Concerning the nature of the cryosectioning process

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Abstract
SUMMARY: Intentional melting of frozen‐thin‐sections induces ultrastructural alterations. Cross sections through frozen dried and embedded cryosections revealed that even at the surface of such a section no melting artefacts are visible. One surface of the cryosection (obtained at 168 K) has a saw‐teeth appearance whereas the other surface is rather smooth. The rate of freeze‐drying in the cryochamber of the microtome was estimated to be in order 3·3 nm/min at 183 K and 22·5 nm/min at 193 K for sections, about 120 nm thick, of rat kidney frozen in Freon 22 without any chemical fixation or cryoprotection. Although freeze‐drying will normally not interfere with the cryo‐sectioning process itself, it is a process which cannot be neglected during handling of sections. The available evidence indicated that frozen‐thin‐sections represent the frozen tissue with respect to the ultrastructure and probably also with respect to the chemical composition.