GERMICIDAL ACTION OF FREEZING TEMPERATURES 



429 



Comparing the percentage reduction which occurs in the fluid 

 sugar solutions, and the solidified water kept at the same tem- 

 perature for the same period of time, and with all other factors 

 as nearly identical as possible, it is readily seen that the death- 

 rate is much higher in the solidified tubes. This indicates a 

 very conspicuous role played by crystallization as such, regard- 

 less of the factor of cold. 



This was tested still farther by actually freezing the strongest 

 sugar solution to make certain that the solute itself did not 

 somehow fortify against cold. Some of the results are given in 

 table 6. 



In this table the reductions obtained in the solidly frozen 

 sugar solutions are uniformly higher than those obtained in the 



B. coll frozen solid at 



TABLE 6 

 ■10°C. for three hours in a solution of glucose 56 grams per 

 liter and in tap water 



previous results and are quite comparable with the reductions 

 in the water controls. 



From the foregoing discussions and data we venture to draw 

 certain conclusions, appreciating, however, that the work is not 

 extensive enough to render any of these statements final. 



1. Intermittent freezing of bacteria exerts a more effective 

 germicidal action than continuous freezing. 



2. The reduction is much less in milk and cream than in pure 

 tap water when freezing temperatures are applied, due, no 

 doubt, to physical protection offered to the bacteria by the 

 colloidal and solid matter in suspension. 



3. The degree of cold below freezing is not a very important 

 factor in the destruction of bacteria. There is no critical 



