350 PHYSIOLOGY OF BACTERIA 



tion is given by weight, and not by hydrogen ions. 

 The death rate by acetic acid, (with n = 1) is propor- 

 tional to concentration, and therefore a straight line. 



As has been shown before, the death rate in acid solutions depends 

 primarily upon the hydrogen ion concentration. From Table 

 108, it is evident that in hydrochloric acid, the death rate is pro- 

 portional to the square root of the hydrogen ions {n = 0.5) while 

 with acetic acid, it is proportional to the square (n = 2) and with 

 butyric acid, proportional to the 4th power of the hydrogen ion 

 concentration (n — 4). This is hard to explain, even if we assume 

 a special effect of the kations or the undissociated molecules. Neither 

 these results nor the investigations of Winslow and Lochridge (1906) 

 and of Norton and Hsu (1916) are based on direct pH measurements. 

 Since the development of quicker methods of direct pH measurement, 

 two papers have given extensive data on this point, those of Cohen 

 (1922) and of Myers (1929). 



Table 104 p. 340 by Cohen covers a wide range of 

 pH . If the death-rate were proportional to the H+ or 0H~ 

 concentration, then the rate divided by this concentra- 

 tion should give a constant. This is not the case; 

 but a constancy over a wider range is obtained if we 

 divide the rate by the square root of H+ or 0H~ concen- 

 tration {n = 3^^). 



The same is true with Myers' experiments on the 

 death of spores of a bacillus similar to B. cereus, in 

 buffered solutions of highly alkaline washing powders. 

 All of Myers' results are expressed by the time required 

 to kill 99% of the bacteria, since the increasing death 

 rate (see p. 296) made the determination of an average 

 death rate impractical. 



Excluding the one apparently wrong value of experi- 

 ment No. 10, there is a good consistency of results. 

 Myers found the products of the kilHng-time and 0H~ 

 concentration to be constant for pH 12 to 13. This 

 means that the death-rate is proportional to the 0H~ con- 



