METHODS OF CULTURE AND OF EXAMINATION. 



75 



(338 F.), even the most resistant spores are destroyed. It 

 suffices, further, in this mode of sterilization, to heat the 

 drying chamber in which the instruments to be sterilized are 

 placed, until a thermometer introduced from the top indi- 

 cates a temperature of 170 C. (338 F.) ; then the supply 

 of gas is cut off, and after the apparatus has completely 

 cooled, the now sterile contents are removed. 



Fig. 9. Hot-air sterilizer. 



Live Steam. Most substances, however, that are em- 

 ployed in bacteriologic investigations, especially the nutri- 

 ent media, do not bear sterilization by means of such high 

 degrees of heat as have been mentioned ; they are, there- 

 fore, rendered germ-free by means of live steam. For this 

 purpose they are introduced into a cylindric apparatus, 

 made of galvanized iron or of copper, and covered with felt 

 or with asbestos. (Koch's steam-chamber, Figs. 10, n.) 

 This vessel is divided by means of a perforated shelf or a 

 wire grating into an upper larger and a lower smaller 



