METABOLISM OF MICROBES 97 



suggest that the nitrogen is permanently stored up in microbial 

 cells. Cells of the microorganisms lead a transient life in the soil ; 

 they develop and die within short intervals, depending upon the 

 environmental conditions. Upon their death they become decom- 

 posed with the liberation once more of at least a part of the nitrogen 

 and of the other elements which were assimilated during growth. 

 It can be appreciated that, in the presence of even small amounts of 

 nitrogen and large amounts of nitrogen-free organic matter, there 

 would eventually be no deficiency of nitrogen but even a liberation 

 of most of the nitrogen as ammonia. The process will proceed 

 somewhat slowly, since the organisms must die and be decomposed 

 over a considerable period of time. 



Fig. 48 shows schematically the course of the changes under 

 ideal conditions, or what might be called the perfect case, where 

 the total plant and the microbial cells which are formed are all 

 completely decomposed. In the calculations the assumption has 

 been made that the organisms causing the decomposition assimi- 

 late into their cell substance one-third of the carbon of the material 

 decomposed and eliminate the other two-thirds as carbon dioxide. 

 It is further assumed that the cells of the organisms have a ratio 

 of carbon to nitrogen of 10 to 1. The nitrogen of the original 

 organic material (12.5 pounds) permits the organisms to transform 

 125 pounds of carbon into their cells, since they assimilate ten 

 times as much carbon as nitrogen. Also, since they assimilate 

 only one-third of the carbon that they attack, 250 pounds of carbon 

 will be eliminated as carbon dioxide. This leaves 625 pounds of 

 carbon in the form of residual undecomposed organic matter. 

 Providing the microbial cells suffer complete decomposition, 42 

 pounds of carbon and 4.2 pounds of nitrogen will be synthesized 

 into the new cells which cause this decomposition (A). Since only 

 one-third of the carbon is used by the cells, two-thirds of the carbon, 

 or 83 pounds, will be eliminated as carbon dioxide. Since the cells 

 which were decomposed contained more nitrogen than the new cells 

 required for growth, 8.3 pounds of nitrogen will be eliminated as 

 ammonia. This ammonia permits decomposition of more of the 

 undecomposed organic matter. As a result of this decomposition, 

 166 pounds of carbon go to carbon dioxide, 83 pounds of carbon are 

 assimilated by microbial cells (B), and 376 pounds of carbon still 

 remain undecomposed (C). 



If the total constituents of the microbial cells (A) and (B) are 



