332 



PHYSIOLOGY OF BACTERIA 



cause of death is not that of dry bacteria, it is not oxida- 

 tion. It is some reaction with water, only the rate is 

 decreased because the amount of available water has 



^5* SS'' i5° -jiso ^y ' ^^o 



Fig. 38. — Survivors of young and old cultures of Bacterium coli heated for 

 5 minutes to different temperatures. 



been reduced to a point where it can no more be con- 

 sidered as practically unlimited. 



(e) THERMAL DEATH POINTS 



The above discussions show very plainly that the old 

 definition of the thermal death point as 'Hhe lowest 

 temperature at which an organism would be killed in ten 

 minutes" is without any real meaning because the 

 killing time increases with the number of cells. 



