EXAMINATION OF WATER 123 



examination have already been given, and this is largely in the 

 nature of an investigation by each student. It is not expected 

 that the special methods other than those used in the labora- 

 tory for pathogenic bacteria will be tried. 



Examine the milk tubes of the preceding exercise and the 

 cultures made from them. 



177. Collecting water. If the water is collected from a 

 spigot or pump, allow it to flow for 2 or 3 minutes first, and 

 then collect the desired quantity (100-200 cc.) in a sterile 

 bottle and cork tightly ; if near at hand, absorbent cotton 

 plugs may be used. 



If from a stream or river, withdraw the stopper and immerse 

 the sterile bottle, mouth downward, to the depth desired and 

 allow it to fill. There are several mechanical devices for col- 

 lecting water from considerable depths from the surface. 



