BACTERIOLOGICAL EXAMINATION OF WATER. 157 



face. The sterilised vessels with their stoppers should 

 be thoroughly freed from corrosive sublimate, by 

 rinsiEg them carefully four or five times with water 

 from the same source as that to be examined. On 

 no account must other water be used lest germs not 

 present in the water to be examined should be intro- 

 duced into the vessels, and thus all the good of the 

 sterilisation be annulled. Only when every trace of 

 the sublimate has been removed can the test-tube be 

 filled with the water ; it should then be immediately 

 closed up with the stopper, covered with the india- 

 rubber cap, and labelled. -- 



If a flask is used, which has been sterilised in the 

 hot-air steriliser, it is simply filled and closed, but 

 only half of the lower part of the prepared test-tube 

 should be filled, and the wadding stopper replaced, 

 until it is convenient for the upper part to be melted 

 off. This must of course take place as soon as pos- 

 sible ; if the weather prevents it being done on the 

 spot, the operator must go as quickly as possible to 

 the first convenient place, and heat the thinly drawn 

 out portion of the tube in the flame of a spirit lamp, 

 until both parts can be melted off, without being 

 much drawn out. Two precautions are necessary in 

 the operation, the tube must be very gently heated at 

 first, in order to expel all the moisture from the thin 

 part, and further it must on no account be shaken, or 

 roughly moved until it has thoroughly cooled lest 



