MICROORGANISMS IN WATER 257 



ton has found as many as 100,000 per c.c. All these organisms are mo- 

 tile, liquefy gelatin, and produce gas in dextrose and saccharose broth, 

 and little or none in lactose; reduce nitrates, curdle milk, produce indol, 

 and give a fecal, disagreeable odor in broth or other media. 



Sewage streptococci. — The streptococci found in sewage are probably 

 similar to those found elsewhere; but their appearance in contaminated 

 water may be regarded as indicative of recent sewage contamination, 

 because the bulk of the evidence available seems to show that they are 

 deUcate organisms, which rapidly die outside of the body. While it is 

 easy to ascertain their presence in polluted water, it is almost' impossible 

 to enumerate them; and they do not furnish such good evidence of sew- 

 age pollution as the colon bacillus. They may be said to furnish valu- 

 able confirmatory evidence of sewage contamination. 



B. enteritidis sporogenes. — This resistant, spore-bearing organism is 

 usually present in the intestinal tract of man; is found in sewage, milk, 

 and dust; and occurs in foodstuffs, such as wheat, oatmeal, rice, etc. 

 On account of its ubiquity and the resistance of its spores, it cannot be 

 considered a good indicator of excretal pollution. 



B. coli. — The presence of this organism in potable water is gener- 

 ally accepted as the best bacterial indicator of sewage pollution. It 

 must be remembered, however, that there are many varieties of this 

 organism, to which certain investigators have given specific names, even 

 when the differences from the tj^je organism have been very sUght. It 

 may be well to mention some of these, to avoid confusion in the mind of 

 the reader. The true colon bacillus, B. coli, or B. coli communis, or B. 

 coli communis verus, is a short bacillus with rounded ends, motile, forms 

 no spores and is Gram negative, does not liquefy gelatin, produces 

 acidity and coagulation in litmus milk, gives rise to acid and gas in 

 glucose and lactose media, causes canary-yellow fluorescence in neutral 

 red piedia, and produces indol when grown in peptone water. The term 

 "Excretal B. coli" has been suggested as a convenient designation of an 

 organism which possesses the above characteristics. 



A saccharose fermenting variety of B. coli has been named B. com- 

 munior; and we have a whole series of organisms which differ more oriess 

 in various biochemical reactions, or lack some of their positive reactions. 

 To some of these the name "para-colon" has been given; and the name 

 "para tj^hoid" has been applied to those which more closely approxi- 

 mate to the cultural peculiarities of the t3rphoid bacillus. 



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