3.9.
BUFFERED ALDEHYDES AS PRIMARY FIXATIVES
51
tissues treated first with formaldehyde, which then was followed by osmium tetroxide, could indeed be about as well preserved, and nearly
identical to, similar tissue fixed with osmium tetroxide alone. It was felt
that using formaldehyde for the preliminary stages of fixation would
make obtaining satisfactory human tissue a much easier and more reliable
task. Also, since the formaldehyde could be used easily as a perfusion
medium, tissues that were almost inaccessible for direct fixation with
osmium tetroxide then could be obtained without difficulty (Chapter 2.6).
At the same time as the aforementioned demonstration of the virtues
of formaldehyde, Sabatini, Bensch, and Barrnett (1962) presented a preliminary study of a variety of different aldehydes used as fixatives. Since
the latter authors were interested mainly in their value in histochemical
applications, they were concerned principally with their use as the sole
fixatives to be employed. They concluded that glutaraldehyde was the
best choice in terms of the preservation of cellular morphology. However,
being an effective denaturant, it inevitably blocked some enzymatic reactions of histochemical interest for, presumably, one cannot optimally
preserve form and also retain complete function. Hydroxyadipaldehyde
so far seems to do the least cytochemical damage, athough it is barely
acceptable in terms of morphological preservation (Sabatini, Bensch, and
Barrnett, 1963).
Thus it is that recent years have witnessed a progressive understanding
of how aldehydes can and should be used effectively. Although no doubt
further strides will be made in their development and use, enough is
known now so that some procedures can be presented with confidence
in the sections which follow.
3.9. Buffered Aldehydes as Primary Fixatives
Pease (1962) proposed using a 10% formalin solution (4% formaldehyde) in the same vehicle that Millonig (1961, 1962) employed for osmium tetroxide (Chapter 3.3). Part of the rationale for this was the
deliberate intention to go directly from the formalin solution into the
osmium tetroxide fixative with the least possible disturbance. Also, the
isotonic salts themselves presumably would not be immediately damaging
to tissue. In addition, of course, this phosphate buffer has unusually great
buffering capacity in the range of interest. It is obvious that aldehydes
other than formaldehyde can be substituted in the formulation. Follow-
BUFFERED ALDEHYDES AS PRIMARY FIXATIVES
51
tissues treated first with formaldehyde, which then was followed by osmium tetroxide, could indeed be about as well preserved, and nearly
identical to, similar tissue fixed with osmium tetroxide alone. It was felt
that using formaldehyde for the preliminary stages of fixation would
make obtaining satisfactory human tissue a much easier and more reliable
task. Also, since the formaldehyde could be used easily as a perfusion
medium, tissues that were almost inaccessible for direct fixation with
osmium tetroxide then could be obtained without difficulty (Chapter 2.6).
At the same time as the aforementioned demonstration of the virtues
of formaldehyde, Sabatini, Bensch, and Barrnett (1962) presented a preliminary study of a variety of different aldehydes used as fixatives. Since
the latter authors were interested mainly in their value in histochemical
applications, they were concerned principally with their use as the sole
fixatives to be employed. They concluded that glutaraldehyde was the
best choice in terms of the preservation of cellular morphology. However,
being an effective denaturant, it inevitably blocked some enzymatic reactions of histochemical interest for, presumably, one cannot optimally
preserve form and also retain complete function. Hydroxyadipaldehyde
so far seems to do the least cytochemical damage, athough it is barely
acceptable in terms of morphological preservation (Sabatini, Bensch, and
Barrnett, 1963).
Thus it is that recent years have witnessed a progressive understanding
of how aldehydes can and should be used effectively. Although no doubt
further strides will be made in their development and use, enough is
known now so that some procedures can be presented with confidence
in the sections which follow.
3.9. Buffered Aldehydes as Primary Fixatives
Pease (1962) proposed using a 10% formalin solution (4% formaldehyde) in the same vehicle that Millonig (1961, 1962) employed for osmium tetroxide (Chapter 3.3). Part of the rationale for this was the
deliberate intention to go directly from the formalin solution into the
osmium tetroxide fixative with the least possible disturbance. Also, the
isotonic salts themselves presumably would not be immediately damaging
to tissue. In addition, of course, this phosphate buffer has unusually great
buffering capacity in the range of interest. It is obvious that aldehydes
other than formaldehyde can be substituted in the formulation. Follow-