64 



MICROSCOPY OF THE LIVING EYE 



D.I.S.R. : Direct illumination with observation along the axis 



of specular reflection. 

 P.I. : Proximal illumination. 

 S.S. : Sclerotic scatter. 

 R.I. : Retroillumination. 

 Retroillumination has already been referred to (Figs. 5, 6 and 7), 



Fig. 33. 



Fig. 34. 



Figs. 33 and 34. — " Sclerotic scatter." 



and it remains only to add a few remarks about it. It not being- 

 possible to use a primary source of light for retroillumination of 

 the living human eye (as could be done for the study of zoological 

 tissue specimens), resource can be had only to a patch of light 

 directed on to a demarcating surface (Figs. 41 and 45B) or to the 

 visible passage of a beam of light directed through relucent tissue 

 behind the feature under observation, e.g., a small vacuole in the 

 anterior lens-cortex (Fig. 35) is readily seen against a small visible 



