Osmium postfixation is established as a routine procedure for
transmission electron microscopy (TEM). On the one hand, this routine
procedure leads to good results for TEM, but on the other hand results
in blackened tissue samples that do not allow examination of any
structures within the embedded tissue sample by a light microscope.
Equivalent fixation results for TEM are achieved with
imidazole–osmium postfixation, and with this postfixation method
tissue is not blackened and can be transilluminated with point light
sources. This allows easier recognition of histological details within
tissue samples and makes it possible to screen embedded samples for
appropriate ultrastructural processing. Jejunum is used to demonstrate
the method.