he cool or hot incubator.

~Litmus Whey Agar~ is prepared in a similar manner to Whey Gelatine, with
the substitution of 15 grammes of agar for the gelatine.

~Malt Extract Solution (Herschell).~--

1. Measure into a flask distilled water 1000 c.c.

2. Weigh out

Extractum malti (malt extract) 25 grammes

and add to distilled water in flask.

3. Boil for five minutes, allow to stand, and decant off clear fluid
from sediment.

4. Tube and sterilise as for nutrient bouillon.

_Media for the Study of Earth Bacteria, Nitrogen Fixers._

~Earthy Salts Agar (Lipman and Brown).~--(_For the enumeration of soil
organisms._)

1. Measure out

Agar 20 grammes.

Emulsify in 200 c.c. distilled water.

2. Wash the agar emulsion into a tared 2-litre flask with 400 c.c.
distilled water.

3. Weigh out

Peptone 0.5 gramme.

Emulsify in 50 c.c. distilled water and add to the contents of the
flask.

4. Bubble live steam through the mixture for twenty minutes to dissolve
the agar.

5. Weigh out and mix

Dextrose 10.0 grammes.
Potassium phosphate 0.5 gramme.
Magnesium sulphate 0.2 gramme.
Potassium nitrate 0.06 gramme.

and add to the contents of the flask.

6. Adjust the weight of the medium mass to the calculated figure for one
litre (1025 grammes) by the addition of distilled water at 100 deg. C.

7. Titrate the medium mass and adjust the reaction to +5.

8. Cool to 60 deg. C. Clarify with egg and filter.

9. Tube in quantities of 10 c.c. and sterilise as for nutrient agar.

~Beyrinck's Solution. I.~--(_For the cultivation of nitrogen fixing
organisms._)

1. Weigh out and mix 1 gramme potassium hydrogen phosphate, 0.2 gramme
magnesium sulphate, and 0.02 gramme sodium chloride.

2. Dissolve in water 1000 c.c., in a 2-litre flask.

3. Add 1 c.c. of a one per thousand aqueous solution of ferrous
sulphate.

4. Add 1 c.c. of a one per thousand solution manganese sulphate.

5. Weigh out 20 grammes dextrose and add to the contents of the flask
(dextrose up to 40 grammes may be used for the different organisms).

6. Steam for twenty minutes, filter.

7. Tube, and sterilise as for nutrient bouillon.

~Beyrinck's Solution. II.~--(_For growth of Azobacter._)

Proceed as in preparing solution No. I, substituting mannite for
dextrose in step 5.

~Winogradsky's Solution (for Nitric Organisms).~--

1. Weigh out and mix.