TUBERCLE BACILLUS. 85 



the contrast-stain being added to the decolorizing agent. The 

 smear is stained with ZiehPs solution as before, after which 

 it is immersed for a few minutes in Gabbett's solution : 



Methylene-blue, 2 grams; 



Sulphuric acid (25 per cent. 



aqueous solution), 100 c.c. 



Wash in water, dry, and mount in balsam. The tubercle 

 bacillus is stained a bright red, everything else is stained blue. 

 The objection to this method is that it is impossible to deter- 

 mine, without removing the specimen from the stain and 

 washing, just when decolorization is complete. The acid 

 and the methylene-blue may be used separately. 



Ziehl-Neelson method: The cover-glass is floated on the 

 carbol-fuchsin solution, film side down, for from three to five 

 minutes, or until it commences to steam ; or the stain is heated 

 first and then poured over the film and allowed to act for a 

 few minutes. Decolorize in 25 per cent, nitric acid or sul- 

 phuric acid until the film is a very light brown or yellow. 

 AYash in 60 per cent, alcohol for a few minutes, then water ; 

 mount in balsam after drying. A contrast-stain may be used 

 if desired. 



Ehrlich method : Float or immerse the cover-glass in anilin- 

 water gentian-violet and place it in the incubator for 

 twenty-four hours. Wash in water, and alternately in 33 per 

 cent, nitric acid and 60 per cent, alcohol until the color has 

 almost entirely disappeared. After a final washing in the 

 alcohol, wash in water and counter-stain with vesuvin or 

 Bismarck-brown. Methylene-blue may also be used. Wash 

 in water, dry, and mount in balsam. The tubercle bacilli are 

 stained a dark blue, and the other bacteria and the tissue-cells 

 are colored brown. 



Dorset method : Dorset found that Soudan III. has a se- 

 lective action on the tubercle bacillus because of the large 

 proportion of fat (40 per cent.) contained in the bacillus. 

 Immerse the film for ten minutes in a cold saturated 80 per 

 cent, alcoholic solution of Soudan III. Remove the excess 

 of stain with successive washings of 70 per cent, alcohol. 



