Page 342 - Fundamentals of Light Microscopy and Electronic Imaging

MATERIALS FOR DEMONSTRATIONS AND EXERCISES 325

Chapter 9: Polarization Microscopy

Materials

2 dichroic sheet polarizers
light box or overhead projector
sheet of cellophane
cellophane tape
red-I plate ( -plate)
dichroic sheet polarizers, 2 4 cm strips, with one edge parallel to transmission
axis of polarizer
red-I plates; 2 4 cm strips, with edges parallel to the axes of the refractive index
ellipsoid of the plate (see instructions for cutting strips)
corn starch, a few grains of starch mounted on a slide under a coverslip with a drop
of glycerol
leaf of Amaryllis or Diffenbachia, a drop of plant cell sap mounted on a slide under
a coverslip
onion skin, a thin sliver mounted on a slide in a drop of water under a coverslip
preparation of squashed Drosophila thorax, mounted on slide in drop of water
under a coverslip
stained section of pine wood, Pinus strobus, radial section (Carolina Biological
Supply)
stained section of buttercup root, Ranunculus (Carolina Biological Supply)
stained section of striated muscle, H&E (Carolina Biological Supply)
razor blades for cutting materials
Pasteur pipettes and rubber bulbs

Preparation of Red-I Plates for Student Microscopes
On a light box, rotate two dichroic sheet polarizers to obtain extinction. Between the
polars insert the red-I plate that is to be cut into 2 4 cm strips for the student micro-
scopes. With the polars crossed and held in a fixed position, rotate the red-I plate until
the bright interference color is observed. The axes of the refractive index ellipsoid of the
plate are now oriented at 45° with respect to the transmission axes of the crossed polars.
Attach a strip of cellophane tape to a microscope slide and insert the slide between the
crossed polars. The long axis of the tape is parallel to the long axis of the refractive
index ellipsoid ( slow axis of the wavefront ellipsoid) and will serve as a reference.
Rotate the microscope slide through 360°. At two positions the tape will look bright yel-
low, and at two positions rotated by 90° with respect to the first, the tape will look pale
yellow. In between these two axes the tape will have the same red color as the red-I plate
by itself. The orientation of the tape giving the bright yellow color marks the high
refractive index axis of the red-I plate. Mark this axis on the red-I plate as a short line
with a marker pen. The red-I plate can now be cut into strips with a paper cutter care-
fully so that one edge of the strips is perfectly parallel to the axis drawn on the plate.
Blacken this edge with the marker pen and draw an ellipsoid at a corner of the plate with
its short axis parallel to the blackened edge.