36 GENERAL MICROBIOLOGY 



EXERCISE 8. PREPARATION OF NUTRIENT GELATIN 



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

 water; 150 gms. gelatin; 10 gms. peptone, Witte's; 5 

 gms. salt; 10 gms. egg albumen (or one egg); water bath; 

 thermometer; 3.5 liter agate ware pail; long heavy stirring- 

 rod; titration apparatus; N/20 NaOH; N/l NaOH; 

 phenolphthalein (indicator); distilled water; coarse bal- 

 ances; large gas burner; large funnel; plaited filter paper; 

 filling funnel; sterile test tubes; sterile 500 c.c. Erlenmeyer 

 flasks; apparatus for steam sterilization; running-water 

 bath or refrigerator. 



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 15% gelatin, 1% Witte's peptone, and 0.5% 

 salt to the mixture. 



3. Heat this mixture in a water bath to dissolve the 

 gelatin, peptone and salt, stirring occasionally. 



4. Cool to 40-50 C. This is imperative. 



5. Then 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, add enough water to form a paste and stir 

 until smooth; then add the remaining water. One egg 

 well beaten may be substituted.) Mix all thoroughly. 



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

 autoclav at 105 C. for thirty minutes. 



7. Titrate with N/20 NaOH. 



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

 normal NaOH or normal HC1. Re titrate and adjust again 

 if necessary. 



9. Counterpoise and note the weight. 



10. Boil fifteen minutes over the free flame, stirring con- 

 stantly. 



11. Counterpoise and restore any loss by evaporation 

 with distilled water. 



12. Filter while boiling hot through plaited filter paper 



