ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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reagents used upon it, without fear of damaging it in any way. The 
mirrors are very large, 68 mm. in diameter, plane and concave. The 
usual somewhat cumbersome methods of securing black or white^back- 
grounds are superseded in this stand by a plate, black on one side, 
white on the other, hinged to the stage frame, just beneath the front left- 
hand corner, by means of an arm of the proper length to bring the plate 
(black or white side up as required) directly in contact with the lower 
surface of the stage, or permitting it to be carried outward, beneath and 
against the hand -rests. When transmitted white light is wanted, the 
arm of the plate is brought to the vertical position and the white side 
of the plate used as a reflector, as this arrangement of the plate does not 
Fig. 51 . 
in any way interfere with the illumination or the use of the camera 
lucida. 
The lenses are focussed by means of diagonal rack-and-pinion of 
extremely long range, acting on a triangular rod. The working distance 
may be increased to 125 mm. by means of a second rod attached to the 
arm and adjustable in the main focussing rod. 
Bausch and Lomb’s New Complete Substage. — Figs. 53 and 54 
show the substage closed and separated. It has been especially designed 
to afford greater stability and convenience than are usually attained. 
The entire substage is supported on a heavy metal bar joined to the 
main arm of the Microscope, and to which it is attached by slide with 
rack-and-pinion, whereby the whole substage may be adjusted with 
reference to the Microscope stage. The substage is composed of three 
Q 2 
