12 



ELEMENTS OF WATER BACTERIOLOGY 



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 con- 

 tained 8 to 51 bacteria per c.c., Loch Katrine 74, and 

 the Loch of Lintralthen an average of 170. The water 

 of Lake Champlain 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 Burling- 

 ton. Certain surface water-supplies near Boston studied 

 by Nibecker and one of us (Winslow and Nibecker, 1903), 

 gave the following results: 



