140 bacteriological chemistry 



Table 11 



Neutralisation of /j-aminobeiizoic acid in prt-sence of various bacteria. 



Table 1 1 shows that the relative efficiency of the two 

 drugs in inhibiting the use of p-aminobenzoic acid by 

 various organisms is constant, which means that the 

 drugs act in the same way in preventing the growth of 

 all the organisms. This confirms the suggestion by 

 Woods that different sulphonamides are more effective 

 against some bacteria than against others, because the 

 microbes have different abilities to synthesise ^j-amino- 

 benzoic acid. 



It is clear from Table 10 that the sulphonamide 

 drugs are widely different in their ability to compete 

 with 2)-aminobenzoic acid in the enzyme system involving 

 the latter, sulphathiazole being some 80 times as effective 

 as sulphanilamide. This has been explained by Bell and 

 Roblin as due to the closeness of resemblance of the 

 drug to the ^^-aminobenzoic acid ion in molecular structure 

 and distribution of electric charges. That the effective- 

 ness of the various sulphonamide drugs is closely related 

 to their degree of ionisation is shown by the following 

 values taken from C. L. Fox and H. M. Rose {Proc. Soc. 

 Exp. Biol. Med. 50 (1942) 142) :— 



