1060 A. F. Vass 
increase could not have been due to growth and reproduction of the 
bacteria in the unfrozen soil solution, as suggested by Brown, but that it 
must have been due to the breaking up of the clumps of bacteria. 
The results from the liquid-air treatment would indicate that there is 
a breaking up of the clusters of bacteria sufficient to show a marked 
increase above the number in normal soil. When it is considered that 
probably many of the bacteria were killed by the low temperature, it seems 
evident that the breaking-up process must be even greater than the 
plate counts indicate. 
AMMONIFICATION AND NITRIFICATION IN FROZEN SOILS 
In order to test the bacterial activities in frozen soils more carefully, 
the ammonifying and nitrifying powers of frozen soils were studied. 
Peptone and casein were added to the soils at the rate of $ gram to 100 
grams of soil. Thedeterminations of ammonia were made at the beginning 
of the experiment and at the end of five days. One-half of the samples 
were placed in the incubator at 22° C., and the other half were kept frozen 
during the experiment. The determinations of nitrates were made at 
the beginning of the experiment and at the end of four weeks. The 
samples were treated the same as in the ammonification experiment. 
The results are shown in table 6: 
TABLE 6. AMMONIFICATION AND NITRIFICATION IN FROZEN AND IN UNFROZEN SOILS 
Parts per million of dry soil 
Ammonia nitrogen Nitrate nitrogen 
Treatment 
At At At iN 
beginning | the end | beginning | the end 
of of of of 
experiment} 5 days |experiment} 4 weeks 
Soil and peptone, frozen......... BL eoste misters 65.4 68.7 112 118 
Soil and peptone, incubated............... 65.4 382.9 112 253 
Soil/and! casein trozen.5 6 2). aca eee 56.1 DRS 112 116 
Soil and casein, incubated................. 56.1 336.9 112 237 
These results show that there is little or no change going on in the 
soil solution when it is in a frozen state. This indicates that no proto- 
plasmic activity, such as growth or reproduction, is taking place. 
