EXAMINATION OF WATER 589 



procedure. On the other hand, Thresh l lays a good deal 

 of stress on it, and the following are standards suggested 

 by him, based on an examination for, and detection of, 

 B. coli and B. Welchii : 



1. Water showing the absence of organisms capable of fermenting 

 glucose, and of the B. Welchii. These we regard as being free from 

 any evidence of pollution. 



2. Waters showing the absence of organisms capable of fermenting 

 glucose, but containing the B. Welchii, or its near ally. In the few 

 cases of this kind which have come under our observation we have 

 inferred the absence of sewage pollution, but the possible presence 

 of water derived from fertile soil. This inference has been verified 

 on more than one occasion. 



3. Waters containing organisms capable of fermenting glucose, 

 but not lactose, but free from the spores of the B. Welchii. These 

 are regarded as unpolluted. 



4. Waters differing from No. 3 only in containing spores of the 

 B. Welchii. These we regard as free from sewage pollution, but 

 as probably containing soil washings. 



5. Waters containing lactose fermenters, none of which belongs 

 to the Bacillus coli group, and free from the spores of the B. Welchii. 

 These we do not regard as being sewage-polluted, but as containing 

 surface water or subsoil washings. 



6. Waters resembling No. 5, but containing the spores of the 

 B. Welchii. These waters are usually from a source requiring careful 

 watching, manurial matter probably being used on the collecting 

 area. 



7. Waters containing organisms of the colon group other than 

 the B. coli, but no spores of the B. Welchii. These we do not regard 

 as dangerously polluted, but as probably coming from a source 

 such as that referred to under No. 6. 



8. Waters containing organisms of the colon group other than 

 the B. coli, and also spores of the B. Welchii. Pollution indicated, 

 but possibly from a source not close at hand. The necessity for 

 frequent examination is essential, especially after heavy rains, as 

 such waters usually sooner or later show more serious signs of 

 pollution. 



9. Waters containing the true B. coli, but no spores of the B. 

 Welchii. Such waters are occasionally met with. No opinion can 

 be expressed without an intimate knowledge of the source. We 



1 Public Health, 1904. 



