Page 46 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy and Physiology of the Cell / 31

2. Embedding the tissue in a material that as an H & E stain. The hematoxylin tends
to stain acidic portions of a cell dark blue
will permit cutting very thin sections.
VetBooks.ir Paraffin is used for producing sections of or purple (these basophilic areas include
5 to 10 μm thickness; sections as thin as
the cell nucleus, which contains nucleic
1 to 2 μm can be obtained by embedding acids), and the eosin tends to stain the
in a plastic, such as glycol methacrylate. basic portions of a cell pink to red (these
Since most embedding media are not acidophilic areas include much of the
water soluble, the fixed tissue must be more basic protein within the cell).
dehydrated and then infiltrated with Wright’s stain, used to stain blood cells
some material such as xylene, which is (see Fig. 1‐9), stains basophilic areas blue
miscible with the embedding medium. with methylene blue and acidophilic
Frozen tissues need not be embedded. areas red with eosin. Sections can also
3. Sectioning the tissue into very thin be treated with a variety of chemical
slices so that the sections may be placed solutions to demonstrate the presence of
on a glass slide. A microtome is used for certain types of chemicals or the activity
this purpose. It consists of a sharp blade, of enzymes in the tissue or cell, a tech­
a mechanism for moving the tissue past nique called histochemistry (Fig. 2‐6).
the blade, and then advancing the tissue The presence of specific types of mole­
a defined distance after each cutting. cules can be determined by exposing
Frozen tissues are sectioned in a cry­ the section to a solution containing
ostat, which is a microtome housed in a antibodies to those molecules. This tech­
freezer cabinet. nique is called immunocytochemistry.
4. Staining the section so that different cells 5. The last step, of course, is the actual
or different parts of cells can be differen­ examination of the stained section of
tiated according to color. Hematoxylin tissue on the slide by means of a micro­
and eosin are stains commonly used scope and light transmitted through the
together, and this treatment is described section.

Figure 2-6. Serial sections of horse triceps brachii muscle histochemically stained for enzymatic activity.
The same muscle cells (I and II) are visible in both sections. (A) Calcium‐dependent ATPase activity. (B)
Activity of a mitochondrial oxidative enzyme.