METHODS OF CULTURE. 



45 



Cotton Plugs or Corks. All the glass vessels (test-tubes, flasks, 

 etc.) must be closed with cotton plugs, the cotton being easily 

 sterilized and preventing the entrance of germs. 



Test-tubes. New test-tubes are washed with hydrochloric 

 acid and water to neutralize the alkalinity often present in 

 fresh glass. They are then well washed and rubbed with a 

 brush, placed obliquely to drain, and when dry corked with 



FIG. 18. 



FIG. 19. 



iilll 



: iHi 



Wire-Cage. 



Cotton plugged Test-Tubes. 



cotton plugs. Then put in the hot-air oven (little wire-cages 

 being used to contain them) for fifteen minutes, after which they 

 are ready to be filled with the nutrient media. (The cotton 

 should fit firmly in the tube and extend a short space beyond it.) 



Test-tubes without flaring edges are more desirable since the 

 edges can easily be drawn out so as to seal the tube. 



Instead of test-tubes, ordinary 3 oz. panel medicine bottles 

 can be used for retaining the nutrient media and cultures. 



According to late investigations, the glass tubes become suffi- 

 ciently sterile in the steam-chest without the preliminary sterili- 

 zation in the dry oven. 



