Abstract
M. tuberculosis var. hominis produces in Long''s medium in the presence of p-aminobenzoic acid (PABA) and procaine in a conc. of 1:750 to 1:4000, a bright yellow pigment. The influence of different substances (Mg, Fe, poisons, aromatic amines, etc.) upon the formation of this pigment is studied. It is supposed that this pigment is produced by the action of a specific "PABA-oxidase," and that the pigment itself is an oxidation product of PABA.