CHAP, in The absorption of Nitrogen 339 



He showed that their functions are specific, one can attack 

 ammonia only, the other only nitrites. 



The two organisms possess the very important pecu- 

 liarity that they grow freely only on substrata containing 

 no organic carbon, indeed are actually injured by its 

 presence. It follows, therefore, that they can obtain their 

 carbon only from the carbon dioxide of the air or from 

 the carbonates in the solution. By careful quantitative 

 experiments he proved, as Godlewski did later, that the 

 former is the source of supply, and therefore they resemble 

 green plants in this particular, though unlike the latter 

 they contain no chlorophyll. To this subject we shall 

 return. 



The two organisms differ in appearance, the nitrous 

 bacteria, of which there are several species, exhibiting two 

 types. Those found in the soils of Europe, Asia, and Africa, 

 are oblong, globular, or oval in shape, and are furnished 

 with a single cilium ; they form a cloudy zoogloea, which 

 sinks to the bottom of the liquid. The species found in 

 America and Australia are cocci and have no cilia ; they 

 do not form a zoogloea. The nitrate organisms are slender 

 rods, and are among the smallest of all known organisms. 

 They form a kind of mucinous zoogloea in liquid cultures. 

 Neither organism forms spores. The two classes exhibit 

 great differences in their power of oxidizing nitrogen, the 

 nitrite forms being much the more energetic. 



Winogradsky succeeded best in cultivating them upon 

 a substratum of gelatinous silica, with no organic material 

 added. In 1899 he published, in collaboration with his 

 pupil Omelianski, the results of some experiments made 

 upon the influence of sundry organic substances on the 

 growth of both organisms. In both cases growth is very 

 greatly impeded by traces of glucose, asparagin, glycerin, 

 and urea, indeed very small quantities inhibit it entirely. 

 A curious exception occurs in the case of bouillon, in 



Y2 



