Etiology Morphology Staining 399 



Etiology. The cause of leprosy is without doubt the 

 lepra bacillus, discovered by Hansen in 1879, and subse- 

 quently clearly described by Neisser. 



Though the lepra bacillus has certain features as its 

 resistance to acids in common with the tubercle bacillus, 

 there is not the slightest evidence of any real identity. 



Morphology. The bacillus is about the same size as 

 the tubercle bacillus perhaps a little shorter and stouter 

 and lacks the slight curve of the latter. Its protoplasm 

 commonly presents open spaces or fractures, giving it a 



Fig. 115- Lepra bacilli. Smear from a lepra node stained with carbol- 

 fuchsin (Kolle and Wassermann). 



beaded appearance, like the tubercle bacillus. The organ- 

 ism occurs singly or in irregular groups. There is no 

 characteristic grouping and filaments are unknown. The 

 bacillus is not motile and has no flagella and no spores. 



Staining. It stains in very much the same way -as the 

 tubercle bacillus, but permits of a more ready penetra- 

 tion of the stain, so that the ordinary aqueous solutions 

 of the anilin dyes color it quite readily. The property of 

 retaining the color in the presence of the mineral acids also 

 characterizes the lepra bacillus, and the methods of Ehrlich, 

 Gabbet, and Unna, for staining the tubercle bacillus, can 

 be used for its detection. It stains well by Gram's method 

 and by Weigert's modification of it, by which beautiful 

 tissue specimens can be prepared. 



