52 



MANUAL OF BACTERIOLOGY. 



It has been shown by Theobald Smith that the discontinuous 

 method cannot be relied upon to sterilize fluids in shallow layers 

 that are freely exposed to the air. For if the spores of anaero- 

 bic bacteria happen to be present in such fluids, they will not 

 develop into the adult form between the apphcations of heat, 

 under aerobic conditions. 



Fig 12. — Diagram oe the Arnold Steam Sterilizer. 



The form of steriHzer most widely used in the United States 

 is that which is known as the Arnold Steam Sterilizer. 



The Arnold steriHzer consists of a cylinder of tin or copper 

 with a cover, which is enclosed in a movable, cyUndrical outer 

 cover or hood. The inner cylinder has an opening in the 

 bottom through which steam may enter, the steam coming from 

 a small chamber underneath with a copper bottom to which 

 the flame is appHed. The pecuKarity of this form of sterilizer 



