STERILIZATION UNDER PRESSURE. 45 



the water in the reservoir becoming exhausted and the 

 consequent destruction of the sterilizer. 



Fig. 2 gives an illustration of this apparatus. 



Fig. 2. 



For sterilization by steam wnder -pressure several 

 special forms of apparatus exist. The principles of 

 them all are, however, the same. They provide for Ihe 

 generation of steam in a chamber from which it cannot 

 escape when the apparatus is closed. Upon the cover of 

 this chamber is a safety-valve, which can be regulated so 

 that any degree of pressure desirable can be maintaiiu'd 

 within the sterilizing chamber. These sterihzers are 

 known as " digestors " and also by tlie French name 

 "autoclav." Their construction can best be understood 

 by reference to Fig. 3. 



The dry sterilizers used in laboratories are simply 

 double- walled boxes of Russian or Swedish iron (Fig. 4), 



3" 



