DISINFECTION STUDIES 219 



to mortality at the maxiimun or logarithmic rate. This provides 

 an opportunity for studying the early response of the organism 

 to the disinfection process. 



3. The period of induction is decreased by higher acidity and 

 by higher temperature. It appears to have^a duration inversely 

 proportional to some exponent of the temperature. It is analo- 

 gous to the induction period occurring in chemical reactions. 



4. At constant pH, the relative resistance of Bad. coli to 

 Bad. typhosum decreases with rise in temperature from 0° : 10° : 

 20° : 30° m the ratio of 67 : 51 : 18 : 8. 



5. At 20°C. Bad. typhosum possesses the greatest tolerance 

 within a narrow zone of hydrogen ion concentration delimited 

 by pH 5.0 and 6.4. A slight increase in acidity beyond the 

 zone results in conditions of maximum mortahty. J'or Bad. 

 coli the zone is wider and centered about absolute neutrality. 

 Cohen and Clark (1919) found that the pH optima for growth 

 and fermentation of bacteria may be different. It is now shown 

 that the optimum for tolerance may also be distinct. 



6. The mortality of bacteria whether by strong disinfectants or 

 by milder agents follows the laws of logarithmic decline. It is 

 shown that the course of the disinfection process can be expressed 

 by mathematical relations comparable to those used in dealing 

 with monomolecular chemical reactions. 



I desire to express my cordial appreciation for important criti- 

 cism and suggestions to Drs. C.-E. A. Winslow, E. Elvove, S. C. 

 Brooks and especially to Dr. W. Mansfield Clark. 



REFERENCES 



American Public Health Association, Report of Committee on Standard Methods 

 of Examining Disinfectants. 1918. Am. Jour. Pub. Health, 8, 506. 



ARRHENrus, S. 1889 The reaction velocity of the inversion of sucrose by acids. 

 Zsch. f. physik. Chem., 4, 226. 



Arrhenitjs, S. 1915 Quantitative laws in biological chemistry. London. 



Barber, M. A. 1908 The rate of multiplication of B. coli at different tempera- 

 tures. Jour. Inf. Dis., 6, 379. 



Beckwith, T. D. 1920 The viability of B. typhosus in alkaline bile in vivo. 

 Proc. Soc. Exp. Biol. Med., 18, 36. 



Beneke, W. 1895 DiezurEmiihrungder SchimmelpilzenothwendigenMetalJe. 

 Jahrb. f . wissensch. Bot.inik, 28, 487. 



