CHAPTER XXy. 



The most important of the organisms found in the soil — The nitrifying 

 bacteria— The bacillus of tetanus— The bacillus of malignant oedema- The 

 bacillus of symptomatic anthrax. 



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 momentous 

 biological phenomena that are there constantly in pro- 

 gress. Of these, the one that is of greatest importance 

 comprises those changes that accompany the widespread 

 process of disintegration and decomposition, to which 

 reference has already been made. This resolution of 

 dead, complex, organic compounds into simpler struc- 

 tures that are assimilable as food for growing vege- 

 tation is dependent upon the activities of bacteria 

 located in the superficial layers of the ground. It is 

 not throughout 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 group of species, acting singly or together 

 (symbiotically). Our knowledge upon the subject 

 is not sufficient to permit of our following 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 forma- 

 tion of carbonic acid, ammonia, and water as conspicuous 

 end-products ; it suffices to say that, wherever dead 

 organic matters are exposed to the action of the great 



