and B in equal volumes, and allow the
mixture to stand for 12 hours with occasional stirring.

2. Filter, and collect precipitate on filter paper.

3. Wash precipitate thoroughly with distilled water, and dry.

4. Weigh out 0.15 gramme of the dried precipitate; rub up in a mortar
with 5 c.c. of methylic alcohol (Merck's puriss, for analysis).

Allow undissolved powder to settle, then decant the supernatant fluid to
a clean 100 c.c. measuring cylinder.

5. Add further 5 c.c. alcohol to sediment in mortar and repeat the
process, and so on until all the sediment has been dissolved.

6. Now make up the fluid in the measuring cylinder to 100 c.c. by the
addition of more methylic alcohol.

METHOD.--

1. Prepare film, dry, but _do not fix_.

2. Flood the unfixed film with stain, allow it to act 30 seconds.

3. Add double the volume of distilled water to the stain on the film,
and mix with glass rod or platinum loop.

4. Allow this diluted stain to act five minutes.

5. Wash off with distilled water.

6. Leave some water on film for thirty seconds to intensify the colour
contrasts.

7. Dry and mount.

METHODS OF DEMONSTRATING STRUCTURE OF BACTERIA, ETC.

~To Demonstrate Capsules.~

~1. MacConkey.~--

_Stain._--

Weigh out

Dahlia 0.5 gramme
Methyl green (00 crystals) 1.5 grammes

rub up in a mortar with

Distilled water 100.0 c.c.

Add

Fuchsin, saturated alcoholic solution 10.0 c.c.

and make up to 200 c.c. by the addition of

Distilled water 90.0 c.c.

Filter.

Allow the stain to stand for two weeks before use; keep in a dark place
or in an amber glass bottle. Owing to the unstable character of the
methyl green, this stain deteriorates after about six months.

METHOD.--

1. Prepare and fix film in the usual manner.

2. Flood the cover-slip with the stain and allow it to act for five to
ten minutes.

3. Wash very thoroughly in water; if necessary, direct a powerful stream
of water on the film from a wash-bottle.

4. Dry and mount.

~2. Muir's Method.~--

1. Prepare, dry and fix film in the ordinary manner.

2. Flood the film with carbolic fuchsin, warm until steam
begins to rise. Allow the stain to act for thirty seconds.

3. Wash quickly with methylated spirit.

4. Wash thoroughly with water.

5. Subject the film to the action of the following mordant
for five second