46 LABORATORY GUIDE IN BACTERIOLOGY 



to allow liquids to pass through, but no solids or organ- 

 isms. 



i. Arrange a Berkefeld filter so as to connect with 

 the suction pump, and filter a quantity of unsterilized 

 broth (Fig. 24). 



FIG. 24 

 Action of Berkefeld Filter 



a. Berkefeld filter 



b. Filtered liquid 



c. Side tube with cotton filter 



d. Intercepting flask 



e. Connection with aspirator 

 /. Rubber hose 



2. Set aside, and observe the results. The filter (a), 

 after being connected with the flask, is sterilized in the 

 autoclav. The cotton plug at c prevents the air, which 

 is sucked back, from carrying germs. The flask d will 



