ON THE EYE, S5 



light which enters the eye. Vide plate 7 ; letter 

 A represents the eye in an obscure Hght, Let- 

 ter B, in a strong light. The non-enjoyment 

 of this faculty is a certain indication of blind- 

 ness. To examine a horse's eyes properly, he 

 should be placed under a stable door, with his 

 head facing the light. In this situation the pu- 

 pils of both eyes should be exactly of the same 

 dimensions. As he advances more into the 

 light, the pupils should contract ; but if either 

 of them does not contract, the horse is certainly 

 blind of that eye. 



The disease which occasions this species of 

 blindness is termed, in pathology, the Gutta 

 serena, and arises from a palsy in the optic 

 nerve. It is so little perceptible, that few but 

 anatomists can detect it. 



Another cause preventing the impression 



of light on the optic nerve, is more perceptible, 



but equally incurable, viz. an opacity in the 



D 2 surface 



