THE PREPARATION OF CULTURE MEDIA 127 



2. Weigh with containing vessel. 



3. Dissolve by warming. 



4. Adjust weight, determine volume, titrate, and adjust reaction. 



5. Cool to 60 C., add whites of two eggs, and stir thoroughly. 



6. Heat for thirty minutes, stir thoroughly, and heat for fifteen 

 minutes. 



7. Adjust weight. 



8. Filter through cotton. 



9. Sterilize. 



Meat-Infusion Gelatin. 1. Infuse 500 gms. lean meat twelve to 

 twenty-four hours with 1,000 c.c. of distilled water in refrigerator. 



2. Strain through wet cotton flannel or wet cheese-cloth and make 

 up volume to 1,000 c.c. 



3. Add 5 gms. common salt, 10 gms. Witte's pepton, and 120 gms. 

 of the finest French sheet gelatin. 



4. Weigh with containing vessel. 



5. Warm over flame or water bath, stirring till pepton and gelatin 

 are dissolved and not allowing temperature to rise above 50 C. 



6. Determine volume. 



7. Titrate and adjust reaction to neutral. 



8. Heat in Arnold sterilizer for thirty minutes; shake or stir well 

 and heat again for fifteen minutes. 



9. Determine weight and restore loss by evaporation. 



10. Determine volume, titrate, and adjust reaction to desired point, 

 if necessary (one per cent acid). 



11. Heat five minutes over free flame, constantly stirring, if ad- 

 justment of reaction has been necessary. 



12. Filter- through absorbent cotton, passing the filtrate through 

 the same filter until clear. 



13. Titrate and record the final reaction. 



Place gelatin in cotton-plugged sterile 250 c.c. flasks or about 8 c.c. 

 in plugged sterile test tubes and sterilize for thirty minutes in the Arnold 

 sterilizer on three successive days, leaving at room temperature in the in- 

 terval. Never heat the gelatin for longer than is necessary to comply 

 with directions, or it may not be solid enough for use. With some 

 brands of gelatin it may be necessary to add thirteen per cent in order 

 to obtain sufficient stiffness. 



Agar. Meat-Extract Agar. 1. To 1,000 c.c. of distilled water (or 

 tap water) add 15 gms. of thread agar, 10 gms. of Witte's pepton, and 

 5 gms. of Liebig's meat extract, and 5 gms. of common salt. 

 10 



