DETEEMINATION OF ORGANISMS 67 



According to the English Committee appointed to 

 consider the Standardization of Methods for the Bac- 

 terioscopic Examination of Water (1904), the ratio 

 of the 20 count to the 37 count in good waters is 

 generally considerably higher than 10 to i. " With a 

 polluted water this ratio is approached, and frequently 

 becomes 10 to 2, 10 to 3 or even less." 



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 degrees was less than 8 per c.c., as will be 

 seen by reference to the table on the following page. 

 The highest individual counts obtained were 95 in a 

 meadow pool, 83 in a brook, and 74 in a barnyard well, 

 the latter probably actually polluted. Only two samples 

 in the whole series, one from the well above mentioned, 

 gave any red colonies on the agar plates. 



For a series of shallow surface wells recently examined 

 by one of us (S. C. P.) a similar relation is indicated 

 in the table on page 69; 124 samples which showed no 

 colon bacilli and were apparently unpolluted, gave an 

 average of 190 bacteria per c.c. at 20 and 8 at 37 

 with less than one red colony per c.c.; 23 samples 

 which did contain colon bacilli averaged 570 bacteria 



