284 EXPERIMENTAL PHYSIOLOGY. 



LESSON LXIII. 



KUHNE'S ARTIFICIAL EYE MIXING 

 COLOUR SENSATIONS COLOUR- 

 BLINDNESS. 



I. Kiihne's Artificial Eye. (Fig. 137.) 



(a.) Fill the instrument with water, and place it in a 

 darkened room with the cornea directed to a hole in a 

 shutter, through which sunlight is directed by means of a 

 heliostat. If this is not available, use an oxy-hydrogen 

 lamp or electric light to throw parallel rays of light on the 

 cornea. If these cannot be had, use a fan-tailed gas burner, 

 but in this case the illumination and images will be very 

 feeble. To enable one to observe the course of the rays of 

 light, pour some eosin or fluorescin into the water in the 

 instrument. 



(6.) Formation of the image on the retina. Observe the 

 course of the rays of light, which come to a focus behind the 

 lensthe principal posterior focus. Move the ground glass 

 representing the retina, and get a clear inverted image of 

 the source of light. N.B. In this instrument accommoda- 

 tion is effected not by altering the curvature of the lens, as 

 in the normal eye, but by moving the retina. 



(c.) Place convex and concave lenses between the source 

 of light and the cornea; observe how each alters the course of 

 the rays and their focus. 



(d.) After having an image well-focussed upon the retina, 

 move the latter away from the lens, when the image becomes 

 blurred owing to diffusion. If, however, a slip of zinc, with 

 a hole cut in it to act as a diaphragm to cut off some of the 

 marginal rays, be interposed, the image is somewhat im- 

 proved. 



(e.) After seeing that the light is sharply focussed on the 

 retina, remove the lens to imitate cataract and observe 

 that the rays are focussed quite behind the retina. 



