es, and emulsify it with 200
c.c. distilled water previously heated to 60 deg. C.

2. Weigh out powdered agar, 13 grammes, and emulsify with 200 c.c. cold
distilled water.

3. Mix the two emulsions and wash into a tared 2-litre flask with 600
c.c. distilled water.

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

5. Cool to 60 deg. C. and clarify with egg as for nutrient agar (_vide_
page 168).

6. Filter through Papier Chardin, using the hot-water funnel.

7. Weigh out _French_ maltose, 40 grammes, and dissolve in the agar.

8. Tube, and sterilise as for nutrient agar.

~English Proof Agar (Blaxall).~--Substitute Witte's peptone for that of
Chassaing, and proceed as for French proof agar.

~French Mannite Agar, Sabouraud.~--(_For cultivation of Favus._)

Proceed exactly as in preparing French Proof agar _vide supra_
substituting Mannite (38 grammes) for maltose.

_Media for the Study of Milk Bacteria._

~Gelatine Agar.~--This medium is prepared by adding to nutrient gelatine
sufficient agar to ensure the solidity of the medium when incubated at
temperatures above 22 deg. C. If it is intended to employ an incubating
temperature of 30 deg. C., 10 per cent. gelatine and 0.5 per cent. agar
must be dissolved in the meat extract before the addition of the peptone
and salt; while for incubating at 37 deg. C., 12 per cent. gelatine and
0.75 per cent. agar must be used. Avoid the addition of more agar than is
absolutely necessary, otherwise the action upon the medium of such
organisms as elaborate a liquefying ferment may be retarded or
completely absent.

1. Measure out 400 c.c. double strength meat extract into a "tared"
2-litre flask, and add to it gelatine, 100 grammes.

2. Weigh out powdered agar, 5 grammes, emulsify with 100 c.c., cold
distilled water and add to the contents of the flask.

3. Dissolve the agar and gelatine by bubbling live steam through the
flask for twenty minutes.

4. Weigh out peptone, 10 grammes; salt, 5 grammes; emulsify with 100
c.c. double strength meat extract previously heated to 60 deg. C., and
add to the contents of the flask.

5. Replace in the steamer for fifteen minutes. Then adjust the weight to
the calculated figure for one litre (in this instance 1120 grammes) by
the addition of distilled water at 100 deg. C.

6. Estimate the reaction; control the result. Then add sufficient
caustic soda solution to render the reaction +10.