AXTISEPTICH 155 



may be seen in tlie following table, but when tlie amouut 

 of dissociated drug was computed it was found not to 

 differ much for the four compounds. Thus, although the 

 actual amounts of sulfa drugs which were needed to re- 

 tard growth were high as compared to those of p-ammo 

 benzoic acid, the concentrations of dissociated drug were 

 not very different from those of the acid, their ratio be- 

 ing in the neighborhood of 1. 



Ratio of 



Ratio of PABA^ to dissoci- 



PABA^ to drug ated drug 



Sulfanilamide 1 :5,000 1 :1.4 



Sulfapyridine 1: 40 1:1.4 



Sulfathiazole 1: 8 1:4.9 



Sulfadiazine 1: 8 1:6.4 



1. p-amino benzoic acid. 



Bell and Roblin (1942) reasoned that the more a sul- 

 fonamide resembles ^-amino benzoic acid, the greater its 

 bacteriostatic effect should be. In an extensive study, 

 they measured the two dissociation constants of 50 sul- 

 fonamides, and a very definite correlation between acidic 

 dissociation and antiseptic efficiency was found. ''The 

 more negative the SO2 group of an N^-substituted sul- 

 fanilamide derivative, the greater is its bacteriostatic 

 power." 



Kumler and Daniels (1943) point to some inconsis- 

 tencies in the data of Bell and Roblin, and believe that 

 the main factor in bacteriostasis is the balance of elec- 

 tric charges in the molecule. They explain the activity 

 of the sulfonamides primarily by "the contribution of 

 resonating form with a coplanar amino group. The neg- 

 ative character of the SO2 group is a concomitant factor 

 associated with this resonating form"; it is not the pri- 

 mary factor as Bell and Roblin thought. 



The understanding of the action of sulfonamides is 

 complicated by the discovery of other antagonizing sub- 



