i AND ii AGAR-AGAR TUBES 91 



The tubes afterwards must be sterilised in the autoclave, 

 being at the same time covered up with stout tinfoil. 



When the sterilisation is complete, place some tubes on 

 the sloping tray and allow the agar-agar to set on the slant ; 

 allow the other tubes to set in an upright position. 



The latter may be sloped at any time by again melting 

 the agar-agar in the autoclave and placing the tubes on 

 the sloping tray. 



XII. GLYCERINE AGAR-AGAR AND GRAPE-SUGAR 

 AGAR-AGAR. 



(a) Glycerine agar-agar. 



(1) To every/100 cc. of liquid agar-agar, add 5 to 6 cc. of 

 pure glycerine, and mix thoroughly. 



(2) Fill test-tubes in the usual manner, and sterilise 

 them in the autoclave. 



(3) Some tubes should be allowed to set on the slant, 

 others in an upright position. 



(b) Grape-sugar agar-agar. 



(1) To every 100 cc. of liquid agar-agar add 2 grammes of 

 grape-sugar, and shake till the sugar is dissolved. 



(2) Fill test-tubes in the usual manner, and sterilise 

 them in the autoclave at 120 C. 



(3) Allow the agar-agar to set in an upright position. 



If the grape - sugar agar - agar is to be used for 

 anaerobic cultivations, the tubes must be filled to 

 two-thirds of their height. 



