210 * MICHIGAN ACADEMY OF SCIENCE. 



the peptone. No reaction for nitrites was obtained until the cultures 

 were old and then only a trace. Whether this was due to spontaneous 

 chemical changes is a question. The fact that the control, which re- 

 mained sterile, showed a trace of nitrite would lead one to suspect that 

 such was the case. The work was duplicated in order to verify it and 

 the same results were obtained. These results agree with Maassen (Cent, 

 f. Bakt. 1902 II No. 5. S. 152) who grew 109 common bacterial species 

 in a mineral solution containing peptone, and who says in stating his 

 results; "Considerable ammonia was also produced on account of the 

 vigorous peptonization." 



2. Do the Micro-Orgauisms Have a Seducing Action upon Nitrites? 



To determine whether the micro-organisms were capable of reducing 

 nitrites a nutrient mineral solution having nitrite for its basis was pre- 

 pared, and cultures were made and handled in the same manner as in* 

 the previous work. Tests were made at various intervals, but in only one 

 case, B. mycoides, was any decrease in nitrates apparent. 



3. Action of the Organisms upon Ammonium Salt. 



Cultures were made in a nutrient mineral solution having for its basis 

 ammonium sulphate, and Nessler determinations were made at intervals 

 to discover, if any, the decrease in the amount of ammonia. Duplicate 

 tests were made at different periods, the results of which corresponded. 

 At no time was any change observed in the ammonia content, showing 

 that these bacteria have not the power of reducing ammonium sulphate, 

 and furthermore that this salt prevented the production of ammonia 

 from the peptone which was present in the solution. 



4. The Effect of the Presence of Organic Matter upon Denitrification. 



Klinneman, a German investigator, in 1898. in experiments carried 

 on with a micro-organism which he had isolated from horse dung, found 

 that the amount of denitrification decreases as the amount of organic 

 matter increases, which observation was also made by Matz and Wagner, 

 who stated that as "humification" proceeds, the power of destroying 

 nitrate decreases. On the other hand, Pfeiffer states that denitrification 

 can take place only in the presence of straw, feces or vegetable tissue 

 which act as food substance for the denitrifying organisms. Stutzer and 

 Maul isolated two micro-organisms which gave very marked nitrate re- 

 ducing po\>'er when grown in a solution containing a small amount of 

 organic matter. Maassen states that in a strictly inorganic solution he 

 obtained very little reduction of nitrate by common bacteria. In our 

 studies along this line five solutions were used, differing only in the 

 nature of the material furnishing the combined nitrogen to be acted upon, 

 the basis of the different solutions being as follows: Ammonium nitrate 

 and Potassinni nitrate. Asparagin. Potassium nitrite, and Potassium 

 nitrat<' and nil rite combined in ecpial amounts. The other elements 

 necessary to ])lant growth were added in various salts, but none of the 

 solutions excepting the asparagin contained any organic matter. The 

 cultures were tested at the end of forty-five days for the reduction pro- 



