EXAMINATION OF WATER FOR MICRO-ORGANISMS 79 



liering to the tube when the mixture is made in the 

 test-tube before pouring on to the plate or into the dish. 

 Such loss is, however, quite insignificant, and does not 

 materially influence the result. Another advantage 

 obtained by substituting dishes for plates is in the 

 greater ease with which the former can be transported. 

 It is often advisable to undertake the bacteriological 

 examination of a water on the spot, especially in cases 

 where the investigation is required at a considerable 

 distance from the laboratory, and whereas the trans- 

 ference of gelatine-plates would be almost impossible, 

 the safe conveyance of such dish-cultures is attended 

 with no difficulty whatever. 



In connection with the use of pipettes for the measur- 

 ing out of the water, care should be taken that they are 

 sterilised in the same way as all pieces of glass appa- 

 ratus in the hot-air oven. As it is very important 

 that the pipettes should not be greasy, they must be 

 thoroughly cleaned ' by soaking them successive!}^ in 

 strong sulphuric acid, water, caustic soda, water, and 

 hydrochloric acid, after which they are thoroughly 

 washed and finally rinsed with distilled water. They 

 are then placed, point downwards, in a cylindrical glass 

 or tinned iron vessel covered with a beaker, and the 

 whole sterilised in the hot-air oven. The beaker cover- 

 ing the pipettes is then just raised each time a pipette 

 is removed for use, the pipette being of course held by 

 its upper extremity, which will not come in contact 

 with the water. Immediately after the pipette is finished 

 with it should be placed in a beaker containing distilled 

 water, or, better, strong sulphuric acid, especially if 

 pathogenic organisms are believed to be present. 



