s:

Corrosive sublimate, saturated aqueous solution 2 c.c.
Tannic acid, 20 per cent. aqueous solution 2 c.c.
Potash alum saturated aqueous solution 5 c.c.

6. Wash thoroughly in water.

7. Treat with methylated spirit for about sixty seconds.
(The preparation should now be pale red.)

8. Wash thoroughly in water.

9. Counterstain in methylene blue, aqueous solution thirty
seconds.

10. Wash in water.

11. Dehydrate in alcohol.

12. Clear in xylol and mount in xylol balsam.

~3. Welch's Method.~--

1. Prepare and fix film in the usual manner.

2. Flood the slide with acetic acid 2 per cent.; allow the
acid to remain in contact with the film for two minutes.
This swells up and fixes the capsule and enables it to take
the stain.

3. Blow off the acetic acid by the aid of a pipette.

4. Immerse in aniline gentian violet, five to thirty
seconds.

5. Wash in water.

6. Dry and mount.

~4. Ribbert's Method.~--

_Stain._--

Measure out and mix:

Acetic acid, glacial 12.5 c.c.
Alcohol, absolute 50.0 c.c.
Distilled water 100.0 c.c.

Warm to 36 deg. C. (e. g., in the "hot" incubator) and
saturate with dahlia. Filter.

METHOD.--

1. Prepare and fix films in the usual manner.

2. Cover the film with the stain and allow it to act for one
or two seconds only.

3. Wash thoroughly in water.

4. Dry and mount.

~To Demonstrate Flagella.~

~1. Muir's Modified Pitfield.~--This is the best method and gives the most
reliable results, for not only is the percentage of successful
preparations higher than with any other, but the bacilli and flagella
retain their relative proportions.

(a) ~Mordant.~--

Tannic acid, 10 per cent. aqueous solution 10 c.c.
Corrosive sublimate, saturated aqueous solution 5 c.c.
Alum, saturated aqueous solution 5 c.c.
Carbolic fuchsin (Ziehl) 5 c.c.

Mix thoroughly.

A precipitate forms which must be allowed to settle for a few hours.

Decant off the clear fluid into tubes and centrifugalise thoroughly.

This solution is at its best some four or five days after manufacture;
it keeps for about a couple of weeks, but must be re-centrifugalised
each t