of organisms in some one direction will usually be
sufficient to demonstrate the nature of this motion.

(c) Locomotive movement, or ~true motility~, is determined by observing
some one particular bacillus changing its position in the field
independently of, and in a direction contrary to, other organisms
present.

When the examination is completed and the specimen finished with, the
"fresh specimen"--i. e., the slide with the cover-slip attached--must
be dropped into the lysol pot. In the hanging-drop specimen, however,
the cover-slip only is infected, and this may be raised from the ring
cell by means of forceps and dropped into the disinfectant.

_Permanent Staining of the Hanging-drop Specimen._--Occasionally it is
necessary to fix and stain a hanging-drop preparation. This may be done
as follows:

1. Remove the cover-slip from the cell by the aid of the forceps.

2. If the drop is small, fix it by dropping it face downward, whilst
still wet, on to the surface of some Gulland's solution or corrosive
sublimate solution (_vide_ page 82) in a watch-glass. If the drop is
large, place it face upward on the rubber mat, cover it with an inverted
watch-glass, and allow it to dry. Then fix it in the alcohol and ether
solution (_vide_, page 82).

3. Dip the cover-glass into a beaker containing hot water in order to
remove some of the vaseline adhering to it.

4. Wash successively in alcohol, xylol, ether, and alcohol, to remove
the last traces of grease.

5. Wash in water.

6. Stain, wash, dry, and mount as for an ordinary cover-slip film
preparation (_vide_ pages 83-85).

~2. Killed, Stained.~--In this method three distinct processes are
necessary:

"Preparing" and "fixing" the film.
Staining.
Mounting.

_Preparing the Film._--

1. Flame a cover-slip and place it on a piece of filter paper.

2. Place a drop of water on the centre of the cover-slip by means of
platinum loop.

3. Obtain a small quantity of the material to be examined upon a
sterilised platinum loop (see pages 74-76, steps 2 to 11) and mix it
with the drops of water on the cover-slip.

4. Spread the drop of emulsion evenly over the cover-slip in the form of
a square film to within 1 mm. of each edge of the cover-slip.

5. Allow it to dry completely in the air.

_Fixing._--Fix by passing the cover-slip, held in the fingers, three or
four times through the flame of a Bunsen burner.

In some instances (e. g., when the films