Studies on Salt Action. 



313 



water, are definitely toxic. What conditions could have existed in 

 the earlier work, at uncontrolled Ph, to make 1.0 isotonic CaCl 2 

 toxic and 5.0 isotonic NaCl nearly non-toxic? 



The key to this riddle, first suggested by the experiments 

 reported here two years ago, has been found in the influence of 

 salt content upon the power of a bacterial suspension to regulate 

 its reaction. We find, as shown below, that in an unadjusted 

 alkaline water solution containing bacteria the reaction quickly 

 reverts toward the neutral point, while in a similar isotonic CaCU 

 solution the reversion is much slower. In slightly acid solutions 

 (Ph 6.0) this difference in behavior is not apparent. 



Distilled Water. 



Isotonic CaCh 









Per Cent. 







Per Cent. 





Ph 





Bacteria 



Ph 





Bacteria 





Initial. 



9 Hrs. 



Surviving 



Initial. 



9 Hrs. 



Surviving 









After 9 Hrs. 







After 9 Hrs. 



Unadjusted. 



9.2 



8.0 



9i 



9.2 



8.9 



< 1 



Adjusted. . . 



6.0 



6.1 



76 



6.0 



6.5 



90 



These last experiments indicate again that at a P H controlled 

 between 6.0 and 7.0 neither water nor 5.0 isotonic CaCl 2 has toxic 

 action; that in water with an initial Ph over 9.0 the reaction falls 

 to about 8.0 in 9 hours and no toxic effect is manifest; and finally 

 that in an isotonic CaCl 2 solution of initial P H over 9.0 the re- 

 action changes but slightly and the bacteria show the high mor- 

 tality to be expected in such an alkaline solution. The only 

 anomaly that remains is the fact that the alkalinity of the unad- 

 justed water solution although it falls considerably still remains 

 rather high. In these last experiments a P H of 8.0 after 9 hours 

 is non-toxic while as previously indicated a P H maintained at 

 8.0 throughout an experiment is toxic. We may explain this on 

 the probable assumption that in a solution whose reaction is being 

 brought toward neutral by the regulating action of contained 

 bacteria there are zones immediately surrounding the bacterial 

 cells which have an alkalinity lower than the average for the sus- 

 pension as a whole. Thus our P H readings in such a suspension 

 do not represent the actual concentration of hydrogen ions about 

 the cell as they do in a suspension of artificially controlled reaction. 



