244
7.
"STAINING"
Daems and Persijn (1963) also have compared lead staining after both
osmium and formalin fixations, and have been led to postulate similarly
that there are at least three mechanisms of attachment of the lead to
different reacting groups. The most generally important reaction results
in a staining of cytomembranes, regarded as dependent upon the presence
of negatively charged reduced osmium on the polar groups of the
phosphatides. The staining of substances such as glycogen may be based
on the chelation of lead by hydroxyl groups of carbohydrates. Finally,
the nucleoprotein staining has a preference for RNA-containing proteins,
while DNA-containing proteins are preferentially stained by uranyl
acetate. The action of osmium tetroxide is thought of as actually depressing the staining of RNA-proteins, and abolishing that of DNA-proteins.
Marinozzi (1963) also finds that the presence of reduced osmium in
tissue sections is important in staining reactions with phosphotungstic
acid. This is demonstrated dramatically by oxidizing the bound osmium
before applying the stain. Under these circumstances, the collagen continues to stain vigorously. However, then cell organelles do not stain
appreciably except for the extraordinary exception of the plasma membrane and its derivatives. Thus is disclosed a remarkable difference
between the plasma membrane and other cytomembranes of the cells!
Marinozzi (1963) points out that this picture is duplicated by material
fixed in aldehyde, and which therefore, lacks reduced osmium. The
presence of reduced osmium apparently plays a less important role in
staining with uranyl acetate.
Without seeking chemical explanations of effects, Mercer (1963) also
has tried to systematize the staining reactions of alkaline lead hydroxide,
phosphotungstic acid, and uranyl acetate after both osmium tetroxide
and formaldehyde fixations. He made an effort to quantify the information, and presented this in the form of a table. However, there are so
many exceptions and qualifications, both stated and unstated, that its
value seems limited.
The role of reduced osmium is indicated in yet another reaction which
Marinozzi (1961) studied. This concerns the silver impregnation of tissues
resulting from the deposition of metallic silver from an ammoniacal silver
salt solution. Small crystals of silver then appear in proportion to the
amount of reduced osmium that is present. In unbleached tissue fixed
with osmium tetroxide, the pattern of silver deposition follows cytomembranes, and is diffusely distributed wherever there are diffuse protein
concentrations. In addition, silver is deposited in all areas which would
7.
"STAINING"
Daems and Persijn (1963) also have compared lead staining after both
osmium and formalin fixations, and have been led to postulate similarly
that there are at least three mechanisms of attachment of the lead to
different reacting groups. The most generally important reaction results
in a staining of cytomembranes, regarded as dependent upon the presence
of negatively charged reduced osmium on the polar groups of the
phosphatides. The staining of substances such as glycogen may be based
on the chelation of lead by hydroxyl groups of carbohydrates. Finally,
the nucleoprotein staining has a preference for RNA-containing proteins,
while DNA-containing proteins are preferentially stained by uranyl
acetate. The action of osmium tetroxide is thought of as actually depressing the staining of RNA-proteins, and abolishing that of DNA-proteins.
Marinozzi (1963) also finds that the presence of reduced osmium in
tissue sections is important in staining reactions with phosphotungstic
acid. This is demonstrated dramatically by oxidizing the bound osmium
before applying the stain. Under these circumstances, the collagen continues to stain vigorously. However, then cell organelles do not stain
appreciably except for the extraordinary exception of the plasma membrane and its derivatives. Thus is disclosed a remarkable difference
between the plasma membrane and other cytomembranes of the cells!
Marinozzi (1963) points out that this picture is duplicated by material
fixed in aldehyde, and which therefore, lacks reduced osmium. The
presence of reduced osmium apparently plays a less important role in
staining with uranyl acetate.
Without seeking chemical explanations of effects, Mercer (1963) also
has tried to systematize the staining reactions of alkaline lead hydroxide,
phosphotungstic acid, and uranyl acetate after both osmium tetroxide
and formaldehyde fixations. He made an effort to quantify the information, and presented this in the form of a table. However, there are so
many exceptions and qualifications, both stated and unstated, that its
value seems limited.
The role of reduced osmium is indicated in yet another reaction which
Marinozzi (1961) studied. This concerns the silver impregnation of tissues
resulting from the deposition of metallic silver from an ammoniacal silver
salt solution. Small crystals of silver then appear in proportion to the
amount of reduced osmium that is present. In unbleached tissue fixed
with osmium tetroxide, the pattern of silver deposition follows cytomembranes, and is diffusely distributed wherever there are diffuse protein
concentrations. In addition, silver is deposited in all areas which would