42 



MICROSCOPY OF THE LIVING EYE 



a rectangular aperture in the centre (Fig. 10). It is necessary for 

 proper adjustment of the apparatus that the lamp filament should 

 be correctly focused, and set (in respect of " twist "), and centred 

 (by the screws a, a, a), and finally locked (by the screw L), so that 

 the image of the filament is in focus on the diaphragm-plate of the 

 lens FL, and vertically set, and centred on the aperture in this 



Fig. 9. — Zeiss Model of the Gullstrand Slit-Lamp and Czapski 



Binocular Microscope. 



plate, as in E, Fig. 10, in which A, B, C and D represent errors of ad- 

 justment in one or other of these respects. The slit-lamp is mounted 

 on a jointed swivel-arm, R (Fig. 9), which provides for variable 

 direction and for coarse adjustment of the focusing of the beam 

 on to the eye under observation, the final and fine adjustment of 

 the focusing being accomplished by the screw X (Figs. 8 and 9). 

 I like the means of coarse adjustment of focusing provided in the 

 Bausch and Lomb slit-lamp, viz., by mounting the arm B in 

 runners so that its optical length can be varied at will. It may 



