CULTIVATION OF BACTERIA 65 



each day for three days in succession in the Arnold sterilizer, 

 or one exposure in the autoclave, five to fifteen minutes, at 

 15 pounds pressure; 120 C. is sufficient to sterilize most 

 culture-media. 



Fractional Sterilization of Tyndall. Granted that so 

 many spores originally exist in the object to be sterilized, it 



Fig. 16. Autoclave. Horizontal form. 



is subjected 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 C. 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 be destroyed. 

 5 



