5O Elements of Water Bacteriology. 



per c.c. (Philbrick, 1905) and the water of Lake Zurich 

 with an average of 71 in summer and 184 in winter 

 (Cramer, 1885) may be taken as typical of good potable 

 waters; and numbers much higher than these are open 

 to suspicion, since all contamination whether contributed 

 by sewage or by washings from the surface of the ground 

 is a possible source of danger. The excess of bacteria 

 in surface-waters during the spring and winter months is 

 by no means an exception to the general rule that high 

 numbers are significant, since the peril from supplies of 

 this character is clearly shown by the spring epidemics of 

 typhoid fever which at the times of melting snow visit 

 communities making use of unprotected surface-waters. 

 Streams receiving direct contributions of sewage exhibit a 

 similar excess of bacteria at all times, numbers rising to an 

 extraordinary height near the point of pollution and fall- 

 ing off below as the stream suffers dilution and the sewage 

 organisms perish. Miquel (Miquel, 1886) records 300 

 bacteria per c.c. in the water of the Seine at Choisy, above 

 Paris; 1 200 at Bercy in the vicinity of the city, and 200,000 

 at St. Denis after the entrance of the drainage of Paris. 

 Prausnitz (Prausnitz, 1890) found 531 bacteria per c.c. 

 in the Isar above Munich, 227,369 near the entrance of 

 the principal sewer, 9111 at a place 13 kilometers below 

 the city, and 2378 at Freising, 20 kilometers further 

 down. Jordan (Jordan, 1900), in his study of the fate of 

 the sewage of Chicago, found 1,245,000 bacteria per c.c. 

 in the drainage canal at Bridgeport, 650,000 twenty-nine 



