COLON-AEROGENES FORMS FROM NATURAL WATERS 67 



to avoid development of Bad. cloacae. The committee's recom- 

 mendation (1912) for enrichment with tiansfer "as soon as gas 

 is formed (usually in sixteen to twenty-four hours)" has persisted 

 in many laboratories and is perhaps worth reviving officially, 

 not so much to avoid overgrowth as to prevent undue modifica- 

 tion. For the same reason the Voges-Proskauer reaction tested 

 at the end of ten to fourteen hours' incubation in available 

 American peptone broth is preferable to reliance upon the methyl 

 red reaction, which requires 5-day incubation in a broth for 

 which materials are not generally at hand. The uric acid test 

 seems worthy of at least provisional acceptance because of the 

 simplicity of the reaction and the facility afforded for confirming 

 or correcting the somewhat erratic results observed in the Voges- 

 Proskauer reactions of soil and water borne strains. 



SUMMARY 



Strains isolated from natui-al waters are grouped by their lac- 

 tose, uric acid, adonitol, and methyl red reactions in Difco pep- 

 tone broth (0,5 per cent and 0.75 per cent), and 35 strains espe- 

 cially studied are so arianged as to make evident the conflict 

 between the Voges-Proskauer reaction and the methyl red reac- 

 tion of strains in standard Witte peptone broth. There is lack 

 of agreement in the discrimination of high and low ratio types. 

 The uric acid positive reaction correlates best with the char- 

 acters of the aerogenes type in carbohydrates, etc. 



Upon the assmnption that the ui ic acid reaction of colon forms 

 from soils sufficiently characterizes them, this reaction may 

 prove useful in checking and correcting the assignment of strains 

 to the low ratio type indicative of possible fecal pollution. 



Five sporebearers were isolated. It is probable that the 

 number of these and of other anomalous forms is far less than 

 would have been discovered had we been able to use Witte pep- 

 tone in all methyl red tests. 



The sugar reactions of members of the larger group seem to be 

 as well tested in 0.2 per cent sugars as in the 1 per cent broths 

 of the old standard procedure. 



For the purpose of sanitary examination of waters it is desir- 

 able that the laboratory procedure be completed as early as con- 



