LOGARITHMIC ORDER OF DEATH 



59 



time of Bacterium coli or Staphylococcus aureus was dou- 

 bled or even tripled by the addition of dead cells of the 

 same species, provided that the cells were young when 

 killed. Old cells gave no protection, (cf. Table 11). 

 "Watkins and Winslow (1932) observed the same effect 

 in disinfection by alkali as well as by heat (Table 12). 

 Such decrease in the death rate by accumulation of dead 

 cells would tend to make the survivor curve slightly con- 

 cave upwards, and this is the most commonly observed 

 shape. 



TABLE 12 

 Decrease of the death rate constant corresponding to an increase 

 in cell concentration. (Data of Watkins and Winslow, 1932.) 



No satisfactory explanation has been given which cov- 

 ers all cases. It is obviously impossible to assume an 

 equilibrium between dead and living cells correponding 

 to the equilibria of chemical reactions. Watkins and 

 Winslow state: "We can only suggest the possibility that 

 a zone of protective substances in the menstruum sur- 

 rounding a given cell may react upon the chemical or 

 physical condition of the cell wall itself in such a way 

 as to make it more resistant to the influence of heat." 



Recently this problem has come to the foreground 

 again in the study of the efficiency of the sulfonamide 

 compounds. It is usually stated that amino benzoic acid 

 (which neutralizes the effect of sulfa compounds) is re- 

 leased in small quantities from autolyzing cells. This 



