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 ina 
water bath at 62°C. for 2 hours each day for 4 consecutive days. 
67. Preparation of Loeffler’s blood serum. This consists of 
1 part neutral bouillon (prepared from meat) containing 1% 
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 necessarily be 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 
go° 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 clean dish, and beat until the yolk and white are thoroughly 
nixed. Add an equal volume of glycerin bouillon of a reaction 
+ 1.3. Place in tubes, care being taken to avoid bubbles. 
sterilize by heating, preferably in a serum water bath at from 
75° to 80° 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, 
o£ 5% glycerin bouillon, to afford sufficient moisture. This is 
nost used at the present time for the cultivation of tubercle 
yacteria. 
69. Preparation of nitrate bouillon. Take peptonized bouillon 
oo cc. Add potassium nitrate (0.5 %) « gram. Dissolve the 
iitrate in the bouillon, put in tubes, and sterilize the same as 
youillon. 
The nitrate of sodium or ammonium may be substituted for 
hat of potassium. The salt may be added in the proportion 
if from o.1 to 1% to meet special demands. 
For other methods and special media, see text-books. 
70. Grouping of culture media. For convenience in reference 
nd assignment of media, the culture media most commonly 
