DIFFERENTIAL DIAGNOSIS. 283 



syphilis bacillus becomes almost instantly decolorized 

 by treatment with mineral acids, particularly sulphuric 

 acid, whereas the smegma bacillus resists such treatment 

 for a much longer time, and the lepra and tubercle 

 bacillus for a still longer time. On the other hand, if 

 decolor! zation is practised with alcohol, instead of acids, 

 the smegma bacillus is the first to lose its color. The 

 bacillus tuberculosis and the bacillus of leprosy are con- 

 spicuously retentive of their color even after treatment 

 with both acids and alcohol. 



To differentiate, then, between the four organisms he 

 recommends the following order of procedure, based on 

 the above reactions : 



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

 with sulphuric acid; the syphilis bacillus becomes decol- 

 orized, 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. 



The differential diagnosis between the last two organ- 

 isms is less satisfactory ; they both take on the same 

 stains and both retain them or give them up under 

 treatment with the same decolorizers. The results of 

 investigations, however, indicate differences in the rate 

 of staining and decolorization, and it is accepted by 

 many of those who have compared the two organisms 

 that the lepra bacillus takes up staining very much more 

 readily than does the tubercle bacillus, often staining 

 perfectly by 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. 



