PERIODIC OPHTHALMIA. Ill 



to the progeny, and it is equally certain that it is a specific 

 disease. Periodic ophthalmia differs very materially in 

 several important respects from simple ophthalmia. The 

 disease is by no means uncommon even at the present day^ 

 although less frequently met with than some years ago, 

 when it was very common, and was very generally regarded 

 and spoken of as the bane of horse-flesh. Attention to the 

 common-sense rules of breeding and hygienic principles have 

 done much towards, and may possibly at some time in the 

 future complete, the extinction of periodic ophthalmia. 



Causes. — The causes of periodic ophthalmia are somewhat 

 obscure. Extremes of heat and cold serve as exciting causes, 

 although in all probability there must exist within the 

 system a predisposition to an attack ; in other words, the 

 disease must exist within the system in a latent form, and 

 extreme heat, or cold and other exciting causes only serve 

 to develop and cause it to become manifest. Improperly- 

 ventilated or badly-lighted stables, hard work, overheating, 

 poor food, neglect, etc., where there is any tendency to the 

 disease, either hereditary or otherwise, most certainly exert 

 a powerful influence in the development and production of 

 periodic ophthalmia. The primary stage of the disease may 

 be characterized as the inflammatory or acute stage, or in 

 some cases it occurs in the sub-acute form. During the 

 next, or second stage, the inflammatory action begins to 

 subside, and in five or six days the eye has regained almost 

 its normal appearance, the duration of an attack usually being 

 ten or fifteen days. The eye may not suff"er another attack 

 for four or five years, or it may be attacked again in four or 

 five weeks. Ten or a dozen attacks may be undergone, and 

 still the eye look pretty well and vision be retained. How- 

 ever, such is the case only where the inflammatory action 

 during each attack is of a very mild character. On the 

 other hand, one or two attacks of a very severe type may 



