56
3.
FIXATION
were well preserved and in normal place. Thus, there was no separation
of the sensory retina from the pigment cell layer.
It is important to note that osmium tetroxide does not penetrate
tissue any better after aldehyde fixation than when used as the primary
fixative. Thus, if a secondary fixation with osmium tetroxide is desired, it
is imperative that tissue be minced or sliced as thin as one ordinarily
would if relying entirely upon osmium tetroxide. In effect this means
making slices just about as thinly as can be made free-hand with a sharp
razor blade. The investigator easily and convincingly can demonstrate
this to his own satisfaction if he will dice slabs of tissue after osmication.
Unblackened centers will be the rule if the minimum diameter is more
than about a millimeter.
Sabatini, Bensch, and Barrnett (1963) have discredited the value of
formaldehyde. As will become evident below, their interest in formaldehyde was only incidental, for above all else they were concerned with
aldehydes as the sole fixatives to be employed in histochemical studies.
What happened as a result of secondary fixation with osmium tetroxide
was only of minor importance to them. Thus, it is likely that their poor
evaluation of formaldehyde should be discounted in considering its usefulness for cytological morphology. The small size of the formaldehyde
molecule in comparison with most other aldehydes surely favors a particularly rapid penetration into tissues, and makes it especially useful
when perfusions are contemplated.
Luft's (1959) criticisms of formaldehyde as a fixative probably also
should be discounted since he was using a Veronal buffer with it as many
other people, including this author, also have done in the past. Holt and
Hicks (1961), however, state that "it [Veronal] reacts with formaldehyde
as to produce a substance with no buffering capacity within the physiological range of pH values."
3.10. Aldehydes as Fixatives for Histochemistry
There is a considerable, although scattered, literature concerned with
using formaldehyde
fixation
preceding histochemical reactions. Dr.
Bernhard and his group in Paris have been particularly active in recent
years in coupling the use of this fixation with embedments in "water
soluble" plastic resins (Chapter 4.16) which subsequently allowed some
3.
FIXATION
were well preserved and in normal place. Thus, there was no separation
of the sensory retina from the pigment cell layer.
It is important to note that osmium tetroxide does not penetrate
tissue any better after aldehyde fixation than when used as the primary
fixative. Thus, if a secondary fixation with osmium tetroxide is desired, it
is imperative that tissue be minced or sliced as thin as one ordinarily
would if relying entirely upon osmium tetroxide. In effect this means
making slices just about as thinly as can be made free-hand with a sharp
razor blade. The investigator easily and convincingly can demonstrate
this to his own satisfaction if he will dice slabs of tissue after osmication.
Unblackened centers will be the rule if the minimum diameter is more
than about a millimeter.
Sabatini, Bensch, and Barrnett (1963) have discredited the value of
formaldehyde. As will become evident below, their interest in formaldehyde was only incidental, for above all else they were concerned with
aldehydes as the sole fixatives to be employed in histochemical studies.
What happened as a result of secondary fixation with osmium tetroxide
was only of minor importance to them. Thus, it is likely that their poor
evaluation of formaldehyde should be discounted in considering its usefulness for cytological morphology. The small size of the formaldehyde
molecule in comparison with most other aldehydes surely favors a particularly rapid penetration into tissues, and makes it especially useful
when perfusions are contemplated.
Luft's (1959) criticisms of formaldehyde as a fixative probably also
should be discounted since he was using a Veronal buffer with it as many
other people, including this author, also have done in the past. Holt and
Hicks (1961), however, state that "it [Veronal] reacts with formaldehyde
as to produce a substance with no buffering capacity within the physiological range of pH values."
3.10. Aldehydes as Fixatives for Histochemistry
There is a considerable, although scattered, literature concerned with
using formaldehyde
fixation
preceding histochemical reactions. Dr.
Bernhard and his group in Paris have been particularly active in recent
years in coupling the use of this fixation with embedments in "water
soluble" plastic resins (Chapter 4.16) which subsequently allowed some