1066 A. F. Vass ‘ 
samples. The normal is considered as 100 per cent and the decrease is 
given as per cent killed. It is interesting to note that the concentration of 
the medium had no effect when the temperature was lowered below the 
eutectic point of the sugar, but at temperatures about the EuieGae point 
the sugar showed a marked protective action. 
TABLE 9. INFLUENCE OF DEXTROSE ON THE RESISTANCE OF BACTERIA TO 
Low TEMPERATURES 
Bacteria Bacteria 
count Per cent count Per cent 
Dextrose Normal ~ when ai when of 
SENDS (per cent) bacteria frozen in | bacteria} _frozenin_ | bacteria 
count liquid air killed | ice and salt | killed 
for for 
5 minutes 2 hours 
lea eee oe eee mee None No-growth | -.3 252 icncs cs cae) | een eee 
Dae RN fay 0.01 880 ,000 570,000 35 17,600 98 
Sel Siena reine tes 0.05 1,960,000 | 1,240,000 37 98 ,000 95 
Annie Cee 0.1 3,600,000 | 2,400,000 23 398 ,000 89 
Dig mee epee Ep 0.5 4,700,000 | 2,490,000 47 1,220,000 74 
eee Mies Seer 1.0 16,400,000 | 9,480,000 42 6,890 ,000 38 
UL tes MeO: Soda 5.0 24,100,000 | 16,390,000 32 15,660 ,000 39 
Sag eae eee. 10.0 11,300,000 | 8,140,000 28 10,850,000 4 
Qe eae eet 15.0 8,200,000 4,670,000 43 8,006,000 2 
GENERAL DISCUSSION 
It is evident from the data given that the so-called increase in the 
number of bacteria in frozen soils is due, not to an actual multiplication 
and growth of the bacteria in the soil solution as suggested by Conn, but 
rather to a breaking up of the clumps of bacteria which results in an 
increased number of colonies on the agar plates. This view is substantiated 
by the fact that the same increase and decrease in counts may be obtained 
in the laboratory by freezing the soil for a few minutes and then thawing 
it out by means of water blanks at different temperatures. 
The fact that the same marked increase may take place in soils when 
frozen in liquid air at a temperature of —190° C. for a few hours, invalidates 
Brown’s theory that the increased growth takes place in the uncongealed 
hygroscopic water of the soil, for at this low temperature the amount 
of water remaining uncongealed could hardly be considered sufficient for 
the favorable growth of bacteria. 
