SALT EFFECTS IN BACTERIAL GROWTH 



515 



Inasmuch as the anionic effects seem to be predominant in 

 chemical reactions it was decided to try the effects of salts having 

 a common cation (sodium). The salt concentration chosen to 

 be used was 0.20 molar, which was low enough to give the ionic 

 effects and not too pronounced osmotic effects of the salts. To 

 eliminate as nearly as possible H-ion effects the pH was adjusted 

 to 7.0, colorimetrically, before final sterihzation. 



TABLE 1 

 Showing the effect of various sodium salts upon the rate of growth of Bact. coli 



* Mono-and di-sodium phosphate were mixed in proper proportions to give 

 a pH of approximately 7.0. 



t The sodium lactate used was prepared by adding NaOH to lactic acid until 

 a pH of 7.0 was reached. 



Table 1 shows the effects of various sodium salts upon the 

 growth of Bact. coli. The table indicates that the CI, I, NO3, 

 SO4, PO4, and lactate ions accelerate growth of Bact. coli, while 

 the other ions tried inhibit to a greater or less extent. Using 

 the CI, I, SO4, and lactate ions in the same concentrations, the 

 series was repeated with the following results: 



Tinif 

 Medum hours 



1 per cent pepton 4J 



1 per cent pepton 0.20 M NaCl 3^ 



1 per cent pepton 0.20 M Nal 3^ 



1 per cent pepton 0.20 M Na lactate 3i 



1 per cent pepton 0.20 M NajSOi ^ ^ 



