GENUS BACTERIUM 247 



also an organism resembling somewhat the tubercle that is 

 parasitic for cattle, producing a very chronic catarrhal con- 

 dition of the intestines (Johne's disease). It invades the- 

 intestines and is found in the tissues immediately beneath the 

 mucous membrane. - v 



Morphology. Bacterium tuberculosis appears as a slender \ 

 rod 1.5 to 4.0 /* in length and from 0.2 to 0.5 /* in width. The 

 ends are usually rounded. The organisms may be straight 

 slightly curved. As a rule, the curve is more pronounced 



the human variety. The di- 

 ameters are quite uniform 

 throughout. In the human 



/ variety, especially as found 



/ in tuberculous sputum, they 



are quite frequently beaded 

 and stain somewhat irregu- 

 larly. The unstained areas 

 are regarded as vacuoles. 

 The bovine variety is slightly- 

 shorter than the one from 



Fig. 56. Photograph from a man ft i s usually from 1.5- 

 preparation of tuberculous milk , ,, * , ,. 



. . to 3 u in lensrth and trom 



showing tubercle bacteria in the 



center x 500 0.3 to 0.8 ju in thickness- 



wheii found in the tissues, 



milk or feces. They do not so frequently present irregu- 

 larly stained areas. A number of observers have demon- 

 strated branched forms of this organism. 6 



Staining. The tubercle bacterium does not stain readily 

 with the ordinary aniline dyes. Once stained, however, the- 

 dye is retained, even after the application of alcohol and acids. 

 It is for this reason that they are often spoken of as "acid 

 fast" or "acid proof" bacteria. This property seems to 

 depend upon the presence of fatty substances contained in 

 the organism. 7 The dyes that have been used successfully to- 



6 Nocard and Roux. Annales de 1'Inst. Pasteur, 1887. 

 Mafucci. Zeitschrift f. Hygiene, Bd. '. \ 



7 Bienstock. Fort. d. Med., 1886. 



