FILTRATION OF CULTURE MEDIA 



19 



be run off into any suitable sterile vessel. When the bulb is emptied, replace the 

 test-tube, tighten the clip, open G, and repeat the operation.] 



2. The filtrate may also be collected through a piece of glass tubing connected 

 by a piece of india-rubber tubing a few centimetres long to the nozzle of the filter 

 (fig. 16). The bougie, with rubber and glass tubing attached, is wrapped in paper 



FIG. 16. Alternative method 

 of collecting the filtrate. 



FIG. 17. Flask with three tubulures for the 

 collection and distribution of the filtrate. 



and sterilized. When required for use, the bougie is fixed in its metal cylinder, 

 the paper removed from the rubber and glass collecting tubes, and the latter pushed 

 through the paper cap covering the mouth of the sterile vessel in which the filtered 

 liquid is to be collected. If the collecting vessel be plugged with wool, the tube 

 is inserted between the neck and the plug, the tube being surrounded as completely 

 as possible with wool and pushed downwards until the orifice projects below the 

 wool. 



3. Another arrangement is to use a flask with three tubulures, such for instance 

 as that shown in fig. 17. The flask must of course be sterile; the wool in the mouth 

 of the india-rubber tubing B is removed, and the tube itself attached to the nozzle 

 of the filter. When filtration is completed the tubing is removed from A, which 

 is then plugged with a sterile plug, all necessary precautions being taken to prevent 

 contamination. To manipulate the filtrate the tubulure C is broken and the 

 liquid run out by simply inclining the flask. The third tubulure D is plugged 

 with wool. 



Filtration by compression involves the use of a costly piece of apparatus, 

 and is limited in practice to the filtration of viscous fluids. 



B. Filtration by aspiration. 



Aspiration is the means usually employed for the filtration of fluids. The 

 methods by which the principle of filtering by aspiration is applied vary in 

 detail, and the technique of a few of the simplest and easiest devices will 

 be described. 



[1. Fit up and sterilize a Cobbett's bulb exactly as described for filtration 

 under pressure (p. 18), and clamp it to a suitable stand. Connect the bulb 

 to a wash-bottle with a piece of red rubber pressure-tubing, but between the 

 bulb and the wash-bottle insert either a three-way tap or a T-piece of glass 

 tubing the vertical limb of which is closed by india-rubber tubing and a 

 clip, then connect the wash-bottle to the pump. 



