DISINFECTION STUDIES 201 



organisms in distilled water and tap water, and we must there- 

 fore conclude that in this bacterial species plasmolysis is not a 

 very prominent phenomenon. 



Winslow and Falk (1918) have demonstrated very interesting 

 salt effects and antagonisms upon Bad. coli dying in water; and 

 Hohn and Sherman (1921) note similar effects upon growing 

 bacteria. The suggestion of Zeug should be recalled in this 

 connection. It is conceivable that such effects occurred in our 

 experiments but were overshadowed by other more prominent 

 factors. In the hght of our experience with the activity of 

 unbuffered suspension media upon bacterial death we must 

 appreciate at once the great experimental difficulties involved 

 in the study of pure salt effects, and the need for caution in their 

 interpretation. 



The behavior of Bad. typhosum at different hydrogen ion 

 concentrations 



The study of the mortality of bacteria at constant hydrogen 

 ion concentration was made in M/500 solutions of Clark and 

 Lubs' phthalate and phosphate buffers. It was considered 

 desirable to keep the concentration of salt down to a minimum, 

 and this dilution of the buffers was found to be the lowest that 

 would maintain the pH unchanged under our conditions. 



Experiment 5 {Bad. typhosum at pH 3.8, 5,0, 5.4, 6.4, 7.1, 

 7.6, 8.7 and 9.5) was performed to determine if constancy of pH 

 would condition a uniformity in the results from duplicate bottles; 

 and to learn the effect of pH at constant temperature (20°C.) 

 upon the viabiUty. Figure 5 shows that the effect of maintain- 

 ing a constant pH throughout the experiment was to produce a 

 high uniformity in the results from duplicate bottles.* As a 

 consequence, duplicate curves, while determined in all cases, 

 are omitted from the rest of the charts for the sake of clarity in 

 presentation. 



Reference to figure 5 shows that decline occurs at all hydrogen 

 ion concentrations, and is least at pH 5.0 and 5.4. At pH 3.8, 



' These are not selected specimens, but include all the tests made. 



