1 68 Elements of Water Bacteriology. 



stock. As Savage says, " we know that nearly all the coli- 

 like organisms in feces are quite typical B. coli, that in- 

 sewage a good many atypical varieties are present, and 

 that in contaminated water and soil the proportion present 

 is still larger." The presence of these forms in water 

 must, in the light of present knowledge, be considered 

 suspicious, though not an indisputable evidence of con- 

 tamination. The only safe rule, when atypical forms are 

 found without standard B. coli, is to secure another sample 

 for examination. Fortunately this condition rarely occurs, 

 since typical colon bacilli are generally found in duplicate 

 samples when the atypical forms are present. 



B. cloacae, which differs from B. coli in the liquefaction 

 of gelatin, stands in much the same position as the atypical 

 forms of the colon bacillus. We have seen that organisms 

 which ferment dextrose and lactose are rarely found in 

 normal waters, and this form must, therefore, be regarded 

 with suspicion. Detailed studies of its distribution are 

 necessary, however, before its presence can be given the 

 same weight as that of the colon bacillus. 



There are numerous other sewage bacteria whose 

 presence is more or less characteristic of polluted waters. 

 Organisms of the Proteus group are sometimes present, 

 exhibiting marked morphological variations, from the 

 coccus form to long twisted threads, and forming on 

 gelatin irregular amoeboid colonies with filiform processes 

 extending into the surrounding gelatin. The B. subtilis 

 group of strongly aerobic spore-forming bacilli, giving a 



