74 METHODS OF CULTIVATION OF BACTERIA. 



tube. The fluid escapes by an aperture at the bottom. 

 Such a filter is very suitable for domestic use, or for use in 

 surgical operating-theatres. As considerable pressure is 

 necessary, it is evident it must be put on a pipe leading 

 directly from the main. Sometimes, when fluids to be 

 filtered are very albuminous, they are forced through a 

 porcelain cylinder by compressed carbonic acid gas. In 

 ordinary bacteriological work, however, it is usually more 

 convenient to suck the fluid through the porcelain by 

 exhausting the air in the receptacle into which it is to flow. 

 This is conveniently done by means of a Geissler's water- 

 exhaust pump (Fig. 27, ), which must be fixed to a tap 

 leading directly from the main. The connection with the 

 tap must be effected by means of a piece of thick-walled 

 rubber-tubing as short as possible, wired on to tap and 

 pump, and firmly lashed externally with many turns of 

 strong tape. Before lashing with the tape the tube may be 

 strengthened by fixing round it with rubber solution strips 

 of the rubbered canvas used for mending punctures in the 

 outer case of a bicycle tyre. A manometer tube (b) and a 

 receptacle (c) (the latter to catch any back flow of water 

 from the pump if the filter accidentally breaks) are inter- 

 cepted between the filter and the pump. These are usually 

 arranged on a board a, as in Fig. 27. Between the tube / 



and the pump a, between the 

 tube d and the filter, it is con- 

 venient to insert lengths of 

 flexible lead -tubing connected 

 up at each end with short, stout- 

 walled rubber-tubing. 



Various modifications of the 

 filter are used, (a) An apparatus 

 is arranged as in Fig. 28. The 

 FIG. 28. Chamber-land's fluid to be filtered is placed in 



candle and flask arranged for the cylindrical vessel a. Into 

 filtration. , . ., ,. ,,, . , 



this a "candle or "bougie of 



porcelain dips. From the upper end of the bougie a glass 

 tube with thick rubber connections, as in Fig. 28, proceeds to 



