Tue INFLUENCE OF Low TEMPERATURE ON Sort BAcTERIA 1047 
Conn attempted to divide the soil bacteria into three classes — rapid 
liquefiers, slow growers, and Actinomyces. He found the greatest increase 
in the group of slow growers when the soils were frozen. In the quan- 
titative work in the pure cultures he noted that certain types of soil bac- 
teria occur thruout the year, while others apparently exist for short 
periods only and tend to recur at other times under similar conditions. 
He suggested the possibility that a different class of bacteria is in the 
ascendancy in winter from those which are benefited by the warm weather 
of summer; in which case the increase is not due directly to the low tem- 
perature, but to the depressing effect of the cold upon the group of bac- 
teria which is able in summer to keep the winter bacteria in check. 
Hutchinson (1911-12) noted that biological changes in the soil take 
place at a greater rate in the soils of India than in the European soils. 
The temperature of the India soils ranges from 25° to 30° C. during the 
srowing season, whereas that of the European soils ranges from 16° to 
18° C. At the lower temperatures ammonification and nitrification go 
on at the same rate, but in the soils of India there tends to be an accu- 
mulation of ammonia due to the increased activities of the ammonifying 
bacteria at the higher temperature. 
The work of Conn was continued by Brown and Smith (1912) in their 
investigations of the bacterial activities of frozen soils. They made 
‘quantitative determinations of the number of bacteria in the soil during 
the fall, winter, and spring seasons. They noted a gradual decrease in 
the number of bacteria as the temperature was lowered. This decrease 
continued with more or less variation until March 1, when there was a 
marked increase. They suggested that their results confirm Conn’s 
conclusion that bacteria are alive and multiply in frozen soils. They 
studied what they called the ammonifying, nitrifying, denitrifying, and 
nitrogen-fixing powers of frozen soils. These tests were made by inocu- 
lating 100 grams of an air-dry soil with a soil infusion representing five 
grams of the frozen soil to be treated. The nitrogenous materials added 
were stirred into the unsterilized soil by means of sterile spatulas. The 
authors conclude that frozen soils possess a much greater ammonifying 
power than do non-frozen soils, and that the ammonifying power of the 
soil increases until the temperature almost reaches zero, when a decrease 
occurs, and this is followed by a gradual increase which continues until the 
ammonifying power reaches its maximum at the end of the frozen period. 
