io8 



PATHOGENIC BACTERIA. 



in order that a single contaminating organism, should 

 it enter, may not spoil the entire bulk. A very con- 

 venient simple apparatus used by bacteriologists for fill- 

 ing tubes with liquid media is shown in Figure 17. It 



FIG. 17. Funnel for filling tubes with culture-media (Warren). 



need not be sterilized before using, as the culture-medium 

 will be sterilized by the intermittent method after the 

 tubes are filled. The test-tubes and flasks into which 

 the culture-medium is filled must, however, be previously 

 sterilized by dry heat. The dry-heat sterilization is done, 

 of course, after the cotton plugs are in place. 



Bouillon is the basis of most of the culture-media. 

 The addition of 10 per cent, of gelatin makes it " gela- 

 tin ;" that of i per cent, of agar-agar makes it "agar- 

 agar. ' ' The preparation of these media, however, varies 

 somewhat from that of the plain bouillon. 



