CHAPTER XXXVII 



BACTERIOLOGY OF WATER AND SEWAGE— SEWAGE 

 DISPOSAL 



Bacteria are normally present in most natural waters. 

 Occasionally springs or wells may be found from which 

 the water is practically sterile, but these are uncommon. 

 Unpolluted waters from various sources, therefore, may be 

 regarded as having each its characteristic flora. 



Many distinct kinds of bacteria have been recorded from 

 natural waters. Frequently the pigment-producing forms 

 are relatively abundant, particularly the chromogenic 

 micrococci and sarcinee, yellow, orange and red. 



The number of bacteria normally present per cubic cen- 

 timeter in water varies greatly with the source and the 

 conditions under which the water has been kept. It has 

 already been noted that occasionally waters may be found 

 which are practically sterile. At the other extreme we may 

 find waters such as those heavily contaminated with sewage 

 in which bacteria are present by the hundreds of thousands 

 or even millions per cubic centimeter. Whenever there are 

 considerable quantities of organic matter present in water, 

 there is naturally a rapid multiplication of bacteria, pro- 

 viding temperature and other conditions are satisfactory. 



Economic »Importance of Impure "Water 



An impure water may be defined as one which contains 

 disease-producing bacteria or which contains an excessive 

 quantity of organic material susceptible to putrefaction 

 or decay. 



A number of diseases of man and animals are trans- 

 mitted through drinking water. The most common of these 



431 



