130 



Elements of Water Bacteriology. 



Houston (1905) gives the following table which may be 

 taken as another fair example of the distribution of B. 

 coli in small streams and lakes. Of the two lakes studied, 

 Loch Ericht is free from the pollution of human or domes- 

 ticated animals while Loch Laggan receives some drainage 

 from farm lands; both are of large size. The brook and 

 river samples were collected from adjacent streams. 



DISTRIBUTION OF B. COLI IN SURFACE WATERS. 



(HOUSTON, 1905.) 

 Percentage of Samples showing B. coli in each Dilution. 



As an example of a heavily polluted stream, on the other 

 hand, the following table on page 131 maybe cited. It 

 shows in a striking way the increase of B. coli in the 

 Thames on its passage through London and its progressive 

 purification below. 



The river at the lower stations in this table was con- 

 siderably diluted with sea-water, yet it showed clearly 

 its large proportion of sewage. Normal sea-water, even in 

 the neighborhood of the shore, shows B. coli only in large 

 samples. Houston (1904), in another communication, 

 reports the examination of 168 samples of sea-water near 

 the English coast. None of the samples showed B. coli 



