ELEiMENTS OF WATER BACTERIOLOGY 



CHAPTER I 

 THE BACTERIA IN NATURAL WATERS 



Bacteria and Their Nutritive Relations. Bacteria are 

 the most numerous and the most widely distributed 

 of living things. They are present not merely at the 

 surface of the earth or in the bodies of water which 

 partially cover it, as is the case with most other Hving 

 things, but in the soil itself, and in the air above, and 

 in the waters imder the earth. 



Probably no organisms are more sensitive to external 

 conditions, and none respond more quickly to slight 

 changes in their environment. Temperature, moisture, 

 and oxygen are of importance in controlling their distri- 

 bution; but the most significant factor is the amount 

 of food supply. Bacteria and decomposing organic 

 matter are always associated, and for this reason a 

 brief consideration of the general . relation of bacteria 

 to their sources of food supply must precede the study 

 of their distribution in any special medium. 



The bacteria possess greater constructive ability 

 than any animal organisms. They lack, however, 



