CHAPTER XXVI. 



The nitrifying bacteria The bacillus of tetanus The bacillus of malig- 

 nant oedema The bacillus of symptomatic anthrax Bacterium 

 Welchii Bacillus sporogenes. 



THE NITRIFYING BACTERIA. 



BY the employment of bacteriological methods in 

 the study of the soil much light has been shed upon 

 the cause and nature of the interesting and momen- 

 tous biological phenomena there constantly in prog- 

 ress. Of these, the one that is of the greatest im- 

 portance comprises those changes that accompany the 

 widespread process of disintegration and decomposi- 

 tion, to which reference has already been made. (See 

 Chapter I.) This resolution of dead complex organic 

 compounds into simpler structures that are assimilable 

 as food by growing vegetation is dependent upon 

 the activities of bacteria located in the superficial 

 layers of the ground. It is not a simple process, 

 brought about by a single, specific species of bacteria, 

 but represents a series of metabolic alterations, each 

 definite step of which is most probably the result of 

 the activities of different species or groups of species, 

 acting alone or together. Our knowledge upon the sub- 

 ject does not permit us to follow in detail the manifold 

 alterations undergone by dead organic material in the 

 process of decomposition that results in its conversion 

 into inorganic compounds, with the formation of carbonic 

 acid, ammonia, and water as the conspicuous end-products. 

 It suffices to say that wherever dead organic matters are 



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