FILTRATION OF CULTURES 



75 



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 

 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 

 i r i and pump are intentionally drawn to a larger 



porcelain by exhaust- ^ & the manomete r 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, g\ 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 

 breaks) are intercepted between the filter and the 



FIG. 31. Chamberland's candle 

 and Hask arranged for filtra- 

 tion. 



