166 BACTERIOLOGY. 



France, the autoclave (Pig". 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 lig"ht 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 g-aug-e indicates 110 the 

 supply of g-as 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 g-as. 



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. 



