4 6 



ELEMENTS OF WATER BACTERIOLOGY. 



In unpolluted waters not only the absolute number of 

 organisms developing at the body temperature, but its 

 ratio to the gelatin count, is very different. Rideal (Rideal, 

 1902) states that the proportion between the two counts 

 in the case of a London water in a year's examination 

 was on the average one to twelve. Mathews (Mathews, 

 1893) in 1893, gave the following figures, the contrast 

 between the ponds and streams which were presumably 

 exposed to pollution on the one hand, and the wells, 

 springs, and taps on the other, being marked. 



Sources of Water. 



Average Number of 

 Colonies per c.c. 



Wells, springs 



Reservoirs 



Ponds 



Taps 



Streams 



In 1903 Nibecker and one of ourselves (Winslow and 

 Nibecker, 1903) made an examination of 259 samples 

 of water from presumably unpolluted sources in Eastern 

 Massachusetts, including public supplies, brooks, springs, 

 ponds, driven wells, and pools in the fields and woods, 

 with a view to testing the value of the body-temperature 

 examination. In many cases the samples showed high 

 gelatin counts, since some of the waters were exposed to 

 surface wash from vacant land, but the average number 

 of organisms developing on lactose agar at 37? was less 



