METHODS EMPLOYED IN BACTERIOLOGICAL INVESTIGATIONS, 9 



(liiVereut soil coiulitions. Though it is recognized that the methods 

 suggested by different investigators are not adequate for accurate 

 quantitative investigations of bacterial functions and conditions in 

 various soils, the methods wliich at this time have been found most 

 convenient and suitable for the investigations under discussion are 

 briefly reviewed.^ 



COUNTS OF BACTERIA. 



Samples of soil were collected with as strict aseptic precautions as 

 it is possible to observe untler field conditions. Sterile salt-mouth 

 bottles were used as containers, and the soil auger used for taking up 

 the soil was carefully cleaned and flamed over an alcohol lamp before 

 sampling each stratum. In the laboratory 1-gram portions were 

 removed from the bottles with a sterile scoop which held the required 

 quantity, transferred to 300 cubic centimeters of sterile water in 

 500-cubic-centimeter flasks, and the whole shaken thoroughly at short 

 intervals for fifteen minutes. One-cubic-centimeter portions of these 

 infusions were then removed with sterile pipettes and added to 10 

 cubic centimeters of melted beef agar, ami plates poured in the ordi- 

 nary manner and incubated at 28° C. Counts of bacteria were made 

 at the end of five-day periods. 



AMMONIFICATION. 



Sterile peptone solutions having the following composition were 

 inoculated with 5 per cent of soil and the ammonia determined at the 

 end of seven and fifteen days by distillation with magnesia: 



Peptone 15 grams. 



Dipotassium phosphate 3 grams. 



Magnesium sulphate 3 grams. 



Sodium chloric! 3 grams. 



Water 1, 000 c. c. 



^ Lipman, J. G. Experiments on the Transformation and Fixation of Nitrogen by 

 Bacteria. Twenty-fourth Annual Report, New Jersey State Agricultural Experiment 

 Stations, 1903, pp. 217-285. 



Lipman, J. G., and Brown, Percy E. Methods Concerning Ammonia Formation 

 in Soils and Culture Solutions. Report, Soil Chemist and Bacteriologist, New Jersey 

 Agricultural College Experiment Station, 1908, pp. 95-105. 



Lipman, J. G., and Brown, Percy E. Notes on Methods and Culture Media. Report, 

 Soil Chemist and Bacteriologist, New Jersey Agricultural College Experiment Station, 

 1908, pp. 129-136. 



Lipman, J. G. Azotobacter Studies. Report, Soil Chemist and Bacteriologist, 

 New Jersey Agricultural College Experiment Station, 1908, pp. 137-143. 



Lohnis, F. Ein Beitrag zur Methodik der bakteriologischen Bodenuntersuchung. 

 Centralblatt fiir Bakteriologie, Parasitenkunde und Infektionskrankheiten, pt. 2, 

 vol. 12, no. 6-8, pp. 262-267, June 24, 1904; no. 11-16, pp. 448-463, July 14, 1904; 

 vol. 17, no. 14-16, pp. 518-528, December 7, 1906; vol. 20, no. 24-25, pp. 781-799, 

 April 15, 1908; vol. 24, no. 5-7, pp. 183-192, August, 1909. 



Remy, Theodor. Bodenchemische und Bakteriologische Studien. Landwirt- 

 schaftliche Jahrbiicher, vol. 35, Supplement 4, pp. 1-62. Berlin, 1906. 



78011°— Bui. 211—11 2 



