BACTERIOLOGICAL TECHNIC 



13 



sheet-copper walls {e, e) to the large compartment 

 {b). Larger forms on the same principle are in use 

 (Fig. 8). 



The media to be sterilized are placed in the large 

 chamber {d, Fig. 7). The water is then heated until 

 steam is generated, and the action of the steam on the 

 media is continued for 20 minutes from the time steam 



Fig. 6 



Arnold Steam Sterilizer 



The hood is taken off and 



the door opened, showing 



inside arrangement 



Fig. 7 

 Arnold Steam Sterilizer 



a. Inner water compartment 



b. Outer water compartment 



c. Perforated bottom 

 d. Sterilizing chamber 



e. Sheet-copper walls 



begins to rise. This process is repeated on two succeed- 

 ing days, so that the media have been exposed to the 

 steam for three days. On the first day all vegetative 

 forms are killed. The media are then kept at room or 

 incubator temperature, so that spores which may be 

 present and are not killed by the first exposure may 

 develop into vegetative forms and be killed by the 

 second exposure. If after this any spores should 



