228 MICROSCOPIC AND CULTURAL STUDY OF BACTERIA 
layer of absorbent cotton in a large glass funnel. Pass through filter 
until clear. It is frequently necessary to clarify agar with eggs. After 
the reaction is adjusted, cool to 50° C. add 2 eggs beaten up in water 
and mix thoroughly. Heat slowly to the boiling-point, boil ten min- 
utes, and filter through absorbent cotton; sterilize in the autoclave. 
(h) Prepare "double-strength" meat infusion; 1000 gm. of finely 
comminuted lean meat are suspended in 1 liter of water; infuse in 
the ice-box for twenty-four hours; heat to boiling and filter through 
filter paper. Prepare nutrient meat infusion broth with this strong 
infusion as a basis and adjust the reaction to twice the desired acidity— 
thus, if + 1 is to be the final reaction, make the infusion broth -|- 2. 
Dissolve 24 gm. agar in 1 liter of water, boiling steadily until complete 
solution is attained. Add to the meat infusion broth, boil for ten 
minutes and clarify with eggs in the usual manner. Filter and sterilize. 
Hormone Agar. Huntoon;^ Bailey Modification. ~ 1. Dissolve L5 gm. 
of shredded agar in 1 liter water, and cool to 50° to 60° C. 
2. Add 500 gm. lean beef (or beef heart) rather finely chopped, bring 
slowly to the boiling-point, and simmer for twenty to thirty minutes. 
8. Filter through a coarse filter— 16 meshes to the inch, and after the 
liquid has passed through, spread the residue evenly on the filter, and 
refilter the liquid three or four times. The medium may be quite clear 
if the process is repeated. 
4. Add to each 1000 cc. of filtrate 10 gm. peptone,^ and 5 gm. XaCl. 
Simmer for five minutes. 
5. Adjust the reaction (usually to pH 7.5). 
6. Allow to stand until the precipitate settles, and decant. 
7. Tube and sterilize, preferably at not over 5-pounds pressure, in the 
autoclave. 
Meat Extract J/yar.— Meat extract agar is made by substituting 
meat extract solution for meat infusion; otherwise the process is the 
same. The medium must be clarified with eggs. 
Glycerin Aqar.— Three per cent of glycerin is added to meat infusion 
agar immediately before filtration. The reaction for cultivation of 
the human type of the tubercle bacillus should be + 1 acid to phenol- 
phthalein. Tubercle bacilli do not thrive in media neutral to phenol- 
phthalein. 
Eberson's Yeast Medium.*— 1 . Prepare double strength maltose broth : 
2 per cent peptone, 2 per cent maltose, 0.6 per cent XaCl. Do not 
adjust reaction. 
2. Inocidate with yeast culture, allow to grow forty-eight hours 
at 37° (\ in shallow layers. 
3. Heat in double boiler one hour. Boil five minutes. 
4. Filter through filter paper. 
• Jour. Infec. Dis., 1918, 23, 169. 
2 Ibid., 1925, 36, 340. 
^ Proteose peptone makes the best medium for fastidious organisms. 
^ .Jour. Am. Med. Assn., 1919, 72, 852; see also Burky: Ibid., 1924, 83, 999. 
