TUBERCULOSIS. 263 



(a) Demonstration of the Bacilli in Sputum (Pus}. For con- 

 venience of observation the sputum is spread upon a black plate 

 or upon a glass dish with a black background (of paper). The 

 well-known yellowish masses (" lentils") are sought for and 

 one of these or some other purulent portion of the sputum is 

 placed, by means of forceps, upon a cover-slip, and spread as 

 uniformly as possible upon its surface. After the cover-slip prep- 

 aration has dried in the air, it is passed, in the usual manner, 

 with the aid of the forceps, three times through the flame ; then 

 a few drops of a freshly prepared aniline-water fuchsin-solution 

 or of a carbol-fuchsin solution are added, and the preparation is 

 heated over the flame until the vapor of steam distinctly escapes. 

 After the lapse of a minute the cover-slip is moved to and fro 



Fig- 57- Tubercle-bacillus in sputum (Fninkel and Pfeiffer). 



for several seconds in dilute nitric acid (from fifteen to twenty 

 per cent.), for purposes of decolorization, and it is then intro- 

 duced into alcohol (seventy per cent.) for the removal of the 

 coloring-matter dissolved by the nitric acid. These two man- 

 ipulations are repeated until the preparation appears scarcely 

 stained. In the preparation everything has now been decolor- 

 ized, and only the tubercle-bacilli, if these be present, have 

 retained the stain. The alcohol is removed with distilled water. 

 In order that the stained tubercle-bacilli may be more sharply 

 differentiated from their surroundings, the preparation is coun- 

 terstained by exposure for a short time to the action of a 

 dilute aqueous solution of methylene-blue or vesuvin. It is then 

 again rinsed with distilled water, and is finally mounted in the 



