Stains and Staining 53 



lignified walls begin to fade. If staining mitotic figures, draw 

 the stain from the spindle, but stop before the chromosomes begin 

 to weaken. When the desired differentiation has been reached, wash 

 out the acid in 50 per cent alcohol, if acid has been used. About 5 

 minutes should be sufficient. 



If safranin is to be used alone, pass through 50, 70, 85, 95, and 

 100 per cent alcohol, through the xylol-alcohol, then through xylol 

 to balsam. If clove oil is used, omit the xylol-alcohol, but follow 

 the clove oil with xylol to hasten the hardening of the preparation. 



If a second stain is to be added, transfer from the 50 per cent 

 alcohol to any alcohol stain. If the second stain is an aqueous 

 stain, rinse the slide or sections for a minute in water before applying 

 the stain. 



Safranin is the most generally useful of all the red stains, and, 

 fortunately, it is quite durable. Lignified, suberized, cutinized, and 

 chitinized structures stain red, as do also the chromosomes, nucleoli, 

 and centrosomes. 



Acid Fuchsin. Use a 1 per cent solution in water or in 70 per cent 

 alcohol. The solution in alcohol is preferable if sections are to be 

 mounted in balsam. This stain often acts with great rapidity, 

 2 or 3 minutes being sufficient. The method for using acid 

 fuchsin with woody tissues is given in the chapter on "Freehand 

 Sections" (chap. vi). In staining embryo-sacs, pollen grains, and 

 such structures, longer periods are better. Stain 1 or 2 hours, 

 and then differentiate in a saturated solution of picric acid in 70 

 per cent alcohol. This may require 30 seconds, or even several 

 minutes. Rinse in 70 per cent alcohol until a bright red replaces the 

 yellowish color due to the acid, and then proceed as usual. 



Congo Red.- -This is an acid stain resembling acid fuchsin. 

 For cytological work use a \ per cent aqueous solution; for 

 anatomical work use a saturated solution. It is a good stain to use 

 after malachite green or anilin blue. Transfer to the Congo red 

 from water, stain 15 minutes, wash in water, transfer for wood 

 sections to 85 per cent alcohol, and wash until the green or blue color 

 of the previous stain begins to show through the red. Then treat 

 quickly with absolute alcohol, clear in xylol, and mount in balsam. 



