s
disc.]

5. Remove the sterile discs from the oven by means of sterile forceps,
place each inside a sterile capsule, and moisten with a little sterile
water.

6. Sterilise in the steamer at 100 deg. C. for thirty minutes on each of
three consecutive days.

~Gypsum Blocks (Engel and Hansen).~--

These are in the form of truncated cones and for their preparation small
tin moulds are required, each having a diameter of 5.5 cm. at the base
and 4 cm. at the truncated apex. The height (or depth) of a mould is 4.5
to 5 cm.

1. Mix powdered calcined gypsum into a stiff paste with distilled water.

2. Fill the paste into the moulds and allow it to set and dry by
exposure to air.

3. Remove the block from the mould and transfer it to a double glass
dish of adequate size (7 cm. diameter x 7 cm. high).

4. Sterilise block in its dish for one hour in the hot-air oven at
115 deg. C.

5. Carefully open the dish and add sterile distilled water to moisten
the block and form a layer in the bottom of the dish 1 cm. deep.

~Wine Must.~--(Wine must is obtained from Sicily, in hermetically sealed
tins, in a highly concentrated form--as a thick syrup--but not
sterilised.)

1. Weigh out "wine must," 200 grammes, place in a 2-litre flask and add
distilled water, 800 c.c.

2. Weigh out ammonium tartrate, 5 grammes, and add to the dilute must.

3. Place the flask in a water-bath regulated to 60 deg. C. for one hour
and incorporate the mixture thoroughly by frequent shaking.

4. Filter through papier Chardin.

5. Tube, and sterilise as for nutrient bouillon.

~Wheat Bouillon (Gasperini).~--

1. Weigh out and mix wheat flour, 150 grammes; magnesium sulphate, 0.5
gramme; potassium nitrate, 1 gramme; glucose, 15 grammes.

2. Dissolve the mixture in 1000 c.c. of water heated to 100 deg. C.

3. Filter through papier Chardin.

4. Tube, and sterilise as for nutrient bouillon.

~Bread Paste.~--

1. Grate stale bread finely on a bread-grater.

2. Distribute the crumbs in sterile Erlenmeyer flasks, sufficient to
form a layer about one centimetre thick over the bottom of each.

3. Add as much distilled water as the crumbs will soak up, but not
enough to cover the bread.

4. Plug the flasks and sterilise in the steamer at 100 deg. C. for
thirty minutes on each of _four_ consecutive days.

_Media for the Study of Parasitic Moulds._

~French Proof Agar (Sabouraud).~--

1. Weigh out Chassaing's peptone, 10 gramm