THE HORSE IN SICKNESS AND DISEASE 287 



usually developed except in the adult horse. Professor 

 Spooner attributes it to a pressure or defect of the great 

 sciatic nerve wl)ich supplies the muscles of the hinder 

 extremities. It is correspondent to chorea, or St. Vitus's 

 dance, in man. There is no treatment available. String- 

 halt has been decided not to be unsoundness ; and we 

 often see instances where this singular spasm is merely 

 momentary at going off, disappears, and the horse has a 

 more than ordinary amount of strength and courage. 



II.— Diseases of the Eye. 



GLASS EYE — SIMPLE OPHTHALMIA — SPECIFIC OPHTHALMIA 

 (moon blindness) — CATARACT — FUNGOID GROWTHS — 

 OBSTRUCTED LACHRYMAL DUCT — WARTS. 



The eye of the horse is exceedingly liable to disease. 

 The " haw " (membrana nictitans), at the inner corner of 

 the eye, is, in health, a thin, slippery membrane, thicker 

 or more cartilaginous towards its base, where it is embedded 

 in fat ; its action is to remove dust, insects, etc., which may 

 have fallen on the cornea. It is no unusual thing for a 

 thickening of this part to take place, and it will then 

 protrude itself on the fore part of the eyeball. In this 

 disease the retractor muscle pulls back the eye to protect it 

 from the irritating effect of the light, and this thickening 

 of the haw pushing it forward, and the adjacent parts being 

 also thickened, no retraction can take place. 



The olden practice of cutting out this is absurd, and ought 

 never to be resorted to. Ignorant farriers have, in this 

 state, taken the enlarged haw for an extraneous excrescence, 

 and cut it out, the eye, consequently, being left unguarded. 

 Bleeding, gentle physic, and cooling applications, will effect 

 a cure. 



GUTTA SERENA. 



This disorder, called by farriers glass eye, from the pecu- 

 liar greenish, glassy appearance it assumes, is dependent 

 on a panxlysis of the optic nerve in its expansion on the 

 retina. This, however, is disputed by some, who consider 

 it to arise from inflammation, by which coagulable lymph 

 is effused over the optic nerve, rendering the retina 



