516 



GEORGE E. HOLM AND JAMES M. SHERMAN 



Table 1 indicates that there is a marked effect of salts upon 

 the growth of Bad. coli, and it would seem that it is largely due 

 to the anion. 



To find out to what extent the cation affects such growth the 

 effect of the following salts were tried: KCl, NaCl, NH4CI, 

 MgCls, CaCl2, and FeCls. Table 2 gives the effects of 0.20 

 molar concentrations of these salts upon growth. Table 2 

 seems to indicate that there is little difference between the effects 

 of the Na, K, and NH4 ions. Since in the case of MgCl2 we have 

 twice the concentration of CI ions which we have in the former, 

 a true comparison cannot be made if the anionic effects pre- 

 dominate. To make our experiments comparable we compared 

 growth in a 0.20 molar NaCl pepton mediimi with growth in 



TABLE 2 

 Showing the effect of various cations upon the rate of growth of Bact. coli 



1 per cent pepton 



1 per cent pepton 0.20 M NaCl. . 

 1 per cent pepton 0.20 M KCl. . . 

 1 per cent pepton 0.20 M NH4CI 

 1 per cent pepton 0.20 M MgCla. 

 1 per cent pepton 0.20 M CaClj. 

 1 per cent pepton 0.20 M FeCU. , 



0.10 molar MgCl2 pepton medium. The effects of 0.40 molar 

 NaCl and 0.20 molar MgCli were also tried. 



The results are shown in table 3. lMgCl2 and NaCl, therefore, 

 in concentrations where the number of CI ions is the same, are 

 comparable in effect. That there is a cation effect in greater 

 concentrations, however, is shown by the fact that the time for 

 0.20 molar MgCl2 is 12 hours, while that for 0.40 molar NaCl 

 is but 4f . Doubling the NaCl concentration changes the time 

 rate very httle, while doubhng the MgCl2 concentration more 

 than triples the time. This is strong evidence that there is a 

 cation effect, though it may not be so marked as the anion 

 effects. CaCl2 has a much stronger inhibiting effect while 

 FeCls entirely inhibited growth in the concentration used. 



