158 ELEMENTS OF WATER BACTERIOLOGY 



Massachusetts ponds which indicate clearly the coin- 

 cidence of the distribution of B. coli in single centimeters 

 of surface waters, with actual sanitary conditions. 

 They show also the slight significance of the test for 

 this organism in larger volumes of water. Almost 

 every source gave positive tests in loo c.c, while v/ith 

 i-c.c. samples only those lakes appear suspicious which 

 are, in fact, exposed to dangerous pollution. 



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 domesticated 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 table on page 1 59 may be 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. 



