ALBUMINS OR PROTEINS. 195 



Davy l called attention to the fact that gaseous nitrogen was set free 

 from decomposing organic material in the soil. Gayon and Dupetit 2 

 were, however, the first to announce that the nitrogen originated from 

 the nitrates. Since that time a large number of bacteria have been isolated 

 which produced nitrogen from nitrates. Gayon and Dupetit cultivated 

 two varieties of anaerobic bacteria from the soil, which they called bacterium 

 denitrificans, a and /?. Denitrifying bacteria can live without oxygen. 

 They utilize the nitrates as a source of energy. They work, in a sense, in 

 constant opposition to the nitrifying bacteria. With a liberal supply of 

 oxygen the latter will predominate, while if the oxygen supply be dimin- 

 ished, the reverse will be true. There is no doubt but that appreciable 

 amounts of nitrogen are being continually set free. Nitrogen would be 

 constantly withdrawn in this way from the organized world were it not 

 for the fact that other processes are at work to recombine it. We also 

 know that atmospheric nitrogen and oxygen are combined under the influ- 

 ence of electrical discharges, producing nitric acid. The amount of nitrogen 

 combined in this manner must necessarily be small. It is certainly insig- 

 nificant in comparison with the production of nitrogen from other sources. 

 During recent years various bacteria have been isolated which possess the 

 faculty of assimilating, or " fixing," the atmospheric nitrogen. Berthellot 3 

 first called attention to this process. He found an enrichment of soils 

 which were free from higher plants, and whose only source of nitrogen 

 was the atmosphere. Winogradsky 4 was the first to succeed in isolating 

 a bacterium which was capable of fixing nitrogen directly from the air. 

 This was the anaerob Clostridium Pasteurianum. Winogradsky showed 

 that a culture of this bacillus, shut off from every other source of nitrogen 

 except the air, was capable of assimilating 24 . 7-28 . 9 grams nitrogen in 

 15-20 days. It is interesting to note that this Clostridium is not found 

 alone, but is accompanied by two aerobic bacteria. Evidently this is a 

 case of symbiosis. The aerobic bacteria remove the oxygen which is 

 deleterious to the development of the Clostridium. They undoubtedly 

 receive nitrogenous material from the latter in return. Since this dis- 

 covery other bacteria have been isolated, which possessed the ability of 

 assimilating free nitrogen. Kr tiger and Schneidewind 5 describe a bacte- 

 rium, a culture of which in 62 days converted 4 . 6-8 . 5 grams atmospheric 

 nitrogen into albuminous nitrogen. It is noteworthy that the Clostridium 

 has been found in the slime of ocean bottoms, and in the plankton of salt 



1 Elements of Agricultural Chemistry. 

 3 Compt. rend. 95, 644 (1882). 



3 Ibid. 101, 775 (1885); 104, 205 and 625 (1887); 106, 569, 1049, 1214 (1888); 107, 

 372 (1888) ; 108, 700 (1889) ; 109, 277 and 417 (1889) ; 115, 569 (1892) ; 116, 842 (1893). 



4 Compt. rend. 116, 1385 (1893); 118, 353 (1894). 

 6 Landwirtsch. Jahrb. 29, 801 (1900). 



