138 BACTERIOLOGICAL CHEMISTRY 



of the drug. Another explanation was that sulphanilamide 

 was oxidised to the hydroxyl-amino compound, 



NHOH.<^ ^SOg-NHg, which was known to inhibit the 



power of catalase to destroy hydrogen peroxide ; 

 in presence of the drug, therefore, organisms such as 

 streptococci and pneumococci, which are sensitive to 

 hydrogen peroxide, are killed by its accumulation. 



2)-Aminobenzoic acid inhibits the bacteriostatic 

 effects not only of sulphanilamide, but also of the 

 other sulphonamide drugs, such as sulphapyridine and 

 sulphathiazole, which have the common grouping 



— NH./ \sO2.NH2. Neither ortho- and meto-amino 



benzoic acids, ^^-aminophenyl acetic acid, 



NHj. / y CH2.COOH, nor 2)-aminophenylglycine di- 



hydrochloride, HCI.NH2. ^ ^CH.COOH, ^^^^ replace 



NH2.HCI 

 /)-aminobenzoic acid in inhibiting the sulphonamides . 

 On the other hand ^^-aminobenzoic acid can reverse the 

 effect of other drugs which have groupings similar to 

 sulphanilamide, such as ^^-aminobenzamide, 



NH2<^ ^CCNH,, or atoxyl, NHa<^ ^AsOaH, 



which slows down the respiration of Esch. coli. However, 



it has no effect on the drug marf anil, NH2CH2./ "^SOa.NHa, 



in vitro although it reverses its effect in vivo. 



It has been found that over a wide range of concen- 

 trations the molar concentration of /j-aminobenzoic acid 

 necessary to reverse the bacteriostatic action of sul- 

 phanilamide is proportional to the molar concentration of 



,, 1 .. ^, .. concentration of dm tr ,. , . , 



the latter. The I'atio : — rr: which lust 



concentration ot /j-AB *' 



