302 PHYSIOLOGY OF BACTERIA 



This rate is increasing with higher organisms, but con- 

 stant or decreasing with bacteria, except in the above- 

 mentioned three cases. 



Young cells, a few hours after having been transferred 

 into a new medium, are more sensitive to adverse condi- 

 tions than cells of the same culture after growth has 

 ceased. 



The time required to kill all bacteria in a given volume 

 increases with the number of cells, regardless of the 

 means used to kill them. 



The last survivors of a disinfection experiment, as 

 a rule, do not give cultures of a higher resistance than 

 the original strain. 



SUMMARY OF THEORIES 



The logarithmic order of death cannot be explained 

 by a graded resistance unless several assumptions 

 are made which have no biological justification other 

 than to fit this purpose. 



If the order of death is computed under the assumption 

 that the destruction of one certain molecule in the cell 

 is sufficient to prevent growth, the resulting order of 

 death corresponds to that observed with bacteria of 

 uniform age. The computation for the assumption 

 that several or many molecules must have reacted 

 before death occurs, gives survivor curves corresponding 

 to those observed with multicellular organisms. 



The order of death of cells with only one ''reacting 

 molecule" shows a constant death-rate and a straight 

 line in the logarithmic survivor curve. If the cells 

 under test are not all of the same physiological condition, 

 but show differences in resistance, (each grade of resist- 

 ance having a constant death-rate) the logarithmic 

 survivor curve will sag below the straight line and the 



