"}?. 



In another series of experiments, the B. coli were sus- 

 pended in glucose solutions of ditferent concentrations 

 and then subjected to varying degrees of cold, from - 0.5° 

 to - 6°. The concentrations of glucose were such that the 

 solutions did not solidify at the temperatures used, so that 

 the effect of cold alone, without crystallization, could be 

 determined. The results were compared with those ob- 

 tained with tap-water suspensions of bacteria subjected 

 to the same temperatures. At - 0.5°, an average of 93.67o 

 of the organisms were killed in the frozen tap water, 

 while in the unfrozen glucose solution 46.47^ were de- 

 stroyed. At -6°, an average of 99.2% perished in the 

 frozen medium, and 49.5% in the unfrozen solution. 

 When both the glucose and the tap water suspensions 

 were frozen solidly at - 10° for 3 hours, the percent killed 

 in the former varied from 77.5% to 99%, while in the 

 latter it ranged between 98.1% and 99.8%. 



Tanner and Williamson (1928) exposed 4 species of 

 common bacteria to temperatures of -13° to -15° for 2 

 to 16 weeks, and found that this prolonged freezing de- 

 stroyed some species completely, while others were still 

 alive after 160 weeks at - 15°. 



According to Onorato (1902), the Hemophilus influen- 

 zae is destroyed in blood broth after a stay of 21/2 hours 

 at - 15° or 11/0 hours at - 20°. 



Smith and Swingle (1905) exposed B. typhosus, in 

 bouillon cultures, to - 17.8° for 2 hours and found that, 

 on an average, 99.5% were killed. 



Keith (1913) observed that when B. coli, in solidly 

 frozen tap water, were kept at - 20°, only a fraction of 

 one percent remained alive after 5 days, and that storage 

 of a few weeks at that temperature resulted in a complete 

 destruction of the bacteria. Moreover, when B. coli were 

 in pure milk or in milk diluted to various degrees with 

 water, a larger proportion of bacteria survived the freez- 

 ing of the undiluted than of the diluted milk. 



According to de Jong (1922), the bacteria of dysentery 

 were killed after a relatively short exposure to -20°. 



