48 



Killinr) of Bofnjtis Spores hy Phenol 



Again, to tako an illustration from anthrax spores as used by Chick : 

 the observed logarithmic curve given by her (Table II, p. 99 in her 

 first paper) is derivable from the frequency shown in Fig. 11 when 

 i^/log T = 55-8. 



It is not suggested that the expression -R/log T is necessarily the 

 correct expression of the relationship between the times required to kill 

 and the resistances. We have not sufficient data to arrive at a correct 

 formulation of this relationship. But it is brought forward to show that 

 by some expression of the kind, which takes into account the alteration 

 in the rate of interaction between cell and poison produced by alteration 

 in the strength of the poison, it is possible to obtain a logarithmic sur- 

 vivor curve from a frequency distribution of approximately normal 

 shape, and that the occurrence of the logarithmic survivor curve does 

 not compel us to look for its explanation in a direction entirely other 



16 

 12 



8 



4 



20 40 60 80 100 120 140 160 180 



Fig. 11. Transposition of anthrax survivor curve (Chick) into frequency. 



than that of differences in degree of resistances. The logarithmic and 

 sigmoid curves are both dependent on the distribution of resistances in 

 the suspension of spores or bacteria. They are both particular cases in 

 the relationship between the resistance and the time required for kilhng; 

 and may be regarded as different expressions of the same general prin- 

 ciple, not as indicating phenomena of entirely different order. 



It is not overlooked that this way of regarding the results has its 

 own difficulties, the chief of which is that for a given distribution there 

 is one value, and only one, of R/log T, which gives the best approach 

 to a logarithmic survivor curve. But the value of this expression may 

 vary over a considerable range without any great departure from the 

 logarithmic type, and the value of k in the formula kt = log a/a — x 

 may also vary correspondingly. It also explains some facts which are 

 otherwise difficult to interpret. 



