BACTERIA AND ICE 157 



offered the stoutest resistance under freezing were 

 extremely sensitive to this treatment if the process 

 was carried on intermittently, or, in order words, if 

 the temperature surrounding them was alternately 

 lowered and raised. 



In this manner the bacteria may be said to be 

 subjected to a succession of cold shocks, instead 

 of being permitted to remain in a continuously 

 benumbed condition. The vitality of typhoid 

 bacilli was put to the test under these circum- 

 stances, the freezing process being carried on over 

 twenty-four hours, during which time, however, it 

 was three times interrupted by the ice being 

 thawed. The effect on the typhoid bacteria was 

 striking in the extreme ; from there being about 

 40,000 present in every twenty drops, representing 

 the number originally put into the water, there 

 were only ninety at the end of the twenty-four 

 hours ; and after a further period of three days, 

 during which this treatment was repeated, not a 

 single bacillus could be found. This signal sur- 

 render to scientific tactics forms a marked contrast 

 to the stout resistance maintained for over 103 

 days under the ordinary methods of attack. 



But, although the typhoid bacillus appears to 

 submit and meekly succumb to this plan of cam- 

 paign, yet the conclusion must not be rashly 



