106 
PRINCIPLES OF BACTERIOLOGY 
7. Enriched Media 
All of the meat infusion media (No. 2 and No. 4) can 
be enriched, by adding glucose 1 to 2 per cent, or a few 
drops of ascitic fluid or of defibrinated or whole blood, or 
glycerin. 
When ascitic fluid is added greatest aseptic precautions 
should be observed, as after its addition no further steril¬ 
ization by heat is permissible since it would coagulate the 
albuminous part of the ascitic fluid. An ordinary meat 
infusion agar is made as above described, tubed and 
sterilized. When ascitic fluid is to be added, melt the 
agar tubes by heating in water bath, cool to 45° C., then 
(with all aseptic precaution) add to each tube a few 
drops of ascitic fluid, flaming the test tubes before and 
after the addition; incubate all tubes at 37° C. for 
twenty-four hours to see if they are sterile. 
For defibrinated or whole blood, do just as for the as¬ 
citic fluid agar, except that a few drops of defibrinated or 
whole blood is added. To obtain defibrinated blood, 
bleed a rabbit from the carotid artery or jugular vein into 
a sterile flask with 10 to 20 glass beads, shake the blood 
thoroughly, add a few drops to each tube of melted and 
cooled agar, and incubate for twenty-four hours to test 
sterility. 
If sugar is added (usually glucose 1 to 2 per cent) 
sterilize for twenty minutes instead of thirty minutes in 
Arnold’s sterilizer on three successive days. 
8. Gelatin Agar 
Gelatin agar is used to determine the gelatin-liquefying 
properties of bacteria. 
(a) To 1,000 c.c. of water add 5 grams of Liebig’s 
meat extract, 5 grams of sodium chloride, 10 grams of pep- 
