1048 A. F. Vass 
The nitrifying power of the frozen soils was weak and the ammonifying 
power was strong. The nitrogen-fixing power increased with the con- 
tinuance of the frozen period, being independent of moderate changes in 
moisture conditions. In the fall the nitrogen-fixing power of the soil 
increased until the soil became frozen, when it almost ceased, after which 
a lesser nitrogen-fixing power was established. 
Brown and Smith advanced the theory, which Conn suggested in an 
earlier publication, that the hygroscopic water in soils, remaining un- 
congealed, may serve as favorable media in which the bacteria may live 
and multiply to a comparatively large extent. 
Czermak (1912) studied the changes in the so- -called physical proper- 
ties of soils resulting from their subjection to low temperature, high 
temperature, and the action of salts. He noted that when the soil col- 
loids were coagulated by freezing, the soil surface and the hygroscopicity 
were reduced, and part of the nitrogen in the soil solution was absorbed, 
thus reducing the amount of available nitrogen. Alternate freezing and 
thawing increased the coagulation of the soil colloids. The length of 
time was more important than the intensity of the freeze. Hoffmann 
(1914), however, found little or no variation in the surface area of soils 
due to freezing. 
Lyon and Bizzell (1913) studied the effect of freezing on the nitrifying 
power of the soil. They noted that freezing produced a soil favorable 
for nitrate formation. This was attributed to the beneficial effect of low 
temperature in overcoming the depressing influence of the crop pre- 
viously grown. 
Russell and Hutchinson (1913) offer an explanation very similar to 
Conn’s to account for the increase of bacteria in frozen soils. They sug- 
gest that the protozoa may be the hostile organisms holding the bacteria 
in check in the unfrozen soils. 
Conn (1914) verified in later studies what he had previously andl 
that the increase in bacteria in frozen soils is not due to the increase in 
moisture content which usually occurs in winter, and that the same 
increase may take place in potted soils where there is no possibility of 
the bacteria being carried up mechanically from lower depths during the 
process of freezing. He suggested the possibility that the mcrease may 
not be an actual multiplication but may result from the breaking up of 
the masses of bacteria by freezing. He considers this to be extremely 
