Special Methods 



133 



will give good results. A solution recommended by Bensley is good 

 also for plant material. 



Bensley's Solution.- 



Osmic acid 2 per cent 1 part 



Corrosive sublimate (HgCl 2 ) 2^ per cent 4 parts 



Add one drop of glacial acetic acid to 10 c.c. of this solution. 

 Fix for 24 to 48 hours and wash thoroughly in water. On the slide, 

 bleach with hydrogen peroxide; wash in water; treat with the iodine 





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pa^^ 







FIG. 24. Cells from the periblem of the root-tip of Allium cepa: A, mltochrondria ; 

 B, canaliculi; fixed in Bensley's solutions and stained in iron-alum haematoxylin. X1200. 



solution used in testing for starch; then wash in water. The slide 

 is now ready for staining. We recommend the usual Haidenhain's 

 iron-alum haematoxylin. 



Bensley recommends the following method which we have found 

 rather uncertain, but which, when successful, yields magnificent 

 preparations: On the slide, bleach for 2 or 3 seconds in a 1 per cent 

 aqueous solution of permanganate of potash; then treat with a 

 5 per cent aqueous solution of oxalic acid until the preparation 

 becomes white (a few seconds); wash in water, and then stain as 

 follows : 



1. Copper acetate (neutral) saturated solution in water, 5 to 10 minutes. 



2. Wash in water. 



3. ^ per cent haematoxylin, 5 to 10 minutes. 



4. Wash in water. 



5. Potassium bichromate (neutral) 5 per cent solution in water until the 

 preparation blackens, usually 30 seconds or less. 



