128
4.
EMBEDDING
methacrylate as a satisfactory embedment. Although in this case the
methacrylate was used only to soften the final plastic so that it could
be sectioned, it seems likely that it could be partly or entirely removed
by solvent action after sectioning. If the sections retained sufficient support from the polystyrene to be useful, they certainly then would have
an increased contrast.
The special properties of the "water-soluble" plastics discussed in the
previous section have excited people's interest, and at times it has
proved almost mandatory to blend them with more conventional resins
to produce embedments which section well. Ordinarily, then, resins have
been chosen from the same general family.
Commercial polyester resins usually are blended resins to start with,
with styrene being the ordinary dilutant which copolymerizes into the
final plastic. As much as 70% styrene may be used. Vestopal W apparently contains substantial quantities of styrene. Selectron 5003 contains
about 35%. The physico-chemical properties of the final plastic depend
much more upon the character of the blended polyester than upon the
styrene.
4.18
Gelatin Embedding
A general technique of gelatin embedding has been developed by Gilev,
which was published in detail in 1958. Apparently independently, Fernandez-Moran and Finean (1957) have also successfully experimented
with a similar technique to study nerve myelin by low angle X-ray
diffraction, as well as by electron microscopy. Since the present author
has not had experience with this embedding medium he will only attempt a short summary here, and refers the interested reader to the
original literature for further details.
Residual, uncombined fixative should be fully washed out of the
tissue before beginning impregnation. Even after extensive washing
Gilev reports there is some interaction between osmium tetroxide and
the embedding gelatin.
Next, the tissue is infiltrated with successively stronger gelatin solutions. Fernandez-Moran and Finean used a commercially available,
standard bacteriological gelatin; Gilev purified a food gelatin by somewhat elaborate means. The former workers used relatively short time
intervals to complete infiltration with a 30% solution to which 2% glyc-
4.
EMBEDDING
methacrylate as a satisfactory embedment. Although in this case the
methacrylate was used only to soften the final plastic so that it could
be sectioned, it seems likely that it could be partly or entirely removed
by solvent action after sectioning. If the sections retained sufficient support from the polystyrene to be useful, they certainly then would have
an increased contrast.
The special properties of the "water-soluble" plastics discussed in the
previous section have excited people's interest, and at times it has
proved almost mandatory to blend them with more conventional resins
to produce embedments which section well. Ordinarily, then, resins have
been chosen from the same general family.
Commercial polyester resins usually are blended resins to start with,
with styrene being the ordinary dilutant which copolymerizes into the
final plastic. As much as 70% styrene may be used. Vestopal W apparently contains substantial quantities of styrene. Selectron 5003 contains
about 35%. The physico-chemical properties of the final plastic depend
much more upon the character of the blended polyester than upon the
styrene.
4.18
Gelatin Embedding
A general technique of gelatin embedding has been developed by Gilev,
which was published in detail in 1958. Apparently independently, Fernandez-Moran and Finean (1957) have also successfully experimented
with a similar technique to study nerve myelin by low angle X-ray
diffraction, as well as by electron microscopy. Since the present author
has not had experience with this embedding medium he will only attempt a short summary here, and refers the interested reader to the
original literature for further details.
Residual, uncombined fixative should be fully washed out of the
tissue before beginning impregnation. Even after extensive washing
Gilev reports there is some interaction between osmium tetroxide and
the embedding gelatin.
Next, the tissue is infiltrated with successively stronger gelatin solutions. Fernandez-Moran and Finean used a commercially available,
standard bacteriological gelatin; Gilev purified a food gelatin by somewhat elaborate means. The former workers used relatively short time
intervals to complete infiltration with a 30% solution to which 2% glyc-