PHYSIOLOGY OF THE EYE OF THE HORSE. 665 
experienced considerable alteration. The usual and the most 
conspicuous result is cataract^ when the animal is left totally 
and incurably blind. The causes of this malady had, until the 
labours and researches of our Professor, never been clearly de¬ 
fined. Some contended that the remote cause of this disease 
was the plethoric state of the horse when he arrives at an adult 
period, that is, when he ceases to grow. Previously to this age, 
the blood has not only to nourish the body, but to increase it 
also by the addition of parts ; but the animal having arrived at 
maturity, it has only to support the organs it has already formed, 
and there must be a superabundant quantity thrown on the 
system. 
This theory, however ingenious, is by no means sufficient to 
account for the constitutional predisposition evident in this dis¬ 
ease ; nor, in fact, is the disease confined to the adult period. 
I have seen it at two years old. Hurtrel d’Arboval, and other 
French authors, assert the same, as well as Mr. Castley. 
After extensive observation, it is now acknowledged to be an 
hereditary disease, i. e. there is a constitutional predisposition 
dependent undoubtedly on structural speciality, derived from the 
parent. The knowledge of this may be turned to account by 
breeding only from such parents as have not exhibited this struc¬ 
tural aptitude, and by which means, if we fail to cure, we may 
contribute to prevent. 
Colour has been thought to influence the liability to the 
affection, but no two persons agree as to the shades most ob¬ 
noxious. The wall-eyed horse is, by general consent, thought to 
be exempt. The size of the animal may have some connexion 
• w'ith it, for blindness is much more rare among ponies than 
among larger horses ; and it is a general opinion, and one which 
appears founded on experience, that small retracted eyes, parti¬ 
cularly in the heads of coarse, fleshy horses, are more predisposed 
to disease than others. 
Hurtrel d’Arboval lays much stress on dentition, as an occa¬ 
sional exciting cause; and the French winters seem to be also 
much impressed with the tendency of some particular food, and 
the nature and quality of some pasturage, to produce inflammation 
of the eye. With regard to simple ophthalmia, clover seems to 
lie under this censure, and hard food has been thought to be 
concerned with it, by the additional mastication which it re¬ 
quires ; but, gentlemen, the majority of these suppositions arc 
altogether fallacious. 
There may be a predisposition to this disease, but we must 
also have an exciting cause. The extensive observation and 
diligent research of Professor Coleman led him to believe that 
VOL. viir. 4 H 
