THE BACTERIA OF NEBRASKA SOIL WITH SPECIAL 



REFERENCE TO THE FIXATION OF NITROGEN, 



AMMONIFICATION, DENITRIFICATION IN 



NON-PROTEIN MEDIA INCLUDING 



OBSERVATIONS ON THE REDUCTION OF 



NITRATES BY SOIL BACTERIA 



IN GENERAL 



HISTORICAL 



This work was undertaken with the idea of ascertaining 

 if possible, some of the many chemical changes taking place 

 through the action of bacteria indigenous to Nebraska soil. 



The fixation of nitrogen was first observed by M. Berthelot 

 in 1885. He subsequently was able to prove that this pheno- 

 menon is not brought about exclusively by a purely chemical 

 process, but is due to the activity of micro-organisms. The 

 discovery of an anaerobic organism by S. Winogradsky in 

 1893, Clostridium pasteurianum, which he found fixed from 

 2.5 to 3 mg of nitrogen per gram of dextrose consumed, marked 

 the first advance along this important line. Recent observers 

 have added a few organisms to the list, Beyerinck, Lohnis 

 and Lipman having labored successfully in this field. 



In 1887 Schlossing and Muntz hazarded the opinion that 

 the formation of nitrate within the soil is due to the vital 

 activity of soil bacteria, and in a subsequent communication 

 these two workers detailed some of the conditions requisite 

 for the inception and course of nitrification. Much opposition 

 developed from the advocates of the chemical theory. A re- 

 examination of the comprehensive work of H. Plath by Lon- 

 dalt, who undertook the task in consequence of an objection 

 raised by B. Frank, led to a complete confirmation of Plath's 

 discoveries in all particulars. It was thus ascertained in 1888, 

 by the exclusion method, that in the oxidation process now 

 under our notice the role of oxygen-carrier is played by living 

 organisms, and that nitrification consequently is a physiological 

 process. The discovery and closer investigation of these un- 

 known organisms was shortly afterwards effected by S. Wino- 



