65 

 V. THE COLON GROUP AS AN INDEX OF POLLUTION 



Safe Water. A safe water for human consumption may be defined 

 as one which is free from harmful constituents important among which 

 are disease producing microorganisms. The logical and most direct pro- 

 cedure to determine the potability and safety of a water would be to 

 determine the presence or absence of pathogenic bacteria but unfortun- 

 ately this task is an impossible one for routine and recourse must there- 

 fore be taken to an indirect index of the probable presence of harmful 

 germs. Since the diseases transmissable through water are primarily of 

 intestinal origin the detection of the presence of intestinal material natur- 

 ally leads to the presumption that a potential danger exists, for if such 

 material is present it is very probable and certainly possible that intes- 

 tinal disease germs are also present. 



A number of tests both chemical and bacteriological have been sug- 

 gested as indicators of intestinal pollution. The bacterial examination, 

 by reason of the large number of bacteria present in feces and sewage and 

 the ease with which they may be detected in water, is a particularly delicate 

 test. Three groups of bacteria have been regarded as indicators of pol- 

 lution: 



The colon group. 



Sewage streptococci. 



Spore forming anaerobes. 



An organism to be considered an ideab index of fecal pollution should 

 have the following characteristics: 



1. It should be distinctively and characteristically of human or 

 animal intestinal origin. 



2. It should be absent or extremely rare in nature outside of the 

 intestinal tract. 



3. It must be capable of easy and rapid detection. 



4. Its incidence in water should bear some constant relation to the 

 sanitary survey or our knowledge as to the probability of pollution, par- 

 ticularly with sewage. 



5. It should be distinctly more viable and more resistant in water 

 and to treatment than are the intestinal pathogens (Bact. typhi, Bact. dysen- 

 teriae, etc.), but not excessively so. 



Such an ideal index is not available but the general concensus of opin- 

 ion among English and American bacteriologists is favorable to the em- 

 ployment of the Colon group for this purpose. Although bacteria of this 

 group are not restricted in habitat to the intestinal tract of man being 

 characteristic also of the intestinal tract of the lower animals, it is never- 

 theless true that there is a correlation between the quantitative incidence 

 of a least the coli section and known pollution. The whole group is easy 

 of detection as will be seen from the following considerations. It is more 

 viable than Bact. typhi but yet dies off relatively quickly; colon bacilli 

 are present in relatively large numbers in water known to be polluted but 

 only infrequently in natural supplies. A correlation has been established 



