PREPARATION OF CULTURE MEDIA 17 



point at 4 (result: Fig. 8, e). The shaded part is now 

 eight layers deep. 



5. Turn the folder face down, and repeat the opera- 

 tions exactly as in 3 and 4 (result: Fig. 8, /). 



6. Take up and open the large middle fold (result: 

 Fig. 8, g). The two halves must now be symmetrical. 



7. Fold so as to make the lines 1-3 and 1-4 meet 

 at the center line 1-2 (result: Fig. 8, h). 



8. Now pick up and fold backward so as to have i 

 cover 2 in the back (result: Fig. 8, i). 



9. Cut through the line 1-2 and open up. The 

 extreme ends will be found without a fold, and may be 

 folded so as to make nine sharp edges. 



This filter is then evenly inserted into the funnel, 

 spreading the folds at a distance 

 from each other as nearly alike 

 as possible. Great care should be 

 taken to make the folds and the 

 point sharp, as this insures rapid 

 filtering of the liquid and prevents 

 the filter from tearing. A wire 

 rack may be used, but does not FIG. 9 



yield nearly so good results (Fig. 9). 



Another method, simple and yielding excellent results, 

 is the use of absorbent cotton. Take a piece about 3 

 inches square, and cover lightly the lower end of the 

 funnel with it. Take a larger piece, also square, judging 

 the size according to the size of the funhel; pull it gently, 

 so as to make the layer of cotton thinner, without showing 

 any open spaces; and spread this around the inner sur- 

 face of the funnel. 



If a vacuum pump is available, the medium may be 



