THE RELATION OF PROTOZOA TO CERTAIN 

 GROUPS OF SOIL BACTERIA^ 



T. L. HILLS 



From the Laboratory of Agricultural Bacteriology, University of Wisconsin 



INTRODUCTION 



The theory advanced by Russell and Hutchmson (1909; 1913) 

 that protozoa are an important factor in limiting bacterial ac- 

 tivity and consequent fertility in the soil has aroused no little 

 interest. Their work has stimulated much investigation, some 

 of the results of which seem to uphold their theory, while others 

 do not substantiate it. 



It was thought that results of interest might be obtained by fur- 

 ther studies concerning the effect of the protozoa on certain bio- 

 logical processes of the soil — ammonification, nitrification and 

 free nitrogen fixation. 



For this study soil cultures of Miami silt loam soil from the 

 Experiment Station Farm were used. The moisture content was 

 maintained at as near one-half saturation as possible. 



AMMONIFICATION 



In this work 300 gram portions of soil were placed in each of 

 18 flasks. The flasks were of 500 cc. capacity, Erlenmeyer form, 

 and rather narrow so that the soil was in approximately 2 inch 

 layers. The proper amount of moisture was added, the flasks 

 plugged, and sterihzed at 15 pounds pressure for two hours. 

 This was found sufficient to kill all the bacteria. Upon coohng, 

 one half of the flasks were inoculated, each with 2 cc. of a suspen- 



1 Presented at Seventeenth Annual Meeting of the Society of American Bac- 

 teriologists, Urbana, 111., December 29, 1915. 



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