28 GENERAL MICROBIOLOGY 



EXERCISE 6. PREPARATION OF MEAT INFUSION 



Meat infusion is the foundation of the ordinary nutrient 

 media, as broth, gelatin and agar, and also of a large number 

 of special nutrient media, as sugar broths, etc. 



Under these directions sufficient meat infusion is pre- 

 pared to make 1 liter each of nutrient broth, gelatin and 

 agar. 



Apparatus. 1.5 kilograms (3 Ibs.) finely chopped fresh 

 lean beef; 1500 c.c. tap water; 3.5 liter agateware pail; 

 large funnel; ring stand; clean cloth; 1 liter measuring 

 cup; three sterile 1 liter Erlenmeyer flasks; refrigerator; 

 apparatus for steam sterilization (autoclav preferable). 



Method. 1. To 1.5 kilograms of finely chopped, fresh 

 lean beef in a 3.5 liter agateware pail, add 1500 c.c. of tap 

 water,* mix thoroughly and allow to stand in a cool place 

 (refrigerator preferred) for sixteen to twenty-four hours only. 



2. Set up a large funnel in a ring stand and place a piece 

 of clean cloth in the funnel. Place a measuring cup under 

 the funnel. 



3. Strain the meat infusion through clean cheesecloth, 

 thoroughly pressing out all the juice. 1.5 liters should be 

 recovered. If any loss occurs make up to 1500 c.c., using 

 tap water. 



This resulting sanguineous fluid contains the soluble 

 albumins of the meat, the soluble salts, extractives and coloring 

 matter, chiefly hemoglobin. 



4. Place 500 c.c. of meat infusion in each of three sterile 

 1 liter Erlenmeyer flasks. Replace the plugs, and heat in 

 the autoclav at 120 C. for thirty minutes. This is a safer 

 procedure than heating for a longer time in flowing steam. 



During this heating the albumins coagulable by heat are 

 precipitated. 



It has been found necessary and also more convenient 

 to prepare and sterilize meat infusion before proceeding with 

 the preparation of the different media in which it is used, 

 * Approximately 500 c.c. of water to each pound of meat. 



