iS ELEMENTS OF WATER BACTERIOLOGY. 



It is plain that water absolutely free from bacteria is 

 not ordinarily obtained from any source and that even 

 deep wells contain quite appreciable numbers. The 

 peculiar character of the organisms present in the latter 

 case is manifested in many cases by the slow develop- 

 ment at room temperature (no growth until* the third 

 day in some cases), the entire absence of liquefying 

 colonies, and the abundance of chromogenic species. 



