Tue INFLUENCE OF Low TEMPERATURE ON Soit BacTerRIA 1061 
EFFECT OF LOW TEMPERATURE ON BACILLUS RADICICOLA 
Since little or no work has been done in studying the effect of low 
temperature on pure cultures of the soil bacteria, it was deemed advisable 
to use the non-spore-bearing organism Bacillus radicicola, because of its 
economic importance. Since this is the organism used for inoculating the 
legume plants, it was thought that if low temperature does have a marked 
effect on its development, this fact might throw some light on the soil- 
inoculation question. 
The method employed was to grow the bacteria in pure cultures in 
nutrient solutions, sand, and soil, and then subject them to different 
degrees of temperature for varying lengths of time. The nutrient solution 
used was the one recommended by Wilson (1917) in his studies of Bacillus 
radicicola. ‘The saccharose in the original solution was replaced by 
mannite, using 1 gram per liter. The larger amount of sugar tended to 
increase the viscosity of the growth, which rendered it less favorable 
for quantitative work. The soil used was of the Dunkirk series. Counts 
were made by the agar-plate method. The medium used was the same as 
the nutrient solution mentioned above, with the addition of 1.5 per cent 
agar. The 10 grams of soil —or, in the case of the nutrient solution, 
1 cubic centimeter — was added to water blanks until the desired dilution 
was obtained. Five plates were poured from each dilution, and three 
dilutions were used in all cases for pouring the plates. Separate counts 
were made in all cases and the averages of the five plates were taken for 
the final counts. The results in table 7 represent the findings on 1350 
plates. 
All freezing was done in thin-walled glass tubes. In the solution tests 
the bacteria were grown in the test tubes in which they were later frozen. 
Five-hundred-gram portions of the sterile soil and sand were inoculated 
with the bacteria and maintained for one week at 25° C. Tests were 
made of these samples by weighing out one-gram portions into sterile 
tubes and subjecting them to the low temperatures. The samples were 
then added to 500-cubic-centimeter water blanks, in a frozen condition. 
An attempt was made to keep uniform all conditions that were not being 
studied. By lowering the tubes gradually into the liquid air it was possible — 
to freeze them without breaking the glass. 
In interpreting the results shown in table 7, the fact must be kept in 
mind that the present method of determining the number of bacteria is very 
