nutrient agar (_vide_ page
168).

5. Filter through papier Chardin, using the hot-water funnel.

6. Tube, and sterilise as for nutrient agar.

~Litmus Whey.~--

1. Curdle fresh milk by warming to 60 deg. C. and adding rennet.

2. Filter off the whey through butter muslin into a sterile flask.

3. Neutralise to litmus by the cautious addition of citric acid solution
4 per cent. (Do not neutralise with _mineral_ acid.)

4. Heat in the steamer at 100 deg. C. for one hour to coagulate all the
proteid.

(If the whey is cloudy when removed from the steamer allow it to stand
for forty-eight hours in the ice chest and then decant off the clear
fluid--or filter through a Berkefeld filter candle.)

5. Filter into a sterile flask.

6. Tint the whey with litmus solution to a deep purple red.

7. Tube, and sterilise as for milk.

~Litmus Whey (Petruschky).~--

1. Measure out into a flask

Fresh milk 1000 c.c.

2. Add

Hydrochloric acid (or glacial acetic acid) 1.5 c.c.

and boil.

3. Filter off coagulated casein.

4. Neutralise to litmus by the addition of n/1 caustic soda solution and
boil. Whey now cloudy and acid again.

5. Again neutralise to litmus by addition of n/10 caustic soda solution.

6. Filter.

7. Tint the whey with neutral litmus solution to a deep purple colour.

8. Tube and sterilise as for milk.

~Litmus Whey Gelatine.~--

1. Measure out milk 1000 c.c. into a tared 2-litre flask.

2. Add hydrochloric acid (or glacial acetic acid) 1.5 c.c. and boil for
five minutes.

3. Filter off the casein, and make the whey faintly alkaline to litmus.

4. Weigh out

Peptone 10 grammes

and emulsify in a few cubic centimeters of the whey and return to the
flask.

5. Weigh out

Gelatine 50 grammes

add it to the whey in the flask and incorporate the mixture by bubbling
through live steam.

6. Clear with egg and filter.

7. Make the weight of the medium mass to the calculated figure for one
litre (1060 grammes) by the addition of distilled water.

8. Weigh out

Dextrose 15 grammes

and dissolve in the fluid whey gelatine.

9. Add sterile litmus solution to the required tint.

10. Tube and sterilise for twenty minutes in steamer at 100 deg. C. on
each of five successive days.

This medium will remain semi-fluid at the room temperature, and may be
used for cultures in t