DIFFERENTIAL DIAGNOSIS. 371 



1. Treat the preparation, .stained with carbol-fuchsin, 

 with dilute sulphuric acid; the so-called syphilis bacillus be- 

 comes decolorized, the reaction being almost instantaneous. 



2. If it is not at once decolorized, treat with alcohol ; 

 if it is the smegma bacillus, this will rob it of its color. 



3. If it is still not decolorized, it is either the lepra 

 or tubercle bacillus. 



Grethe recommends 1 the following as a trustworthy 

 means of distinguishing between the tubercle bacillus and 

 the smegma bacillus : stain in hot carbol-fuchsin solution, 

 wash in water, and treat the preparation with a saturated 

 solution of methylene-blue in alcohol. If the question- 

 able organism is the tubercle bacillus, it retains its red 

 color ; if the smegma bacillus, the red color is dissolved 

 by the alcohol and the blue color is substituted for it. 



The differential diagnosis between the tubercle bacil- 

 lus and the lepra bacillus is less satisfactory ; they both 

 take the same stains, and both retain them or give 

 them up under treatment with the same decolorizers. 

 The results of investigations, however, indicate differ- 

 ences in the rate of staining and decolorization, and it is 

 stated by many of those who have compared the two 

 organisms that the lepra bacillus takes up stain very 

 much more readily than does the tubercle bacillus, 

 often staining perfectly after an exposure of only a few 

 minutes to cold watery solutions of the dyes ; but when 

 once stained it retains its color much more tenaciously 

 when acted upon by decolorizing-agents than does the 

 latter organism. 



According to Baumgarten, the lepra bacillus is stained 

 by an exposure of six to seven minutes to a cold, satu- 

 rated watery solution of fuchsin, and retains the stain 

 1 Fortschritte der Medicin, 1896, No. 9. 



