SALT EFFECTS IN BACTERIAL GROWTH 



517 



Our results so far have been obtained upon media adjusted 

 to a pH of approximately 7.0. Since we know that the H-ion 

 concentration materially affects growth of bacteria, it is of both 

 interest and value to know to what extent the salts modify the 

 time element at pH values on either side of neutrality. Table 4 

 shows these effects with the salts given and at the H-ion con- 

 centrations stated. The results indicate that the different salts 



TABLE 3 



Showing the effects of various concentrations of NaCl and of MgCh upon the rate 



of growth of Bact. coli 



TABLE 4 



Showing the effects of various salts upon the growth of Bact. coli at different H-ion 



concentrations 



1 per cent pepton 



1 per cent pepton 0.20 M NaCl 



1 per cent pepton 0.20 M Na3S04. . . . 

 1 per cent pepton 0.20 M Na citrate 



TIME OP VISIBLE GROWTH AT pll 

 VALUES OP 



5.2 



hours 



m 



26 



6 2 



5f 



4^ 



7.6 



hours 



3^ 

 4i 

 71 



8.2 



hours 



8 

 3 

 3i 

 22 



9.2 



houra 



32 

 14 



have marked changes of effect with changes in pH. In general 

 we may say that NaCl and NaaSOi widen the optimum range of 

 growth, while Na citrate narrows this pH range. 



DISCUSSION 



The data presented show in a general way some correlation 

 between the so-called lyotropic series and the order of effect 

 upon the growth of Bact. coli. There are, however, ions^which 



