CHAPTER XXV. 



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 

 progress. Of these, the one that is of the greatest 

 importance comprises those changes that accompany 

 the widespread process of disintegration and decompo- 

 sition, to which reference has already been made (see 

 Chap. I.). This resolution of dead, complex, organic 

 compounds into simpler structures that are assimilable 

 as food for growing vegetation 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 groups of species, 

 acting singly or together (symbiotically). Our knowl- 

 edge 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 decomposi- 

 tion that results in its conversion into inorganic com- 

 pounds, with the formation of carbonic acid, ammonia, 

 and water as conspicuous end-products. It suffices to 



