THE BACTERIA IN NATURAL WATERS 



27 



In the ordinary standard 48-hour period very few- 

 bacteria develop from normal spring-waters. Thus 

 in an examination of spring-waters made by the Mas- 

 sachusetts State Board of Health in 1900 (Massachusetts 

 State Board of Health, 1901), of 37 springs which were 

 practically unpolluted and had less than o.io part 

 per lODjOoo excess of chlorine over the normal, 54 sam- 

 ples were examined and gave an average of 41 bacteria 

 per c.c. Only 6 samples showed figures over 50. 



It now remains to consider the other great di\asion 

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

 wells, which, if carefully constructed, should ordinarily 

 be free from all surface-water contamination, and should 

 show low bacterial counts. The results tabulated below 

 obtained by Houston in the examination of a series of 

 deep wells of high quahty at Tunbridge Wells are 

 fairly typical. 



BACTERIAL CONTENT OF DEEP WELL WATERS 

 (Houston, 1903) 



Bacteria per c.c. 



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; and the results 

 of certain examinations of other wells and springs, 

 recently made by the authors, are given in the table 

 on page 28. 



