LOGARITHMIC ORDER OF DEATH 



43 



Fig. 7. Semi-logarithmic plot of survivor curves of Staphylococcus 

 aureus killed by 0.6% phenol. (From data of Chick, 1908; the two 

 curves have been drawn to the same scale.) 



that young bacterial cells succumb more readily to harm- 

 ful influences than old cells. The term "old cells" is ap- 

 plied to cells of cultures which have nearly or completely 

 reached the maximal population. With the customary 

 technique of the bacteriologist and with the customary 

 test cultures, this stage is reached in about 24 hours. 

 *' Young cells" are cells from cultures 2 to 8 hours old. 

 An increase of the age beyond that required to reach the 

 maximal population does not usually increase the resis- 

 tance of the cells very much. Although many cells lose 

 their viability after the stage of maximal population is 

 passed, those cells which remain viable do not seem to be 

 weakened by old age, and their resistance to disinfect- 

 ants or heat is not decreased. However, they require a 

 longer time for adjustment before they can start to mul- 

 tiply again in a new medium. 



