LABORATORY AND TEACHING METHODS 



6S9 



rectangular frame into which a drawing board is fitted. The fitting is grooved to 

 allow the adjustment of the illuminant L by the lever G, the stage 0, and the objec- 

 tive holder H, the face being graduated to J^ cm. in order that the correct position of 

 the stage O, which varies according to the objective in use (see Table A), can be 

 determined. The same table gives the correct size of diaphragm, five accompanying 

 each outfit, viz.: 12, 18, 24, 32 and 46 mm. diameter. The cover-glass faces the ob- 

 jective when the slide with object is placed in position. The objective carrier H 

 which has a rack and pinion for coarse adjustment and a micrometer screw for fine 

 adjustment occupies a constant position on the fitting B, viz., i cm. from the lower 



Fig. 233. — Ether or rhigoline freezing attachment for freezing microtomS. 



end, but can be removed if necessary. The fine adjustment can be controlled by 

 a long rod similar to that used for the setting of the arc. 



Above the stage two lenses of digerent foci are mounted in a swing-out (iCj, 

 Fig. 234) which has a sliding focussing adjustment and iris diaphragm, and is so 

 contrived that either of the condensers or the diaphragm only can be interposed in 

 the optic axis. The microscope body T can be removed from the fitting M, into which 

 it pushes, and the triple nosepiece is mounted on a sliding attachment, so that it can 

 be interchanged from a similar slide carrying the microsummar lenses. The draw 

 tube should always be set at 152 mm. when working with the nosepiece; otherwise, 

 at 170 mm. Should the apparatus be required for projection the whole optical 



