L'4 



For certniii slraiiis, -190° was more lethal than -20°, 

 wliile I'or some others it Mas less. 



Kasaiisky (1899) found that B. pestis, cultured on agar 

 and kept at -31° in the frozen condition for 4 months, 

 hut thawed 8 times during the interval, showed a weaken- 

 ing of its virulence. 



Sanderson (1925) gives the following figures as repre- 

 senting the proportion of B. coli which were killed after, 

 respectively, the first, the tenth, and the fifteenth freezing 

 at-78°:167o, 86%, 94%. 



According to Klepzoff (1895), bacteria are killed when 

 exposed to the temperature of liquid air. 



D'Arsonval (1898) reported that the chromogenic func^ 

 tion of B. pyocyanus was slightly impaired by exposure 

 to liquid air temperature. The effect ^vas more accentu- 

 ated if the cultures had previously been dried. 



Macfadyen and Rowland (1900a) mention a slight 

 weakening in the activity of some species of bacteria, 

 after the latter had been left for 7 days in liquid air. 



According to White (1901), a culture of bacteria, ex- 

 posed for 2 hours to liquid air temperature, presented a 

 large number of killed organisms; only the more resistant 

 ones survived. 



Smith and Swingle (1905) subjected bouillon cultures 

 of B. typhosus to liquid air temperatures for 2 hours, and 

 found that, on an average, 99.3% were killed but the few 

 organisms which survived produced normal colonies. 



Rivers (1927) froze a broth suspension of B. coli 12 suc- 

 cessive times in liquid air. Before freezing, there were 

 180,000,000 viable organisms per cc ; after the 12 freezings 

 and thawings, this number was reduced to 40,000. Greater 

 dilution of the suspension decreased the percentage of 

 survivors. 



According to Park, Williams and Krumwiedc {loc. cit., 

 p. 295) 30% of the staphylococci subjected to freezing in 

 liquid air for 30 minutes, remained viable. 



A brief review of the investigations on pathogenic 

 bacteria has been pul)lished by Hampil in 1932. 



