2.4.
PRESERVATION OF NATURAL SURFACES
21
essential that its capsule be removed. In general, enclosing connective
tissue membranes prove to be very effective barriers to osmium tetroxide
penetration, and one cannot get adequate fixation through them. This is
true even when the capsule appears to be very delicate in a gross sense.
Thus, the capsule of a mouse kidney or the pia of a rat brain, delicate as
these structures seem, demonstrably block the penetration of
fixative.
These membranes, however, can be peeled off without difficulty by grasping them with finely sharpened jeweler's forceps and tearing. Fixative is
then flushed on the exposed surface.
It is of the utmost importance that any oozing blood or tissue fluid be
flushed away quickly with excess fixative. The fixative, of course, will
soon seal the tissue so that oozing will stop. This flushing can be done
most simply with a medicine dropper type of pipette. A few squirts and
gentle rubbing with the blunt tip of the pipette are all that are normally
needed. Do not, however, take a full pipette and squirt and suck. This
contaminates all of the fixative. It is better to begin with 3 or 4 drops,
and to keep repeatedly flushing these away until the exposed area is
cleaned. One must be particularly careful not to contaminate the main
bottle of fixative with the tissue exudates.
Before beginning these procedures the animal should have been so
arranged or tilted that excess fixative can drain away from the pertinent
area. It is often expedient to let it drain into cotton pads. If osmium
tetroxide fixative is being used, fumes escape in dangerous quantities.
A person should be most careful of his eyes while doing this. It is advisable to have a small fan blowing the fumes away from the operator. One
must also breathe naturally for the nose gives warnings of concentrations
dangerous to the eyes. The danger lies in holding the breath and carelessly moving in close.
Ordinarily a freshly exposed organ surface can be sealed and cleaned
within 2 or 3 minutes. From that point on, one need only trickle
fixative
through a thin pad of absorbent cotton to continue fixation. The thinnest wisp of cotton is placed on the organ surface, just enough to keep a
fluid layer on the surface so that it does not require too much attention.
But the pad should be so thin that the addition of 2 or 3 drops of fixative
will amount to a fresh bath. The procedure then is to add a couple of
drops of fixative to the cotton every 2 or 3 minutes.
After 10 or 15 minutes it can be assumed that the fixative has penetrated as deeply as it usefully will. At this time the preserved surface
PRESERVATION OF NATURAL SURFACES
21
essential that its capsule be removed. In general, enclosing connective
tissue membranes prove to be very effective barriers to osmium tetroxide
penetration, and one cannot get adequate fixation through them. This is
true even when the capsule appears to be very delicate in a gross sense.
Thus, the capsule of a mouse kidney or the pia of a rat brain, delicate as
these structures seem, demonstrably block the penetration of
fixative.
These membranes, however, can be peeled off without difficulty by grasping them with finely sharpened jeweler's forceps and tearing. Fixative is
then flushed on the exposed surface.
It is of the utmost importance that any oozing blood or tissue fluid be
flushed away quickly with excess fixative. The fixative, of course, will
soon seal the tissue so that oozing will stop. This flushing can be done
most simply with a medicine dropper type of pipette. A few squirts and
gentle rubbing with the blunt tip of the pipette are all that are normally
needed. Do not, however, take a full pipette and squirt and suck. This
contaminates all of the fixative. It is better to begin with 3 or 4 drops,
and to keep repeatedly flushing these away until the exposed area is
cleaned. One must be particularly careful not to contaminate the main
bottle of fixative with the tissue exudates.
Before beginning these procedures the animal should have been so
arranged or tilted that excess fixative can drain away from the pertinent
area. It is often expedient to let it drain into cotton pads. If osmium
tetroxide fixative is being used, fumes escape in dangerous quantities.
A person should be most careful of his eyes while doing this. It is advisable to have a small fan blowing the fumes away from the operator. One
must also breathe naturally for the nose gives warnings of concentrations
dangerous to the eyes. The danger lies in holding the breath and carelessly moving in close.
Ordinarily a freshly exposed organ surface can be sealed and cleaned
within 2 or 3 minutes. From that point on, one need only trickle
fixative
through a thin pad of absorbent cotton to continue fixation. The thinnest wisp of cotton is placed on the organ surface, just enough to keep a
fluid layer on the surface so that it does not require too much attention.
But the pad should be so thin that the addition of 2 or 3 drops of fixative
will amount to a fresh bath. The procedure then is to add a couple of
drops of fixative to the cotton every 2 or 3 minutes.
After 10 or 15 minutes it can be assumed that the fixative has penetrated as deeply as it usefully will. At this time the preserved surface