250 



BACTERIOLOGY. 



sent various appearances, the most common being that 

 shown in Fig. 54. 



The gelatin between the growing colonies takes on a 

 bright yellowish-green color, but as growth is compar- 

 atively rapid, it is quickly entirely liquefied, and one 

 often sees the colonies floating about in the pale-green 

 fluid. 



FIG. 52. 



FIG. 53. 



Colony of b. pyocyanus after twenty-four 

 hours on gelatin at 20-22 C. 



FIG. 54. 





Stab culture of b. 

 pyocyanus in gel- 

 atin after twenty- 

 eight hours at 22 C. 



Colony of b. pyocyanus after forty-two hours 

 on gelatin at 20-22 C. 



On agar-agar the growth is dry, sometimes with a 

 slight metallic lustre, and is of a whitish or greenish- 

 white color, while the surrounding agar-agar is bright 

 green. With time this bright green becomes darker, 

 passing to blue-green, and finally turns almost black. 



