The Elements of Bacteriological Technique Part 46

~Naegeli's Solution.~--

1. Weigh out and mix

Dibasic pota.s.sium phosphate (K_{2}HPO_{4}) 1.0 gramme Magnesium sulphate 0.2 gramme Calcium chloride 0.1 gramme Ammonium tartrate 10.0 grammes

and dissolve in

Distilled water 1000 c.c.

2. Tube or flask; sterilise as for nutrient bouillon.

~Plaster-of-Paris Discs.~--

1. Take large corks, 2.5 cm. diameter, and roll a piece of stiff note-paper round each, so that about a centimetre projects as a ridge above the upper surface of the cork, and secure in position with a pin (Fig. 112).

2. Mix plaster-of-Paris into a stiff paste with distilled water, and fill each of the cork moulds with the paste.

3. When the plaster has set, remove the paper from the corks, and raise the plaster discs.

4. Place the plaster discs on a piece of asbestos board and sterilise by exposing in the hot-air oven to 150 C. for half an hour.

[Ill.u.s.tration: Fig. 112.--Cork and paper mould for plaster-of-Paris 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 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 gla.s.s dish of adequate size (7 cm. diameter 7 cm. high).

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

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 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; pota.s.sium nitrate, 1 gramme; glucose, 15 grammes.

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

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 C. for thirty minutes on each of _four_ consecutive days.

_Media for the Study of Parasitic Moulds._

~French Proof Agar (Sabouraud).~--

1. Weigh out Cha.s.saing's peptone, 10 grammes, and emulsify it with 200 c.c. distilled water previously heated to 60C.

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 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.