346 PHYSIOLOGY OF BACTERIA 



The analogy between the action of hot water and that 

 of alcohols and phenols is borne out by experiments with 

 thermophilic bacteria. These organisms are somewhat 

 less sensitive to phenol than Bad. coli, but more sus- 

 ceptible to p.-nitrosodimethyl-aniline. 



The consequence of this specificity is that the phenol 

 coefficient (p. 353) which indicates how many times 

 more toxic a certain disinfectant is than phenol, must be 

 expected to vary considerably with different organisms. 

 This has been observed by several authors . For example, 

 the following phenol coefficients of sodium hypochlorite 

 were obtained with different bacteria by Zoller and 

 Eaton (1923). 



Mycob. tuberculosis 42 . 8 



BacL alcaligenes 100 . 



B. anthrads 160 



Bact. neapolitanum 200 



Gonococcus 280 



Proteus vulgare 330 



{d) EFFECT OF CONCENTRATION OF POISON UPON DEATH 



RATE 



The influence of the concentration of a poison upon 

 the death rate has been formulated according to physico- 

 chemical principles first by Watson (1908), after Ikeda 

 (1897) and Chick (1908) had given empirical formulae. 

 Later investigators came independently to the same 

 equations, namely Paul, Birstein and Reuss (1910b) 

 and Phelps (1911). 



Assuming that n molecules of the disinfectant must 

 react with one cell before the cell loses the power of 

 reproduction, the reaction constant, or death rate, must 

 be proportional to the nth power of the concentration. 



K = A:c" 



