STERILIZATION OF CULTURE MEDIA. 



53 



uniformly, but should not be packed so closely that there is difficulty 

 is removing them. 



Steam Sterilizers. Steam at the ordinary pressure of the atmo- 

 sphere has the same temperature as boiling water, and in practice is 

 preferable to a water bath for several reasons. The form of steam 

 sterilizer adopted by Koch, after extensive experiments made in col- 

 laboration with Loftier and Gaffky, is now generally used in bacte- 

 riological laboratories. This is shown in Fig. 24. It consists of a 

 cylindrical vessel of zinc which is covered with a jacket of felt. 

 The cover, also covered with non-conducting material, has an aper- 

 ture at the top for the escape of steam. A glass tube, which is in 

 communication with the interior of the vessel, serves to show the 



FIG. 24. 



FIB. 55 



height of the water when the apparatus is in use. The bottom of 

 the cylindrical vessel should be of copper. A Bunsen burner having 

 three jets will commonly be required to keep the water in ebullition 

 and the upper part of the steam sterilizer filled with "live steam," 

 which should escape freely from the aperture in the cover to insure 

 a temperature of 100 C. in the steam chamber. A perforated zinc 

 or copper shelf in the interior of the cylinder serves to support the 

 flasks, etc., which are to be sterilized. Usually they are lowered 

 into the cylinder in a light wire basket, or tin pail with perforated 

 bottom, of proper diameter to sli-p easily into the sterilizer. 



Fig. 25 is a sectional view of this sterilizer. 



The steam sterilizer shown in Fig. 26 ' is an American invention, 



1 The Arnold steam sterilizer, manufactured at Rochester, N. Y. 



