182
5.
SECTIONING
one can have a frosted appearance and yet have unchattered sections. The
frosted look, no doubt, represents light being reflected by interfaces within
the section. These can either be the cracks and disturbances created by
chatter, or they can legitimately be reflections from refractile material
within the specimen.
If one suspects chatter, there are two things to consider that can be
corrected without seriously interrupting sectioning. An oversized block is
by far the commonest reason for chatter, and an operator with any
experience at all may realize that consciously or unconsciously he has
overstepped the limits. It is, of course, quite possible to trim, and
particularly to narrow, a block without removing it from the microtome
holder. The other thing to consider is the knife tilt, which often needs
some adjustment to get good sectioning underway.
The beginner using a hand-operated microtome is apt to have a little
difficulty establishing a smooth and slow cutting stroke. At first he is not
sufficiently relaxed and his tight muscles make spastic movements. This
may produce very coarse chatter in the sections so that their interference
colors show obvious banded patterns. This is not too serious for there
may be reasonable numbers of thin zones mixed with thick ones, and
these will be satisfactorily sectioned.
Scratches, of course, may show up [Fig. 21(a)]. A few scratches are not
of importance for one ultimately can work between them satisfactorily.
Many scratches ordinarily mean a contaminated knife edge which will
have to be abandoned. If one sees a few scratches at first which quickly
become numerous, the operator should suspect that dirt is present either
in or around the specimen.
5.23. Contamination—Principal Cause of Sectioning
Difficulty!
Contamination of the knife edge is by far the most common and insidious deterrent to success. The inexperienced investigator is not apt to
recognize the warning signals, or appreciate all of the traps.
The precautions necessary to avoid contamination while a knife is
being made have already been considered. The walls of the trough also
have been indicated as a potential source of trouble. In moving sections
about in the trough, there is real danger of introducing oily contamination from dirty tools. One has to be careful of the acetone (reagent grade)
5.
SECTIONING
one can have a frosted appearance and yet have unchattered sections. The
frosted look, no doubt, represents light being reflected by interfaces within
the section. These can either be the cracks and disturbances created by
chatter, or they can legitimately be reflections from refractile material
within the specimen.
If one suspects chatter, there are two things to consider that can be
corrected without seriously interrupting sectioning. An oversized block is
by far the commonest reason for chatter, and an operator with any
experience at all may realize that consciously or unconsciously he has
overstepped the limits. It is, of course, quite possible to trim, and
particularly to narrow, a block without removing it from the microtome
holder. The other thing to consider is the knife tilt, which often needs
some adjustment to get good sectioning underway.
The beginner using a hand-operated microtome is apt to have a little
difficulty establishing a smooth and slow cutting stroke. At first he is not
sufficiently relaxed and his tight muscles make spastic movements. This
may produce very coarse chatter in the sections so that their interference
colors show obvious banded patterns. This is not too serious for there
may be reasonable numbers of thin zones mixed with thick ones, and
these will be satisfactorily sectioned.
Scratches, of course, may show up [Fig. 21(a)]. A few scratches are not
of importance for one ultimately can work between them satisfactorily.
Many scratches ordinarily mean a contaminated knife edge which will
have to be abandoned. If one sees a few scratches at first which quickly
become numerous, the operator should suspect that dirt is present either
in or around the specimen.
5.23. Contamination—Principal Cause of Sectioning
Difficulty!
Contamination of the knife edge is by far the most common and insidious deterrent to success. The inexperienced investigator is not apt to
recognize the warning signals, or appreciate all of the traps.
The precautions necessary to avoid contamination while a knife is
being made have already been considered. The walls of the trough also
have been indicated as a potential source of trouble. In moving sections
about in the trough, there is real danger of introducing oily contamination from dirty tools. One has to be careful of the acetone (reagent grade)