MECHANISM OF DEATH 313 



Bacteria in oil or other water-free fluids die in the same 

 way as do dry bacteria. 



The rate of death of dry bacteria is greatly affected 

 by the medium upon which they are dried. 



SUMMARY OF THEORIES 



The primary cause of death of dry bacteria is an 

 oxidation process; the death rate is proportional to the 

 square root of the oxygen concentration. 



The temperature coefficient of this oxidation process is 

 either normal (experiments with micrococci, range 

 7-37°C. and lactic acid bacteria, range 0-30''C.) or 

 higher, but not above 10 (experiments with yeast, 

 range 30-100°C.). The temperature coefficient probably 

 increases with an increasing moisture content of the 

 test organism. There is no evidence that the cause of 

 death of dry bacteria at temperatures above the maxi- 

 mum for growth is different from that at temperatures 

 of normal life. 



The cause of death of dry bacteria in the absence of 

 oxygen is still unknown. 



V. DEATH BY FREEZING 



Death of bacteria by freezing has been studied to 

 a considerable extent from the viewpoint of typhoid 

 epidemics from river ice, and also on account of food 

 preservation by freezing. The data obtained are not 

 very uniform, sometimes they are contradictory, and 

 make it probable that several factors enter which had 

 not been controlled in the experiments published. 



If we consider freezing to be a solidification of water, 

 then freezing is identical in its effect with drying, and 

 death by freezing should follow the same general 

 rules and laws as that by drying. However, there 



