82 



LIGHTING AND FOCUSING 



[CU. II 



backward motion. It is a modification of the mechanical stage of Tolles. 

 The modification consists in doing away with the thin plate and having a 

 clamp to catch the ends of the glass slide. The slide is then moved on the 

 face of the stage proper. This modification was first made by Mayall. It has 

 since been modified by Reichert, Zeiss, Leitz, and others in Europe and by 

 the Bausch & Lomb Optical Co., Qeeen & Co., and the Spencer Lens Co., in 

 America. — Jour. Roy. Micr. Soc, 1885, p. 122. See also Zeit. Wiss. Mikro- 

 skopie (II) 1885, pp. 289-295; 1887 (IV, pp. 25-30). 



Those figured below have the great advantage of ready removal from the 

 stage of the microscope, thus leaving it free. They have also the very excel- 

 lent feature that with them one can explore an entire slide full of- serial sec- 

 tions, as the sections are ordinarily mounted, i.e. , under a cover-glass 24X50 

 mm. 



73 



74 





75 



Figs. 73-75. Specimens Showing the Use of the Marker. 



In Fig. 7_j a section of a series is marked to indicate that this section shows 

 something especially well. In Fig. 7./ some blood corpuscles showing ingested 

 carbon very satisfactorily are surrounded by a minute ring, and in Fig. 75 the 

 lines of a micrometer are ringed to facilitate finding the lines. 



