~Fish Bouillon.~--

1. Weigh out herring, mackerel, or cod, 500 grammes, and place in a
large porcelain beaker (or enamelled iron pot).

2. Weigh out sodium chloride, 26.5 grammes; potassium chloride, 0.75
gramme; magnesium chloride, 3.25 grammes; and dissolve in 500 c.c.
distilled water. Add the solution to the fish in the beaker.

3. Place the beaker in a water-bath and proceed as in preparing meat
extract--i. e., heat gently at 40 deg. C. for twenty minutes, then rapidly
raise the temperature to, and maintain at, the boiling-point for ten
minutes.

4. Strain the mixture through butter muslin into a clean flask.

5. Weigh out peptone, 5 grammes, and emulsify with about 200 c.c. of the
hot fish water; incorporate thoroughly with the remainder of the fish
water in the flask.

6. Heat in the steamer at 100 deg. C. for twenty minutes to complete the
solution of the peptone.

7. Filter through Swedish filter paper.

8. When the fish bouillon is cold, if it is to be used as fluid medium,
make up to 1000 c.c. by the addition of distilled water. If, however, it
is to be used as the basis for agar or gelatine media store it in the
"Double Strength" condition.

9. Tube and sterilise as for nutrient bouillon.

As an alternative method "Marvis" fish food (16 grammes) may be
substituted for the 500 grammes of fresh fish.

~Fish Gelatine.~--

1. Measure out double strength fish bouillon, 500 c.c., into a "tared"
2-litre flask.

2. Add sheet gelatine, 100 grammes, cut into small pieces.

3. Bubble live steam through the mixture for fifteen minutes to dissolve
the gelatine.

4. Weigh the flask and its contents; adjust the weight to the calculated
figure for one litre of medium (1135.5 grammes) by the addition of
distilled water at 100 deg. C. (_vide_ page 166).

5. Cool to below 60 deg. C., and clarify with egg.

6. Filter through papier Chardin.

7. Tube, and sterilise as for nutrient gelatine.

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

~Fish Gelatine-Agar.~--

1. Weigh out powdered agar, 5 grammes, and emulsify it with 200 c.c.
double strength fish bouillon.

2. Wash the emulsion into a "tared" 2-litre flask with 300 c.c. fish
bouillon.

3. Weigh out sheet gelatine, 70 grammes, cut it into small pieces and
add it to the contents of the flask.

4. Bubble live steam through the mixture to dissolve the gelatine and
agar.

5. Weigh the flask and contents. Adjust the weight