224 ELEMENTS OF WATER BACTERIOLOGY 



more delicate and more certain index of the quality 

 than may be obtained by chemical analysis. In a 

 number of instances, springs located in pastures have 

 become slightly polluted by animals, but to so small 

 an extent that the chemical examination gave no indi- 

 cation of trouble. The bacteria, however, increased 

 greatly in number, and colon bacilli could be readily 

 isolated from 75 per cent of the i-c.c. samples of a 

 long series used in making the presumptive test. A 

 single case may suffice as an illustration. This was a 

 spring located on a hill in Hopkinton, Mass. 

 The chemical analysis was as follows : 



Color None 



Turbidity None 



Sediment None 



Odor (hot) None 



Odor (cold) None 



Parts per Million. 



Total solids S3- 0000 



Loss on ignition 7 . 0000 



Fixed residue 26 . oocxd 



Hardness 11. 0000 



Chlorine 10 . 0000 



Nitrogen as — 



Albuminoid ammonia 0.0000 



Free ammonia o . 0000 



Nitrites o . 0000 



Nitrates o . 0000 



The bacteriological examination showed a total count 

 of 375 bacteria per c.c. and a 37° count of 350 per c.c. 

 The presumptive tests for Bacillus coli showed that 

 gas-producing organisms were present in a majority 

 of I -c.c. samples, and typical colon bacilli were isolated. 

 In this case the contamination was brought about by 

 cattle gaining access to the area immediately surround- 



