CULTURAL TECHNIQUE 



Filtering of media. Bouillon may be filtered through 

 paper. The paper made by Schleicher & Schtill, and known 

 as No. 520 N, is well adapted for the filtering of all kinds of 

 media. The paper can be purchased in the form of 

 folded filters. 



Gelatin may be filtered by placing in a large fun- 

 nel a small mass of copper turnings or clean ex- 

 celsior ; over these a small piece of absorbent cotton ; 

 then a layer of absorbent cotton large 

 enough to reach to the top of the 

 funnel. The layers of cotton should 

 be thin so as not to retain much of 

 the medium. Over the absorbent 

 cotton place a piece of wet cheese 

 cloth. Pour the medium into the 

 funnel carefully. In case it has been 

 correctly prepared, it will filter 

 rapidly and be perfectly clear. 



Agar may be filtered in the same 

 manner as gelatin. 



The media should be placed in 

 test tubes, 7-8 cc. in each tube. 

 Extreme care should be taken to 

 avoid wetting the upper part of the 

 tube with the media, as this causes the cotton to adhere to 

 the glass. A funnel arranged as illustrated in Fig. 4 is con- 

 venient; the glass tip should be slightly expanded at the 

 lower end, and long enough so it can be held between the 

 fingers and thus kept out of contact with the wall of the tube. 

 The pinchcock should be closed rapidly so that no dripping 

 will occur, and thus avoid soiling the mouth of the tube. The 

 storage flasks should not be filled more than two thirds full ; 



FlG. 3. Al'l'AUATLS FOR 

 FILTERING MEDIA 



The absorbent cotton is 

 supported by excelsior 



