MECHANISM OF DEATH 283 



ity/' is mathematically identical with the ''deathrate'' 



1 log a - log 6 4. J u 



A = fTZoI ^s computed above. 



This similarity has led some bacteriologists to the 

 belief that bacteria are sufficiently small to react like 

 molecules. Others, however, have assumed that the 

 logarithmic order of death is ultimately due to the 

 logarithmic order of some chemical reaction causing 

 the death. 



Some bacteriologists and biologists have been very 

 much opposed to such mechanistic views and claim 

 that the order of death is due to a graded variation of 

 resistance of the individuals. However, it is not easy to 

 explain the logarithmic order in terms of a graded 

 resistance. Figures 27 and 29 show in their block curves 

 the number of deaths per unit time. The resistance 

 should be graded in a similar way which would require 

 that the most sensitive bacteria are present in the 

 largest numbers. This is quite different from the grada- 

 tion of higher organisms (Figs. 28 and 30). 



Reichenbach (1911) tried to explain this especially 

 graded resistance by the mode of multiplication. He 

 assumes that from each new generation, a definite 

 percentage ceases to multiply, and goes into a state 

 of dormancy in which it becomes the more resistant 

 the longer it remains in this stage. In this way, the last 

 generation which is the largest, is also the most sensitive. 



There is no biological reason to assume that part of 

 the cells of an actively growing culture should go into a 

 resting stage. Besides, Kelly and Rahn (1932), in their 

 study of the fission rates of individual cells, could never 

 observe that any cells stopped growing in the early stages 

 of growth after they once had started multiplying. This 

 holds for Bad. aerogenes and B. cereus as well as for yeast. 



