269 



The influence of carbon disulfid serves as an important example, for, 

 besides a poisonous action, a stimulus directly beneficial to growth has been 

 assumed for it. The latter is thought to be recognized in the fact that a 

 clearly recognizable increase of fertility sets in after the disappearance of 

 the carbon disulfid and its influences which arrest growth. Hiltner suc- 

 ceeded in proving that the carbon disulfid chiefly conditions the changing 

 phenomenon by disturbing the equilibrhtm of the bacterial flora of the soils. 

 By means of its ability for dissolving fats, it suddenly forces back the bac- 

 teria which had prevailed up to that time, just as it also stops entirely the 

 increase of all species, so long as it is present unchanged in the soil. If the 

 poison become diluted, or disappears through conversion, the long repressed 

 numerical growth of the soil organisms increases in such a way, that, for 

 example, an increase of 9 millions of the species growing on meat-pepton- 

 gelatine to 50 millions in one gram of soil could be proved in one case. Thus 

 an increase in the nitrogen production and with it of the potato harvest 

 could be determined chemically by Moritz and Scherpe. 



With reference to the behavior of the nitrogen bacteria described in the 

 second volume^ under soil bacteria, we will here only supplement 

 the facts stated there. After \\^inogradski especially had proved the con- 

 version of the ammoniacal nitrogen to nitric nitrogen to be the successive 

 achievements of two different groups of bacteria (builders of nitrites and 

 nitrates), it was determined by Omeliansky that the nitrogen of the organic 

 substances must have been previously converted by other bacteria to am- 

 monia. Disturbances can easily occur in this work, since these bacteria are 

 most sensitive to dissolved substances. Thus, for example, the activity of 

 the organism forming nitric acid stops absolutely if any traces of ammonia 

 are present. 



In contrast to the above, numerous other species of bacteria (more than 

 twenty have already been identified) possess the ability of denitrification, i. e.; 

 the reduction of the saltpetre to free nitrogen which passes off into the air. 

 People have wanted to trace to this process the fact that fresh stable manure, 

 under certain circumstances, injures the saltpetre contained in the soil and 

 that straw fertilizing acts disadvantageously. This phenomenon is now 

 chiefly explained by the fact that protein forming organisms have laid hold 

 of the available nitrogen in the soil. (Pfeift'er and Lemmermann as well as 

 Gerlach and Vogel). These bacteria transform the saltpetre first into the 

 nitrite and then into protein-like compounds. That definite secondary con- 

 ditions belong here is shown by Hiltner's experiment in which straw fertiliz- 

 ing was proved to be very injurious for potted plants, while the same 

 amounts on open land had a beneficial effect. This contradiction may prob- 

 ably be traced to the fact that the protein thus produced can be transformed 

 more quickly in open ground to products which can be utilized again. 



(Page 89 in th^ German edition.) 



