Aug. 1909.] Soil Bacteriology. 223 



and place as the volumetric or measured samples. There were 

 two sets of gravimetric samples taken, in order to determine 

 whether drying materially decreased the number of bacteria 

 per gram. One set of gravimetric samples with duplicates was 

 taken immediately to the right of the volumetric samples ; the 

 other set with duplicates was taken immediately to the left of 

 the volumetric samples, so as to obtain under the same condi- 

 tions, as nearly as possible, the same type of soil. 



The method employed for taking and caring for individual 

 samples will be discussed under "Quantitative Bacteriological 

 Analysis." After taking the samples to the laboratory, one 

 gravimetric set with duplicates was immediately subjected to 

 culture tests ; the other set with duplicates was placed between 

 sheets of sterile filter-paper until air dry. Twenty-four hours 

 was found sufficient for that purpose. They were then treated 

 as were the other samples. 



BACTERIAL ACTIVITIES AND INFLUENCING CONDITIONS. 



In order to find the influence of aeration upon the biochemic 

 characters of bacteria, determinations were made of the pro- 

 duction of ammonia, reduction of nitrates to nitrites, and the 

 production of gas in one-per-cent. solutions of glucose, lactose 

 and saccharose bouillon. 



Ammonia Production. The relative amounts of ammonia 

 in the different samples of soil were determined in the follow- 

 ing way: One cubic centimeter of soil was completely sus- 

 pended in nineteen cubic centimeters of sterile, ammonia-free, 

 distilled water. Two cubic centimeters of this soil suspension 

 were transferred to fifty cubic centimeters of nutrient agar, 

 having a reaction of 1.5 acid to phenolpthalein. The agar was 

 distributed in Erlenmeyer flasks of 250 cc. capacity. The 

 flasks were then closed and allowed to stand for five days. At 

 the end of that time ten cubic centimeters of sterile, nitrogen- 

 free water were introduced and allowed to stand for ten min- 

 utes. It was then drawn off and tested for ammonia with 

 Nessler's solution. The color reaction was compared with 

 standard solutions and the results recorded as so many parts 

 of ammonia per million. These standard solutions were pre- 

 pared by placing fractional percentages of ammonium chloride 

 in nitrogen-free water. 



Gas Production. The production of gas was determined in 



