44 METHODS OF STUDYING MICROORGANISMS 



that is, only one kind. After the glassware contains the 

 medium, which is destroyed by dry heat, steam sterili- 

 zation is used. The best method of sterilization is by 

 the autoclave or pressure boiler, since all organisms are 

 killed by one atmosphere of pressure to the square 

 inch in addition to the ordinary atmospheric pressure. 

 Because of the delicacy of some of the nutrient media, 

 it is, however, necessary to sterilize these at the usual 



FIG. 18 



Arnold steam sterilizer. 



pressure of the atmosphere in streaming steam. For 

 this purpose a double jacketed boiler with the steam 

 introduced into the inner chamber (Arnold steam 

 sterilizer) is used. 



While this sufficiently indicates the uses of sterili- 

 zation for the preparation of food for bacteria, a few 

 words upon sterilization in general are necessary. 

 This term is usually reserved for the killing of bacteria 



