30 GENERAL MICROBIOLOGY 



This process is most efficient when the egg albumen coagu- 

 lates slowly. 



As egg albumen begins to coagulate at about 57 C. it is 

 absolutely imperative for good results that the medium be 

 cooled to 40-50 C. before the addition of egg albumen. 



Although egg albumen contains small amounts of sol- 

 uble matter not coagulable by heat, as sugar, extractives 

 and mineral matter, all of which will serve as microbial 

 food, its purpose in nutrient media is primarily for its clari- 

 fying action. 



Apparatus. 500 c.c. sterile meat infusion; 500 c.c. tap 

 water; 10 gms. peptone, Witte's; 5 gms. salt; 10 gms. egg 

 albumen (or one egg); 3.5 liter agate-ware pail; titration 

 apparatus; N/20 NaOH; N/l NaOH; phenolphthalein 

 (indicator); distilled water; 5 c.c. pipette; large stirring 

 rod; coarse balances; large gas burner; large funnel; 

 plaited filter paper; filling funnel; sterile test tubes; sterile 

 1 liter flask; apparatus for steam sterilization-. 



Method. 1. Put the contents of a flask of meat infusion 

 (500 c.c.) in an agate pail and add 500 c.c. of tap water. 



2. Add 1% of Witte's peptone and 0.5% of salt. 



3. Add 10 gms. of egg albumen which has been well 

 mixed with 100 c.c. of tap water. (Put the egg albumen 

 in a tumbler and add enough water to form a paste. Stir 

 until smooth. Then add the remaining water. One egg* 

 well beaten may be substituted.) Mix all thoroughly. 



4. Heat in flowing steam for forty-five minutes or in the 

 autoclav at 120 C. for thirty minutes. 



5. Titrate with N/20 NaOH. 



6. Adjust the reaction of the medium to +15 with 

 normal NaOH or normal HC1. Retitrate and adjust again 

 if necessary. 



7. Counterpoise and note the weight. 



8. Boil fifteen minutes over a free flame, stirring con- 

 stantly. 



* It is not necessary to add water to the egg. 



