KINDS OF BACTERIA IN THE SOIL 123 



tions, whose presence is dependent more or less upon 

 accident. Others there are which must be considered as 

 normal inhabitants of the soil. To the latter class belong 

 many of the putrefying and denitrifying organisms, as 

 well as the nitrifying and nitrogen-fixing bacteria which 

 are described in the succeeding pages. The number of 

 these found by Lohnis in samples of soil taken from a 

 field in January and July respectively were : 



Jan. July- 

 Putrefactive bacteria, . . 3,750,000 5,000,000 

 Urea-splitting . . - 50,000 50,000 

 Nitrifying . .' 7,500 2,500 

 Denitrifying . . ; 50,000 50,000 

 Nitrogen-fixing . . 1,125 750 



Certain anaerobic spore-bearing forms are frequently 

 met with also. Among the bacteria of especially common 

 occurrence in most field and garden soils may be men- 

 tioned : Bs. mycoides, Bs. subtilis, Bs. vulgatus, Bs. 

 megatherium, Bact. fluovescens liquefaciens, Bact. fl. non- 

 liquefaciens, Bs. putrificus, Micrococcus candicans, various 

 forms of Proteus, and certain species of Cladothrix. 



Bact. coliis commonly present in soils which are polluted 

 with sewage, or to which dung and similar organic excreta 

 have been recently added, but is not usually found, or 

 only in relatively small numbers, in virgin soils. 



In addition to these, certain pathogenic species, such 

 as Streptococcus pyogenes, Bs. tetani, and Bs. adernatis 

 malignly are not uncommonly met with in the soil. 



Gottheil made an extensive study of the spore-bearing 

 bacteria attached to the roots of carrot, beet, radish, 

 turnip, parsley, cabbage, and other plants, and found 



