In vitro bone-marrow derived colonies cultured in agar and prepared in
Epon 812 for electron microscopy occassionally produce blocks that are too
soft for sectioning. We attribute this softness to the retention, after
standard dehydration, of water by the agar and to the relatively slow
penetration of the agar by Epon-based embedding media. The agar cannot be
removed or replaced since this would disrupt the colony integrity and
prevent the study of cell-cell relationships. This paper describes the
procedures and results of more extensive specimen dehydration and of
embedding with Epon-replacement formulations.
