THE PREPARATION OF CERTAIN SPECIAL MEDIA 43 



In this case it is often necessary to sterilize the liquid serum 

 after it has been distributed in tubes. This can be done in a 

 water bath at 62 C. for 2 hours each day for 4 consecutive days. 



67. Preparation of Loeffler's blood serum. This consists of 

 i part neutral bouillon (prepared from meat) containing i / 

 grape sugar and 3 parts liquid blood serum. Mix and dis- 

 tribute in sterile test tubes, incline, and solidify the same as 

 blood serum. The temperature should be about 75 C., and 

 the exposure will be necessarily longer than for the pure blood 

 serum. When it is to be used for the cultivation of diphtheria 

 organisms it can be set at a much higher temperature (80 to 

 100 C.). Label and store. 



68. Preparation of egg medium. The whole egg is pref- 

 erable. Carefully break the shell of the required number 

 (3, 6, or more) of fresh eggs, drop the entire contents into 

 a sterile beaker, and carefully stir with a sterile glass rod, care 

 being taken to avoid air bubbles. After the egg is well mixed 

 it is poured into test tubes (6 to 10 cc. in each) and sterilized 

 by heating, preferably in a serum water bath at 70 C. for 

 from 4 to 5 hours each day for 2 days. After sterilization the 

 tubes, if test tubes, should be sealed. Before using, add a few 

 drops of sterile water or, better perhaps, of 5 % glycerin or of 

 glucose to afford sufficient moisture. This is most used at the 

 present time for the cultivation of tubercle bacteria (Dorset, 

 Am. Med., April 5, 1902). 



69. Preparation of nitrate bouillon. Take peptonized bouillon 

 200 cc. Add potassium nitrate (0.5%) i gram. Dissolve the 

 nitrate in the bouillon, put in tubes, and sterilize the same as 

 bouillon. 



The nitrate of sodium or ammonium may be substituted for 

 that of potassium. The salt may be added in the proportion 

 of from o.i to i% to meet special demands. 



For other methods and special media, see text-books. 



70. Grouping of culture media. For convenience in reference 

 and assignment of media, the culture media most commonly 



