METHODS OF CULTURE. 



47 



Fractional Sterilization of Tyndall. Granted that so many 

 spores originally exist in the object to be sterilized, it is sub- 

 jected to 60 C. for four hours, in which time a part at least of 

 those spores have developed into bacteria, and the bacteria 

 destroyed by the further application of the heat. The next day 

 more bacteria will have formed, and four hours' subjection to 

 60 heat will destroy them, and so at the end of a week, using 

 four hours' application each day, all the spores originally present 

 will have germinated and the bacteria destroyed. 



FIG. 18. 



FIG. 19. 



Wire-Cage. 



Cotton plugged Test-Tubes. 



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. 



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 



