3*2 



Scientific Proceedings (123). 



studies on the toxic influence of calcium and sodium salts upon 

 Bad. communis] and two years ago one of us 2 called attention to 

 the possible influence upon such salt effects of the reaction of the 

 solution. 



In our earlier experiments the reaction of the distilled water 

 and salt solutions to which the bacteria were exposed was not con- 

 trolled though the media were in general alkaline (Ph 8.0-9.0). 

 Under these conditions we obtained the following results with 

 various concentrations of NaCl and CaCl 2 . 



Per Cent, of Bacteria Surviving after 9 Hours. 



Tonicity of Salt. 





0. 



O.I 



0.2 



0.5 



1.0 



30 



5-0 



7.0 



10.0 



NaCl 



89 



us 







83 



64 



58 



20 



< 1 



CaCl, 



89 



70 



92 



45 



22 



< 1 



< 1 



< 1 



< 1 



Later experiments, in which the hydrogen-ion content was 

 maintained at various desired levels by repeated readjustment, 

 gave quite different results, as indicated below. 



Per Cent, of Bacteria Surviving after 9 Hours. 





PH. 



50 



5-5 



6.0 



7.0 



7-5 



8.0 



Water 



82 





106 



54 





12 





27 



20 



87 



76 



8 



9 





134 





128 



106 







These results (which are all based on averages of a sufficient 

 number of tests to eliminate chance variations) were at first highly 

 puzzling. In the unadjusted alkaline solution 5.0 isotonic NaCl 

 was moderately toxic and 1.0 isotonic CaCl 2 highly toxic. At ad- 

 justed P H values on the other hand 5.0 isotonic NaCl remained at 

 practically all reactions slightly more toxic than water but 1.0 

 isotonic CaCl 2 entirely lost its toxicity and became actually stimu- 

 lating, at least at Ph values between 5.0 and 7.0. It appeared 

 therefore that neither 5,0 isotonic NaCl nor 1.0 isotonic CaCl 2 is 

 in itself toxic at adjusted P H values between 6.0 and 7.0; and that 

 at an adjusted Ph much over 7.0 both salts, as well as distilled 



1 Falk, Proc. Soc. Exp. Biol., 1920, xvii, 210. 



