PERIODIC OPHTHALMIA. 85 



to the animal again, when a fresh invasion of the disease involves 

 either it or its fellow in all the danger out of which it has but just 

 escaped, every succeeding relapse leaving the organ in a more 

 deteriorated condition. It may commence in both eyes, and relapse 

 in one ; or begin in one, and relapse in both : this last case, how- 

 ever, I believe to be the rarest. And it is surprising how many re- 

 turns of the disease some horses will experience before the eyes 

 become disorganized; for that alone appears to put an end to 

 relapses : there is a horse at present in my regiment, who has had 

 fifteen attacks in his eyes, alternatively, and stilJ, from preserving 

 some vision, is doing his duty ; another has had seven attacks in 

 the same eye ; two others have experienced each of them five 

 attacks, and have gone quite blind. It has been said, that as soon 

 as cataract is completely formed, relapses cease. This, however, 

 is not always the case. The disease will often re-appear, again 

 and again, even after the pupil is completely opaque. In fine, as 

 I said before, nothing short of the disorganization of the entire 

 globe of the eye appears to put an end to its merciless visitations : 

 so long as any structure is left for it to prey upon, so long may 

 the devouring malady be expected to return. 



The Changes of Structure the Diseased Eye Under- 

 goes are, with few exceptions, the results of successive attacks of 

 inflammation, and in general require some considerable time for 

 their completion ; and when once such changes are commenced, it 

 is a rare circumstance for the disease not to return at intervals, until 

 the eye has for every purpose of vision become a total wreck. A 

 first attack, mild in its character and not of long duration, may 

 leave the eye altered only in such respects as in the course of a 

 long intermission may be rectified : deposits into the chamber will 

 be removed ; effusions into the substance of the cornea and iris in 

 time become absorbed ; the former regaining its original pellucidity, 

 the latter its usual colour and contractility. Commonly, however, 

 after a second paroxysm, and occasionally indeed after a first, there 

 will remain more or less haziness of the cornea, through which we 

 indistinctly perceive the iris, lustreless and murky in its aspect, 

 with the pupil contracted, and without any of its natural bright blue 

 to be seen. The corpora nigra also appear more pendulous than 



