374 PERIODIC OPHTHALMIA. 



tating effect on the general system, and thus predisposes to 

 the disease. This influence is especially marked in the case 

 of foals early separated from their dams and supported on 

 fodder raised on marshy pastures. Horses imperfectly sup- 

 ported in other respects are similarly predisposed. 



5th. Certain kinds of eye seem especially disposed to con- 

 tract this malady. It is more prevalent in the small sunken 

 eye than in that which is full, bright, and prominent. Per- 

 civall mentions black eyes as being most obnoxious to the 

 malady, while Messrs Castley and Goodwin have seen lighter 

 eyes suffer in an equal degree. 



6^. Consanguinity is mentioned by Eeynal as a predispos- 

 ing cause, its mode of action being by reducing the stamina of 

 the progeny. 



*lth. Of all influences tending to the development of the 

 disease, none is more clearly established than the hereditary 

 predisposition. Our best Yorkshire breeders would not em- 

 ploy a blind sire or dam, and, where such are had resort to, 

 the progeny usually inherit the propensity in a marked 

 degree. A similar conclusion has been arrived at by the 

 best English and foreign veterinarians ; and Eeynal remarks 

 that predisposition may remain latent in one generation and 

 re-appear in the next. 



Young horses, about the time of teething, are frequent sub- 

 jects of the disease, and, accordingly, the French and some 

 English veterinarians attribute it to the local plethora atten- 

 dant on dentition. Percivall and D'Arboval have noticed its 

 greater prevalence in geldings than in mares, a circumstance 

 which has been explained by the greater local irritation in the 

 former, connected with the cutting of the canine teeth. 



Symptoms. The malady may make its onset slowly, and 

 show itself by a profuse flow of tears and some redness of the 

 conjunctiva; but more commonly it originates suddenly, often 



