Elements of Water Bacteriology. 



SEASONAL VARIATIONS IN BACTERIAL CONTENT OF 

 RIVER WATERS. BACTERIA PER C.C. MONTHLY 

 AVERAGES. 



• Houston, 1906a, 1906b. 



' 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 iiicrease con- 

 tamination by introducing fresh wash from the surface 

 of the groimd. More prolonged moderate rain, however, 



