568 



PATHOGENIC MICROORGANISMS 



Later the bacilli sink to the bottom of the flat depression, leaving a clea* 

 supernatant fluid of peptonized gelatin. 



In broth, growth takes place rapidly, but does not lead to an even, 

 general clouding. There is usually an initial pellicle formation at the 

 top where the oxygen supply is greatest. Simultaneously with this a 

 slimy mass appears at the bottom of the tube, owing to the sinking of 



FIG. 124. ANTHRAX COLONY ON AGAR. 



bacilli to the bottom. Apart from isolated flakes and threads the inter- 

 vening broth is clear. Shaken up, the tube shows a tough, stringy mass, 

 not unlike a small cotton fluff, and general clouding is produced only 

 by vigorous mixing. . 



Upon agar plates, growth at 37.5 C. is vigorous and colonies appear 



