EXAMINATION OF WATER 



387 



When examining water bacteriologically, especial care is 

 necessary when taking a sample for analysis, in order to 

 prevent outside contamination and to secure an average 

 sample. About 50 c.c. should be collected in a sterile bottle 

 or flask, which should be contained in sterile metal cases. 

 Stoppered bottles should always be used, and all containing 

 vessels should have been previously sterilised in the hot- 

 air steriliser for three hours at 150° C. The most satis- 

 factory receptacles for water intended for bacteriological 

 examination are exhausted and sterile glass bulbs, the 

 necks of which have been drawn out to a point. This fine 

 point is broken with a pair of sterile forceps under the 

 surface of the water, and after the latter has rushed in and 

 filled the vacuum the bulb is sealed up again with the aid 

 of a spirit-lamp. 



In collecting samples from rivers, lakes, tanks, or ponds, 

 it is best to take the bottle out of the sterile metal case, 

 take out the stopper, and hold the neck of the bottle 



25—2 



