30 



LOGARITHMIC ORDER OF DEATH 



The following table shows the relation between the 

 deathrate constant K and the percentage of bacteria 

 killed per time unit, which is (100-s). 



Sandholzer and Katzin (1942) found a simple way of 

 expressing the logarithmic relation in practical appli- 

 cations. They point out that, for a survival ratio of 10%, 



Kt = log. 



a 



and therefore 



0.1a 



t = 



= log 10 = 1 



K 



Then, instead of speaking of deathrates or percentage 

 of survivors, they use as basis of all their calculations 

 this "decimal reduction time," i.e., the time necessary to 

 reduce the bacterial population to one-tenth of its orig- 

 inal value. It is obvious that a doubling of this time 

 will reduce the number of bacteria to 1% of the initial 

 number, and trebling would leave only 1 out of 1,000 cells 

 alive. This terminology is applied to the pasteurization 

 of milk. The decimal reduction time is more readily vis- 

 ualized than the death rate. Generally speaking, death 

 time is more commonly used in applied sterilization and 

 disinfection than death rate. 



