Quantitative Bacteriological Examination. 31 



cautions are necessary. The pump should be in con- 

 tinuous operation for five minutes at least, and preferably 

 for half an hour before the sample is taken, in order to 

 avoid excessively high numbers due to the growth of 

 bacteria within the well and pump, the bacterial condition 

 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 thirty-six 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 PUMPING ON THE BACTERIAL CONTENT 

 OF WELL-WATER. 



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



after continuous pumping for many hours 140 



later 68 



' after continuous pumping for fifteen minutes .... 578 



after continuous pumping for many hours 179 



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 



