THE GERMICIDAL ACTION OF FREEZING TEMPERA- 

 TURES UPON BACTERIA 



C. M. HILLIARD and MILDRED A. DAVIS 



Simmons College, Boston, Massachusetts 



Received for publication October 10, 1917 



Temperature is one of the cardinal factors influencing life 

 activities of micro-organisms. The majority of bacteria are 

 unable to exercise normal metabolism at temperatures below 

 6°C. or above 45°C. 



Temperatures above the maximum are injurious to bacteria, 

 and any appreciable increase above this critical point leads to 

 death. Death of bacteria, due to high temperature, is not 

 instantaneous, but proceeds in an orderly fashion at a rate which 

 is predictable, though very rapid increases in the degree of heat 

 may accelerate death so that it appears immediate. This has 

 been explained as the outcome of accelerated metabolism which 

 leads to auto-destruction. The destructive influence of other 

 disinfectants, both physical and chemical, proceeds in a similar 

 manner and may have a similar explanation. 



Cold as a disinfectant seems to be an exception to this rule; 

 in fact it has the opposite effect, as metabolism is arrested to 

 its lowest ebb by temperatures lower than the minimum, and 

 just below this critical point survival should, theoretically, be at 

 its maximum. \^Tien the temperature is depressed to the freez- 

 ing point or below, new factors enter into the problem and it is 

 with these that this paper is primarily concerned. 



The influence of low temperatures on micro-organisms has 

 received relatively little attention. In 1882 Pumpelly found 

 that samples of ice cut from the center of the block and inocu- 

 lated into sterile beef broth showed living contamination. 



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