THE SIGNIFICANCE OF B. COLI IN WATER. 81 



in the warm intestinal canal richly supplied with food a 

 favorable habitat? 



The answer to these questions is of much theoretical 

 interest, but need not be further considered here. The 

 practical sanitary conclusions to be drawn are as follows: 



i. 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 (1 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 clear 

 that the colon bacillus finds in the intestine of the higher 

 vertebrates an environment better suited to its growth 

 and multiplication than any other which occurs in nature. 

 It is almost certain that the only way in which large 

 ' numbers of these organisms gain access to natural waters 

 is by pollution with the domestic, industrial, and agri- 

 cultural wastes of human life. If pollution has been 

 recent, colon bacilli will be found in comparatively small 

 samples of the waters. If pollution has been remote the, 



