1068 A. F. Vass 
in almost all cases. When the soil was thawed rapidly by rain, the count 
in the thawed soil was very much higher than when the thaw was gradual, 
indicating a breaking-up process due to the rapid thaw. When the con- 
ditions for an actual increase and growth were brought about by the 
addition of dextrose to the soil, the unfrozen sample showed a much 
greater increase in bacteria content than did the frozen sample. All 
this would seem to prove that frozen soil is not as favorable a medium as 
unfrozen soil for the growth of bacteria. That the increase is not due 
to mechanical transportation by moisture coming up from below during 
heavy frosts was shown by Conn in his work with potted soils, and also 
in the results herein reported, in which the same marked increase was 
obtained when small amounts of the soil were frozen in test tubes and 
an entire portion was used in making the dilutions. 
The conclusions of Brown and Smith in regard to bacterial activities 
in frozen soils have not sufficient evidence to give them weight. It is 
interesting to note how their idea of a summer and a winter flora has 
been made to fit in with their results. Altho they concluded that the 
ammonifying power of the frozen soil is increased, the smallest amount 
of ammonia was produced from the sample taken during the coldest period 
of the tests. When it is considered that Brown and Smith used a soil 
infusion representing 5 grams of the frozen soil to inoculate 100 grams of 
air-dry soil, the results are not surprising. It would seem that the experi- 
ment under such conditions could better be called a study of the effect 
of storing air-dry soil on the bacterial flora therein, Imasmuch as the 
number of bacteria present in the air-dry soil was several times that in 
the 5 grams of frozen soil. Duplicate tests might perhaps have eliminated 
the marked variations obtained by Brown and Smith. The tests that 
should have shown the difference, if there really was one, were those on 
nitrification, for the condition surrounding those tests are more easily 
controlled, and the measured product, nitrates, is not so easily lost as are 
some of the other products. The nitrification results of Brown and Smith 
indicated that if there was a difference their method was not sufficiently 
accurate to show it. It would seem that a similar conclusion may be 
applied to all their results. 
Brown and Smith concluded from their nitrification results that the 
nitrifying power of the soil was rather weak. This is contrary to the 
findings of Lyon and Bizzell, who noted a beneficial effect due to freezing. 
