X STUDIES IN ADVANCED PHYSIOLOGY. 



tion, optic nerves, microscopic structure of the retina). The 

 eye as a purely physical instrument. The normal or emme- 

 tropic eye (myopia, hypermetropia, astigmatism, cataract, 

 spherical aberration, chromatic aberration, muscae-voUtan- 

 tes, presbyopia) . The manipulation of the eye as an opti- 

 cal instrument. How do we focus the eye? The dioptrics 

 of the eye. The luminosity of eyes. The physiology of 

 color sensation. Color blindness. The Young-Helmholtz 

 theory. Normal or trichromatic eyes. The Hering theory. 

 After-images. Explanation of negative after-images. 

 Double vision. The advantages of two eyes. Optical illu- 

 sions . . 529 



