Staining and Mounting Micro-Organisms 159 



glass, and another cover-glass is placed on it; the two 

 glasses are then to be rubbed together to spread the 

 organisms evenly over their surfaces ; they are then 

 separated and allowed to dry. When bacteria are growing 

 on solid material, scrape off a small portion, put on a cover- 

 glass, and treat as above ; separate the covers, and allow to 

 dry. When the cover is quite dry, take it up with a pair 

 of forceps, organisms uppermost, and pass two or three times 

 through the flame of a spirit-lamp ; this will fix the albumen 

 and fasten the bacteria to the glass. 



To Stain Bacteria on Cover-glasses. — They should be 

 floated with the organisms downwards on a saturated 

 watery solution of any of the following aniline dyes : 

 Methyl blue, methyl violet, gentian violet, fuchsin, vesuvin, 

 or Bismarck brown. From ten to fifteen minutes is enough 

 for the first four stains ; vesuvin and Bismarck brown 

 require about an hour. When the staining is complete 

 wash the cover in distilled water. If the colour is too deep 

 wash it in a \ per cent, solution of acetic acid, and then 

 again in water ; put away to dry. When quite dry add a 

 drop of Canada balsam, and mount on a slide in the usual 

 way. 



When bacteria are present in the organs of animals the 

 tissues should be hardened in methylated spirit for about 

 a week, and very thin sections with a freezing microtome 

 cut from them. The sections may be stained in any of the 

 above dyes ; then wash in water, dehydrate in absolute 

 alcohol, clear in oil of cedar or bergamot, and mount in 

 balsam. 



Staining Bacillus Tuberculosis. 



Ehrlich's Method for Double-staining. — To 100 parts 

 of a saturated watery solution of aniline oil add 11 parts of 

 a saturated alcoholic solution of fuchsin, and filter. Place 

 the covers or sections in the stain in a watch-glass, and 

 warm slowly over a spirit-lamp until vapour rises. Wash 

 in water, and then immerse for about a minute in dilute 



