264 



BACTERIA PATHOGENIC TO MAN 



Biology. The typhoid bacillus is a motile, aerobic, facultative anae- 

 robic, non-liquefying bacillus. It develops best at 37 C.; over 40 and 

 below 30 growth is retarded; at 20 it is still moderate; below 10 

 it almost ceases. It grows slightly more abundantly in the presence 

 of oxygen. It does not form spores. 



RESISTANCE. When a number of typhoid bacilli are dried most of 

 them die within a few hours and a few frequently remain alive for 

 months, but sometimes all the bacilli die very quickly. In their 



FIG. 88 



FIG. 



Typhoid bacilli from nutrient agar. 

 X 1100 diameters. 



Typhoid bacilli from nutrient gelatin. 

 X 1100 diameters. 



resistance to heat and cold they behave like the more resistant, non- 

 spore-bearing bacilli. 



Motility. Typhoid bacilli, when living under favorable conditions, 

 are very actively motile, the smaller ones having often an undulating 

 motion, while the larger rods move about rapidly. In different cultures, 

 however, the degree of motility varies. 



FIG. 90 



FIG. 91 



J 



$ 



Flagella, heavily stained, attached to bacilli. 



Typhoid bacillus with stained flagella. 



FLAGELLA. These are often numerous and spring from the sides as 

 well as the ends of the bacilli, but many short rods have but a single 

 terminal flagellum (Figs. 90 and 91). 



