FILLING THE TUBES. 127 



As soon as the tubes have been filled they are to be 

 sterilized either in the steam sterilizer at 100 C. for 

 fifteen minutes on each of three successive days, being 

 kept during the intervals at room temperature, or they 

 may be sterilized by a single exposure of 15 minutes in 

 the autoclave to a temperature equivalent to steam under 

 about one atmosphere of pressure. 



When sterilization is complete and the medium in 

 the tubes is still liquid, some of them may be placed in 

 a slanting position, at an angle of about ten degrees 

 with the surface on which they rest, and the medium 

 allowed to solidify in this position. These are for the 

 so-called slant-cultures. The remainder may solidify 

 in the erect position ; these serve for making plates. 



