Freeze-drying of tissues for light and electron microscopy

Abstract

An equipment and technique for fixation of tissues by freeze-drying is described. Satisfactory preservation of the structures is obtained both for light microscopy and electron microscopy. In many of the specimens, however, damage to the ultrastructure resolvable by the electron microscope is impossible to avoid. An analysis has been made of the cause of these artifacts and, probably, the critical stage in the treatment is the impregnation of the dry specimens with the fluid plastic. The frequency of occurrence of the damage may be decreased by treating the dry specimens with osmium-tetroxide vapor. It is also important to maintain the specimens below − 70°C until they are dry to avoid ice crystal formation. The artifacts are characteristic and easy to recognize and thus the method gives reliable results. Exocrine pancreas was used as test specimen when checking the preservation of the ultrastructure. The observations upon conventionally osmium-fixed material could be confirmed to a great extent. However, there is one important exception from this. There are no 150 A particles (RNA particles) in the cytoplasm in the frozen-dried cells.