FILTRATION OF CULTURES 



77 



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. The filtra- 

 tion of albuminous 

 fluids may sometimes 

 be facilitated by keep- 

 ing them near blood- 

 heat during the pro- 

 cess. For ordinary 

 bacteriological work, 

 filters of various kinds <L 

 are in the market 

 (such as those of Klein 

 and others), but the 

 most generally con- 

 venient is that in 

 which the fluid is FIG. 30. Geissler's vacuum pump arranged with* 

 sucked through the manometer for filtering cultures. (The tap 

 ... , 3 , and pump are intentionally drawn to a larger 



porcelain by exhaust- sca le than the manometer board to show 

 ing the air in the details.) 

 receptacle into which 



it is to flow. This is conveniently done by means of a 

 Geissler's water-exhaust pump (Fig. 30, #), 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 lash- 

 ing 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 

 (&) and a receptacle (c) (the latter 

 to catch any back flow of water from the pump which may 

 accidentally occur) are intercepted between the filter and the 



FIG. 31. Chamber-land's candle 

 and flask arranged for filtra- 

 tion. 



