QUANTITATIVE EXAMINATION OF WATER 35 



bacteria within the well and pump, the bacterial con- 

 dition of the water as it passes through the ground being 

 what we wish to determine. Thus Heraeus (Heraeus, 

 1886) in a well-water which had been but little used 

 during the preceding 36 hours found 5000 organisms 

 per C.C.; when the well was emptied by continuous 

 pumping, a second sample, after an interval of half an 

 hour, gave only 35. Maschek (Tiemann and Gartner, 

 1889) obtained similar results, shown in the following 

 table: 



EFFECT OF PUMPmC ON THE BACTERI.\L CONTENT OF 

 WTLL-WATER 



Well-water after continuous pumping for fifteen minutes . . 458 



" " " " many hoiirs 140 



" later : 68 



" after continuous pumping for fifteen minutes .. 578 



" ' * " many hours 1 79 



' ' later 73 



After a proper interval of pumping the sample of a 

 well-water may be collected from the pet-cock of the 

 pump or from a near-by tap. With a hand-pump, 

 such as is found in domestic shallow wells, the water is, 

 of course, pumped directly into the sample bottle. 

 The difficulties in securing an average sample from 

 this latter source are often great, since if the flooring 

 about the pump is not tight, as is usually the case, con- 

 tinued pumping may wash in an unusual amount of 

 surface pollution. 



In sampling surface-waters, the greatest precautions 

 must be obser\'ed to prevent contamination from the 

 fingers. In still waters the fairest sample is one taken 



