SUPPURA TION. 263 



The microscope shows the colonies to be round, 

 coarsely-granulated masses with notched or filamentous 

 borders. They have a yellow-green color. Upon the 

 surface they form a deli- _ 



cate clump with a smooth r ' 



surface, finely granular, dis- .T^\ 



tinctly green in the middle &h. 

 and pale at the edges. The 

 colonies sink into the gel- 

 atin as the liquefaction \ 

 progresses. £<> 





•> 







-y-j 



Fig. 58. — Bacillus pyocyaneus: colonies upon gelatin (Abbott). 



In gelatin puncture-cultures most of the development 

 occurs at the upper part of the tube, where a deep saucer 

 of liquefaction forms. The growth slowly descends into 

 the medium, and is the point of origin of a beautiful 

 fluorescence. The bacterial growth sinks to the bottom 

 as it ages. At times a delicate mycoderma forms on the 

 surface. 



Upon agar- agar the growth is at first bright green, 

 developing all along the line of inoculation. The green 

 pigment (fluorescin) is soluble, and soon saturates the cul- 

 ture-medium and makes it very characteristic. As the 

 culture ages, or if the medium upon which it grows 

 contains much peptone, a second pigment (pyocyanin) is 

 developed, and the bright green fades to a deep blue- 

 green, dark-blue, or in some few cases to a deep reddish- 

 brown. 



A well-known feature of the growth upon fresh agar- 

 agar, upon which much stress has recently been laid by 

 Martin is the formation of crystals in fresh cultures. 

 Crystal-formation in cultures of other bacteria usually 

 takes place in old, partially dried agar-agar cultures. The 

 bacillus pyocyaneus, however, produces crystals in a few 



