Tuer INFLUENCE OF Low TEMPERATURE ON SOIL Bacteria 1063 
flora of the soil. The results show no difference between the total counts 
of the normal soil and those of the samples that had been exposed to the 
temperature of liquid air for six hours, or those frozen with ice and salt for 
six hours. The samples exposed to the temperatures of —15° and —190° C. 
both showed a marked increase over that of the normal soil, again indi- 
eating a breaking-up process. It would seem that the non-spore-bearing 
bacteria, such as Bacillus radicicola, are able to withstand the effect of 
low temperature of the soil. Careful work on the bacterial-activity 
problem would doubtless verify this supposition. All evidence points to 
the probability that the effect of freezing on the soil is physical, not 
bacteriological. 
INFLUENCE OF CONCENTRATION OF THE MEDIUM ON THE DEATH 
a OF BACTERIA AT LOW TEMPERATURES 
The results obtained with Bacillus radicicola in solution and soil cultures 
would seem to indicate that the concentration of the solution surrounding 
the bacteria had something to de with the ability of the bacteria to with- 
stand low temperatures. The work of Maximow (1914) showed that such 
a protective action was evident when plants were placed in solutions of high 
concentrations. This protective action noted in the soil may have been 
due to the concentration of the soil solution or to some other factor such as 
the influence of surface tension on the large and the small soil particles. 
If the death of the bacterial cell when frozen is due to the withdrawal 
of water from the semi-permeable membrane, or outer layer of the cell, 
resulting in the precipitation of the proteids, then it should be possible 
to overcome this harmful effect of freezing by increasing the concentration 
of the cell sap. The greater the concentration of the cell sap within 
the cell, the greater would be the osmotic pressure, the greater the 
power of inhibition, and the greater the resistance of the cell to low 
temperatures. 
There is a possibility that the surface tension may be so great on the 
small particles that it would prevent the freezing of the solution. But 
when one considers that a pressure of 2600 atmospheres is necessary to 
prevent starch grains from absorbing water, and a pressure of 13,000 
atmospheres is necessary to prevent water from freezing at —20° C., one 
realizes that if the surface tension does play an important part in the soil 
solution the pressure must be very great. 
