16
2. TISSUE EXPOSURE
out that although various cellular membranes have a striking morphological similarity in electron micrographs there is little doubt that their
stability varies, suggesting that functional and compositional differences
do exist. It is evident that although fixation as soon as practical after
death is unquestionably desirable, there is less urgency than was previously supposed. Some of the structural alterations that were formerly
attributed to rapid post-mortem autolysis actually are artifacts of
specimen preparation. This re-emphasizes more strongly than ever that
there are severe problems in bringing the fixative to the tissue so that it
does not create damage. The critical moment is that time when the
fixative reaches the living cell, not so much when the animal dies.
2.3. Minced Tissue
There are obvious advantages to mincing fresh tissue directly in
fixative. One can start with tissue from any place in an animal body, even
deep within an organ, or from vital areas. With practice and skill the
time taken to mince tissue can be reduced to a minute or even less from
the time the circulation is interrupted in a narcotized animal. Even if an
animal is decapitated it need not take appreciably longer to find and
remove parts of most organs.
The most serious objection to mincing is the inevitable mechanical
disruption of the tissue. This can be minimized by using only brand new
razor blades for cutting. But whether or not this is an important factor
depends most directly on the character of the tissue. Thus, small acini
of glandular organs may be expected to survive quite intact, although
distortions would be expected to occur in the connective tissue stroma.
A relatively homogeneous cellular tissue such as liver minces easily.
Tissue of the central nervous system, unsupported by connective tissue,
usually is very difficult to cut finely in a satisfactory manner. Lung
collapses under these circumstances, and testis falls to pieces, although
segments of tubules are well preserved.
Palade (1952) in his already classic study of buffered osmium tetroxide
keenly appreciated the importance of small size in tissue block preservation. In retrospect the way he minced tissue was as essential to his success
as the formula of his fixative. The beauty of Sjostrand's (1953) study of
retinal rods, also a classic, depended in part upon the good exposure of
these elements that naturally occurs when the sensory retina is pulled
away from the pigment layer.
2. TISSUE EXPOSURE
out that although various cellular membranes have a striking morphological similarity in electron micrographs there is little doubt that their
stability varies, suggesting that functional and compositional differences
do exist. It is evident that although fixation as soon as practical after
death is unquestionably desirable, there is less urgency than was previously supposed. Some of the structural alterations that were formerly
attributed to rapid post-mortem autolysis actually are artifacts of
specimen preparation. This re-emphasizes more strongly than ever that
there are severe problems in bringing the fixative to the tissue so that it
does not create damage. The critical moment is that time when the
fixative reaches the living cell, not so much when the animal dies.
2.3. Minced Tissue
There are obvious advantages to mincing fresh tissue directly in
fixative. One can start with tissue from any place in an animal body, even
deep within an organ, or from vital areas. With practice and skill the
time taken to mince tissue can be reduced to a minute or even less from
the time the circulation is interrupted in a narcotized animal. Even if an
animal is decapitated it need not take appreciably longer to find and
remove parts of most organs.
The most serious objection to mincing is the inevitable mechanical
disruption of the tissue. This can be minimized by using only brand new
razor blades for cutting. But whether or not this is an important factor
depends most directly on the character of the tissue. Thus, small acini
of glandular organs may be expected to survive quite intact, although
distortions would be expected to occur in the connective tissue stroma.
A relatively homogeneous cellular tissue such as liver minces easily.
Tissue of the central nervous system, unsupported by connective tissue,
usually is very difficult to cut finely in a satisfactory manner. Lung
collapses under these circumstances, and testis falls to pieces, although
segments of tubules are well preserved.
Palade (1952) in his already classic study of buffered osmium tetroxide
keenly appreciated the importance of small size in tissue block preservation. In retrospect the way he minced tissue was as essential to his success
as the formula of his fixative. The beauty of Sjostrand's (1953) study of
retinal rods, also a classic, depended in part upon the good exposure of
these elements that naturally occurs when the sensory retina is pulled
away from the pigment layer.