3.7.
CRITERIA OF GOOD FIXATION
47
dicate the nature of some of the pitfalls. It remains a truism that the
morphologically most generally
satisfactory micrographs are those of
osmium tetroxide-fixed material, even though this fixative may have been
used secondarily.
Different cell types differ so much, both qualitatively and quantitatively, that it is difficult to categorize the criteria of good fixation. However, the following generalizations may be considered guideposts. Figures
2(a) and (c) compare fair and bad fixation in one cell type, and illustrate
most of the features discussed below.
Nuclei which are uniformly and finely granular are usually associated
with other desirable features. Obviously aggregated chromatin masses are
suspect; although in a few cell types (i.e., plasma cells), this pattern is so
dominant that it may almost always be evident. Also, if osmium tetroxide
fixatives are used secondarily to an aldehyde fixation, obvious chromatin
masses are regularly seen in many cell types (Figs. 3 and 10).
Mitochondria ordinarily are fairly sensitive indicators of fixation. In
many cell types they easily become obviously swollen and empty looking.
Other cell features may be none the less fairly well preserved.
Cells which have a good deal of endoplasmic reticulum, usually have
this partly in the form of flattened cisterns which are arranged in stacks.
It can be expected that the width and arrangement of the cisterns should
be reasonably uniform. They may become irregularly swollen when
poorly preserved.
The apparent gap between the outer and inner nuclear membranes is
fundamentally a continuation of cisterns of the endoplasmic reticulum.
As such, this should be of nearly uniform width.
Golgi membranes and vacuoles seem quite resistant to the vagaries of
fixation, and may have good appearance even though the other organelles
are severely damaged.
The plasma membrane at the surface of the cell certainly should be
complete. Deep basal infoldings of this membrane, such as those found
in the proximal and distal tubules of the kidney, should be separated by
a nearly uniform gap.
The "ground substance" of cytoplasm should be very finely precipitated
and not at all conspicuous in most cells. Irregular masses of material,
coating organelles and inclusions, indicate coarse aggregation of the
proteins.
The apical ends of secretory cells are apt to be more sensitive to deleterious influences than the basal ends (cf. Fig. 2). If the former seem more
CRITERIA OF GOOD FIXATION
47
dicate the nature of some of the pitfalls. It remains a truism that the
morphologically most generally
satisfactory micrographs are those of
osmium tetroxide-fixed material, even though this fixative may have been
used secondarily.
Different cell types differ so much, both qualitatively and quantitatively, that it is difficult to categorize the criteria of good fixation. However, the following generalizations may be considered guideposts. Figures
2(a) and (c) compare fair and bad fixation in one cell type, and illustrate
most of the features discussed below.
Nuclei which are uniformly and finely granular are usually associated
with other desirable features. Obviously aggregated chromatin masses are
suspect; although in a few cell types (i.e., plasma cells), this pattern is so
dominant that it may almost always be evident. Also, if osmium tetroxide
fixatives are used secondarily to an aldehyde fixation, obvious chromatin
masses are regularly seen in many cell types (Figs. 3 and 10).
Mitochondria ordinarily are fairly sensitive indicators of fixation. In
many cell types they easily become obviously swollen and empty looking.
Other cell features may be none the less fairly well preserved.
Cells which have a good deal of endoplasmic reticulum, usually have
this partly in the form of flattened cisterns which are arranged in stacks.
It can be expected that the width and arrangement of the cisterns should
be reasonably uniform. They may become irregularly swollen when
poorly preserved.
The apparent gap between the outer and inner nuclear membranes is
fundamentally a continuation of cisterns of the endoplasmic reticulum.
As such, this should be of nearly uniform width.
Golgi membranes and vacuoles seem quite resistant to the vagaries of
fixation, and may have good appearance even though the other organelles
are severely damaged.
The plasma membrane at the surface of the cell certainly should be
complete. Deep basal infoldings of this membrane, such as those found
in the proximal and distal tubules of the kidney, should be separated by
a nearly uniform gap.
The "ground substance" of cytoplasm should be very finely precipitated
and not at all conspicuous in most cells. Irregular masses of material,
coating organelles and inclusions, indicate coarse aggregation of the
proteins.
The apical ends of secretory cells are apt to be more sensitive to deleterious influences than the basal ends (cf. Fig. 2). If the former seem more