TECHNICAL AND SANITARY PROBLEMS 1069 



rise to dysentery and various diarrhoeal disturbances. Presumably 

 these bacteria behave in the same manner as the typhoid fever 

 bacillus. 



The routine methods of bacteriology at the present time do not 

 permit of a trustworthy determination of the above-mentioned 

 pathogenic bacteria. It is true that in some instances such have 

 been isolated from water but the process is a difficult one and nega- 

 tive results are of little value. This being the case, modern sani- 

 tarians do not attempt to determine the safety of water by searching 

 for these pathogenic organisms. Instead they make tests to 

 determine the presence and abundance of an organism which is 

 commonly found in the intestines of man and warm blooded animals 

 generally known as bacillus coli. This test can be made with a 

 fair degree of reliability and it is much used. 



B. Coli as an Index of Contamination. Unpolluted ground waters 

 contain practically no B. coli but in proportion as waters are subject 

 to contamination with excremental substances the numbers of B. 

 coli increase. All surface waters are likely to contain these germs, 

 but in unpolluted sources, such as uninhabited woodland areas, the 

 numbers are very small indeed. Even the broad waters of the 

 Great Lakes contain B. coli in small numbers though very often 

 they are absent from the quantities usually used in the test. Rivers 

 which drain farm lands contain B. coli in larger numbers; streams 

 and fresh waters which receive sewage contain them in still larger 

 numbers. B. coli, therefore, may be fairly regarded as a valuable 

 index of fecal contamination. This is so far true that the U. S. 

 government has established bacteriological standards for drinking 

 water served by interstate carriers which includes a permissible 

 limit for the number of B. coli. As stated by the U. S. Public 

 Health Service, waters in which B. coli are absent from two out 

 of five portions of 10 cc. may be used, but waters in which B. coli 

 is found in three or more out of five 10 cc. portions would be con- 

 demned. The dividing line apparently comes at a figure which is 

 about 150 B. coli per liter of water. The whole subject of B. coli 

 in water, the methods of its determination, and the interpretation 

 of its results is one which is now going through a series of evolu- 

 tionary changes. The reader is therefore referred to current 



