90 



such objectionable matter but predominates on the presumably harmless 

 soil and grains. The aerogenes group, as indicated* by laboratory experi- 

 ments and observations in the field, is much more viable in water, where 

 it will persist for long periods, and seems capable of growing, to some 

 extent, in stored treated supplies. 



It is not possible from our present limited knowledge of these two 

 groups to put forth any definite rules for interpreting the significance of 

 their presence in water, but it is felt that the presence of Bact. aerogenes 

 alone should not be regarded as objectionable as is the presence of the 

 Bact. coli in equal numbers. If the sanitary survey is favorable and there 

 is no evidence of the true Ract. coli types in a water supply under different 

 weather conditions, then a considerably greater number of Bact. aerogenes 

 may be tolerated. 



The presence of Bact. aerogenes alone (i. e. not associated with Bact. 

 coli) in a supply may indicate merely remote pollution or soil contamina- 

 tion which is not as objectionable and certainly not as dangerous as 

 sewage pollution. 



Differentiation of the coli and aerogenes types in routine water an- 

 alysis is obviously desirable as it may assist in the detection of the probable 

 source and nature of the contamination. 



