232 ELEMENTS OF WATER BACTERIOLOGY 



sidered positive tests for the colon group, without 

 serious error. 



Numbers of Bacteria in Sewage. The total number 

 of bacteria and the number of colon bacilli naturally 

 vary widely in the sewages of different cities and towns. 

 European sewages, being more concentrated, show 

 as a rule higher numbers than are found in America. 

 Results compiled from various sources show from 

 1,000,000 to 5,000,000 bacteria in the sewages of Essen, 

 Berlin, Charlottenburg, Leeds, Exeter, Chorley, and 

 Oxford, 2,000,000 to 10,000,000 in the sewages of Lon- 

 don, Walton, and W. Derby and over 10,000,000 in the 

 sewages of Paris, Ballater and Belfast (Winslow, 1905). 

 The number of colon bacilli in English sewages varies 

 from 50,000 to 750,000. In American sewages, on the 

 other hand, bacteria are somewhat less numerous. 

 At Lawrence the determinations made from 1894 to 

 1901 showed on the average 2,800,000 bacteria per c.c. 

 At Worcester, Eddy reported 3,712,000 in 1901 (Eddy, 

 1902); at Ames, Iowa, Walker (1901) found 1,248,256 

 in the same year. At Columbus, Johnson (1905) 

 reports an average of 3,600,000 bacteria per c.c; the 

 individual numbers varied from 320,000 to 27,000,000. 

 The number of colon bacilli varied from 50,000 to 

 1,000,000 and averaged 500,000. Day samples of 

 Boston sewage collected three times a week, from 

 October, 1906, to April, 1907, showed an average of 

 1,200,000 bacteria per c.c. In the summer months 

 numbers are notably higher than at other seasons 

 in many sewages. Thus in 1903, Boston sewage con- 

 tained 2,995,000 bacteria in July, 4,263,600 in August, 



