PREPARATION OF CULTURE MEDIA 27 



1. 500 g. (i pound) of lean minced beef, as free as 

 possible from fat and tissues, is added to 1000 c.c. of 

 tap-water and set aside on ice for 24 hours. 



2. Weigh a saucepan, and cook the beef and water 

 for about one hour. 



3. Strain through cheese-cloth, and press all the 

 liquid out in a meat-press (Fig. 15). 



4. Replace the water lost by evaporation. 



5. Dissolve 10 g. of Witte's peptone. 



6. Adjust the reaction. 



7. Filter into flasks, and sterilize in autoclav at 120° 

 for 10 minutes. It may then be distributed into culture- 

 tubes. 



Fresh meat, as well as extract of meat, often contains 

 a small amount of muscle-sugar (glycogen). If it is 

 necessary to prepare a sugar-free broth, a pure culture 

 of Bacillus coli is added to the mixture of chopped beef 

 and water, and this is incubated at 37° for 24 hours. 

 After this the preparation is the same as described. 



EXERCISE V. PREPARATION OF POTATO 



1. Select several large potatoes, and cleanse by brush- 

 ing all dirt off carefully and washing in water. 



2. Punch out cyhnders with a borer of suitable size, 

 trim them, and cut them into two equal parts (Fig. 16). 

 Cut with a sharp knife along the diagonal. 



3. Immerse the pieces in running water for 24 hours. 



4. Insert one half-cyhnder into each potato-tube 

 so that the wide end rests on the constriction, then pour 

 a small amount of water into it. If the potato-tubes 

 have no constriction, place a small wad of cotton in the 

 bottom and moisten this with water (Figs. 17 and 18). 



