2,86 MANUAL OF BACTERIOLQGY. 



Bacillus tuberculosis. — A slim bacillus 1.5 to 4 /-< in length, 

 which very frequently presents a beaded appearance, owing 

 to its being dotted with bright, shining spots. Branching 

 forms have been described. The tubercle bacillus is con- 

 sidered by some to be a member of the actinomyces group. 

 It is.not motile. It has not been proved that spores are formed ; 

 nevertheless certain structures, like caseous lymph-nodes, have 

 been shown to be capable of infecting guinea-pigs with tuber- 

 culosis, although tubercle baciUi could not be demonstrated 



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Fig. 85. — Bacillus tuberculosis, from a Pure Culture. Mix looo.) 



in them with the microscope. This makes it seem possible 

 that the organisms were present as spores which eluded the 

 microscopical examination. The tubercle baciUi stain with 

 the ordinary aniline dyes and by Gram's method, but they do 

 not take the stains as readily as most other bacteria, and require 

 prolonged exposure to the dye, on warming of the stain. When 

 once stained, however, with aniline-water dyes or carbol- 

 fuchsin, they are not readily decolorized by acids and alcohol, 

 which fact distinguishes them from all other known bacteria 



