no 



BACTERIOLOGICAL LABORATORY TECHNIC 



not solidify when cold, the sugar is caramelized and the media 

 blackened. 



Potato tubes are harder to sterilize at times, and it is safer 

 to repeat the operation in twenty-four hours. 



Fractional method of sterilization, or Tyndallization, is accom- 

 plished by heating the media to iooC. on three successive days 



FIG. 23. Arnold sterilizer. 



in a lyoch or Arnold sterilizer. By heating culture media to this 

 temperature, all the vegetative, or adult, forms are killed, while 

 the spores are not affected; after the first sterilization, at room 

 temperature, the spores vegetate and become adult bacteria, 

 when on the second sterilization they are non-resistant to iooC. 

 and are killed. Spores remaining after this develop into adult 

 forms again and are killed on the third day, at the third steriliza- 

 tion. This fractional sterilization is employed under many 



