SULPHANILAMIDE-^-AMINOBENZOATE COMPETITION 113 



now subcultured into fresh sulphanilamide-free medium, 

 growth will occur as usual. Sulphanilamide is consequently 

 said to be "bacteriostatic," in that it prevents multiplication 

 without necessarily killing the organisms. The quantity of 

 sulphanilamide which is bacteriostatic for any given organism 

 varies greatly with the constitution of the medium in which 

 the test is carried out. For instance, media which contain 

 peptone or yeast extract can support growth in the presence 

 of much higher concentrations of sulphanilamide than simple 

 synthetic media. This is explained in the case of yeast 

 extract by the presence in the extract of a substance which is 

 antagonistic to sulphanilamide in that it prevents its bacterio- 

 static action on the bacteria. Woods investigated the 

 properties of this anti-sulphanilamide substance, and showed 

 that it has the properties both of a weak organic acid and of a 

 diazotisable aromatic amine. He then tested the anti- 

 sulphanilamide activity of jo-amino-benzoic acid, and found 

 that 1 molecule can neutralise the bacteriostatic action of 

 5000-25,000 molecules of sulphanilamide. No other substance 

 of this nature that was tested has such marked anti-sul- 

 phanilamide activity and, shortly after, other workers were 

 able to isolate jt?-amino-benzoic acid itself from yeast extracts. 

 In the extracts p-amino-benzoic acid exists in the free state 

 and also combined as a peptide with glutamic acid, and the 

 amount of (free -\- combined) substance is sufficient to account 

 for the total anti-sulphanilamide activity shown by the 

 extract. At the time of the demonstration of its anti-sulphani- 

 lamide action, no function had been attributed to ^-amino- 

 benzoic acid in bacteria, but within a few months two 

 Australian workers, Eubbo and Gillespie, were able to show 

 that it acts as a growth factor for CI. acetohutylicum. The 

 list of organisms which require ^-amino-benzoic acid as a 

 growth factor has now been exteruded to include certain 

 Acetobacter, Lactobacilli, and a mutant strain of Neurospora. 

 Eecently j9-amino-benzoic acid has been shown to form part 

 of the molecule of folic acid (Table VIII) which is required 

 by many of the Lactobacteriaceae. 



CHEM. A. B. S 



