BACILLUS TYPHOSUS 



209 



FIG. 29. Typhoid Bacilli. 



often more slender (Fig. 29). When growing under favorable 

 conditions they are actively motile ; in hanging drop preparations 

 made from young cultures the short forms move rapidly with a 

 darting movement, while the 

 attached, thread-like forms 

 have a slower and more un- 

 dulating motion. They pos- 

 sess twelve or more peritrichic 

 flagella, which are longer and 

 more wavy than those of the 

 colon bacillus (Fig. 30). With 

 the ordinary anilin dyes they 

 stain rather slowly, they are 

 Gram negative, and do not 

 form spores. 



Cultivation. The typhoid 

 bacillus is aerobic and facultative anaerobic. Its optimum tem- 

 perature is about 37 C. On culture media growth does not take 

 place below 9 C. or above 42 C. In a gelatin stab there is a 



fine white growth along the 

 line of inoculation. The main 

 growth, however, is on the sur- 

 face, which spreads outwards 

 toward the sides of the tube as 

 a thin leaf-like film. On agar 

 colonies appear in twenty-four 

 hours as thin disks, white or 

 bluish gray in color, and with 

 slightly scalloped margins. 

 Broth is uniformly clouded. 

 Occasionally a thin film forms 

 on the surface after eighteen 

 to twenty-four hours' growth. 

 The tests with sugars furnish a means of differentiating the 

 typhoid bacillus from other members of the colon-typhoid group. 

 The typhoid bacillus produces acid without gas in maltose, glu- 



FIQ. 30. Typhoid Bacilli, showing 

 Flagella. 



