THE BACTERIA IN NATURAL WATERS. 17 



bottling and the multiplication of the water bacteria 

 gave numbers rising to 243,000, only 14 out of 50 samples 

 being under 1000. 



It now remains to consider the other great division of 

 ground-waters, namely, deep, "driven," or "tubular" 

 wells, which, if carefully constructed, should ordinarily be 

 perfectly free from all surface-water contamination. The. 

 numbers of bacteria in such sources has been reported 

 by but few investigators. A series of wells in and near 

 Boston was found to give the following figures (Sedgwick 

 and Prescott, 1895). 



Well. Depth, Feet. Bacteria per c.c. 



No. 1 193 269,254 



2 100 30 



3 454 206, 214 



4 254 150, 135 



5 228 



6. 



192, 193 



Second sample 262, 258 



7 2I 3 139. 140 



8 213 101,106 



Second sample 408, 416 



9 377 48, 54 



Second sample 158, 149 



10 227 1240,1376 



11 130 440,480 



12 200 525 



13 180 60, 57 



14 75° 38 



Again it should be noted that the period of incubation 

 for these samples was at least five days. Fifteen driven 

 wells in the neighborhood of Boston examined in 1903 

 showed at the end of 48 hours an average of only 18 

 colonies per c.c. 



