468 



JAMES M. SHERMAN AND GEORGE E. HOLM 



same medium to which had been added NaCl to make a 0.20u 

 solution. These media were adjusted colorimetrically, the end 

 point being determined with methyl red, and it is of course 

 recognized that there may be a slight error in the measurements. 

 The significant fact is not whether the point established is ex- 

 actly pH 4.8 but that the limiting H-ion zone of growth may be 



TABLE 3 



The shifting of the limit of growth of Bad. alkaligcnes at S7°C. in the acid region 



by the addition of NaCl 



1 per cent pepton 



1 per cent pepton 



1 per cent pepton 0.20m NaCl 

 1 per cent pepton . 20m NaCI 



TEfiT 

 NTM- 

 BER 



HE REQUIRED TO BHOW TURBIDITY AT 

 pH VALUES OF 



hours 



90 



No growth 



24 



24 



5.4 



hours 



No growth 

 No growth 



24 



24 



5 2 



hours 



No growth 

 120 



TABLE 4 

 The effect of h'aCl and Na citrate upon Bad. coli at various H-ion concentrations 



1 per cent pepton 



1 per cent pepton . 20m NaCI . . 



1 per cent pepton 0.20m Na 



citrate 



TIME REQUIRED TO SHOW TURBIDITT AT pH VALUE OF 



9 2 



hoUTB 



32 

 14 



No growth 



modified by the addition of NaCl to the medium. The results 

 of five different tests made under these conditions are recorded 

 in table 2. 



Although the widening effect upon the pH limit of growth is 

 not general for all bacteria which we have tried, we have found 

 the effect upon Bact. alkaligenes to be even more pronounced 

 than the effect upon Bact. coli. This is shown in table 3. 



Tables 2 and 3 show that there is actually an extension of the 

 zone in which Bact. coli and Bact. alkaligenes will grow in the 



