COLON-AEROGENES FOR]\IS FROM NATURAL WATERS 65 



such anomalies as have been emphasized in this work and men- 

 tioned in the earlier cited references. 



A considerable number of methyl red positive strains gave 

 deferred fermentation of lactose (after three. days) which is 

 in line with the observations of Bronfenbrenner and Davis 



(1918) on Bad. coli from foods. Similar behavior of colon forms 

 in gentian violet broth has been ascribed by Hall and Ellefsen 



(1919) to the inhibitive effect of the dye: it may have been in 

 part attributable to the inhibitory effect of lactose itself, noted 

 by Smith (1893), confirmed by Burling and Levine (1916), and 

 recognized in the latest recommendation of the committee of the 

 American Public Health Association (1920), which reduces the 

 percentage of lactose in broth to 0.5 per cent. If our observa- 

 tion holds, that 0.2 per cent of lactose and other sugars and 

 alcohols suffices in culture broths, some relief might be expected 

 from delayed development of gas; but our strains reacted simi- 

 larly in both 1 per cent and 0.2 per cent sugar broths throughout. 

 In the most striking instances of erratic behavior studied there 

 was no marked difference in the time of beginning gas production 

 by typical and atypical forms. 



The list of anomalous strains is undoubtedly incomplete: 

 Levine, Burton and Rettger, and Burton in his thesis, to which 

 we have had access through the courtesy of the author, Bron- 

 fenbrenner and Davis, and Rettger and Chen suggest abundant 

 material not yet reducible to the fixed categories of any classi- 

 fication. This may be said also of the sporebearing forms; 

 although some of them can hardly be confused with typical 

 Bad. coli, several are likely to lead to misapprehension as to the 

 safety of a water supply. 



INTERPRETATION OF LABORATORY RESULTS 



If the atypical strains, sporebearers and vegetative forms 

 herein listed and cited, are considered as intermediate or transi- 

 tion forms from accepted colon or aerogenes types, the question 

 of sanitary interpretation in unavoidable. Any of the lactose 

 fermenting organisms (29 of the 31 especially studied) wotild 

 lead to the condemnation of a water supply according to the 



JOUnNAL OP BACTERIOLOGY, VOL. VI, NO J 



