DISEASES OF HORSES 345 



teats use an ointment of vaseline 1 ounce, balsam of tolu 5 grains, 

 and sulphate of zinc 5 grains. (Spl. Rpt. Horse, Dept. Agr. 1911.) 



DISEASES OF THE EYE. 



We can scarcely overestimate the value of sound eyes in the 

 horse, and hence all diseases and injuries which seriously interfere 

 with vision are matters of extreme gravity and apprehension, for 

 should they prove permanent they invariably depreciate the selling 

 price to a considerable extent. A blind horse is always dangerous in 

 the saddle or in single harness, and he is scarcely less so when, with 

 partially impaired vision, he sees things imperfectly, in a distorted 

 form or in a wrong place, and when he shies or avoids objects which 

 are commonplace or familiar. When we add to this that certain dis- 

 eases of the eyes, like moon blindness, are habitually transmitted 

 from parent to offspring, we can realize still more fully the import- 

 ance of these maladies. Again, as a mere matter of beauty, a sound, 

 full, clear, intelligent eye is something which must always add a high 

 value to our equine friends and servants. 



THE EYEBALL. 



A full description of the structure of the eye is incompatible with 

 our prescribed limits, and yet a short description is absolutely essen- 

 tial to the clear understanding of what is to follow. 



The horse's eye is a spheroidal body, flattened behind, and with 

 its posterior four-fifths inclosed by an opaque, white, strong, fibrous 

 membrane (the sclerotic), on the inner side of which is laid a more 

 delicate friable membrane, consisting mainly of blood vessels and 

 pigment cells (the choroid), and that in its turn is lined by the ex- 

 tremely delicate and sensitive expansion of the nerve of sight (the 

 retina). The anterior fifth of the globe of the eye bulges forward 

 from what would have been the direct line of the sclerotic, and thus 

 forms a segment of a much smaller sphere than is inclosed by the 

 sclerotic. Its walls, too, have in health a perfect translucency from 

 which it has derived the name of transparent cornea. This trans- 

 parent coat is composed, in the main, of fibers with lymph inter- 

 spaces, and it is to the condition of these and their condensation and 

 compression that the translucency is largely due. This may be shown 

 by compressing with the fingers the eye of an ox which has just been 

 killed, when the clear transparent cornea will suddenly become 

 clouded over with a whitish blue opacity, and this will remain until 

 the compression is interrupted. The interior of the eye contains 

 three transparent media for the refraction of the rays of light on 

 their way from the cornea to the visual nerve. Of these media the 

 anterior one (aqueous humor) is liquid, the posterior (vitreous hu- 

 mor) is semi-solid, and the intermediate one (crystalline lens) is 

 solid. The space occupied by the aqueous humor corresponds nearly 

 to the portion of the eye covered by the transparent cornea. It is, 

 however, divided into two chambers, anterior and posterior, by the 

 iris, a contractile curtain with a hole in the center (the pupil), and 

 which may be looked on as in some sense a projection inward of the 

 vascular and pigmentary coat from its anterior margin at the point 



