236 



Bacteriological Department. 



[Bull. 161 



should samples be collected from the above types of soil by the 

 gravimetric method and the comparative results expressed as 

 so many bacteria per gram, the number of bacteria in an acre- 

 foot of the sandy loam would in reality be compared with the 

 number of bacteria in 1.21 acre-feet of the silt loam. 



In quantitative bacteriological work, when comparative re- 

 sults are desired, the volumetric method has the following pos- 

 sible advantages over the gravimetric method : 



1. Pt is more convenient. 



2. It allows less chance for contamination. 



3. It represents more accurately an aliquot part of an acre- 

 foot of soil. 



The last advantage appears to be true because of the differ- 

 ence in specific gravity of soils. 



Drying Effect. When we compare tables I and II with III 

 and IV, we find no appreciable difference in results between 

 those soil samples which were allowed to dry twenty-four hours 

 before inoculation and those from which inoculations were 

 made immediately after collection. 



TABLE IX PLOT A. Summarized total number bacteria given in table V. 



TABLE X-PLOT A. Summarized total number of bacteria given in table VI. 



