166 BACTERIOLOGY. 



France, the autoclave (Fig. 27), is used almost exclu- 

 sively. The apparatus, although expensive, and requiring 

 careful, intelligent usage, is by no means difficult to handle. 

 By means of the autoclave it is possible to have a sterile 

 medium in about half an hour after this has been prepared. 

 No well equipped laboratory should be without this appa- 

 ratus. 



A temperature of 120-130°, if allowed to act for 15 min- 

 utes or longer, may render the medium acid, or may give 

 rise to decomposition products, which will inhibit the sub- 

 sequent growth of bacteria. This is especially true of 

 media which contain sugar, as for instance milk. In either 

 case the medium becomes worthless. A temperature of 110° 

 has very little effect on the media, and, if allowed to act 

 for 15 minutes will sterilize the same. 



The following directions should be closely observed when using an 

 autoclave: 



1.— See that sufficient water is present. 



2. — Place the lid in position and fasten tight, by hand. The wrench 

 should not be used, if possible. 



3. — Open the steam-valve, and light all the burners. See that 

 they do not " shoot back." 



4. — After the steam has issued violently for about 1 minute close 

 the steam-valve. The steam is allowed to escape in order to expel all 

 the air that is present in the autoclave. 



5. — The pressure now rises, and when the gauge indicates 110° the 

 supply of gas to the inner ring of burners is shut off, and that to the 

 outer ring is turned down as low as possible. A few trials will enable 

 one to turn down these burners so that the temperature of 110° will 

 continue constant. 



6.— Maintain a temperature of 110° for 15 minutes, then turn off 

 all gas. 



7. — When the temperature has fallen to 100°, or less, the steam- 

 valve can be opened, but not before. If the latter is opened when the 

 temperature is above 100°, the sudden release of pressure will cause 

 the liquid in the tubes or flasks to boil over. After the steam-valve 

 has been opened the lid of the autoclave may be loosened and re- 

 moved, without waiting for the apparatus to completely cool. 



