CHAPTER XXIV. 



The most important of the organisms found in the soil The nitrify- 

 ing bacteria The bacillus of tetanus The bacillus of malignant 

 oedema The bacillus of sj^mptomatic 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 singly or together (symbiotically). Our knowl- 

 edge upon the subject is not sufficient to permit us to 

 follow in detail the manifold alterations undergone 

 by dead organic material in the process of decomposi- 

 tion that results in its conversion into inorganic com- " 

 pounds, with the formation of carbonic acid, ammonia, 

 and water as the conspicuous end-products. It suffices 



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