502 SPECIFIC OR PERIODICAL OPHTHALMIA, 



only one attacked ; and why also the complaint should be 

 confined to the horse, and not equally take place in the 

 mule and ass. It is, however, in the native countries of 

 the last mentioned animals, more frequent than in our 

 colder clime. We have, moreover, by a source of extensive 

 observations, pretty clearly estabhshed its hereditary nature : 

 the constitutional disposition does descend from the parents 

 of both sexes to the offspring ; and this knowledge may be 

 hereafter turned to account by our breeding only from such 

 horses as have not a tendency towards specific ophthalmia. 

 The wall-eyed horse, by general consent, is said to be 

 exempt ; yet Mr. Castley met with two cases of this kind 

 in one regiment. Size of body is thought to have some 

 connexion with it, seeing that blindness is much more rare 

 among ponies than among larger horses ; and it is the 

 general opinion, that small retracted eyes, particularly in 

 the heads of coarse fleshy horses, are more predisposed to 

 disease than others. 



The occasional causes are probably various. A determi- 

 nation to the head must be the consequence of the exertion 

 which a horse is exposed to when he is first put to active 

 and laborious exercise, particularly that of drawing ; and 

 this, as he is unused to it, must act considerably in distend- 

 ing the vessels of these organs. Hurtrel d'Arboval lays 

 much stress on dentition as an occasional cause ; and in 

 this process it is certain much blood must centre about the 

 eyes. Early breaking horses into harness by collar pres- 

 sure must also hinder the free return of blood from the 

 head, and produce congestion. There is great reason to 

 think, that disturbances in the digestive functions are pre- 

 disponents. The acrimonious fumes of a hot foul stable, to 

 a young animal that has been only used to a barn and pad- 

 dock, may call it into action. Of all causes, foul stables, and 

 improper food, serve to keep alive the disorder. Formerly, 

 when animals were little cared for, specific ophthalmia was 

 a frequent disease. Now, when horses are better under- 

 stood, and more carefully tended, a man may be in practice 

 ten years without encountering a single instance of its 

 ravages. Cart-horses are most subject, because they are 

 of all animals worst stabled. Ponies are all but exempt ; 

 these diminutive creatures being sufiered to go at large. 



