LEPROSY BACILLUS. 315 
culosis and the bacillus of leprosy are both very retentive 
of their color, even after treatment with acids and 
alcohol. If, then, we treat the preparation, stained with 
earbolfuchsin, with sulphuric acid, the syphilis bacillus 
becomes almost at once decolorized. If it is not imme- 
diately decolorized, treat with alcohol; if it is then 
decolorized, it is the smegma bacillus. If it is still 
not decolorized, it is either the leprosy or the tubercle 
bacillus. 
By these methods the differential diagnosis can usually 
be made. Inall investigations of importance, however, 
animal inoculations should also be made, as by this 
means alone can a positive diagnosis from tuberculosis 
be established. Especial care should be observed in 
the examination of syphilitic ulcers of the genital re- 
gion, as in this situation the smegma bacilli are almost 
always present. 
LEPROSY BACILLUS. 
The bacillus of leprosy was discovered by Hansen 
and Neisser (1879) in the leprous tubercles of persons 
afflicted with the disease. This discovery was confirmed 
by many subsequent observers. 
Morphology. Small, slender rods resembling the 
tubercle bacilli in form, but somewhat shorter and 
not so frequently curved. The rods have pointed ends, 
and in stained preparations unstained spaces, similar to 
those observed in the tubercle bacillus, are seen. They 
stain readily with the aniline colors and also by Gram’s 
method. Although differing from the tubercle bacillus 
in the ease with which they take up the ordinary aniline 
dyes, they behave like tubercle bacilli in retaining their 
