OUR BEST FEATURES 



features. We know that it is essentially like a 

 camera, with its dark chamber (the inside of the 

 eyeball), its lens, its sensitive plate (retina), its 

 iris-diaphragm for regulating the amount of light 

 admitted through the pupil. We know also that 

 it differs from an ordinary camera in altering the 

 focus not by regulating the distance between the 

 lens and the plate but by changing the curvature 

 of the elastic lens through the pull of the ciliary 

 muscles. We also know that the human eye 

 differs from a single camera in being linked with its 

 fellow of the opposite side so as to provide for 

 a binocular, stereoscopic mental image and that the 

 two eyes are biconjugate, that is, by means of its 

 six eye muscles (Fig. 98), each eye can move in 

 harmony with its fellow so as to keep a moving 

 object in focus; also that the eye is a living 

 mechanism provided with elaborate systems for 

 the elimination of waste, for automatic renewal 

 of all parts and for the lubrication, cleaning and 

 protection of its exposed surface. 



The retina carries a coloring matter named 

 rhodopsin or visual purple, ' which becomes rapidly 

 bleached on exposure to sunlight. No doubt the 



' Cunningham, D. J., 1902, Textbook of Anatomy, p. 689. 



189 



