MICROORGANISMS IN WATER. 195 



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 

 delicate 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 sewage 

 pollution as the colon bacillus. They may be said to furnish valuable 

 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 generally 

 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 type organism have been very slight. 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 media, 

 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 or less 

 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 typhoid" has been applied to those which more closely approximate 

 to the cultural peculiarities of the typhoid bacillus. 



For practical purposes in the analysis of water, these distinctions are 

 unnecessary. 



Bact. lactis aerogenes, a short, thick, capsulated, non-motile bacterium 

 related to B. coli, is also an intestinal organism, and must be regarded as 

 an indicator of sewage pollution. 



