44 



LO(h\RlTHMI<' ORDER OF DEATH 



When old cells are transferred to a new environment 

 they are dormant and do not all begin to grow at the same 

 time. Some cells start much earlier than others, and the 

 general picture is probably similar to that of the germin- 

 ation of Aspergillus spores shown in Figure 12. This 

 leads to great contrasts in sensitivity since very young 

 and very old cells occur side by side. If such cultures 

 are treated with antiseptics or heat, the survivor curves 

 are very markedly concave upwards. They become more 

 and more nearly straight as the culture gets older. This 



Time of irradiation in seconds 



Fig. 8. Order of death of Bacterium coli killed by X-rays. The solid 

 line represents the order of death when the bacteria were exposed to 

 X-rays immediately after being spread on agar; the dotted line, when 

 they were exposed a few hours after being spread. (From data of 

 Wyckoff and Rivers, 1930.) 



