DISINFECTION STUDIES 



207 



mortality curve is very nearly a straight line, but at the lower 

 end there is a tendency to flatten out somewhat. In the case 

 of Bad. coli (fig. 7) there is a suggestion of this tendency at the 

 beginning of the curve. If we take the average velocity coeffi- 

 cients for comparison, the results may be arranged as in table 4. 

 We note in the case of Bad. typhosum that the increase in the 

 death rate is fairly regular for 10° intervals, being 1.02, 1.53 

 and 1.77 from 0° to 30°C., while for coli the corresponding in- 

 creases are 2.12, 4.36 and 3.76. With Bad. coli the eflfect of 

 temperature is to increase the velocity for the 10° intervals from 

 0° to 30°C. in the ratio of 1 : 2 : 9 : 35 which corresponds closely 

 to the exponential series: 2° : 2' : 2' : 2^ Such a relation is 

 not evident in the behavior of Bad. typhosum. 



TABLE 4 

 Average velocity coefficients for the death of Bad. typhosum and Bact. coli at pH S.6 



at different temperatures 



Qio is the temperature coefficient for the indicated 10° interval. 



If the ratio of velocity coefficients be considered a measure of 

 the relative resistance of these organisms, we observe that at 

 0°C. Bact. coli is 67 times as resistant as the typhoid bacillus. 

 As the temperature is increased by ten-degree intervals the rela- 

 tive resistance of Bad coli decreases so that at 30°C. it is only 

 eight times that of Bact. typhosum. 



