7.6.
LAWN'S
PERMANGANATE
STAIN
239
in Chapter 5.26. After staining they are picked up on grids, essentially
as though they were floating in a trough. They are then given a short
wash and dried, when they are ready for use.
In the older literature one encounters reports of investigators using
phosphotungstic acid immediately after fixation, but this achieved a bad
reputation because undoubtedly this substance can cause much tissue
damage if not handled with some finesse. Phosphotungstic acid in aqueous
solution has a low pH. The acidity, perhaps, causes most of the damage.
To avoid this some investigators have block stained by adding phosphotungstic acid to absolute alcohol during the dehydration of the
specimen (Huxley, 1959), which probably is less damaging, although still
open to some question. Usually, also, this is not an effective way of staining
with phosphotungstic acid, for much of the stain is apt to be removed by
the embedding materials. Thus, efforts to achieve effective block staining
before embedding usually have been disappointing.
After sections have been stained with phosphotungstic acid they should
be dipped momentarily, either in water or dilute alcohol, depending upon
the vehicle of the stain. If very dilute phosphotungstic acid has been used
(approximately 0.1%) a wash is not necessary.
Watson (1958) has indicated that phosphotungstic acid solutions are
most effective as stains when used without alkalization.
7.6. Lawn's Permanganate Stain
Potassium permanganate can be used as a stain, even for material
embedded in epoxy resins. Lawn (1960) advocates for this purpose a 1%
solution, made up at least one day in advance, and which is not filtered.
Such a solution will have a scum on its surface which must be avoided.
Staining solution should be removed with a pipette from beneath the
surface film in the stock bottle. Mounted sections are floated face down
on this newly created surface and stained for 15 minutes to 2 hours. Lawn
recommended sweeping the surface of the staining solution clean with
FIG. 29. Araldite embedded monkey aorta, heavily stained with phosphotungstic
acid. Cytoplasmic proteins are diffusely stained. Cytomembranes, such as the plasma
membrane and pinocytotic vesicles (p.v.), are stained, but without the intensity imparted by alkaline lead or uranyl stains. However, extracellular components are
vigorously stained, including collagen, elastin, basement membranes (b.m.), and what
are regarded as other mucopolysaccharides (mucop'sacch.).
LAWN'S
PERMANGANATE
STAIN
239
in Chapter 5.26. After staining they are picked up on grids, essentially
as though they were floating in a trough. They are then given a short
wash and dried, when they are ready for use.
In the older literature one encounters reports of investigators using
phosphotungstic acid immediately after fixation, but this achieved a bad
reputation because undoubtedly this substance can cause much tissue
damage if not handled with some finesse. Phosphotungstic acid in aqueous
solution has a low pH. The acidity, perhaps, causes most of the damage.
To avoid this some investigators have block stained by adding phosphotungstic acid to absolute alcohol during the dehydration of the
specimen (Huxley, 1959), which probably is less damaging, although still
open to some question. Usually, also, this is not an effective way of staining
with phosphotungstic acid, for much of the stain is apt to be removed by
the embedding materials. Thus, efforts to achieve effective block staining
before embedding usually have been disappointing.
After sections have been stained with phosphotungstic acid they should
be dipped momentarily, either in water or dilute alcohol, depending upon
the vehicle of the stain. If very dilute phosphotungstic acid has been used
(approximately 0.1%) a wash is not necessary.
Watson (1958) has indicated that phosphotungstic acid solutions are
most effective as stains when used without alkalization.
7.6. Lawn's Permanganate Stain
Potassium permanganate can be used as a stain, even for material
embedded in epoxy resins. Lawn (1960) advocates for this purpose a 1%
solution, made up at least one day in advance, and which is not filtered.
Such a solution will have a scum on its surface which must be avoided.
Staining solution should be removed with a pipette from beneath the
surface film in the stock bottle. Mounted sections are floated face down
on this newly created surface and stained for 15 minutes to 2 hours. Lawn
recommended sweeping the surface of the staining solution clean with
FIG. 29. Araldite embedded monkey aorta, heavily stained with phosphotungstic
acid. Cytoplasmic proteins are diffusely stained. Cytomembranes, such as the plasma
membrane and pinocytotic vesicles (p.v.), are stained, but without the intensity imparted by alkaline lead or uranyl stains. However, extracellular components are
vigorously stained, including collagen, elastin, basement membranes (b.m.), and what
are regarded as other mucopolysaccharides (mucop'sacch.).