THE EYE. 41 



veterinary surgeons, who are devoting their lives to 

 such subjects. 



Caution, — Do not mistake the optic nerve which 

 can be seen through the pupil of the horse for a 

 cataract, but which is distinguished by the ' catop- 

 tric test.' 



iVo^e.— The whole retina Fig. 5, D R, receives 

 images except the end of the optic nerve itself. To 

 prove this close your left eye by placing your left 

 hand over it, then hold Fig 5 at arms length and 

 look fixedly at the cross, and you see the black spot 

 as well. Now, still looking at the cross, move it 

 gently towards you and as it approaches your face 

 the black spot for a time ceases to be seen. The 

 distance is generally seven or eight inches from the 

 face. 



