BACTERIA OF THE SOIL 285 



water from them, etc. Whenever a grave is opened that 

 contains the body of a person dead of an infectious disease, or 

 an attempt is made to move a cemetery, fear is invariably 

 aroused among people living in the neighborhood. There is 

 very little evidence, however, to show that any of the bacteria 

 of human disease can live for any length of time in the soil. 

 Bact. anthracis without spores live only a few days, B. 

 typhosus and Msp. comma only a few weeks, and the Bact. 

 tuberculosis not over a few months. The antagonism of 

 other forms is undoubtedly a potent factor in their early de- 

 struction. It is easily seen, then, that with the exception of 

 the B. tetani, whose distribution in the soil is practically world- 

 wide, that the disease-producing bacteria have only a very 

 local distribution, and these localities bear a definite relation 

 to some preexisting case of disease. Other soil bacteria of a 

 very great importance are the legume and nitrifying bacteria. 

 A discussion of the biology of these is found elsewhere. 



The Legume or Nitrogen-fixing Bacteria. This group of 

 soil bacteria has already been referred to and their biology 

 discussed, but it is desirable in this connection to emphasize 

 their importance as nitrogen gatherers. Nitrogen is an essen- 

 tial plant food. When the supply is limited in a soil, it is 

 found necessary to replace it. Nitrogen fertilizers are, at the 

 present time, very expensive. It has been known for a very long 

 time that certain leguminous plants were able to increase the 

 nitrogen supply of the soil, and it was later found that this 

 activity was associated with the presence of nodules on these 



