CHAPTER II* 



MICROBIOLOGY OF SEWAGE 

 THE BACTERIAL FLORA OF SEWAGE 



COMPLEXITY OF FLORA. Sewage is made up of the miscellaneous 

 and varied wastes of human life and activity, and the bacteria which are 

 found therein are the result of a haphazard and chance admixture of 

 substances of diverse origin and character. The resulting flora is not 

 only of great diversity and variability, but it is with few exceptions non- 

 characteristic. In brief, the medium with which we have to deal has 

 had an origin too indefinite and a history too short to have permitted 

 the establishment of anything approaching a constant or characteristic 

 bacterial flora. 



TYPICAL FORMS. Our interest in this sewage flora is a very practical 

 one, being confined to those organisms which carry on the work of bio- 

 logical purification and to certain pathogens which for obvious reasons 

 require special treatment. We are interested chiefly in what these bac- 

 teria do rather than in what they are, and our classification is influenced 

 accordingly. It is based, not upon the species or the genus nor even 

 upon the group or type, that proves so convenient in general bacterial 

 classification, but upon a sort of physiological or functional type, having 

 to do solely with the activities of the organisms in sewage and in its puri- 

 fication. Bacteria performing a common function or producing a com- 

 mon result are members of one type. Individuals may belong to several 

 of our types and there are doubtless a great many that belong to none. 

 These latter simply have no place assigned them as yet in the role of 

 sewage purification, because they possess none of the recognized typical 

 functions. 



Apparent exception may be taken to these general principles in 

 the case of such organisms as the B. coli, sewage streptococci and 

 B. enteritidis. These are, to a certain extent, characteristic sewage 

 bacteria. But interest hi them as individuals is confined to water 



Prepared by Earle B. Phelps. 



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