SALT EFFECTS IN BACTERIAL GROWTH' 



II. THE GROWTH OF BACT. COLI IX RELATION TO H-ION 

 CONCENTRATION 



JAMES M. SHERMAN and GEORGE E. HOLM 



Prom the Research Laboratories of the Dairy Division, United States Department 

 of Agriculture, Washington, D. C. 



Received for publication, January 7, 1922 



It has been shown in a previous publication (Holm and Sher- 

 man, 1921) that sodium chloride and various other neutral salts 

 in 0.20m concentration affected the rate of growth of Bact. coll. 

 Using neutral salts with a common cation (sodium) but with 

 various anions a marked difference was observed between the 

 action of the various salts. The effect of the chlorides of sodium, 

 potassium and ammonium seemed to be approximately the 

 same while the calcium and iron salts tested retarded greatly or 

 inhibited growth. These experiments were carried out at a 

 pH of approximately 7.0 and with a salt concentration of 0.20m 

 in 1 per cent'pepton. 



In as much as we know that there are limiting pH values for 

 bacterial growth, varying with different organisms, it would be 

 of interest and value to know just to what extent this neutral 

 salt action is affected by various H-ion concentrations In 

 the following experiments, as in our former communication, the 

 rate of growth was determined by the time that expired between 

 inoculation and the first sign of turbidity. The medium used 

 was 1 per cent pepton to which had been added various amounts 

 of salts, and the H-ion concentration adjusted by the use of 

 concentrated HCl and NaOH solutions. 



The effects of various concentrations of NaCl at various H-ion 

 concentrations were first tried. The H-ion and salt concentra- 



' Published with the permission of the Secretary of Agriculture. 



465 



JOURNAL OF DACTFRIOLOOT, VOL. VII, NO. 5 



