THe INFLUENCE OF Low TEMPERATURE ON SOIL BACTERIA 1053 
apples and pears, there was no indication that the rate of thawing had 
anything to do with the amount of killing at a given temperature. 
SCOPE OF THE PRESENT INVESTIGATION 
With the results of the aforesaid workers in mind, the author undertook 
the investigations herein reported in an attempt to answer the following | 
questions: (1) Is there an actual growth and reproduction of the bacteria 
in frozen soils or solutions? (2) What is the effect of low temperature on 
Bacillus radicicola in solution, sand, and soil cultures? (3) To what is the 
protective action noted in solution and soil cultures due? (4) Why have 
so many investigators obtained such divergent results in their work with 
bacteria at low temperatures? 
_ The widely varying results obtained by Conn, by Brown and Smith, 
and by Harder, would seem to indicate that the number of bacteria 
occurring in frozen soils as determined by the agar-plate method is due not 
to an actual multiplication of the bacteria but to some unknown condition. 
The findings of Harder would indicate that the moisture content is of 
prime importance, whereas Brown and Smith did not consider it so 
important. Conn found that potted soils showed the same marked increase 
as the field soils. Harder was unable to show this increase in the potted 
soils, and concluded that the bacteria were carried up from the lower 
depths by heavy frosts. 3 
It is contrary to the general conception of plant and animal life to 
hold that bacteria will grow and multiply more rapidly at temperatures 
below zero than at the so-called favorable temperatures. The work of 
Conn, of Brown and Smith, and of Harder, gives little or no evidence to 
show that the bacteria do actually multiply in frozen soils, for the increase 
in bacteria counts noted by these investigators was based on the colonies 
appearing on the agar plates, and, as is well known, this method is in many 
cases a poor indicator of the actual number of bacteria present. The 
method is perhaps of value in a comparative way when comparing sub- 
stances that have received more or less of the same treatment, but it seems 
very doubtful whether it has any real value when comparing normal and 
frozen soils. The results obtained by Brown and Smith are very good 
examples of this. 
If there is not an actual increase in the number of bacteria in frozen 
soils — and it does not seem probable that there is — the large number of 
