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 sub- 

 stances 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 biological 

 purification and to certain pathogens which for obvious reasons require 

 special treatment. We are interested chiefly in what these bacteria 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 purification. Bacteria 

 performing a common function or producing a common 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. enter itidis. These are, to a certain extent, characteristic sewage 

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

 bacteriology. If they have any functions in the bacterial changes of 

 sewage, they receive attention as members of a corresponding type, not 



* Prepared by Earle B. Phelps. 



212 



