200
6.
SECTION MOUNTING
A variant procedure adds 1-10% water to a 0.5-2.0% Formvar solution
in ethylene dichloride. The mixture then is shaken vigorously to form
a milky emulsion. A drop of this is allowed to fall on a clean water surface, whereupon it spreads out and hardens as a film upon which grids
can be placed and picked up as previously indicated (Chapter 6.2). If
10% dioxane is added to the original solution, the film is said to spread
better than if pure ethylene dichloride is used. Also, it might be supposed
that the finest emulsion might be created by supersonic vibration. Many
of the holes formed in such a film remained bridged with extremely
thin films. If it is desired that these be entirely eliminated (as certainly
would be the case if the film is to be carbonized), dried grids should be
dipped for about 30 seconds in acetone.
Yet another method dissolves Formvar in dioxane to which about
10% water is added. A drop of this is allowed to spread out on a glass
slide, and this film subsequently is floated off and grids mounted upon
it as previously described.
The method is particularly useful for studying very minute objects
that are fairly common in the sections so that there is a good statistical
chance of finding the object nicely centered in a hole in the mesh.
Since the useful holes are much smaller than a single cell, this means
that organelles or inclusions such as mitochondria, cilia, or specific
granules are likely candidates for this treatment. It has also proved
pertinent when studying particulate matter with "negative staining"
techniques (Chapter 11) to suspend the material in fluid films across
such holes. The two sides are then symmetrical, and one avoids interpretive problems which arise when particles are allowed to dry down
upon surfaces.
6.5. The Mechanics of Carbon Evaporation
An ideal supporting film must be strong, stable, and thin. It should
also be made up of light atoms, be elastic, and adhere tenaciously to
metal supporting grids. Carbon falls short of the ideal in the last two
of these characteristics, so that pure carbon films are, in fact, somewhat
difficult to handle. They are extremely brittle and do not adhere to grids
at all well, but they do possess a rock-like stability even when they are
so thin as to have excellent electron transparency. Furthermore, they
can be used as stabilizing support for plastic films that otherwise would
6.
SECTION MOUNTING
A variant procedure adds 1-10% water to a 0.5-2.0% Formvar solution
in ethylene dichloride. The mixture then is shaken vigorously to form
a milky emulsion. A drop of this is allowed to fall on a clean water surface, whereupon it spreads out and hardens as a film upon which grids
can be placed and picked up as previously indicated (Chapter 6.2). If
10% dioxane is added to the original solution, the film is said to spread
better than if pure ethylene dichloride is used. Also, it might be supposed
that the finest emulsion might be created by supersonic vibration. Many
of the holes formed in such a film remained bridged with extremely
thin films. If it is desired that these be entirely eliminated (as certainly
would be the case if the film is to be carbonized), dried grids should be
dipped for about 30 seconds in acetone.
Yet another method dissolves Formvar in dioxane to which about
10% water is added. A drop of this is allowed to spread out on a glass
slide, and this film subsequently is floated off and grids mounted upon
it as previously described.
The method is particularly useful for studying very minute objects
that are fairly common in the sections so that there is a good statistical
chance of finding the object nicely centered in a hole in the mesh.
Since the useful holes are much smaller than a single cell, this means
that organelles or inclusions such as mitochondria, cilia, or specific
granules are likely candidates for this treatment. It has also proved
pertinent when studying particulate matter with "negative staining"
techniques (Chapter 11) to suspend the material in fluid films across
such holes. The two sides are then symmetrical, and one avoids interpretive problems which arise when particles are allowed to dry down
upon surfaces.
6.5. The Mechanics of Carbon Evaporation
An ideal supporting film must be strong, stable, and thin. It should
also be made up of light atoms, be elastic, and adhere tenaciously to
metal supporting grids. Carbon falls short of the ideal in the last two
of these characteristics, so that pure carbon films are, in fact, somewhat
difficult to handle. They are extremely brittle and do not adhere to grids
at all well, but they do possess a rock-like stability even when they are
so thin as to have excellent electron transparency. Furthermore, they
can be used as stabilizing support for plastic films that otherwise would