DISTRIBUTION OF BACTERIA. 133 



CHAPTER III. 



DISTRIBUTION OF BACTERIA. 



The Bacteria of the Soil. Bacteria are present in the 

 soil in enormous numbers 100,000 or more in i c.c. of 

 virgin soil, according to Fliigge. The depths to which 

 they penetrate will depend upon the character of the soil 

 and the character of the life upon it, and whether or not it 

 has been artificially disturbed, as by cultivation. In gen- 

 eral, at a depth of 1.25 meters (about four feet) the num- 

 ber will have become very small, and a little deeper the soil 

 will be entirely sterile. 



The bacilli of tetanus and malignant edema, and bacillus 

 aerogenes capsulatus are present in the soil of many locali- 

 ties. According to Woodhead, certain savage tribes of 

 Africa and the East Indies use as an arrow-poison soil that 

 is capable of producing tetanus. The bacillus of anthrax 

 may be found in soil which has been infected with this 

 organism. 



Most of the bacteria of the soil are harmless or useful 

 saprophytes. 1 The nitrifying bacteria described by Wino- 

 gradsky and by Jordan and Richards belong to the latter 

 class. There occur in soil organisms which have the power 

 of converting ammonia into nitrous acid which forms 

 nitrites, and others which complete the change of nitrites 

 into nitrates. Both varieties are widely distributed. These 

 organisms will not grow on ordinary culture-media, and 

 their cultivation presents great difficulties. Probably a good 

 many bacteria have similar properties to some extent. The 



1 See Conn, " Agricultural Bacteriology." 



