SIGNIFICANCE OF COLON GROUP IN WATER 149 



of positive results. He concludes that B. coli is widely 

 distributed in the outer world. It is almost always 

 found in soil from cultivated fields or from traveled 

 places. The farther a source is removed from travel 

 and from cultivation the more rarely is the colon 

 bacillus found; but it is never altogether absent. On 

 plants or parts of plants it is frequently found when they 

 come from cultivated land; on plants from waste places 

 it is rarely found. It seems probable that colon bacilli 

 may be even more widely distributed in a thickly 

 settled and intensively cultivated country like Ger- 

 many than in the United States. 



The Number of Colon Bacilli, not Their Mere Pres- 

 ence, as an Index of Water Pollution. The more 

 important practical conclusions to be drawn from these 

 various investigations seem to be as follows: 



1. Bacteria corresponding in every way to B. coli are 

 by no means confined to animal intestines, but are 

 widely distributed elsewhere in nature. 



2. The finding of a few colon bacilli in large samples 

 of water, or its occasional discovery in small samples, 

 does not necessarily have any special significance. 



3. The detection of B. coli in a large proportion of 

 small samples (i c.c. or less) examined is imperatively 

 required as an indication of recent sewage pollution. 



4. The number of colon bacilli in water rather than 

 their presence should be used as a criterion of recent 

 sewage pollution. 



With these qualifications the value of the colon test 

 was never more firmly established than it is to-day. 

 Whether or not originally a domesticated form, it is 



