METHODS OF USING CULTURE MEDIA 187 



sealed at the small end, plugged with cotton above the 

 constriction and sterilized. . The medium, agar or gelatin, 

 which has been previously inoculated with the anaerobic 

 culture, is then drawn up into the tube, after breaking off 

 the tip, as far as the constriction. The tube is then sealed 

 in the flame at the small end and also at the constriction. 

 Since it is full of the medium and sealed, access of air is 

 prevented. This forms an excellent means for "isolation" 

 (Chapter XVIII) ; the tube needs merely to be cut with a 

 file at the point where colonies appear, then these may be 

 readilv transferred. 



Fig. 122. — Mgnal tul)es. X ^. 1, the sterile tube ready for inoculation; 



2, fourth dilution tube showing a few isolated colonies, one near the figure; 



3, third dilution showing colonies isolated but numerous; 4, second dilution 

 tube showing colonies still more numerous; 5, first dilution tube showing 

 colonies so numerous and small as to give a cloudy appearance to the tube. 

 In use tube 2 would be filed in two at the colony and inoculations made 

 from it. 



B. ''Fermentation tubes" form a simple means for growing 

 liquid cultures of anaerobes, the growth occurring in the 

 closed arm only, while with facultative anaerobes, growth 

 occurs both in the closed arm and in the open bulb. A little 

 "paraffin oil" (a clear, heavy petroleum derivative) may be 

 poured on the fluid in the open bulb as a very efficient seal, 

 though it is not usually necessary. 



C. " Beep Culture Tubes."— The medium, agar, gelatin or 

 a liquid is poured into tubes until they are approximately 

 one-half full, a little paraffin oil is poured on the surface 

 (not essential always), then the tubes are plugged and steril- 



