6 4 



MANUAL OF BACTERIOLOGY. 



hay and potato, they nevertheless are capable of ruining 

 the culture-media with which one works. 



It has been shown by T. 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 anaerobic bacteria happen to be present in such fluids, 

 they will not develop into the adult form between the appli- 

 cations of heat, under aerobic conditions. 



The form of sterilizer most widely used in the United 

 States is that which is known as the Arnold Steam Sterilizer. 



FlC. 12. 



Diagram of the Arnold steam sterilizer. 



The Arnold sterilizer consists of a cylinder of tin or 

 copper with a cover, which is enclosed in a movable, cylin- 

 drical outer cover or hood. The inner cylinder has an 

 opening in the bottom through which steam may enter, the 



