212 



MICHIGAN ACADEMY OF SCIENCE. 



TABLE V. 



Nitrites expressed in grams per litre N2 O3. 



Ammonia expressed in grams per litre NH-,. 



A litre sterile culture solution contains .1204 grams X._, O3. 



A litre sterile culture solution contains .028 grams N H... ' 



The results show that the reduction depends almost entirely upon the 

 presence of at least a small amount of oxygen, and that, except in the 

 case of B. mveoides. a greater sui)ply of air induces a greater amount 

 of reduction. 



CONCLUSIONS. 



1. The three micro-organisms under investigation have the ]»o\vei* of 

 actiftg upon nitrates to reduce them to simpler substances, nitrites, free 

 ammonia, and probably free nitrogen. 



2. The nitrites present in a culture solution having nitrate for its 

 basis result entirely from the nitrate. 



3. A portion of the ammonia usually found in cultures in nitrate 

 solutions containing organic matter, results from the decomposition of 

 this latter material. 



4. For a vigorous. development and activity of these micro-organisms, 

 the presence of at least a trace of organic matter is essential. 



5. Not all bacteria having the power of acting upon nitrates are also 

 capable of exerting a reducing action upon nitrites. 



r>. The bacteria studied can not reduce ammonium sulphate; further- 

 more, the ammonium sulphate checks the production of free ammonia 

 from the peptone in the solution. 



7. These micro-organisms act more vigorously in the presence of an 

 abundant supply of oxygen. 



