264 DISEASES OF THE HORSE. 



cool and clean stable, where there are no emanations from the 

 excrements. 



Mr. Peall, in his observations on the diseases of the horse, 

 relates a striking experiment which he made on a horse affected 

 with ophthalmia. " I have ordered him," he says, " to be re- 

 moved from the stable, where I observed he kept both eyes shnt, 

 into the open air, or to a very cool situation, and have watched 

 the effects of the change. In the course of half an hour, I have 

 commonly found him begin to open his eyes gradually, and in 

 the course of two or three hours, to keep them open boldly, and 

 for a continuance, even though the situation he was placed in 

 was not darkened or shady ; for it cannot be denied that strong 

 light is very prejudicial in such cases. Now, to prove that the 

 stimulus of the volatile alkali (the vapours of foul litter) was 

 more offensive to the inflamed organ than that of light, I have 

 placed the animal again in a hot stable, which did not admit 

 much light ; and, in the course of a few minutes, have observed 

 him begin to close his eyes gradually, and, after an hour or two, 

 to keep them constantly shut. Not satisfied, however, with this, 

 I have removed the horse back again to a cool situation, and 

 have observed the same effects to be produced as have been 

 already detailed." 



It is frequently the case, that as one eye gets better the other 

 is attacked or gets worse ; and it is fortunately sometimes the 

 fact that the loss of one preserves the other : this, however, is, 

 generally speaking, when the disease ends in cataract. — Ed.] 



Cataract. 



[We may consider cataract in three varieties : — total cataract, 

 partial cataract, and specks on the capsule of the crystalline 

 lens, which, however, can scarcely be called cataract. 



Total cataract is an entire opacity of the crystalline lens, so 

 that it no longer admits rays of light to pass through, and blind- 

 ness is, of course, the result. It proceeds from inflammation of 

 the lens, and it usually takes many attacks to produce total 

 opacity. It may be readily detected by exposing the horse to a 

 moderate light, such as that at the stable door, and carefully 

 looking into the interior of the eye. 



Sometimes the opacity is quite white, at other times grey, and 

 occasionally yellow. The lens undergoes some alterations of 

 form when aflected with cataract, becoming much more globular 

 than before. 



In the human subject, it is well known that the operation of 

 couching is practised, which consists either in extracting the 

 lens, or thrusting it back into the vitreous humour, where it 

 becomes absorbed. In the horse, however, this operation is 



