124 



DISINFECTION 



TABLE 10 



Salt Concentrations that limit Growth of Bad. coli in 1 per cent. Peptone Water. 

 Incubation period, 3 days. Molar concentration. 



A further point may be noted from this table, namely, that the bivalent cations 

 tend to be more toxic than the monovalent cations. 



Very much less work has been done on the effect of anions on the growth of 

 bacteria. Falk (1923) points out that the anions play an essentially different 

 part in metabolism from the cations. The former are intimately related to the 

 nutritive metabolism — particularly the anions that contain carbon, sulphur, 

 nitrogen or oxygen — whereas the latter are concerned with the regulative meta- 

 bolism of the organism. Nevertheless, the anions in certain concentrations do 

 undoubtedly possess a toxic action on bacteria. Some figures of Holm and Sher- 

 man's (1921) will exemplify this point. They grew Bad. coli in 1 per cent, peptone 

 water, to which were added various sodium salts, the H-ion concentration being 

 kept practically constant, and compared the rate of growth in the different tubes 

 (Table 11). 



TABLE 11 



1 per cent, peptone 



0-2 M NaCI 



0-2 M NaT 



0-2 M NaNOs .... 

 0-2 M NajSO, .... 

 0-2 M (mixture of Nall^POj 



Na2HP04) 



0-2 M Na lactate . . . 

 0-2 M Na oxalate . . . 

 0-2 M Na acetate . . . 

 0-2 M Na citrate . . . 

 0-2MNaF 



and 



