PATHOGENIC BACTERIA. 261 



a blue or green color, especially in transparent media. This 

 color is not coniined to the growth itself, but a blue or green 

 fluorescence spreads over the whole medium. In an old agar 

 culture the color may become very dark. The pigment forms 

 in the presence of oxygen, and is due, at least in part, to the 

 ptomaine, pyocyanin. On potato the growth is usually brown; 

 the surrounding medium may be tinged with green. Millc 

 is coagulated and peptonized and an acid reaction is developed. 



V'f '.. . 0^*' 



! 



/ 





t . 



! 







\ 



/ 



/ 



Fig. 70. — Bacillus pyocyaneus, Pure Culture. (X 1000.) 



Indol is formed in Dunham's peptone solution. Coagulated 

 blood-serum is hquefied. 



The BaciUus pyocyaneus seems to be rather widely dis- 

 tributed in nature; it has been found on the skin, in nor- 

 mal feces, also in diarrheal discharges and in dysentery. It 

 is the cause of the color in blue or green pus. It has fre- 

 quently been demonstrated in pus, but oftenest perhaps, in 

 mixed infections. It has been found in various abscesses, in 

 otitis media, peritonitis, appendicitis and bronchopneu- 



