PATHOGENIC BACTERIA 



that have an alkaline or neutral reaction. They are facul- 

 tative anaerobic. 



Colonies, Gelatin. After twenty-four hours, small white 

 points which gradually come to the surface, the gelatin being 

 slowly liquefied, a funnel-shaped cavity formed, holding the 

 colony in its narrow part, at the bottom, and on the fifth day 

 all the gelatin is liquid. If the colonies of three days' growth 

 are placed under microscope, they appear as if composed of 

 small bits of frosted glass with sharp irregular points. 



Stab-culture. After thirty hours a growth can be distin- 

 guished along the needle-track, and on the surface a little 

 cavity is formed, filled by a bubble of air, and this liquefaction 

 proceeds until, on the sixth day, it has reached the sides of 

 the tube, tapering, funnel-shaped, to the bottom of the tube. 

 After several weeks the 

 spirilla are found in little 

 collections at the bottom 

 of the fluid gelatin. In 

 eight weeks the bacilli 

 have perished. 



Agar. Stroke cultures. 

 A shiny white layer which 

 lasts many months. 



Potato. A yellow, 

 honey-like, transparent 

 layer, if the potato is 

 kept at animal heat. 



Bouillon. A wrinkled 

 scum is soon formed in 

 bouillon. The spirilla live 

 well and grow in sterilized 

 milk and sterilized water, 



Fig. 72. Cholera colonies after thirty hours 

 (X 100) (Frankel and Pfeiffer). 



remaining virulent in the latter for many months. In ordi- 

 nary water the bacteria present are destructive to the comma 

 bacilli, and they die in a few days. 



Dunham's Peptone Solution. Useful for the development of 

 nitrites and the indol reaction. 



