THE PREPARATION MICROSCOPE. 



207 



tion, the objective can be used alone as a lens, the eye-piece, 

 together with the tube, being unscrewed. The three lenses of the 

 objective can also be unscrewed from one another, and the upper 

 lens alone can be used, the two upper, or the three simultaneously. 

 Magnification of 10, 20 and 30 diameters can be thus obtained. 

 The adjustment is completed by turning the screw-head (sr). 



St 



ot 



FIG. 80. Small dissecting microscope of Zeiss, on foot, two-thirds natural size. 

 ot, stage ; d, lens, sheathing toothed support for lens-arm ; sr, screw for fine adjust- 

 ment ; s, mirror ; p, wooden supports for hands in dissecting, etc. 



On both sides of the stage (ot) " wings " (p} are fixed, to serve 

 as hand supports in dissection. 1 



1 Many excellent simple microscopes exist suitable for dissection and 

 other purposes, and some are referred to in the Introduction. Essentially 

 each consists of a pillar suspending a mirror, the stage, and an arm to carry 

 the lenses, this arm being movable, preferably by rackwork. It is also of 

 the utmost value that the wrists should be supported to steady the hands in 

 their movements, but this can be effected by loose blocks of wood, etc. An 

 instrument satisfying the requirements of even more than a beginner ought 

 not to cost more than about 30s. 



Many simple dissections and other manipulations can however be per- 

 fectly well performed by placing the micro-slide, etc., on a suitable back- 



