278 



PHYSIOLOGY OF BACTERIA 



indicated by the black blocks (the unit being five minutes 

 with fruitflies), we get a probability curve. (Fig. 28.) 



Quite similar curves are obtained when death is caused 

 by chemical poisoning, by drying, or other outside 

 influences. As example may serve (see Table 77 

 and Fig. 30) the death of mustard seeds from treatment 

 with HgCl2 by Hewlett (1909). 



(6) ORDER OF DEATH OF BACTERIA 



With bacteria, the order of death is different. If 

 the outside influence (heat, drying, chemical poison, light, 

 etc.) is sufficient to kill the cells at all, the first unit of 

 time will show the largest number of deaths. 



Madsen and Nyman (1907) and, independently. 

 Chick (1908) were the first to recognize that the order of 

 death of bacteria could be described quite simply by 

 the definition that the rate of death is proportional to 

 the number of living cells. In other words, the per- 

 centage of the survivors dying per unit of time is 

 constant during the experiment, regardless of the number 



of cells present. Let us assume a very simple case: we 

 have 1,000,000 bacteria; the death rate is 90%; this 

 leaves, after the first minute, 10% or 100,000 cells alive. 



