CLEANING AND PREPARING GLASSWARE 



of the tube to the depth of about J of an inch; or roll 

 the cotton into cylinders of the same s^*^/^ 

 diameter as the culure-tube and insert / ^ ~ 

 it into the mouth (Fig. 2). The plug /f7r ^ 

 should allow the interchange of air, 

 and at the same time be tight enough 

 to hold the weight of the tube, and 

 with no crevices on the side. The 

 glass rod should never be pushed 

 through the cotton. 



EXERCISE III Flo . 3 



STERILIZATION OF GLASSWARE Plugged Culture-Tube 



Sterilization is the process of killing all micro-organ- 

 isms. This may be accomplished by heat, by certain 

 chemicals, or by nitration. Sterilization by heat may be 

 accomplished 



1. By dry heat; this method is applied to sterilization 

 of many kinds of apparatus. 



2. By moist heat; this method is applied largely to 



sterilization of culture media, 

 and will be described in 

 Chap. Ill, Exercise II. 



Hot-air sterilizers are boxes 

 with double walls of sheet- 

 iron. The bottom shelf 

 should always be covered with 

 a piece of sheet-asbestos, to 

 prevent too rapid heating of 

 the apparatus. By means of 

 a Bunsen burner with three 

 flames a heat of about 150 

 may easily be maintained. The flames of the burner 



FIG. 3 

 Koch's Hot-Air Sterilizer 



