3.3.
OSMIUM TETROXIDE FIXATIVES
37
time in a refrigerator. At room temperature micro-organisms may grow
in the buffer. On the whole is seems safest to make up relatively small
quantities of buffer and fixative at one time and to use these up within
a few weeks.
Any person with the least acquaintance of tissue studies by electron
microscopy has seen numbers of electron micrographs of cells preserved
with the Palade fixative, or one of its close variants. Most of the electron
micrographs in this book are of material fixed either primarily or secondarily with buffered osmium tetroxide.
3.3. Variations of Osmium Tetroxide Fixatives
The variations of Palade fixative that have been proposed include alterations in its strength, its molarity, its pH, and the effects of particular
ions. Palade, giving a paper at the Third International Conference on
Electron Microscopy in 1954 (published in 1956), was able to reassess fixation problems in the light of much experience, and he discussed some of
these.
Insofar as strength is concerned, it may be mentioned that Palade
originally suggested that a 2% variation of his formulation might be used,
and later Palay and Palade (1955) suggested that even 3 and 4% mixtures
gave better results with tissues "particularly rich in reducing substances,"
in this instance tissue of the central nervous system. The present writer
attempted to make careful comparisons of 1 and 2% solutions when he
was studying the kidney by in situ preservation. The stronger solution
seemed definitely preferable. Perhaps it can be said that the added
strength is sometimes necessary, but more often wasteful.
The group at the Rockefeller Institute recognized almost from the
beginning that the Palade fixative was hypotonic, but they discounted
this as of little importance. However, Caulfield (1957) has published a
variation in which a good deal of sugar is used to increase tonicity. Since
this was published as coming from the Rockefeller Institute, it may be
considered an heir apparent to the original formula. One starts with the
standard 1% buffered osmium tetroxide fixative, and adds 0.045 gm of
sucrose per milliliter of solution.
Caulfield has recognized that there are special problems associated with
the preservation of botanical
material
and for this recommends a fixative
with much less salt, as follows:
OSMIUM TETROXIDE FIXATIVES
37
time in a refrigerator. At room temperature micro-organisms may grow
in the buffer. On the whole is seems safest to make up relatively small
quantities of buffer and fixative at one time and to use these up within
a few weeks.
Any person with the least acquaintance of tissue studies by electron
microscopy has seen numbers of electron micrographs of cells preserved
with the Palade fixative, or one of its close variants. Most of the electron
micrographs in this book are of material fixed either primarily or secondarily with buffered osmium tetroxide.
3.3. Variations of Osmium Tetroxide Fixatives
The variations of Palade fixative that have been proposed include alterations in its strength, its molarity, its pH, and the effects of particular
ions. Palade, giving a paper at the Third International Conference on
Electron Microscopy in 1954 (published in 1956), was able to reassess fixation problems in the light of much experience, and he discussed some of
these.
Insofar as strength is concerned, it may be mentioned that Palade
originally suggested that a 2% variation of his formulation might be used,
and later Palay and Palade (1955) suggested that even 3 and 4% mixtures
gave better results with tissues "particularly rich in reducing substances,"
in this instance tissue of the central nervous system. The present writer
attempted to make careful comparisons of 1 and 2% solutions when he
was studying the kidney by in situ preservation. The stronger solution
seemed definitely preferable. Perhaps it can be said that the added
strength is sometimes necessary, but more often wasteful.
The group at the Rockefeller Institute recognized almost from the
beginning that the Palade fixative was hypotonic, but they discounted
this as of little importance. However, Caulfield (1957) has published a
variation in which a good deal of sugar is used to increase tonicity. Since
this was published as coming from the Rockefeller Institute, it may be
considered an heir apparent to the original formula. One starts with the
standard 1% buffered osmium tetroxide fixative, and adds 0.045 gm of
sucrose per milliliter of solution.
Caulfield has recognized that there are special problems associated with
the preservation of botanical
material
and for this recommends a fixative
with much less salt, as follows: