10.2.
SUSPENDED AND FRAGMENTED MATERIAL
327
provides a particularly powerful tool for the study of fine surface detail.
This last technique is the subject of Chapter 11.
In the course of time, quite a variety of materials have been advocated
as replicating substances. Some of these are plastics that require considerable heat and/or pressure to make the replica and therefore are not
applicable to most biological work. Others are plastics or resins that can
be deposited as films from solutions, and are more generally useful.
Evaporated films, particularly of silica, are used. But when Bradley (1954)
demonstrated that carbon could be evaporated easily in vacuo, it was
realized at once that this was almost the ideal way to replicate most
biological specimens. The chemical inertness of pure carbon allows most
specimens or substrates to be dissolved after depositing the carbon,
leaving the film isolated and cleaned. A carbon replica, thus, can be
formed directly upon the material to be studied, or a thick plastic first
replica may be used as an intermediate step if mechanical force must be
used to strip off the replica. The face of this then is secondarily replicated
with carbon.
It would not be worthwhile in this book, oriented as it is toward work
with ultrathin sections, to attempt a full discussion of all the variants
of these methods. This chapter, therefore, will be limited to the most
generally useful procedures for the biologist, and will only attempt to
point out their main features and advantages. Often the interested investigator will have to consult the original literature for detail; however,
Bradley (1961) has written an extended review.
10.2, Suspended and Fragmented Material
The biochemists and virologists have developed various ways of suspending material which may then appropriately be studied with an
electron microscope. Aliquots can be dried on supporting films and
examined directly, usually either after metal shadowing or following
negative staining. In the former instance, in particular, difficulties begin
when it is realized that there cannot be appreciable salt left in the final
preparation or its crystals will coat the specimen particles and destroy
their imaging. If possible, the best solution to this problem is to design
the experiment in such a way that salt is finally eliminated. If this is not
feasible, perhaps ammonium acetate can be left as the only residual salt.
This can be expected to volatilize in vacuo before shadowing. Ammonium
SUSPENDED AND FRAGMENTED MATERIAL
327
provides a particularly powerful tool for the study of fine surface detail.
This last technique is the subject of Chapter 11.
In the course of time, quite a variety of materials have been advocated
as replicating substances. Some of these are plastics that require considerable heat and/or pressure to make the replica and therefore are not
applicable to most biological work. Others are plastics or resins that can
be deposited as films from solutions, and are more generally useful.
Evaporated films, particularly of silica, are used. But when Bradley (1954)
demonstrated that carbon could be evaporated easily in vacuo, it was
realized at once that this was almost the ideal way to replicate most
biological specimens. The chemical inertness of pure carbon allows most
specimens or substrates to be dissolved after depositing the carbon,
leaving the film isolated and cleaned. A carbon replica, thus, can be
formed directly upon the material to be studied, or a thick plastic first
replica may be used as an intermediate step if mechanical force must be
used to strip off the replica. The face of this then is secondarily replicated
with carbon.
It would not be worthwhile in this book, oriented as it is toward work
with ultrathin sections, to attempt a full discussion of all the variants
of these methods. This chapter, therefore, will be limited to the most
generally useful procedures for the biologist, and will only attempt to
point out their main features and advantages. Often the interested investigator will have to consult the original literature for detail; however,
Bradley (1961) has written an extended review.
10.2, Suspended and Fragmented Material
The biochemists and virologists have developed various ways of suspending material which may then appropriately be studied with an
electron microscope. Aliquots can be dried on supporting films and
examined directly, usually either after metal shadowing or following
negative staining. In the former instance, in particular, difficulties begin
when it is realized that there cannot be appreciable salt left in the final
preparation or its crystals will coat the specimen particles and destroy
their imaging. If possible, the best solution to this problem is to design
the experiment in such a way that salt is finally eliminated. If this is not
feasible, perhaps ammonium acetate can be left as the only residual salt.
This can be expected to volatilize in vacuo before shadowing. Ammonium