46 



lAXSAUlTHMlC ORDER OF DEATH 



Fig. 10. Sharp breaks in survivor curves. 

 Left: Bacterium 8chottmuelleri killed by exposure to 5.5°. 

 Right: Monilia Candida killed by exposure to 50°. 

 (From data of Beamer and Tanner, 1939a, b.) 



Another phenomenon probably due to the effect of 

 age upon the resistance of bacteria, although definite 

 proof is still lacking, is the abrupt break in survivor 

 curves which has been frequently observed in heat disin- 

 fection, but which occurs also in chemical disinfection. 

 Figure 10 shows a typical example. 



The first quantitative records of this phenomenon were 

 made by Gage and Stoughton (1906) who found that 

 when old cultures of Bacterium coli were exposed to 

 heat, a few cells remained alive for a long time after the 

 large majority had died. In one experiment, 99.99% of 

 the cells were killed in 5 minutes at 60^, but a few sur- 

 vived even when heated to 85° for 5 minutes. 



The great practical difficulties arising from this phe- 

 nomenon in pasteurization and sterilization will be dis- 



