The oldest members of the coliform group of bacteria, as the reviewer conceives it, are Klebsiella pneumoniae, or Friedlinder's bacillus, described in 1882, and K. rhinoscleromatis, which v.Fritsch recorded the same year. Next come Escherichia coli and Aerobacter aerogenes, both of which were ushered into the bacteriological world in 1885 by Escherich. Somewhat younger is A. cloacae, described in 1890 by Jordan. Proteus morgani, the problem child of the group, dates from 1908 and the juveniles are E. freundii, recorded in Braak's Delft thesis of 1928, and K. paralytica, the etiological agent of "moose disease," described in 1932 by Cahn, Wallace, and Thomas. These are the principal members of the coliform group as listed in the fifth edition of Bergey's Manual of Determinative Bacteriology (12), a great simplification of the genera Escherichia, Aerobacter and Klebsiella given in the fourth edition (1934) 1 on September 22, 2020 by guest http://mmbr.asm.org/ Downloaded from LELAND W. PARR which contained 35 species. In the latest edition these three genera comprise but ten species.1 With this simplification we are in heartiest accord, but the problem has several aspects. Among them, the principle of simplification, or "lumping," as Skinner and Brudnoy (149) term it, must be defended. The inclusion of the genus Klebsiella2 with the coliform bacteria has to be explained. To claim the Morgan bacillus as a coliform organism will require justification. The broadening of the concept of Escherichia coli to include such forms as E. coli-mutabile and the paracolon bacilli which ferment lactose slowly or not at all is a new development and there are many who will want to know how the "coli-aerogenes intermediates" (180, 165, 25, 123) are classified and why. THE TERM "COLIFORM" The term "coliform" has long been in use by British bacteriologists (4, 23, 59, 92, 100, 132, 133, 160). In America, Breed and Norton (16) suggested the term to describe the lactosefermenting bacteria used as a measure of the pollution of water. In 1937 H. E. Jordan advised that as Editor of the Journal of the American Water Works Association his policy would be to substitute "coliform" bacteria for "B. coli" or "colon group" in papers submitted to him (70). As Jordan also stated, the term "coli-aerogenes" continues as official in water analysis since the eighth edition of Standard Methods of Water Analysis (157) uses it. And "Escherichia-Aerobacter" is also official since that is the terminology employed in the sixth edition of Standard Methods of Milk Analysis (156). SEPARATION OF FRIEDLANDER GROUP FROM OTHER COLIFORM BACTERIA As noted above, the first members of the coliform group to be described were Klebsiella pneumoniae, from acute fibrinous 1The other three species are Klebsiella ozaenae, described by Abel in 1893; K. granulomatis of AragAs and Vianna (1912); and K. capsulata recorded in 1889 by Pfeiffer.

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Although foundation for the recognition of coliform intermediates was laid by Brown (1921), he did not utilize his findings for their demonstration. Brown was interested in mediums containing citrated blood and attempted to determine the effect citrate might have on the growth of organisms likely to be encountered in blood culture work. Koser (1923, 1924a, b, c, d, 1926) applied to coliform bacteria (Breed and Norton, 1937) tests involving utilization of organic acids and their salts. He found that Bacterium coli from feces could not utilize citrate as a sole carbon source in contrast to Bacterium aerogenes. Koser found, particularly in soil and water, organisms classed as coli by the criteria then used but which utilized citrate-carbon and, in this respect, resembled B. aerogenes. In 1924 Koser applied the term "intermediate" to these forms. Recognition of such intermediate forms should make possible a better theoretical understanding of the entire coliform group, than which few in bacteriology are more complex or confused. Any fundamental advance, such as the intermediate concept, should enable sanitary science to define more accurately such terms as "pollution" and "potability" and to answer numerous practical questions posed in this field in recent years. Parr (1936a, b, 1937) defined intermediates as coliform organisms "which have one or more coli characters and one or more of those attributed to aerogenes, and some 'intermediates,' including the typical fecal form, produce hydrogen sulphide." This definition permits the inclusion as intermediates of organisms 1