J. Henderson Smith 



45 



of resistance to deleterious substances," but that the "different Ufetime 

 of the different bacteria does not depend in a sensible degree on their 

 different abihty to resist the destructive action of the poison." 



This objection, however, rests on a misconception or confusion of 

 thought, as has been pointed out by Brooks (U) already. In the frequency 



140 



180 



20 60 100 



Fig. 8. Frequency curve derived from the 0-4 per cent, phenol sigmoid curve in Fig. 1, 

 together with a normal curve (solid line). 



Fig. 9. Frequency curves derived from 0-4, 0-6 and 0-7 per cent, curves, 

 showing increasing departure from normal with increase of phenol. 



curve the base Une represents resistance, increasing in grade or degree as 

 one proceeds along it. E.g. if we were to suppose that the mechanism of 

 resistance is simply the thickness of the spore-envelope, through which 

 the poison has to penetrate, the base-hne would represent increasing 

 thickness measured in some selected unit. In the survivor curve our 



