2.3.
MINCED TISSUE
19
for any reason tissue must be picked up and transferred to the vial of
fixative, toothpicks or cardboard points (Fig. 1) should be used rather
than needles or forceps. If appreciable quantities of plasma or tissue
fluids are transferred to the vial, the first fixative should be discarded at
once and replaced with fresh. It probably helps, too, to agitate the vial
for the first 5-10 minutes.
Since blood and tissue fluid quickly destroy osmium tetroxide fixatives,
any large excess that may be picked up with a fresh piece of tissue should
be blotted on a piece of filter paper before the tissue is put in fixative and
minced. Do not make an attempt to wash tissue with so-called physiologically balanced salt solutions, at least unless careful controls are
studied, for almost invariably they do demonstrable damage.
In working with osmium tetroxide fixative the operator must appreciate
the fact that its fumes are dangerous. They are quite capable of fixing
corneal epithelium. Operations should be done by an open window or in
the cross-current of a fan, or even in a chemical hood. The latter is not
really necessary for fortunately osmium tetroxide fumes warn of their
presence by their characteristic, powerful smell. If one does not hold his
breath he is not apt to move his head in too closely. Some people will wish
to wear gas tight goggles for this work which, no doubt, is a good precaution. Most people will also find that a low power binocular viewer
attached to a head loop will be advantageous. It is quite possible to wear
such a loop over a suitably chosen pair of goggles.
There are occasions (such as when using permanganate fixatives) when
the tissue should be ice cold when it is in the fixative. The tissue almost
has to be minced "dry," in its own juice, on a strip of cardboard, and
subsequently transferred to a previously chilled fixative. Obviously speed
is particularly important under these circumstances, and one should be
careful not to have an absorbent cardboard.
FIG. 1 (a) and (b). Mincing tissue in a drop of osmium tetroxide on a strip of
cardboard. The operator must work very fast and not attempt to sort out pieces of
correct size until later. The specimens should be transferred to a glass container with
a surplus of fixative in it within a minute. This can be done most simply by dipping
the tip of the cardboard strip in the bath, and using a toothpick or cardboard point
to push the specimens. Metal should be avoided as far as possible, although a new
clean razor blade must be used for cutting. This is discarded when black deposits form
on its corners. Pieces of tissue are maneuvered and held in place with toothpicks rather
than metal needles. Small, wide-mouthed,
"weighing
bottles" with ground glass
lids of the type indicated here are almost ideal containers for the minute specimens
during fixation and dehydration.
MINCED TISSUE
19
for any reason tissue must be picked up and transferred to the vial of
fixative, toothpicks or cardboard points (Fig. 1) should be used rather
than needles or forceps. If appreciable quantities of plasma or tissue
fluids are transferred to the vial, the first fixative should be discarded at
once and replaced with fresh. It probably helps, too, to agitate the vial
for the first 5-10 minutes.
Since blood and tissue fluid quickly destroy osmium tetroxide fixatives,
any large excess that may be picked up with a fresh piece of tissue should
be blotted on a piece of filter paper before the tissue is put in fixative and
minced. Do not make an attempt to wash tissue with so-called physiologically balanced salt solutions, at least unless careful controls are
studied, for almost invariably they do demonstrable damage.
In working with osmium tetroxide fixative the operator must appreciate
the fact that its fumes are dangerous. They are quite capable of fixing
corneal epithelium. Operations should be done by an open window or in
the cross-current of a fan, or even in a chemical hood. The latter is not
really necessary for fortunately osmium tetroxide fumes warn of their
presence by their characteristic, powerful smell. If one does not hold his
breath he is not apt to move his head in too closely. Some people will wish
to wear gas tight goggles for this work which, no doubt, is a good precaution. Most people will also find that a low power binocular viewer
attached to a head loop will be advantageous. It is quite possible to wear
such a loop over a suitably chosen pair of goggles.
There are occasions (such as when using permanganate fixatives) when
the tissue should be ice cold when it is in the fixative. The tissue almost
has to be minced "dry," in its own juice, on a strip of cardboard, and
subsequently transferred to a previously chilled fixative. Obviously speed
is particularly important under these circumstances, and one should be
careful not to have an absorbent cardboard.
FIG. 1 (a) and (b). Mincing tissue in a drop of osmium tetroxide on a strip of
cardboard. The operator must work very fast and not attempt to sort out pieces of
correct size until later. The specimens should be transferred to a glass container with
a surplus of fixative in it within a minute. This can be done most simply by dipping
the tip of the cardboard strip in the bath, and using a toothpick or cardboard point
to push the specimens. Metal should be avoided as far as possible, although a new
clean razor blade must be used for cutting. This is discarded when black deposits form
on its corners. Pieces of tissue are maneuvered and held in place with toothpicks rather
than metal needles. Small, wide-mouthed,
"weighing
bottles" with ground glass
lids of the type indicated here are almost ideal containers for the minute specimens
during fixation and dehydration.