22
2. TISSUE EXPOSURE
should be undercut and the thin slab of tissue so obtained transferred to
a vial of fixative. The fixed tissue, of course, has been hardened so that
ordinarily the undercutting can be accomplished fairly exactly at the
boundary between fixed and unfixed tissue. If any large amount of unfixed tissue is removed it sometimes can be scraped or cut away while the
tissue is held on the tip of one's finger, and before putting it into the vial
of fixative, or it can be removed later during dehydration.
The interior linings of organs may present special problems in the
preservation of their natural surfaces. It is often tempting to try a perfusion of fixative, either through a cannula, or simply by direct injection
from a syringe. This may be highly successful if the lumen is small or of
narrow bore so that the organ can be flushed rapidly and adequately with
a great surplus of fixative. To accomplish this, a drainage path must be
established some distance away from the site of perfusion. Although some
organ linings may withstand washing with physiologically balanced salt
solutions, the procedure is dangerous under the best of circumstances and
its effects should be carefully controlled. It is obviously impractical to
flush a large organ with anything but a saline solution or a low cost
fixative such as buffered formaldehyde, used as a primary fixative
(Chapter 3.9). But when organs are of such size, one can open them
surgically and achieve a topical, in situ preservation as discussed previously in this section. The contents of some organs, such as the gall
bladder and parts of the gut, tend to destroy the proper action of the
fixative to such an extent that they require particularly vigorous flushing.
2.5. In Situ Fixation of Cut Surfaces
One often has the problem of wishing to study the deep part of an
organ. Sometimes this can be done best by in situ fixation of a surface
artificially created by simply slashing across the organ. Fixative is then
applied as described in the last section. This method is applicable also to
organs which do not have capsules that can be mechanically removed,
for example, salivary glands, lymph nodes, marrow. Also, when the
afferent blood supply is by way of the capsule and would have to be
sacrificed in any case (such as the adrenal gland), the method would seem
to be advantageous. The technique often is preferable to mincing tissue,
in that delicate stroma is not so severely damaged.
There are apt to be more or less severe difficulties with bleeding when
2. TISSUE EXPOSURE
should be undercut and the thin slab of tissue so obtained transferred to
a vial of fixative. The fixed tissue, of course, has been hardened so that
ordinarily the undercutting can be accomplished fairly exactly at the
boundary between fixed and unfixed tissue. If any large amount of unfixed tissue is removed it sometimes can be scraped or cut away while the
tissue is held on the tip of one's finger, and before putting it into the vial
of fixative, or it can be removed later during dehydration.
The interior linings of organs may present special problems in the
preservation of their natural surfaces. It is often tempting to try a perfusion of fixative, either through a cannula, or simply by direct injection
from a syringe. This may be highly successful if the lumen is small or of
narrow bore so that the organ can be flushed rapidly and adequately with
a great surplus of fixative. To accomplish this, a drainage path must be
established some distance away from the site of perfusion. Although some
organ linings may withstand washing with physiologically balanced salt
solutions, the procedure is dangerous under the best of circumstances and
its effects should be carefully controlled. It is obviously impractical to
flush a large organ with anything but a saline solution or a low cost
fixative such as buffered formaldehyde, used as a primary fixative
(Chapter 3.9). But when organs are of such size, one can open them
surgically and achieve a topical, in situ preservation as discussed previously in this section. The contents of some organs, such as the gall
bladder and parts of the gut, tend to destroy the proper action of the
fixative to such an extent that they require particularly vigorous flushing.
2.5. In Situ Fixation of Cut Surfaces
One often has the problem of wishing to study the deep part of an
organ. Sometimes this can be done best by in situ fixation of a surface
artificially created by simply slashing across the organ. Fixative is then
applied as described in the last section. This method is applicable also to
organs which do not have capsules that can be mechanically removed,
for example, salivary glands, lymph nodes, marrow. Also, when the
afferent blood supply is by way of the capsule and would have to be
sacrificed in any case (such as the adrenal gland), the method would seem
to be advantageous. The technique often is preferable to mincing tissue,
in that delicate stroma is not so severely damaged.
There are apt to be more or less severe difficulties with bleeding when