2G2 DISEASES OF THE HOKSE, 



losing vision at last. Sometimes the crystalline lens Is prin- 

 cipally affected ; in other cases the iris bears the brunt of the 

 attack ; in some instances the aqueous humour and the cornea 

 are principally affected, and in others the vitreous humour and 

 the retina are chiefly diseased. AVhen the crystalline lens is 

 principally affected, it usually becomes opaque, or what is called 

 a cataract forms, which, however, may not be so complete as 

 entirely to destroy vision. When the iris is chiefly inflamed, 

 the case, I imagine, does not terminate so quickly in blindness, 

 but the attacks are often frequent and very troublesome, and 

 attended by much general irritability. 



When the vitreous humour is greatly affected, the interior of 

 the eye often becomes of a yellow muddy colour, and the eye 

 sometimes shrinks from absorption of its substance. 



Causes. — The causes of this severe disease, which so often 

 brings the price of a horse from a hundred guineas down to 

 fifteen, has engaged much attention, and been the subject of 

 some dispute. In the greater number of horses that are thus 

 attacked, there is, beyond all question, a natural predisposition 

 to the disease from weakness of the parts. There are, therefore, 

 two things to consider, — the cause of this predisposition, and 

 the exciting cause itself, or that which immediately produces the 

 disorder. The disposition to the disease is decidedly hereditary. 

 The offspring of parents with diseased eyes become blind far 

 more frequently than the produce of animals with healthy eyes; 

 and to the circumstance of the little care taken in the choice of 

 the dam or tlie sire may to a great extent be attributed the 

 frequency of the disease. We find that sheep and oxen, com- 

 pared with the horse, are rarely attacked with diseased eyes, 

 and even the dog is seldom affected. AVhat then is the difterence 

 in their treatment ? The latter are, in a great measure, left in 

 a state of nature ; whilst the former animal, at an early age, 

 becomes domesticated, is taken into a warm stable, exposed to 

 the fumes from the dung and urine, fed on stimulating food, and 

 often used with great severity, either in the saddle or harness. 

 Hei*e we have several causes : a plethoric state of the system is 

 induced by stimulating food, by which much blood is sent to 

 the head ; this disposition of the blood is still further increased 

 by exertion, particularly in harness, from the pressure of the 

 collar, retarding, in some measure, the return of the blood. 

 The eyes are exposed to the stimulus of ammoniacal gases, the 

 irritating effect of which on our own eyes may be readily ex- 

 perienced ; besides which the young animal is often kept in a 

 dark stable, whence he is often suddenly brought into the full 

 glare of the noon-day sun. Can we wonder that this combination 

 of causes should produce disease, or that the delicate structure 

 of the oriran of vision should be the first to suffer ? We have 



