his 
common lot. The disease does not appear so frequently in the 
pony as in our other horses, nor in the mule or the ass so 
frequently as in the pony. 
It has been said, that the mule and ass are not subject to it; 
but I can bear testimony to the contrary, having seen several 
instances in both these animals; and Mr. Percivall, in his work, 
vol. iii, states, that the mules belonging to the army in the 
Peninsula, were quite as often the subjects of diseased eyes as 
the horses. Yet, it is my opinion, that they are not so much 
subject to it as horses in this country; nor do I conceive any 
stable confinement would render them so. The ass is an animal 
that does not possess an equal degree of nervous sensibility with 
the horse, consequently is less liable to disease. 
In the treatment of this disease it may be expected that I have 
some novel and successful mode of combating it—a specific to 
offer, by which the present inflammation may not only be 
removed, but the eye secured from a future attack—“the gouty 
disease completely eradicated from the constitution;” but this 
specific remedy I fear is at a most awful distance. 
I consider the ophthalmia of the horse to be iritis. Let the 
proximate cause be what it may, it is inflammation of the iris 
in the first instance. It is from the vessels of the iris effusion 
of a coloured fluid takes place, rendering the aqueous humour 
turbid. From these vessels lymph is effused upon the margin 
of the pupil, and corpora nigra (I consider the transparent 
cornea performs no share in the office of secretion by which the 
aqueous humour is formed : the transparent cornea receives blood 
for its own nourishment only ; it would be incompatible with the 
function of the transparent cornea, whose office is to admit the 
rays of light, to perform the office of secretion); the inflammation 
extends to the hyaloid membrane and capsule of the lens; but, 
unless the inflammation be very acute, the lens is not affected by 
the first paroxysm. 
