184 Report of the Department of Bacteriology of the 



Table II. — Bacterial Counts op Potted Soil. 

 Samples taken at Ithaca, N. Y. 



been raised as to the correctness of the results. As yet, however, 

 not much work has been done by others to test out the matter. 

 Some unpublished work, carried on under the direction of W. M. 

 Esten, of the Connecticut Agricultural College, has shown the germ 

 content of soils to increase after freezing. Brown and Smith 9 

 recently made a study of bacteria in frozen soil, obtaining quanti- 

 tative data from eight samples of soil. All of their counts are lower 

 than those which were found in the present work, a fact which can 

 be at least partially explained by their use of a different culture 

 medium and of a shorter period (three days) of incubation. Although 

 some of their counts from frozen soil were lower than others made 

 before freezing, the highest count of all was from soil that had been 

 the longest frozen. This fact is particularly interesting when we 

 consider that the bacteria which show the most striking increase in 

 numbers after freezing grow very slowly on the plates and are largely 

 overlooked when a short period of incubation is used. 



PRESENT WORK. 



PLAN. 



This work was planned to throw light upon the same two ques- 

 tions which it had been hoped to answer by the pot experiment in 

 the earlier work (see page 182). The first question is whether the 

 increase in numbers of bacteria may not be due merely to a rise of 

 the organisms from lower depths, brought about by ascending cur- 

 rents of soil-water. The second is whether it is the low temperature 

 or the high moisture content of winter soil that favors the bacteria. 

 To answer these questions, soil was allowed to freeze in pots, so that 

 its moisture content could be controlled and no water could rise 



9 Brown, P. E., and Smith, R. E. Bacterial Activities in Frozen Soils. 

 Exp. Station, Research Bui. 4 : 158-184. 1912. 



Iowa Agr. 



