MECHANISM OF DEATH 293 



values obtained during the first two minutes of the experiment; 

 they might be caused by the change of medium, or by heat shock. 

 The trend of the death rates in all of Reichenbach's experiments is a 

 gradual decrease of K, and the ''spread" of table 83 shows the 

 relative amount of this decrease. 



If Reichenbach's plate counts are plotted as logarith- 

 mic survivor curves on a standard time scale (Rahn, 

 1930) the striking curves of Fig. 34 are obtained. The 

 youngest culture contains old and young cells which 

 differ greatly in resistance and the survivor curve sags 

 deeply. With increasing age of the culture, the old 

 cells begin to multiply, and finally, after thirteen hours, 

 all cells are in a state of rapid multiplication and fairly 

 uniform resistance. This is depicted graphically by the 

 gradual straightening of the curves. 



(g) FREQUENCY OF THE LOGARITHMIC ORDER OF DEATH 

 WITH BACTERIA 



Some biologists have questioned the logarithmic 

 order of death. Loeb and Northrop (1917) in their 

 study of the death rate of fruit-flies (p. 275 and Fig. 28) 

 make the following statement: 



'' Miss Chick has stated that bacteria are killed by disinfectants 

 at a rate corresponding to that of a monomolecular chemical reaction, 

 i.e., that in each interval of time the same percentage of individuals 

 alive at this time is killed. She was probably led to such an assump- 

 tion by the fact that the ascending branch of the mortality curve 

 in her experiments was generally very steep. The agencies used 

 by her for killing the bacteria were so powerful that the ascending 

 branch became almost a vertical line, thus escaping attention. 

 Hence she noticed usually only the less steep descending branch 

 which could be interpreted as a monomolecular curve for the reason 

 that her experiments lasted only a short time." 



This same objection has been raised again and again; 

 it is believed by many biologists that the logarithmic 



