Fig. 29. 



Young colonies of B. pestis on the surface of an agar plate ; the colonies 

 are thicker and granular in the centre, filmy and slightly irregular at their 

 margin. x 50. 



Fig. 30. 



Characteristic colonies of B. pestis on agar after several weeks' incuba- 

 tion ; the contrast between thickened centre and filmy crenate margin is 

 striking. x 2 J. 



