2OO 



MICROBIOLOGY OF WATER AND SEWAGE. 



mentioned above; but, of course, the character of the bacterial flora is 

 quite different. 



UPLAND SURFACE WATERS. There are few bacteria in upland sur- 

 face waters draining barren uplands. Cultivation, grazing of animals, 

 and human habitation produce other conditions. In pure waters, 50 to 

 300 per c.c. by the gelatin and i to 10 by the agar count are found. 



RIVERS. The greatest variation in the number of bacteria exists in 

 river waters. Many factors, such as sewage contamination, temper- 

 ature, rain fall, vegetable debris, etc., influence the microbial population. 

 A few figures may be given for illustration. 



Bacteriological Examination of Rivers at and below Large Sources of Pollution (Boyce 



and Co-workers). 



In the Chicago drainage canal, Jordan found 1,245,000 bacteria per 

 c.c. at Bridgeport; 650,000 at Lockport, twenty-nine miles below; and 

 3,660 at Averyville, 159 miles below. Below where the sewage of Peoria 

 enters, the numbers rise to 758,000 at Wesley City, and decrease to 

 4,800 at Kampsville, 123 miles from Peoria. 



The river Rhone contains an average of 75 bacteria per c.c. above 

 Lyons and 800 below. The Dee, 88 above Braemar and 2,829 per c.c. 

 below. Many more similar results are found in the literature. 



LAKES. The water of lakes is generally much purer than river water. 

 Near the shore, the bacterial content is higher than farther out, showing 

 the contaminating influence of habitation. Thus Lake Geneva contains 

 as many as 150,000 bacteria per c.c. near the shore, and further out only 



