BACTERIA IN SEWAGE 361 



The important elements present are nitrogen and sulphur. The 

 quantity of these present determines the nature and repulsiveness 

 of the resulting products. 



Bacteria in Sewage. The number and kind of bacteria in sewage 

 varies widely with its composition and origin. According to Fuller 

 it contains 320 billion for each person connected with the sewer 

 system. Johnson found B. coli to average about 500,000 per c.c. 

 He isolated the following species from the crude sewage of Columbus : 



Number of times 

 Species. found. 



B. liquefaciens 21 



B. coli communis 19 



B. liquidus 8 



B. mesentericus vulgatus 7 



B. bruneus 4 



B. hyalinus 3 



B. fuscus 3 



B. delicatulus 3 



B. pyocyaneus 2 



B. fluorescens 2 



B. circulans 2 



B. nibilus 2 



B. weichselbaumii 2 



B. sporogenes 1 



B. stellatus ' 1 



B. heholus 1 



B. cereus 1 



B. cloacae 1 



B. proteus zenkeri 1 



B. rnonadiformis 1 



B. aeris muintissirnus 1 



M. tetragenus mobilis venlriculi 1 



M . casei 1 



M. albicans ampins 1 



M. fervidosus 1 



Str. coli gracilis 1 



Str. enteritis 1 



Sarcina alba 1 



Ps. turcosa 1 



Ps. nebulosa 1 



Ps. ochracea 1 



In addition to these, many of the pathogens may find their way 

 into sewage and survive for various lengths of time. 



However, the interest centers more in the changes produced by 

 the various bacteria found in sewage than in the specific classes. 

 Most of them ai'e not only harmless, but of genuine importance 

 in the economy of Nature through the scavengering work which 

 they accomplish. A few of them are dangerous on account of 

 their causing certain infectious diseases. Many of them play 

 an important role in decomposing sewage with the formatien of 

 malodorous gases and products " associated with putrefactive 

 nuisances. 



The modern tendency is, therefore, to classify sewage bacteria 



