JOHN F. NORTON 365 



have suggested the use of 2 per cent bile with i : 75,000 brilliant green in order to avoid 

 the inhibitory action of the former medium. Hale' has pointed out that the medium of 

 Dunham and Schoenlein allows the growth of Clostridium welchii and that the inter- 

 ference of this organism is more significant than the inhibition of "attenuated colon 

 organisms which have little if any sanitary significance." The question at issue in- 

 volves both laboratory methods and the interpretation of results and has not been 

 satisfactorily solved. The use of a brilliant green bile medium in the isolation of coli- 

 aerogenes group organisms will be referred to later. Other methods for inhibiting the 

 growth of anaerobes have been suggested. Among these may be m.entioned the use of 

 gentian violet advocated by Hall and Ellefson^ for the presumptive colon test. 



While the presence of members of the coli-aerogenes group of bacteria has long 

 been recognized as constituting evidence of contamination in a water supply, it has 

 also been evident as a result of the work of Prescott^ and others that organisms of this 

 group may be found on grains, grasses, and in other places with suflficient frequency to 

 cast doubt upon the value not only of presumptive tests but of the use of the group 

 as a whole to indicate pollution. The advisability of attempting to distinguish be- 

 tween bacterial strains of coli-aerogenes organisms from intestinal and from other 

 sources is a matter of dispute. It is impossible at the present time to differentiate 

 human and animal organisms.^ It is certainly a safe procedure to utilize the 

 group. On the other hand, it is undesirable to condemn a water supply in the absence 

 of other evidence of fecal contamination. More evidence as a foundation for expres- 

 sion of opinion must be produced. 



Meanwhile, two lines of investigation are being pursued: One is concerned with 

 the perfection of methods for identification of the coli-aerogenes group, and the other 

 is directed toward procedures for distinguishing bacteria in this group arising from 

 fecal and from non-fecal sources. The latter will be discussed first. 



Levines has summarized our knowledge of the biochemical reactions of the organ- 

 isms generally regarded as constituting the coli-aerogenes group, and the reader is re- 

 ferred to his publication for details. To this summary must be added Koser's*" work 

 with sodium citrate. Earlier attempts to differentiate fecal and non-fecal coli-like or- 

 ganisms included reliance upon carbohydrate fermentations and indol production. At 

 the present time these activities must be excluded. The most important correlations 

 are those involving the gas ratio, the methyl-red test, the Voges-Proskauer reaction, 

 and ability to grow in a uric acid or sodium citrate medium. Strains of fecal origin 

 characteristically give a low gas ratio (carbon dioxide -^ hydrogen), an acid reaction 

 using methyl red as an indicator, a negative Voges-Proskauer test, and will not grow 

 in Koser's uric acid or sodium citrate medium. Undoubtedly, the correlation between 

 such tests and the source of the organism is not exact and cannot be expected to be. 



' Hale, F. E.: ibid., 2, 24. 1927. 



= Hall, I. C, and Ellefson, L. J.: J. Bact., 3, 329. 1918. 



3 Prescott, S. C: Biological Studies by the Pupils of William Thompson Sedgwick, p. 208. 1906. 



^ See Prescott, S. C, and Winslow, C.-E. A. : Elements of Water Bacteriology (4th ed.), p. 93. 1924. 



sLevine, M.: Bacteria Fermenting Lactose and Their Significance in Water Analysis, Iowa State 

 College Engineering Experiment Station Bull. 62. 1921. 



' Koser, S. A.: /. Bact., 9, 59. 1924. 



