Page 55 - Atlas of Histology with Functional Correlations

the specimens are first immersed. Following glutaraldehyde fixation, the

specimens are rinsed in several buffers and then postfixed in cold osmium
tetroxide, which reacts with phospholipids. Osmium tetroxide imparts an
electron density to the cells and tissues because of its heavy metal. This allows
for image formations for viewing with TEM. Following fixation and
postfixation, the tissues are embedded in epoxy resin, which then polymerizes

and forms a hard plastic tissue block. The plastic blocks are trimmed, and
ultrathin sections are cut from them with a special instrument called an
ultramicrotome, using either a diamond knife or special glass knives. The thin

sections are then collected on small copper grids and stained with uranyl acetate
and lead citrate. Using the TEM, the electron beams pass through the ultrathin
stained specimen, resulting in high-resolution, high-contrast black-and-white
images on the screen for recording.

In contrast to TEM with thin sections, the scanning electron microscope

(SEM) uses larger, solid pieces of tissue to view a three‐dimensional image of
the surface of the specimens. The collected tissue samples are fixed in the same
fixative as that used for TEM, namely, cold-buffered glutaraldehyde, then
dehydrated through an acetone or ethanol series, and dried at the critical point.

The dried samples are then mounted on a stub of metal with adhesive and coated
with evaporated gold palladium.

When viewing the prepared specimen with the SEM, the electron beams do
not pass through the specimen; instead, the specimen is scanned along its
surface. The electrons that are reflected from the surface of the prepared

specimen are then collected by detectors and processed as a black-and-white
image of the surface of the specimen with a three-dimensional appearance.

This atlas contains a number of images obtained by using the transmission
and scanning electron microscopes.

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