210 



BAKNETT COHEN 



the speed with which the bacteria perish increases to a maximum 

 when the curve becomes a straight Une. This phenomenon 

 among bacteria finds its counterpart in certain chemical reac- 

 tions which possess an induction period prior to reaction at the 

 maximum rate. If the time necessary to reach maximum veloc- 

 ity in death rate is short then the calculation of an average 

 velocity coefficient involves an insignificant error. This rep- 

 resents the mathematical equivalent of drawing a straight 

 line as close as possible to the experimental points. If, however, 

 this induction period is prolonged, then such a procedure may 

 involve serious difficulties. 



TABLE 5 

 Average velocity coefficients of mortality of Bad. coli at different pH values and 



temperatures 



An exact numerical measurement of the extent of this devia- 

 tion is unfortunately not possible because of the limitations of 

 the present experimental method. It may, however, be inferred 

 that it is an inverse function of the temperature. E\'idently 

 at 30°C. it lasted about twenty days in experiments 8 and 9; 

 and at 10° and 20°C. the end was not reached in sixty days. As 

 stated above, a comparison of the average velocity coefficients 

 is not justified as a logical procedure under the circumstances; 

 but with this reservation we may consult table 5 to get an idea 

 of the magnitudes involved. 



This table indicates that the pH zone favoring the lowest 

 destruction rate of Bad. coli is around absolute neutrality. It 

 appears that this zone covers a greater range of hydrogen ion 

 concentration than does that of Bad. typhoswn. 



