4 BACTERIOLOGICAL EXAMINATION OF WATER. 



collection of the sample of water which is to be subjected to a 

 bacteriological examination. 



The collection of water for bacteriological examination. Water 

 from a river, well, lake or service-pipe should be collected in 

 glass bottles closed with glass stoppers, previously sterilised by 

 heating in the hot-air chamber to 150 C. for three hours ; if 

 sterilisation cannot be effected, the bottles may be cleaned 

 sufficiently for all practical purposes by washing with a little 

 pure sulphuric acid, all traces of acidity being finally removed 

 by thoroughly rinsing the bottle with some of the water to be 

 examined. In the case of a river or lake the bottle should be 

 plunged below the surface before the stopper is removed ; in this 

 way a sample of the main body of the water will be obtained. 

 In some cases, as when investigating an outbreak of cholera, it 

 is desirable to examine the surface water. This specimen should 

 be collected in a separate bottle and labelled accordingly. If 

 the source of supply is a " service- water, 1 ' the tap should be 

 opened and the water allowed to run to waste for a few minutes 

 before the specimen is collected ; in this way local impurities will 

 be washed out of the tap and the water which has been 

 standing in the service-pipes will be removed. It is always 

 desirable in the case of a " service- water " to obtain a specimen 

 direct from the mains. In the case of a well not in constant 

 use it is generally found that the sample obtained on first 

 pumping contains a very large number of micro-organisms ; so 

 that, to gain an idea of the water which enters the well from the 

 surrounding strata, it is advisable to pump continuously for 

 several hours before collecting the example for examination. 

 After the specimen has been obtained the glass stopper should 

 be covered with oiled silk and carefully tied down. When the 

 source of supply is a shallow stream, such as the feeder of an 

 upland surface water, it is often impossible to use a bottle 

 without disturbing the sediment. Under these conditions a 

 test-tube with stout walls is drawn out just below the open end ; 

 the contained air is then removed by prolonged heating, or more 

 simply by allowing a little water to enter the tube, which is then 

 heated until steam escapes, when the point is rapidly sealed. 

 The fine point of such a tube should be placed under the 

 surface of the stream, and then the tube opened by breaking the 



