ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 347 



thin enough, it is finished oil on the glass plate with the fine carborun- 

 dum, and polished on the No. emery cloth. It is advisable to examine 

 the section under the microscope at this stage to see if it is thin enough, 

 using the polariscope with Nicol prisms crossed. The felspars should then 

 show a grey colour, and the quartz should show no colour above pale 

 yellow. You may not be able to get these colours at first, but do not 

 worry. It is better to leave the section somewhat thick and have a slide 

 of some sort, rather than to try to get it thinner and spoil it. Making 

 good sections is only a matter of practice. After the section is thin 

 enough it is removed from the glass by soaking in methylated spirit if 

 it is cemented with balsam, or in water if cemented with gum. It is 

 then mounted in balsam and benzol in the usual way. Be sure to label 

 the bits of rock carefully during the whole of the operations, or you will 

 find sooner or later that your specimens are hopelessly mixed." 



(4) staining and Injectine:. 



Microscopic Staining with Copying-ink Pencil.* — At a recent 

 meeting of the Zurich Medical Society, Louis E. Merian called attention 

 to the convenience of using coloured pencils in staining microscopical 

 preparations. The idea was suggested to him by a paper of E. Fried- 

 berger in the Military Supplement of the " Miinch. med. Wochenscl r." 

 of Nov. 21 last. Friedberger has invented a universal pencil for 

 staining pus and blood films as well as gonococci, trypanosomes, spiro- 

 cha3tes, and malaria parasites, and he proposes to bring out a Giemsa 

 and a carbol-fuchin pencil after the war. The method of staining 

 suggested was very simple. After fixing, a drop or two of water was 

 placed on the slide, and the coloured pencil rubbed in the water until 

 the required depth of colour was attained. The preparation was then 

 rinsed and dried in the usual way. It occurred to Merian that the 

 ordinary indelible pencil obtainable for Id. (they now cost 4d.) might 

 serve the same purpose. The result proved satisfactory for white and 

 red blood corpuscles, gonococci, and spirochaetes. Of the various makes 

 of indelible pencil obtainable in Switzerland Merian found "A. W. Faber 

 Radium 5800 " the most suitable, while Faber's " Castell," Hardmuth's 

 " Mephisto 73 B. middle," and Rehbach's " Defregger " were also good. 

 Merian claims a special handiness and cleanliness for this method as well 

 as the convenience of carrying the pencil anywhere in the pocket. The 

 stain keeps indefinitely and does not deteriorate as stains do in solution. 

 We have used this method in emergency, finding it to work well for pus, 

 blood and cultures. The drop of water should be placed by the side of 

 the film, the indelible pencil rubbed well into it, and the coloured drop 

 then led over the preparation. 



Improved Technique for Showing Details of Dividing Cells.! 

 Allen offers some suggestions for demonstrating the details of mitosis 



* Lancet, May 12, 1917, p. 714. 



t Anat. Rec, July, 1916, through Traus. Amer. Micr. Soc, xxxv. (1916) 

 pp. 192-3. 



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