164 DENITRIFICATION 



occur, the latter 1.4 to 2.3 ju. long, .4 to 5 p thick, often many 

 together in zoogloea. 



Gelatine. Not liquefied. Surface colonies slightly raised, 

 whitish, smooth at first, later puckered, and 2 to 3 mm. in diameter; 

 deep colonies, small (r to 2 mm.), bluish- white, blackberry form, 

 with opaque yellowish brown centre. 



Agar, Surface colonies, rounded in forty-eight hours at 35 C, 

 i to 2 mm. diameter, centre milk-white, with whitish cleaner space 

 round. 



Potato. At 35 C. in two to three days, a yellowish brown, 

 slightly raised, growth not spreading much. 



Nitrate Bouillon (3 per cent.). In twelve hours turbid; in 

 twenty-four to thirty-six hours much froth, with complete deni- 

 trification and little sediment; remains turbid after frothing 

 ceases. Differs from the preceding in form of deep colony, 

 more uniform staining, want of sliminess, and abundant frothing 

 in nitrate bouillon. 



Bacillus (Proteus) denitrificans,H6flich. An aerobic "proteus- 

 like " bacterium, isolated from horse and cow dung, straw and 

 soil. In bouillon the organisms are motile, 5 to 10 ^ long and 

 .3 to .4 /A thick; they grow into long threads (100 //. long or 

 more), which often break up in three or four days into rods, 

 vibrio, and even coccus forms, all without spores. 



Gelatine. Not liquefied ; the surface colonies are round or 

 irregular at first, and gradually extend over 2 to 3 sq. cm. of 

 surface as a filmy growth, bluish-white and semi-transparent. 

 Deep colonies are whitish, and remain small. Stab a delicate 

 whitish line of very small colonies. 



Agar. In twenty hours, at 35 C., the surface colonies 

 are bluish-white, transparent, very thin, i cm. in diameter. 

 They spread very rapidly, and cover the plate in about two 

 days. 



Potato. No visible growth. 



Nitrate Bouillon (3 per cent.). In twenty hours, at 35 C., 

 diffuse turbidity with denitrification and formation of froth and 



