642 APPLICATION OF METHODS OF BACTERIOLOGY 



of water from a locality, the surrounding waters of which 

 are poor in chlorine, is unquestionably a suspicious indica- 

 tion; but in a district close to the sea or near salt-deposits, 

 for instance, where the proportion of chlorine (as chlorides) 

 in the water is generally high, the value of the indications 

 thus afforded is very much diminished unless the amount 

 found in the sample under examination greatly exceeds the 

 normal "mean," previously determined, for the amount of 

 chlorine in the waters of the neighborhood. 



A striking example of the latter condition occurred in 

 the experience of the writer while inspecting a group of 

 water-supplies on the east coast of Florida. In each in- 

 stance the water was obtained from properly protected 

 artesian wells, ranging from 200 to 400 feet deep, and located 

 within a few hundred yards of the sea. The first sample 

 subjected to chemical analysis revealed such an unusually 

 high proportion of chlorine that, had this sample alone 

 been considered, the opinion that it was polluted by human 

 excreta might have been advanced. To prevent such an 

 error samples of water from a number of wells in the neigh- 

 borhood were examined, and they were all found to contain 

 from ten to twelve times the amount of chlorine that ordi- 

 narily appears in inland waters, the excess being evidently 

 due to leakage through the soil into the wells of water from 

 the sea. In short, the presence of an excess of chlorine in 

 water, while often indicating pollution from human evacua- 

 tions, may nevertheless, sometimes arise from other sources; 

 but the presence in water of bacteria normally found in 

 the intestinal canal can manifestly admit of but one inter- 

 pretation, viz., that fecal matters from either man or 

 animals have at some time been deposited in this water, 

 and that while no specific disease-producing organisms may 



