BACILLUS PYOCYANEUS. 



267 



is developing. With time this color becomes much 

 darker, and in very old agar-agar cultures may become 

 almost black (sometimes very dark-blue green, at others 

 brownish-black). 



FIG. 57. 



FIG. 58. 



Colony of b. pyocyaneus after twenty-four 

 hours on gelatin at 20-22 C. 



FIG. 59. 



Stab-culture of b. 

 pyocyaneus in gel- 

 atin after twenty- 

 eight hours at 22 C. 



Colony of b. pyocyaneus after forty-two hours 

 on gelatin at 20-22 C. 



Its growth on gelatin in stab-cultures is accompanied 

 by liquefaction and the diffusion of a bright-green color 

 throughout the unliquefied medium. As liquefaction 

 continues, and the entire gelatin ultimately becomes 

 fluid, the green color is confined to the superficial layers 

 that are in contact with the air. The form taken by the 

 liquefying portion of the gelatin in the earliest stages of 



