[Preservation of cutaneous structures of egyptian mummies. An ultrastructural study]

The recent development of studies applied to ancient materials may be explained by the application of molecular biology techniques on the extracted ancient DNA mainly the polymerase chain reaction (PCR), the ultrasensitive DNA-amplification technique that hit the headlines in the late 1980s. PCR was used to amplify human immunodeficiency virus (HIV), genetic material in stored tissue specimens and to document people who died in 1976. In addition, recent discoveries of mummified bodies in ice of the Tyrolean Alps or Greenland allowed a new approach in archeological studies. Mummies are a good material for investigations of ancient tissues. The studies concern the techniques of embalming, tissue preservation and palepathological aspects. In cutaneous paleopathology, mummies from Egypt, South or North America and Europe were considered. Various skin lesions were characterized: histiocytoma, Chagas' disease, smallpox, syphilis. Recently drugs (cocaine, hashish and nicotine) were extracted from skin and head hair of Egyptian mummies. Only a few studies were concerned with the ultrastructure of the skin of such mummies.

We had the opportunity to obtain skin samples of two Egyptian mummies. One of them was embalmed between 150 BC-90 AC. The skin was studied by transmission electron microscopy. As the mummified materials had dried out and shrunk, it was necessary to rehydrate them for ultrastructural observation. Skin samples were fragmented into small pieces before fixation with 2 p. 100 glutaraldehyde in sodium cacodylate buffer for 10 days (allowing for removal of the materials used for embalming). The samples were then washed in the same buffer for 10 days. After washing the pieces were post-fixed with 1 p. 100 osmium tetroxyde, dehydrated and embedded in Epoxy medium.

With this process, it was possible to observe the excellent preservation of the cutaneous structures. The epidermis was well preserved. It was possible to observe the different cell layers and mainly the upper layers. The nuclei and the desmosomes of keratinocytes were recognized. Intercellular spaces were narrow. Desmosomes showed dense thickenings of the cell membrane on both sides and an intercellular band with narrow lucent spaces adjacent to the dense cell membrane. The nuclei showed dense spots of chromatin and in the cytoplasm recognizable tonofilament bundles were identified. Langerhans cells and melanocytes were not observed. In the dermis, the collagen fibrils formed thick bundles and showed the characteristic axial periodicity. Elastic fibers were also recognized showing two main components: the amorphous substance and the fibrils. Throughout the dermis, a number of round or oval structures were found. They had the typical appearance of spores of bacteria. In the centre, they had an electron dense and granular core surrounded by an inner membrane and a spore coat.

Only a few investigations were performed on the ultrastructure of the skin of the Egyptian mummies. In the majority of cases, the epidermis was not preserved. The present work demonstrates the good preservation of epidermal structures and specially desmosomes and intercellular connections. The presence of spores of bacteria was previously reported. These spores enter a highly resistant resting phase in order to survive in a dormant state for a long period of starvation or other adverse environmental conditions. Similar investigations were performed on skin obtained from Eskimo mummies preserved by the extremely cold and dry polar weather. In these conditions, the authors reported the observation of melanocytes, vessels and nerves. Additionally, biochemical investigations demonstrated the very good preservation of collagen and glycosaminoglycans of the dermal extracellular matrix.