314 



PHYSIOLOGY OF BACTERIA 



is no evidence at all available that death by freezing is 

 due to an oxidation process as is death by drying. All 

 data on death by freezing indicate that it is not brought 

 about by one fundamental reaction. Hilliard, Torossian 

 and Stone (1915) enumerate the following factors which 

 might cause death during the freezing process: inter- 

 ference of low temperature with metabolism; rupture of 

 membrane by pressure of ice formation in the cell; 

 rupture by external pressure or grinding during crystal- 

 lization; pressure by expansion of the freezing medium 

 in closed receptacle; prolonged suspension of metabolism 

 leading to slow death by old age or by starvation. 



That freezing, i.e., the crystallization of water as 

 such, causes death was shown by Hilliard and Davis 

 (1918) by comparison of the death rate in water which 

 solidified, with that in sugar solutions which did not 

 solidify, at the same temperature. Some of these 

 results are given in Table 92, each datum represent- 

 ing the average of at least four experiments. The 



Table 92. — Death op Bad. coli by Freezing Temperatures 



FOR 3 Hours 



destructive effect of the physical process of freezing 

 was further shown by the very rapid destruction of 



