ORDINARY STAINING-SOLUTIONS 177 



of this mordant should be of a reddish-brown hue, not clear, 

 but somewhat cloudy, and this mordant must be used within 

 five hours after it is made. After that time it loses its fixing 

 power. This is indicated by its gradual clarification and 

 darkened color. It gives the best results when strictly 

 fresh, and accomplishes its work in a much shorter time, so 

 that very little if any heating is required when it is placed 

 on the cover-glass preparation. 



The Stain. To prepare the dye for this method take 

 about 1 gram of ordinary granulated fuchsin, put it in a 

 bottle, and pour over it about 25 c.c. of warm, absolute 

 alcohol. Shake vigorously and let it stand for several 

 hours before using. The carbol-fuchsin is made by diluting 

 the saturated alcoholic solution four or five times with a 

 5 per cent, solution of carbolic acid. Carbol-fuchsin should 

 be freshly made, heated, and filtered before using. 



The application of this method of demonstrating the 

 flagella varies with different organisms with regard to the 

 length of time the mordant and stain are allowed to act, 

 and the amount of sodium hydroxide solution used. Usually, 

 it is well to heat the mordant on the cover-slip to steaming, 

 and allow it to act from one-half to one minute. It is then 

 washed off with water and a small quantity of alcohol 

 poured over the surface and washed off instantly. The 

 water on the cover-slip is now absorbed from the edge of 

 the cover-slip with clean filter-paper. The carbol-fuchsin 

 stain is now applied and heated just enough to generate a 

 thin vapor. The stain should not act for more than from 

 one-half to one minute. The cover-slip is now dried, then 

 xylol is poured over the surface, the excess being removed 

 with filter-paper. The cover-slip is now mounted in xylol 

 balsam. 

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