to the calculated
figure for one litre of medium (1110.5 grammes) by the addition of
distilled water at 100 deg. C. (_vide_ page 166).

6. Cool to below 60 deg. C. and clarify with egg.

7. Filter through papier Chardin.

8. Tube, and sterilise as for nutrient gelatine.

Shake well after the final sterilisation, to aerate the medium.

_Media for the Study of Yeasts and Moulds._

~Pasteur's Solution.~--

(Reaction alkaline).

1. Weigh out and mix the ash from 10 grammes of yeast; ammonium
tartrate, 10 grammes; cane sugar, 100 grammes.

2. Dissolve the mixture in distilled water, 1000 c.c.

3. Tube or flask, and sterilise as for nutrient bouillon.

~Yeast Water (Pasteur).~--

1. Weigh out pressed yeast, 75 grammes; place in a 2-litre flask and add
1000 c.c. distilled water.

2. Heat in the steamer at 100 deg. C. for thirty minutes.

3. Filter through papier Chardin.

4. Tube or flask, and sterilise as for nutrient bouillon.

~Cohn's Solution.~--

1. Weigh out and mix

Acid potassium phosphate (KH_{2}PO_{4}) 5.0 grammes
Calcium phosphate 0.5 gramme
Magnesium sulphate 5.0 grammes
Ammonium tartrate 10.0 grammes

and dissolve in

Distilled water 1000 c.c.

2. Tube, or flask and sterilise as for nutrient bouillon.

~Naegeli's Solution.~--

1. Weigh out and mix

Dibasic potassium phosphate (K_{2}HPO_{4}) 1.0 gramme
Magnesium sulphate 0.2 gramme
Calcium chloride 0.1 gramme
Ammonium tartrate 10.0 grammes

and dissolve in

Distilled water 1000 c.c.

2. Tube or flask; sterilise as for nutrient bouillon.

~Plaster-of-Paris Discs.~--

1. Take large corks, 2.5 cm. diameter, and roll a piece of stiff
note-paper round each, so that about a centimetre projects as a ridge
above the upper surface of the cork, and secure in position with a pin
(Fig. 112).

2. Mix plaster-of-Paris into a stiff paste with distilled water, and
fill each of the cork moulds with the paste.

3. When the plaster has set, remove the paper from the corks, and raise
the plaster discs.

4. Place the plaster discs on a piece of asbestos board and sterilise by
exposing in the hot-air oven to 150 deg. C. for half an hour.

[Illustration: Fig. 112.--Cork and paper mould for plaster-of-Pari