2.8.
SPECIAL PROBLEMS WITH HUMAN TISSUES
29
be used cautiously in new investigations. It is advised only when a serious
connective tissue barrier must be eliminated.
2.8. Special Problems with Human Tissues
The previous sections of this chapter have emphasized ways of bringing tissue in contact with fixative in the most expeditious manner. Obviously most of these procedures are not generally applicable when
human material is to be obtained. Anyone acquainted with the literature
of tissue studies by electron microscopy will realize that published micrographs of human material rarely equal in quality the best that can be
obtained from animals. The difficulties in getting well-preserved human
material very seriously retard the development of pathological knowledge at electron microscopic levels.
The realization that aldehydes can be used as killing agents and primary fixatives (Chapter 3.9) should prove a great boon to those who
would work with surgical material. Their great penetrating power, particularly of suitably buffered formaldehyde, can be relied upon to preserve adequately slices of fresh tissue cut free-handedly as thinly as possible. Or larger masses of tissue can be put in a bath of buffered aldehyde
fixative, and subsequently thin layers of their surfaces can be removed
carefully and used for electron microscopy. In either case, ordinarily the
tissue would be fixed secondarily with osmium tetroxide. It should be
noted that the osmium tetroxide will not penetrate into a slab of aldehyde-fixed tissue any better than into fresh tissue, so that the tissue slabs
or blocks must be very thin or small before secondary fixation is begun
(Chapter 3.9). The real advantage of aldehyde fixation used in this way
is that one gains time. Mincing need not be done immediately under
adverse conditions in the operating room, but pieces of tissue can be
returned to the laboratory for careful dissection and processing. It can
be expected that tissue preserved in this way will be almost indistinguishable from tissue fixed directly in osmium tetroxide; indeed in some respects it can be regarded as better (Chapter 3.11).
The method should help, too, in dealing with tissues that are particularly soft for then they can be hardened with the aldehyde fixation
before attempting to make the thin slabs necessary for adequate penetra-
SPECIAL PROBLEMS WITH HUMAN TISSUES
29
be used cautiously in new investigations. It is advised only when a serious
connective tissue barrier must be eliminated.
2.8. Special Problems with Human Tissues
The previous sections of this chapter have emphasized ways of bringing tissue in contact with fixative in the most expeditious manner. Obviously most of these procedures are not generally applicable when
human material is to be obtained. Anyone acquainted with the literature
of tissue studies by electron microscopy will realize that published micrographs of human material rarely equal in quality the best that can be
obtained from animals. The difficulties in getting well-preserved human
material very seriously retard the development of pathological knowledge at electron microscopic levels.
The realization that aldehydes can be used as killing agents and primary fixatives (Chapter 3.9) should prove a great boon to those who
would work with surgical material. Their great penetrating power, particularly of suitably buffered formaldehyde, can be relied upon to preserve adequately slices of fresh tissue cut free-handedly as thinly as possible. Or larger masses of tissue can be put in a bath of buffered aldehyde
fixative, and subsequently thin layers of their surfaces can be removed
carefully and used for electron microscopy. In either case, ordinarily the
tissue would be fixed secondarily with osmium tetroxide. It should be
noted that the osmium tetroxide will not penetrate into a slab of aldehyde-fixed tissue any better than into fresh tissue, so that the tissue slabs
or blocks must be very thin or small before secondary fixation is begun
(Chapter 3.9). The real advantage of aldehyde fixation used in this way
is that one gains time. Mincing need not be done immediately under
adverse conditions in the operating room, but pieces of tissue can be
returned to the laboratory for careful dissection and processing. It can
be expected that tissue preserved in this way will be almost indistinguishable from tissue fixed directly in osmium tetroxide; indeed in some respects it can be regarded as better (Chapter 3.11).
The method should help, too, in dealing with tissues that are particularly soft for then they can be hardened with the aldehyde fixation
before attempting to make the thin slabs necessary for adequate penetra-