STERILIZATION AND DISINFECTION. 



167 



kill many spores, so that the exposure of culture-media 

 to streaming steam is of little use unless applied in 

 a systematic manner — intermittent sterilization — based 

 upon a knowledge of sporulation. 



In carrying out the intermittent sterilization the cul- 

 ture-medium is exposed for fifteen minutes to the passage 

 of streaming steam in the apparatus or to some tem- 

 perature judged to be sufficiently high, so that the bac- 

 teria contained in it are killed. As the spores remain 

 uninjured, the medium is stood aside in a cool place for 

 twenty-four hours, and the spores allowed to develop into 

 perfect bacteria. 



When the twenty-four hours have passed the culture- 

 medium is again placed in the apparatus and exposed to 



Fig. 12. — Autoclave for rapid sterilization FlG. 13. — Kny-Sprague steam sterilizer, 

 by superheated steam under pressure. 



the same temperature, until these newly-developed bac- 

 teria are also killed. Eventually, the process is repeated 



