98 LABORATORY MANUAL 



Directions: Thoroughly wash all dishes and other 

 apparatus to be used in this exercise. Follow this by 

 dipping each article separately into alcohol. Then 

 place the dishes in the steam sterilizer and heat at a 

 temperature of 150 C. for a period of twenty minutes. 

 If gelatin culture medium is used, mix together the 

 following : 



200 c.c. of water. 



1 gram extract of beef. 



2 grams of peptone. 

 20 grams of gelatin. 



Place the mixture in the dish in which it is to be 

 boiled, heat until the gelatin is thoroughly melted, 

 and then boil briskly for a few minutes. Test with 

 litmus paper. The solution should be slightly alkaline. 

 If it is not, add to it, drop by drop, a solution of 

 sodium hydroxide until it is slightly alkaline to litmus 

 paper. Filter the solution through absorbent cotton 

 and collect the clear liquid in a sterilized flask. Into 

 the sterilized petri dishes pour enough of the medium 

 to cover the bottom of the dish. Cover the dishes 

 immediately, place them in the sterilizer, and heat 

 at a temperature of 150 C. for fifteen minutes. When 

 cooled sufficiently to handle, set aside for twenty-four 

 hours, then heat again at 150 C. for fifteen minutes. 

 After another twenty-four hours repeat the steriliza- 

 tion process. The medium is now thoroughly sterilized 



