24 



STERILIZATION BY FILTRATION 



Fill the cylinder through the funnel with the fluid to be filtered, close the tap 

 and turn on the water. The fluid in the cylinder is aspirated through the filter, 

 along the tubing, and so into the bulb. When all the liquid has been aspirated, 

 turn off the water, open the tap, and disconnect the bulb from the water pump. The 

 lower tubulure of the bulb is sealed during filtration, but is flamed and the point 

 broken off with sterile forceps before distributing the filtrate. 



This is a useful piece of apparatus, but its cost is a disadvantage. 



5. Chamberland's method. If water be not available, a small hand pump, 

 e.y. Potain's, may be used for aspiration. Place the filter B (fig. 25) in a 



FIG. 25. Chamberland's filter. 



tall glass cylinder C, and fill up the latter with the liquid to be filtered. On 

 working the aspirator the fluid is drawn through the filter into the flask A, 

 which has three tubulures. The filter and flask must both be sterilized in 

 the autoclave before use. 



[It will be obvious, of course, that Cobbett's bulb can be used equally with 

 a hand or water pump.] 



3. The filtration of small quantities of liquid. 



The laboratory bougie. When only very small quantities of liquid have 

 to be filtered, as for example in testing a toxin, a small thin-walled bougie 



12-15 cm. long and without a 

 nozzle is very useful. 



Technique. [A. Slip one end of a 

 piece of stout pressure- tubing over 

 the open end of the bougie and secure 

 it with a rubber ligature, then con- 

 nect the other end to the free limb 

 of the U-tube of a Cobbett's bulb. 

 Sterilize in the autoclave. Place the 

 filter in a small glass cylinder or test- 

 tube and fill the latter with the fluid 

 to be filtered. Connect the bulb to a 

 water pump and exhaust. Any fluid 

 remaining in the filter can be recov- 

 ered by holding the filter upside down, 

 and allowing it to run into the bulb.] 

 B. The filter may also be arranged as shown in fig. 26. As in A, a piece of pressure- 

 tubing is firmly fixed by one end to the upper end of the filter, but the other end is 

 attached to one of the two tubulures of the flask B. The other tubulure A is plugged 

 with cotton- wool and connected to a water pump or a small aspirator, e.g. Potain's. 

 Sterilize the apparatus before use. 



FIG. 26. Laboratory bougie for filtering small 

 quantities of liquid. 



