7.2.
PENETRATION OF STAINS
217
plasmic structures. This has since become a classical paper because in
the course of his investigation he discovered and introduced alkaline lead
hydroxide, upon which much of our present staining technique is based.
At the time Watson was using methacrylate embedments, and he could
not have foretold how important his lead stain was to become. People
since have lost interest in most of the other compounds he studied, excepting only uranyl acetate. Previous studies also, which were limited
to methacrylate sections, largely have been forgotten in our need to
achieve staining with epoxy and polyester embedments. Only if a stain
is effective with the latter embedments is it of current interest, and is
included in what follows.
It will also be convenient to include in this chapter certain ancillary
techniques such as autoradiography and antibody stains, as well as the
staining of thick plastic embedded sections for conventional microscopy.
7.2. Penetration of Stains
The following sections present a variety of stains that can be used
effectively with epoxy and polyester sections, as well as with methacrylate.
At the present time the difficulties with staining often are not so much
with the stains themselves, as with their penetration into the insoluble
and often hydrophobic embedments. The different plastics have quite
different properties in this respect.
Methacrylate-embedded sections are by far the easiest of all the common plastics to stain. Staining compounds can be expected to penetrate
rapidly and build up to maximum contrast within a very few minutes.
Usually nothing is gained by exposing methacrylate sections to a staining solution for more than 5 minutes.
Glycol methacrylate is perhaps even more easily stained than the usual
butyl methacrylate, probably in part because the numerous polar groups
exposed in this embedment make such sections relatively hydrophilic.
Difficulties with stain penetration begin with polyester and epoxy
sections. The different embedments have their own characteristics, as
do the different stains. This makes generalizations difficult, and here we
can do little more than indicate variant techniques which may assist
in the penetration of staining materials into sections when this seems
necessary, and with the understanding that these tricks may not be needed.
Ordinarily, the epoxy resin, Araldite, will prove most refractory to
PENETRATION OF STAINS
217
plasmic structures. This has since become a classical paper because in
the course of his investigation he discovered and introduced alkaline lead
hydroxide, upon which much of our present staining technique is based.
At the time Watson was using methacrylate embedments, and he could
not have foretold how important his lead stain was to become. People
since have lost interest in most of the other compounds he studied, excepting only uranyl acetate. Previous studies also, which were limited
to methacrylate sections, largely have been forgotten in our need to
achieve staining with epoxy and polyester embedments. Only if a stain
is effective with the latter embedments is it of current interest, and is
included in what follows.
It will also be convenient to include in this chapter certain ancillary
techniques such as autoradiography and antibody stains, as well as the
staining of thick plastic embedded sections for conventional microscopy.
7.2. Penetration of Stains
The following sections present a variety of stains that can be used
effectively with epoxy and polyester sections, as well as with methacrylate.
At the present time the difficulties with staining often are not so much
with the stains themselves, as with their penetration into the insoluble
and often hydrophobic embedments. The different plastics have quite
different properties in this respect.
Methacrylate-embedded sections are by far the easiest of all the common plastics to stain. Staining compounds can be expected to penetrate
rapidly and build up to maximum contrast within a very few minutes.
Usually nothing is gained by exposing methacrylate sections to a staining solution for more than 5 minutes.
Glycol methacrylate is perhaps even more easily stained than the usual
butyl methacrylate, probably in part because the numerous polar groups
exposed in this embedment make such sections relatively hydrophilic.
Difficulties with stain penetration begin with polyester and epoxy
sections. The different embedments have their own characteristics, as
do the different stains. This makes generalizations difficult, and here we
can do little more than indicate variant techniques which may assist
in the penetration of staining materials into sections when this seems
necessary, and with the understanding that these tricks may not be needed.
Ordinarily, the epoxy resin, Araldite, will prove most refractory to