12 



Elements of Water Bacteriology. 



MONTHLY VARIATIONS IN BACTERIAL CONTENT OF 

 CHESTNUT HILL RESERVOIR, 1893-1903. 



The marked increase in April and September is the 

 notable feature of these analyses; and this is due to the 

 effect of the spring and fall overturns which, in the months 

 in question, stir up the decomposing organic matter at the 

 bottom and distribute it through the reservoir. The 

 slight, but steady, increase during the warm months from 

 May to August is also probably significant. 



On the whole it may be said that the bacterial content 

 of a lake or pond should not be more than one or two 

 hundred per c.c. and may often be under a hundred. The 

 student will find numerous analyses of natural waters in 

 Frankland's classic work (Frankland, 1894). He notes, 

 for example, that the Lake of Lucerne contained 8 to 51 

 bacteria per c.c., Loch Katrine 74, and the Loch of Lin- 

 tralthen an average of 170. The water of Lake Cham- 

 plain examined by one of us (S. C. P.) in 1896 contained 

 on an average 82 bacteria per c.c. at a point more than 

 two miles out from the city of Burlington. Certain 

 surface water-supplies near Boston, studied by Nibecker 

 and one of us (Winslow and Nibecker, 1903), gave the 

 following results: 



