8 



Elements of Water Bacteriology. 



SEASONAL VARIATIONS IN BACTERIAL CONTENT OF 

 RIVER WATERS. BACTERIA PER C.C. MONTHLY 

 AVERAGES. 



Houston, I9o6a, I9o6b. 



New Orleans, 1903. 



Figures obtained through courtesy of F. F. Longley. 



Massachusetts, 1906. 



Harrisburg, 1907. 



In general, bacterial numbers are highest for river- 

 waters in the winter and spring months. The rainfall is 

 the main factor which affects seasonal variations, but its 

 specific effect differs with different streams. The imme- 

 diate result of a smart shower is always to increase con- 

 tamination by introducing fresh wash from the surface 

 of the ground. More prolonged moderate rain, however, 



