i $6 BACTERIA IN DAILY LIFE 



Thus Dr. Prudden froze various bacteria in water 

 at temperatures ranging from - i C. to - 10 C., 

 and he found that different varieties were very 

 differently affected by this treatment; that, for 

 example, a bacillus originally obtained from water, 

 and introduced in such numbers as represented by 

 800,000 individuals being present in every twenty 

 drops, after four days' freezing had entirely dis- 

 appeared, not one having survived. On the other 

 hand, similar experiments in which the typhoid 

 bacillus was used resulted in the latter not only 

 enduring a freezing of four days' duration, but 

 emerging triumphant after it had been carried on 

 for more than 103 days ! 



In these experiments it should be borne in mind 

 that, as the ice was frozen to a solid block or 

 lump, there was no opportunity for the mechanical 

 committal of the bacteria during freezing to the 

 water beneath ; all the bacteria present were im- 

 prisoned in the ice, and the fact that the typhoid 

 bacteria were not destroyed by being frozen shows 

 that they can withstand exposure to such low 

 temperatures, although, as we have seen, the other 

 variety of bacillus employed was destroyed. 



Dr. Prudden, however, discovered an ingenious 

 method by which even typhoid bacilli were com- 

 pelled to succumb when frozen. In the course of 

 his investigations he found that bacteria which had 



