82 ACTIVITIES OF BACTERIA. 



distributed in the soil, in meadows often the nitrite pro- 

 ducers alone, in cultivated soil usually both. Both 

 organisms possess the greatest theoretic interest, since 

 out of inorganic nitrogen and carbonic acid (both free C0 2 

 and Na 2 C0 3 or the presence of a bicarbonate is necessary) 

 they are able to build up their body substances, i. e., 

 albumin, without the aid of chlorophyll, which the higher 

 plants require. 



P. F. Richter (C. B. xviii, p. 129) often observed marked nitrite 

 reaction in urine freshly obtained with a catheter. From one specimen 

 of urine he isolated a medium-sized coccus, which produced very in- 

 tense nitrite reaction in fresh urine in twenty minutes. It also re- 

 duced nitrate to nitrite. 



ii. Transformation of Nitrites (and Nitrates) into 

 Free Nitrogen (Denitrification). 



An entire series of organisms, which are widely distrib- 

 uted in dung, straw, field-soil, and filthy water, set free 

 gaseous nitrogen from nitrites (denitrification). Many are 

 able simultaneously to transform nitrate into nitrite, also 

 alone to set free gaseous nitrogen from nitrates (for ex- 

 ample, Bacterium Stutzeri, B. pyocyaheum — compare 

 special part), while others require synergetic bacteria to 

 change the nitrate into nitrite (for example, Bact. denitri- 

 ficans). Compare Burri and Stutzer (C. B. L. I, 257, 350, 

 392, 422); Weissenberg (A. H. xxx, 274). 



For the demonstration of the denitrifying action of bac- 

 teria, there is added to a liter of ordinary bouillon 2.5 gm. 

 of sodium nitrate or, better, — since only thus are all deni- 

 trifying varieties recognized, — sodium nitrite. 



As was first completely demonstrated in my institute by 

 Weissenberg (Burri and Stutzer had made some similar 

 observations), the reduction of nitrite to nitrogen is much 

 promoted by the exclusion of oxygen, and is markedly or 

 completely inhibited by very free entrance of oxygen 

 (growth in shallow layers of fluids or with air passing 

 through). The organisms thus break up the nitrite to ob- 

 tain oxygen, and there thus originate considerable quan- 

 tities of NaOH or Na 2 C0 3 , so that the fluid becomes 

 strongly alkaline. 



