ntents; then (1115[4] grammes + weight of
the flask) minus (weight of the flask and its contents) equals the
weight of water required to make up the bulk to 1 litre. The addition of
the requisite quantity of water is carried out as follows:

In one pan of the trip balance place the counterpoise of the tared flask
(or its equivalent in weights) together with the weights making up the
_calculated medium weight_. In the opposite pan place the flask
containing the medium mass. Now add boiling distilled water from a wash
bottle until the two pans are exactly balanced.

7. Titrate and estimate the reaction of the medium mass; control the
result. Calculate the amount of soda solution required to make the
reaction of the medium mass +10 (i. e., calculate for 1000 c.c., less
the quantity used for the titrations).

8. Add the necessary amount of soda solution and heat in the steamer at
100 deg. C. for twenty minutes, to precipitate the phosphates, etc.

9. Allow the medium mass to cool to 60 deg. C. Well whip the whites of
two eggs, add to the contents of the flask and replace in the steamer at
100 deg. C. for about half an hour (until the egg-albumen has coagulated
and formed large, firm masses floating on and in clear gelatine).

10. Filter through papier Chardin into a sterile flask.

11. Tube in quantities of 10 c.c.

12. Sterilise in the steamer at 100 deg. C. for twenty minutes on each of
three consecutive days--i. e., by the discontinuous method.

~Nutrient Agar-agar.~--

1. Weigh a 2-litre flask and note the weight--or counterpoise exactly.

2. Measure out double strength meat extract, 500 c.c., into the "tared"
flask.

3. Weigh out and mix 10 grammes of peptone, 5 grammes of salt, and 20
grammes of powdered agar, and make into a thick paste with 150 c.c.
distilled water, and add to the meat extract in the flask; place the
flask in a water-bath.

4. Arrange the steam can and water-bath as already directed (for the
preparation of gelatine) and figured.

5. Bubble live steam (at 100 deg. C.) through the medium mass, for
twenty-five minutes, by which time complete solution of the agar is
effected.

6. Now weigh the flask and its contents; then (1035[5] grammes + weight
of flask) minus (weight of flask and its contents) equals the weight of
water required to make up the bulk of the medium to 1 litre. Add the
requisite amount (see preparation of gelatine, page 166, step 6).

7. Titrate, and estimate the rea