Histological investigations on the Tyrolean Ice Man.

The 5,200-year-old Tyrolean Ice Man discovered in 1991 in the Otztal Alps is the world's most ancient known human glacier mummy. Histological investigation was aimed at 1) optimizing specimen preparation and 2) documenting the preservation state of (sub)cellular components. Minute pieces of frozen tissue were removed endoscopically from rib bone and cartilage, major blood vessels, oral cavity and alimentary tract, liver, spleen, diaphragm, respiratory system, femoral muscle and nerve, sympathetic trunk, brain, and skin. Double fixation with glutaraldehyde followed by osmium tetroxide and embedding in Epon/Araldite epoxy resins proved to be the method of choice for both light and transmission electron microscopy combined with classical histochemistry. In particular, mild evacuation of the desiccated tissue was determined to be essential to ensure homogeneous infiltration with fixatives and resins; as a result, sections of excellent quality could be obtained with any kind of sample. With regard to the preservation degree of (sub)cellular components, distinct tissue-specific patterns were observed. There were highly intact skeletal and connective tissues proper, however, most interestingly, there were remarkably intact nervous tissue components as well. By contrast, epithelial, muscle, and reticular connective tissues as well as blood had generally disintegrated due to autolysis, freeze/thaw damage, and adipocere formation. For a tentative interpretation of these patterns, we considered general aspects of cryopreservation, such as physicochemical properties of subcellular constituents and tissue physiology.