6.2.
PARLODION FILMS
193
step in preparing carbon films since they can be dissolved away after
carbon has been deposited, leaving a pure carbon film behind.
With the advent of thermostable plastic embedments for ultrathin
sectioning there has been a tendency to eliminate supporting films in
order to gain contrast and resolution. These newer plastics can be expected to sustain themselves and remain stable across grid holes of substantial size providing that the sections are nearly free of scratches, tears,
and holes. But this cannot always be promised or realized, particularly
when much collagen is present in the tissue. Thus it is that the recovery
of usable material may be much greater if supporting films are used
than otherwise would be the case. Also it is likely that grids of larger
mesh can be used. Finally supporting films are essential for serial section
work (Chapter 6.11). Actually nowadays we have such intense "electron
stains" available (Chapter 7) that we can afford to use supporting films
for most purposes simply for their convenience. Thus many laboratories
routinely use supporting films even when they are not strictly necessary.
Film making is still a pertinent technology even for the microtomist,
and is discussed in succeeding sections.
6.2. Parlodion Films
Parlodion is the trade name of a nitrocellulose plastic manufactured
by the Mallinckrodt Chemical Works, St. Louis, Missouri. It has perhaps
the highest viscosity of any nitrocellulose which gives it an advantage
over its relatives of forming the toughest possible films with the least
mass of material.
Parlodion films are easily prepared. Stock solutions of 0.5% (or less)
Parlodion are made up in amyl acetate (or sometimes ethyl acetate). It
takes about two days to dissolve. During this time, the plastic swells in
its solvent and becomes deceptively invisible long before true solution
occurs, so it should be stirred from time to time.
Thin Parlodion films are formed on standard 1 X 3 in. microscope
slides, and then they are stripped away from the glass. The microscope
slides should not be too carefully cleaned for then the film may become
too adherent to the glass to strip easily if at all. Thus, new microscope
slides should simply be wiped with a clean towel to remove obvious lint
and dust. Fingerprints on the glass surface, of course, should be avoided.
A slide is dipped into the Parlodion solution and held there for a few
PARLODION FILMS
193
step in preparing carbon films since they can be dissolved away after
carbon has been deposited, leaving a pure carbon film behind.
With the advent of thermostable plastic embedments for ultrathin
sectioning there has been a tendency to eliminate supporting films in
order to gain contrast and resolution. These newer plastics can be expected to sustain themselves and remain stable across grid holes of substantial size providing that the sections are nearly free of scratches, tears,
and holes. But this cannot always be promised or realized, particularly
when much collagen is present in the tissue. Thus it is that the recovery
of usable material may be much greater if supporting films are used
than otherwise would be the case. Also it is likely that grids of larger
mesh can be used. Finally supporting films are essential for serial section
work (Chapter 6.11). Actually nowadays we have such intense "electron
stains" available (Chapter 7) that we can afford to use supporting films
for most purposes simply for their convenience. Thus many laboratories
routinely use supporting films even when they are not strictly necessary.
Film making is still a pertinent technology even for the microtomist,
and is discussed in succeeding sections.
6.2. Parlodion Films
Parlodion is the trade name of a nitrocellulose plastic manufactured
by the Mallinckrodt Chemical Works, St. Louis, Missouri. It has perhaps
the highest viscosity of any nitrocellulose which gives it an advantage
over its relatives of forming the toughest possible films with the least
mass of material.
Parlodion films are easily prepared. Stock solutions of 0.5% (or less)
Parlodion are made up in amyl acetate (or sometimes ethyl acetate). It
takes about two days to dissolve. During this time, the plastic swells in
its solvent and becomes deceptively invisible long before true solution
occurs, so it should be stirred from time to time.
Thin Parlodion films are formed on standard 1 X 3 in. microscope
slides, and then they are stripped away from the glass. The microscope
slides should not be too carefully cleaned for then the film may become
too adherent to the glass to strip easily if at all. Thus, new microscope
slides should simply be wiped with a clean towel to remove obvious lint
and dust. Fingerprints on the glass surface, of course, should be avoided.
A slide is dipped into the Parlodion solution and held there for a few