LESSON XII 



Testing of Filters Filtering through Paper Filtering through a 

 Berkefeld Filter The Effect of Use on a Berkefeld Filter. 



Testing of Filters 



A. FILTERING THROUGH PAPER. 



(1) Take 500 to 1000 cc. of sterile water, and add three 

 broth cultures of the Bacillus prodigiosus (four days old). 



(2) Prepare three gelatine plates from this water, before 

 filtering it. 



(3) Now filter the water through sterile paper, using a 

 sterile funnel and observing aseptic precautions as strictly 

 as possible. 



(4) Prepare three gelatine plates from the filtrate. 

 Place the two sets of plates in the cool incubator and 



compare them from day to day, counting the 

 colonies at the same time. 



Filter paper arrests only a limited number of organ- 

 isms. 



B. FILTERING THROUGH A BERKEFELD FILTER. 



(1) Take 1000 cc. of sterile water, and add three broth 

 cultures of the Bacillus prodigiosus as before. 



