36 • THE ROYAL SOCIETY OF CANADA 



Conn in his summing up of his work in 1913 is still rather dubious 

 about the cause of what he considers a phenomenal increase in the 

 numbers of bacteria in frozen soils. 



The increase in the numbers of bacteria in the frozen soil during 

 the winter season is -not as startling as superficial examination would 

 make it appear. It is a well known fact that in liquids kept at different 

 temperatures bacteria will increase most rapidly at the highest incub- 

 ation temperature, but that the ultimate highest numbers will be counted 

 in the liquid kept at the lowest temperature. Experimenting with 

 soil samples we start out with numbers of bacteria running into the 

 millions, and an increase of each bacterium to two organisms by fission 

 will double the number of millions present. In Conn's experiments 

 of potted soils taken during 1913-14 the lowest count was 24 millions 

 and the highest 50 millions. This reduced to actual increase per 

 single organism is very slight, each organism being subject to one 

 fission divided over a period of two months. Such an increase would 

 be negligible in the usual laboratory practice. At the low temper- 

 ature of the slightly frozen soil bacteria will be preserved a long time, 

 so that it is very possible that when sampling a couple of months apart 

 the same bacteria are encountered in each analysis. In Experiment 

 I bacteria multiplied about four times in the course of a month, a 

 greater increase than showed by Conn, but as the original numbers 

 were smaller the total number was also much smaller than found by 

 Conn. 



The next point deserving consideration is the actual condition in 

 which bacteria find themselves in frozen soil. The other writers have 

 brought forward the theory that only part of the water is actually 

 congealed in frozen soil and that enough moisture is left for the bacteria 

 to continue a slow but persistent growth. All results obtained in 

 this work point to a similar conclusion. In all instances where the 

 influence of the frost was slight, bacteria increased in numbers, severe 

 frost checked this development, and indirectly the water percentage 

 of the soil had to be taken in consideration. When we have two soils, 

 one containing 40% water and the other 20% water, more material 

 will be dissolved in the liquid contained in the first soil. When this 

 liquid concentrates because part of the pure water is congealed more 

 of this concentrated liquid will be left in the soil which originally had 

 the high«r water content. The soil with the greatest amount of 

 liquid can accommodate the greatest number of bacteria, and so we 

 will find in frozen soils the highest number of bacteria in the soil with 

 the highest water percentage. Furthei , in a soil with a small water 

 content the available amount after the greater part is congealed may 

 become so negligible that bacterial development is definitely checked. 



