62 A MANUAL OF BACTERIOLOGY 



SOIL BACTERIA IN RELATION TO NITROGEN COMPOUNDS 



The relations of soil bacteria to compounds of nitrogen have 

 been more extensively studied than their relations to other soil 

 constituents, although there is reason to believe that their rela- 

 tions to sulphates and phosphates are also of great importance. 

 In many soils, however, the amount and form of nitrogen present 

 seems to be the chief chemical factor governing plant production. 

 Bacteria have been found to play an important; part in the trans- 

 formations of soil nitrogen, to say nothing of the ability of some 

 races of bacteria to add considerable stores of nitrogen to the soil. 



Although there are many unsettled problems, and our knowl- 

 edge of these bacteria is far from complete, there is reason to 

 believe that we may control to some extent the addition of 

 nitrogen to cultivated soils, and its subsequent transformations. 



For a more complete discussion of these and allied questions 

 the student is referred to 



CONN. Agricultural Bacteriology, Second Edition. Philadelphia, 1909. 



LIPMAN. Bacteria in Relation to Country Life. New York, 1908. 



VOORHEES and LIPMAN. Review of Investigations in Soil Bacteriology, Bulletin 



No. 194. Office of Experiment Stations, U.S. Department of Agriculture, 



1907. 



MARSHALL. Microbiology. Philadelphia, 1911. 



LAFAR. Handbuch der technischen Mykologie, Bd. III. Jena, 1905. 

 LOHNIS. Handbuch d. landw. Bakteriologie. Berlin, 1911. 

 Numerous papers in journals and agricultural literature. 



In many of the experiments which follow, analyses are to be 

 made which involve more or less chemical work. The chemical 

 methods given in appendixes F, G, H, and I are the simplest 

 which will give anything approximating accurate results in the 

 hands of undergraduate students. They are mainly qualitative. 

 The research worker who has more apparatus and who desires 

 more accurate quantitative results, is referred to works on stand- 

 ard analysis of waters and soils. 



Exercise 90. Ammonification of Peptone by Soil Bacteria 



1. Prepare 400 cc. of Dunham's solution (see Exercise 37). 

 Place 200 cc. in each of two flasks of 500 cc. capacity. 



2. Sterilize the flasks in the autoclave. 



