3.7.
CRITERIA OF GOOD FIXATION
49
watery, with their contents widely dispersed by comparison they probably have been swollen.
One also has to be aware of shrinkage artifacts comparable to those
that should be familiar to every light microscopist. With differential
shrinkage, spaces can be artificially created which may be small or large.
They may form between cells or around inclusions. Connective tissue is
particularly apt to be torn and spaces opened.
Order tends to be degraded by poor preservation. Cytoplasm looks most
complex when it is well preserved. Morphological beauty is a correlate of
good fixation. When the good and the bad are compared there would
rarely be any doubt about which was which. It is for this reason that the
M.D., in particular, is again urged to begin with animal tissue to establish
criteria of good preservation which he must strive for in working with
human tissue.
Damage simulating poor fixation can occur in specimens embedded in
methacrylate. Affected cells appear swollen. All cytomembranes are apt
to show interruptions. Cyto- and nucleoplasm may present a flocculent
appearance. Such "polymerization damage" can result during the polymerization of monomeric methacrylate during embedding procedures. It
is discussed, and ways of avoiding it indicated, in Chapter 4.8. Fortunately, it is usually confined to superficial layers of tissue blocks, although
it is apt to destroy freely suspended cells or cells in tissue culture. This
type of artifact is not seen when other (cross-linked) plastics are used as
embedments.
FIG. 2. A comparison of reasonably well fixed (a) and (b) and poorly fixed (c)
epithelium of the choroid plexus. In the well-preserved specimen this cell type exhibits
a delicate "polypoid" border at the apical end. The nucleoplasm is uniformly granular.
Mitochondria are small dense bodies with well-defined cristae, visible at high magnification (b). The cytoplasm is characterized by large numbers of vesicular structures,
some of which belong to the endoplasmic reticular system. Groups of Golgi membranes
can be found without difficulty (encircled). During poor preservation delicate apical
structures of the cells undergo swelling, vesiculation, and destruction. Deeper cytoplasmic vesicles are sometimes swollen. The mitochondria (arrows) are tremendously
swollen. The nucleoplasm shows evidence of coarse precipitation, particularly in a
marginal aggregation of dense chromatin. Only the Golgi apparatus and some of the
granules remain essentially unaltered. In general, the condition of the mitochondria
and the nucleus are the most sensitive indicators of
fixation
damage. This material
was embedded in methacrylate, and was not stained.
CRITERIA OF GOOD FIXATION
49
watery, with their contents widely dispersed by comparison they probably have been swollen.
One also has to be aware of shrinkage artifacts comparable to those
that should be familiar to every light microscopist. With differential
shrinkage, spaces can be artificially created which may be small or large.
They may form between cells or around inclusions. Connective tissue is
particularly apt to be torn and spaces opened.
Order tends to be degraded by poor preservation. Cytoplasm looks most
complex when it is well preserved. Morphological beauty is a correlate of
good fixation. When the good and the bad are compared there would
rarely be any doubt about which was which. It is for this reason that the
M.D., in particular, is again urged to begin with animal tissue to establish
criteria of good preservation which he must strive for in working with
human tissue.
Damage simulating poor fixation can occur in specimens embedded in
methacrylate. Affected cells appear swollen. All cytomembranes are apt
to show interruptions. Cyto- and nucleoplasm may present a flocculent
appearance. Such "polymerization damage" can result during the polymerization of monomeric methacrylate during embedding procedures. It
is discussed, and ways of avoiding it indicated, in Chapter 4.8. Fortunately, it is usually confined to superficial layers of tissue blocks, although
it is apt to destroy freely suspended cells or cells in tissue culture. This
type of artifact is not seen when other (cross-linked) plastics are used as
embedments.
FIG. 2. A comparison of reasonably well fixed (a) and (b) and poorly fixed (c)
epithelium of the choroid plexus. In the well-preserved specimen this cell type exhibits
a delicate "polypoid" border at the apical end. The nucleoplasm is uniformly granular.
Mitochondria are small dense bodies with well-defined cristae, visible at high magnification (b). The cytoplasm is characterized by large numbers of vesicular structures,
some of which belong to the endoplasmic reticular system. Groups of Golgi membranes
can be found without difficulty (encircled). During poor preservation delicate apical
structures of the cells undergo swelling, vesiculation, and destruction. Deeper cytoplasmic vesicles are sometimes swollen. The mitochondria (arrows) are tremendously
swollen. The nucleoplasm shows evidence of coarse precipitation, particularly in a
marginal aggregation of dense chromatin. Only the Golgi apparatus and some of the
granules remain essentially unaltered. In general, the condition of the mitochondria
and the nucleus are the most sensitive indicators of
fixation
damage. This material
was embedded in methacrylate, and was not stained.