430 C. M. HILLIARD AND MILDRED A. DAVIS 



temperature below freezing where the germicidal effect is greatly 

 accelerated. 



4. The death-rate of B. coli is much higher in media which 

 are frozen solid than it is in the same media not solid and at a 

 slightly lower temperature. 



5. Crystallization, probably resulting in mechanical crushing, 

 is an important germicidal factor in causing the death of bac- 

 teria at zero degrees Centigrade and below. The greatest reduc- 

 tion occurs promptly upon freezing and refreezing, but is not 

 caused so much by the sudden change in temperature as by this 

 mechanical factor. 



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