42 



GENERAL MICROBIOLOGY 



off; replace with the same amount of clean tap water. 



Repeat. 



4. Dissolve over a free flame and boil for five minutes, 

 stirring constantly. The solu- 

 tion must be entirely free from 

 lumps of agar. 



5. Add 1% Witte's peptone 

 and 0.5% salt to the boiling 

 agar. 



6. To 500 c.c. of meat in- 

 fusion add 10 gms. of egg al- 

 bumen 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 and then add the remain- 

 ing water. One egg; well beaten, 



FIG. 9. Hot Water Funnel for may be substituted.) Mix all 

 Filtering Agar or Gelatin. thoroughly 



7. Pour the melted agar mixture slowly into the meat 

 infusion, stirring constantly. Heat in the autoclav at 

 120 C. for forty-five minutes or for an hour in flowing 

 steam. 



Note. The time for this heating may be lengthened to advantage, 

 but never shortened. If agar has not been heated sufficiently before 

 filtration, a flocculent precipitate will form in the tubes upon heating 

 in flowing steam. In most cases this may be caused to disappear by 

 heating for a short time in the autoclav at 15 Ibs. 



8. Titrate with N/20 NaOH. 



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

 normal NaOH or normal HC1. Retitrate and readjust 

 the reaction if necessary. 



10. Counterpoise and note the weight. 



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

 stantly, 



