78 



THE RISE AND FALL OF BACTERIAL POPULATIONS 



carefully studied by Madsen and Nyman (1907), Chick (1908), and Paul (1909). 

 These investigators found that the reaction velocity of disinfection increased with a 

 rise in temperature, according to the formula of Arrhenius, the function 



T-T, 



log 



remaining constant where ti and ^2 represent times taken for disinfection and Tj, and 

 T2 represent absolute temperatures. 



As the temperature at which such a reaction proceeds increases, the velocity of 

 the reaction increases in geometrical progression. If K' and K are the constants of the 

 reaction at the temperatures T' and T, respectively, and d is the temperature coeffi- 

 cient (Phelps), 



K ^ 



By determining the reaction velocity of the lethal process for bacteria at two 

 temperatures 10° C. apart, we may obtain this temperature coefhcient from the 

 formula 



For anthrax spores exposed to 0.5 per cent mercuric chloride 6 = 1.17. I^i general, 

 the mean velocity of disinfection with metallic salts increases two- to four-fold for a 

 10° rise in temperature (centigrade), while with other disinfectants the increase may be 

 considerably greater. 



The effect of temperature upon the natural death of bacteria in water is essen- 

 tially the same, although the absolute value of the coefficient seems to be somewhat 

 lower. Table IX, from Cohen (1922), illustrates this phenomenon. 



TABLE IX 



Velocity Coefficients for Death of Bact. typhosum and 

 Bad. coli at pH 3.5 at Different Teiiper.\tures 



It will be noted that the temperature coefficient for Bact. coli is much lower than for 

 Bact. typhosum but rises much more rapidly for a 10° C. increase. 



A peculiarly interesting contribution was made by Chick (1910) in the demon- 

 stration that the death of bacteria in hot water follows the same general time relation, 

 although of course with an enormously high time factor. In the case of Bact. 

 typhosum the coefficient was 1.635 per 1° C. The whole phenomenon of cell death 



