I. INTRODUCTION Chromogenesis in the coli-aerogenes group of bacteria has been known for a long time, and pigmented strains of coliform bacteria have been studied and described by a great many investigators. Fremlin (1893) in differentiating between Escherichia coli and the typhoid bacillus, among other characteristics noted that Escherichia coli grew with a yellowish tint on potato whereas the typhoid bacillus was colorless on the same medium. Later, Holliger (1902), Levy (1904), and Burri and Holliger (1909) found yellow pigmented coli-like organisms in fermenting dough. The same type of organisms was also reported by Eisenberg (1918). The studies of McConkey (1909), Wood (1919), and Perry (1929) indicate that pigmented coliform organisms were not infrequently found in their surveys. Rogers, Clark, and Evans (1916) and Rogers, Clark, and Lubs (1918) stated that there was a correlation between pigmentation and other physiological characteristics, and proposed that the chromogenic coliform organisms could be differentiated on the basis of color. However, Rogers and his associates did not continue these investigations, and the idea of classification of these organisms using chromogenesis as a differential character was abandoned. Recently, Oesterle (1935) described a yellow pigmented organism and proposed the name Bacterium coli flavum. Parr (1937) isolated a pigmented coli
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