Biology Reference
In-Depth Information
Fig. 1. Depicts (
a
) rodent brain matrix, (
b
) a basket along with a cassette (
arrow
) in to which tissue is placed following fi xation
and trimming of tissue to required size, and (
c
) following placement of the tissue in to a cassette, it is arranged as shown
by an
arrow
. This basket containing approximately 40 cassettes is placed in a tissue processor.
Fig. 2. Depicts (
a
) a tissue processor and (
b
) an embedding center.
The purpose of tissue processing is to embed the tissue in a solid
medium to give tissue enough rigidity to enable thin sections to be
cut. For histology, paraffi n wax is routinely used as an embedding
material. Tissue processing can be done either manually, or by
using an automated tissue processor. To use an automated tissue
processor, a fi xed piece of tissue is placed in a plastic cassette
(Fig.
1b
) and dip it into a large beaker/jar under running tap water.
Tissue is normally washed for approximately 1 h to remove the
excessive fi xative. This will be followed by washing the tissue-con-
taining cassettes in a basket (Fig.
1b
, c) provided with the tissue
processor and placing a basket containing tissue cassettes in the
automated tissue processor (Fig.
2
). Tissue automated processing
is done in the following steps (
4
).
3.2. Tissue Processing
for Embedding
1. Dehydration: During this step, fi xative and water are replaced
by dehydrating fl uids. Routinely used dehydrating fl uids
include ethanol, methanol, isopropyl alcohol, and acetone. To
process brain for histology, ethanol is routinely used by various
laboratories. Tissue must undergo a descending dehydration,
i.e., successive immersion in 70, 95, and 100% ethanol.
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