THE BACILLUS PYOCYANUS. 233 



tered together in irregular masses. It does not form 

 long filaments, there being rarely more than four joined 

 together end to end, and most frequently not even two. 



It grows readily on all artificial media, and gives to 

 some of them a bright-green color, that is most con- 

 spicuous where it is in contact with the air. This green 

 color is not seen in the growth itself to any extent, but 

 is diffused through the medium on which the organism 

 is developing. With time this color becomes much 

 darker, and in very old agar cultures may become 

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

 brownish-black). 



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 development is somewhat that of an 

 irregular, slender funnel. (See Fig. 48.) 



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. 49) ; as growth progresses and liquefaction be- 

 comes more advanced the central mass of the colony 

 sinks into the liquefied depression, while at the same 

 time there is an extension of the colony laterally. At 

 this stage the colony, when slightly magnified, may pre- 

 sent various appearances, the most common being that 

 shown in Fig. 50. 



The gelatin between the growing colonies takes on a 

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



