}Gram's method.
Fuchsin, }

Methylene-blue, }for films stained by fuchsin.
Gentian violet, }

8. _Mounting._--

1. Wash the film carefully in running water.

2. Blot off the superfluous water with the filter paper, or dry more
completely between two folds of blotting paper.

3. Complete the drying in the air, or by holding the cover-slip in the
fingers at a safe distance above the flame of the Bunsen burner.

4. Place a drop of xylol balsam on the centre of a clean 3 by 1 glass
slide and invert the cover-slip over the balsam, and lower it carefully
to avoid the inclusion of air bubbles.

NOTE.--Xylol is used in preference to chloroform to dissolve
Canada balsam, as it does not decolourise the specimen.

~Impression films~ (_Klatschpraeparat_) are prepared from isolated
colonies of bacteria in order that their characteristic formation may be
examined by higher powers than can be brought to bear on the living
cultivation. They are prepared from plate cultivations (_vide_ page 230)
in the following manner.

1. Remove a clean cover-slip from the alcohol pot with sterile forceps
and burn off the spirit.

2. Open the plate and rest one edge of the cover-slip on the surface of
the medium a little to one side of the selected colony. Lower it
cautiously over the colony until horizontal. Avoid any lateral movement
or the inclusion of bubbles of air.

3. Make gentle vertical pressure on the centre of the cover-slip with
the points of the forceps to ensure perfect contact with the colony.

4. Steady one edge of the cover-slip with the forceps and pass the point
of a mounted needle just under the opposite edge and raise the
cover-slip carefully; the colony will be adherent to it. When nearly
vertical, grasp the cover-slip with the forceps and remove it from the
plate. Re-cover the plate.

5. Place the cover-slip, film uppermost, on the rubber mat, and cover
it with an inverted watch-glass until dry.

6. Fix by immersing in one of the fixing fluids previously mentioned
(_vide_ page 82).

7. Clear with acetic acid and alcohol.

8. Stain and mount as an ordinary cover-slip film preparation, being
careful to perform all washing operations with extreme gentleness.

~Microscopical Examination of the Unstained Specimens.~--

1. Place the body tube of the microscope in the vertical position.

2. Arrange the hanging-drop slide on the microscope stage