DISEASES OF THE CORNEA 407 



small portion. It varies in color from a grayish-blue to a pure gray. It 

 is yellowish-gray in some cases (purulent inflammation), but never 

 pure white in color. On careful examination it seems to 1)e diffuse, 

 forming spots or stripes. The lustre of the membrane is dull on its 

 surface and a partial loss of the epithelium is noticed. The other symp- 

 toms are avoidance of light, convulsive movements of the eyelids, and 

 discharge of a thin watery mucus from the corner of the eyelids, visual 

 deficiencies, and in some cases the animarl may be partially or even 

 totally blind. This is especially seen when the opacity of the sclerotic 

 membrane is in the region of the visual line that is opposite the pupil. 



Pathological Anatomy. — We have in other cases of keratitis the 

 appearance of large quantities of round cells in the corneal tissue. These 

 come from the blood vessels of the neighboring membranes, the sclerotic 

 membrane, and the conjunctiva. These are wandering cells which find 

 their way into the cornea. As long as the round cells in the cornea are 

 not crowded together it remains unaltered in its true structure (in- 

 filtration of the cornea), and complete recovery follows after the cells 

 have disappeared. But as soon as the cells are packed too closely to- 

 gether the corneal tissue is partially destroyed by maceration and ne- 

 crosis, followed by a loss of actual substance. If this is surrounded by 

 intact tissue of the cornea, it forms an abscess; if it is open externally, 

 it forms an ulcer. We consider as ulcers, small superficial openings in 

 the cornea which are always round in the early stages, and are caused 

 by infiltrations located closely under the epithelium, forming little 

 blisters or sacs, and finally bursting through the epithelial covering. 

 In the dog, as a rule, they heal without leaving any cicatrix. Still, 

 many cases are seen where they finally close up, leaving a white cicatrix, 

 or else they lead to perforation of the cornea or to a total destruction 

 of the eye by extending into the anterior chamber. 



We find the following forms of inflammation of the cornea: 



(1) Keratitis Super ficialis. — Etiology. — Superficial inflammation of 

 the sclerotic membrane is caused by slight irritations of various kinds 

 (superficial injuries, inversion of the eye-lashes (trichiasis) or entropion). 

 It may also originate, secondarily, from acute conjunctivitis, the in- 

 flammation extending from the conjunctiva to the cornea, irritating 

 eye washes or salves, or from foreign bodies. Keratitis superficialis 

 may also appear as a secondary symptom of distemper, but generally 

 in this case the entire parenchyma is involved. 



The cornea is clouded, opaque and lustreless, having a diffuse 

 grayish-blue or grayish-white coloration, with a slightly irregular surface, 

 but under certain circumstances it may also be covered with small 

 epithelial masses, easily distinguished with the naked eye. In this 

 affection the eyes are watery, which may disappear in a few days 



