48 ESSENTIALS OF BACTERIOLOGY 



sterilization in steam, at 100 C., on three successive days, has 

 been found sufficient for nearly all purposes, while one sterili- 

 zation in the autoclave at 110 C. for fifteen minutes will 

 serve in some cases, especially if the media is for immediate 

 use. 



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. 



Fig. 1 8. Wire cage. 



Fig. 19. Cotton-plugged test-tubes. 



Tin-foil may be used to cover the cotton, or caps made of 

 india-rubber. 



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 

 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.) 



