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ESSENTIALS OF BACTERIOLOGY 



Koch's Steam-chest (Fig. 15). Circulating steam is obtained 

 by aid of Koch's apparatus. This consists of a cylindric tin 

 chest about 2j feet high and about J foot in diameter; divided 

 in its interior by a perforated diaphragm, a, an upper cham- 



Fig. 15. Koch's steam-chest. 



Fig. 16. Arnold's steam sterilizer. 



ber for the steam, c, and a lower one for water, b. Two or 

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

 a 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- 



