88
4.
EMBEDDING
mediate solvent as indicated in the previous section (propylene oxide
for epoxy resins, styrene for polyesters, Chapter 4.3). After the tissue has
been passed through one or two 10-15 minute changes of this with
agitation, the solvent is drained off and 1-2 ml of fresh solvent is used
to cover the tissue blocks. Then resin mixture is added to this in such
an amount that the bath will remain quite fluid even after mixture is
complete. During the next 5-10 minutes this is stirred repeatedly by
shaking, and often with a toothpick, until the bath seems homogeneous.
The container is then put on an automatic shaker of the platform type,
and continuously shaken for 20-30 minutes. It can be expected that
this relatively thin embedding mixture, diluted with an approximately
equal volume of solvent, will exchange fairly rapidly with the pure
solvent within the tissue blocks, and then the embedding medium can
be safely concentrated further.
The second step involves the approximate doubling of the resin concentration by adding additional embedding mixture to the point that
the mixture becomes a little syrupy. It is important
that it remain sufficiently fluid so that the mechanical
shaker will still be effective in sloshing the mixture
about, thereby stirring it. However, before consigning
it to the mechanical shaker for automatic stirring, one should again use
a toothpick to mix the layers. We ordinarily agitate at this step for
30-45 minutes.
Completing the impregnation involves exposing the tissue blocks to
the undiluted plastic mixture. This ordinarily would be of such a viscosity that shaking would be meaningless. Before adding the undiluted
mixture, however, the vessel is drained as completely as is reasonable
by turning it upside down on a paper towel. The undiluted mixture is
added to a depth of 1-2 mm. Particularly at first, the specimens are
stirred about in this several times with a toothpick, or tumbled. Our
usual procedure is to leave tissues in this final mixture for about an hour
with 3-6 stirrings during that interval. Then the tissue blocks are ready
to be transferred into fresh plastic mixture in gelatin capsules.
It is to be noted that the tissue blocks themselves are not handled from
the time they are put in the small weighing bottles until finally they are
removed after infiltration has been completed. This final handling need
not be done with forceps. It is much safer to rely on the viscosity of the
plastic mixture and simply pick up the tissue blocks on the end of a
toothpick or needle for the transfer. This has the additional advantage
4.
EMBEDDING
mediate solvent as indicated in the previous section (propylene oxide
for epoxy resins, styrene for polyesters, Chapter 4.3). After the tissue has
been passed through one or two 10-15 minute changes of this with
agitation, the solvent is drained off and 1-2 ml of fresh solvent is used
to cover the tissue blocks. Then resin mixture is added to this in such
an amount that the bath will remain quite fluid even after mixture is
complete. During the next 5-10 minutes this is stirred repeatedly by
shaking, and often with a toothpick, until the bath seems homogeneous.
The container is then put on an automatic shaker of the platform type,
and continuously shaken for 20-30 minutes. It can be expected that
this relatively thin embedding mixture, diluted with an approximately
equal volume of solvent, will exchange fairly rapidly with the pure
solvent within the tissue blocks, and then the embedding medium can
be safely concentrated further.
The second step involves the approximate doubling of the resin concentration by adding additional embedding mixture to the point that
the mixture becomes a little syrupy. It is important
that it remain sufficiently fluid so that the mechanical
shaker will still be effective in sloshing the mixture
about, thereby stirring it. However, before consigning
it to the mechanical shaker for automatic stirring, one should again use
a toothpick to mix the layers. We ordinarily agitate at this step for
30-45 minutes.
Completing the impregnation involves exposing the tissue blocks to
the undiluted plastic mixture. This ordinarily would be of such a viscosity that shaking would be meaningless. Before adding the undiluted
mixture, however, the vessel is drained as completely as is reasonable
by turning it upside down on a paper towel. The undiluted mixture is
added to a depth of 1-2 mm. Particularly at first, the specimens are
stirred about in this several times with a toothpick, or tumbled. Our
usual procedure is to leave tissues in this final mixture for about an hour
with 3-6 stirrings during that interval. Then the tissue blocks are ready
to be transferred into fresh plastic mixture in gelatin capsules.
It is to be noted that the tissue blocks themselves are not handled from
the time they are put in the small weighing bottles until finally they are
removed after infiltration has been completed. This final handling need
not be done with forceps. It is much safer to rely on the viscosity of the
plastic mixture and simply pick up the tissue blocks on the end of a
toothpick or needle for the transfer. This has the additional advantage