PERIODIC OPHTHAOnA. 561 



generally attended by amaurosis, follows a blow on the eye, 

 or a blow or fall on the edge of the orbit, without any apparent 

 rupture or dislocation. This effect may not show itself for seve- 

 ral years after the injury." — (Mackenzie's Practical Treatise on 

 Eye, 1854) 



" The lens may become opaque in consequence of a blow or 

 concussion of the eye without solution of continuity. I have 

 seen many such instances. 



" In a patient who had received a blow in the eye from the 

 fist, seen by Beer in twenty-four hours after the accident, the 

 capsule was torn, the lens split in two and quite opaque, there 

 was slight effusion of blood into the anterior chamber, and con- 

 siderable ecchymosis of the conjunctiva." — (Laueence on the 

 Eye, 1844) 



2d. " Lenticular cataract consists in a marasmus and opacity 

 of the proper substance of the lens, and not in any opaque 

 deposit ; but nothing is known of the exact nature of the change. 

 It may be looked uj^on in some degree as a natural effect of old 

 age." — (Wharton Jones.) 



The late Sir David Brewster was of opinion that at least one 

 cause of cataract was an inordinate saline condition of the 

 aqueous humour, and that, owing to this extreme salinity of the 

 humour (upon the principle of exosmosis and endosmosis), the 

 fluid contained in the lens became diminished, its concentric 

 laminse being thus separated from each other, and that the 

 proper treatment for cataract was abstraction of the aqueous 

 humour by puncturing the cornea, after which the patient was 

 to abstain from partaking of salt with food. 



All cataracts have been classified under two heads, namely, 

 the true and the s;purious. 



TRUE cataracts. 



The opacity may be seated in the lens itself, or in its capsule, 

 or in both lens and capsule at the same time ; different kinds of 

 true cataracts are accordingly described, namely, lenticular, 

 capsular, and capsulo-lenticular. The distinction of these 

 different kinds is not of such great importance to the veterina- 

 rian as to the human oculist, as operation for the removal of 



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