From the above experimental studies, and from the actual records we conclude that there is no necessity of an inference of the role of p-amino benzoic acid in the bacterial metabolism and how it is antagonised by the sulpha drugs. On the other hand we come to this conclusion from the results of direct observation that bacteria utilises oxygen from blood and tissues with the help of catalase which breaks down oxygenase. These two substances abound in all tissues and blood. Peptone, p-amino benzoic acid, its salts and esters etc antagonise the effect of the unsubstituted compounds of the sulphonamides but have no such action on the substituted compounds of the sulpha drugs.