PSEUDOMONAS sERUQINOSA. 311 



note that the chloroform extracts a blue coloring-matter 

 from the culture, leaving the latter more or less yellow. 



Its growth on gelatin in stab-cultures is accompanied 

 by liquefaction and the diffusion of a bright-green color 

 throughout the surrounding unliquefied medium. As 

 liquefaction continues, and the whole of the gelatin 

 ultimately becomes fluid, the green color is confined 

 to the superficial layers in contact with the air. The 

 form taken by the liquefying portion of the gelatin in 

 the earliest stages of development is somewhat that of 

 an irregular slender funnel. (See Fig. 58.) 



On gelatin plates the colonies develop rapidly ; they 

 are not sharply circumscribed, but usually present at 

 first a fringe of delicate filaments about their periphery. 

 (See Fig. 59.) As growth progresses and liquefaction 

 becomes more advanced the central mass of the colony 

 sinks into the liquid, while at the same time there is 

 an extension of the colony laterally. At this stage the 

 colony, when slightly magnified, may present various 

 appearances, the most common being that shown in 

 Fig. 60. 



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. 



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 into blue-green, and finally turns almost black. 



On potato the growth is brownish, dry, and slightly 



