160 DENITRIFICATION 



in it contained as much as 80 per cent, of nitrous 

 oxide. 



Many denitrifying bacteria, such as the forms examined 

 by Gayon and Dupetit, Warington, Giltay, and Aberson, 

 are insufficiently known to warrant inclusion here ; the 

 chief of the forms capable of setting free nitrogen 

 which have been isolated and accurately described are 

 mentioned below : 



Bact. Stutzeri, L. and N. (Bact. denitrificans II. , Burri and 

 Stutzer). A feebly motile organism isolated from straw, soil, 

 and the air ; grows best with small supply of oxygen. Generally 

 rods with rounded ends and non-motile, grown on agar, 1.5 to 

 2.5 & long, 0.5 to i ^ thick. Sometimes spindle shaped. 

 In nitrate bouillon the rods are thinner (.25 to .3 /a, in 

 thickness). Stains more at poles than in middle, except in 

 very young cultures. 



Gelatine. Not liquefied. Surface colonies dull white, i to 

 2 mm. diameter, with characteristic radial rib-like markings 

 and raised rims : deep colonies are small, white, round or 

 spindle form with ragged edge. Stab beaded, white, slimy after 

 a time. 



Agar. Surface colonies somewhat similar to those of gelatine 

 at first ; later they become flatter and less distinct in character. 



Potato. Growth ribbed ; pale flesh colour on potato feebly 

 alkalinized with .05 per cent, sodium carbonate. 



Nitrate bouillon (.3 per cent.). Demtrification in one to two 

 days or less, with abundant frothing and sediment. 



Bact. denitrificans, L. and N. (Bac. denitrificans /., Burri and 

 Stutzer). An aerobic species obtained from horse dung, straw, 

 and soil. On agar 1.5 to 2.5 p long, .75 ft thick; in bouillon 

 2 to 3 //, long. Rods mostly non-motile, stains uniformly with 

 methyl-violet, but more at poles with carbol-fuchsin. 



Gelatine. Surface colonies are not usually found to develop in 



