METHODS OF CULTURE. 



45 



Koch's Steam-chest. Circulating steam is obtained by aid of 

 Koch's apparatus. This consists v of a cylindrical tin chest 

 .about 2 feet high and about foofem diameter ; divided in its 

 interior by a perforated diaphraglk&i, an upper chamber for 

 the steam, c, and a lower one for , water, 6. Two or more 

 gas-burners placed underneath the chest, which stands on a 



FIG. 16. 



STERILIZING CHAMBER 



**. 



JU A JjL 



Arnold's Steam-sterilizer. 



tripod, supply the heat. In the cover is an opening for a ther- 

 mometer. The chest is usually covered with felt. When the 

 thermometer registers 100 C. the culture-medium or other sub- 

 stance to be sterilized is placed in the steam and kept there 

 from 10 to 15 minutes, or longer, as required. 



Arnold's steam sterilizer will answer every purpose of the 

 Koch steam-chest. It is cheaper, also requiring less fuel to keep 

 it going. The steam does not escape, but is condensed in the 

 outer chamber. (Fig. 16.) 



