Preparation of cryosections with a modified Sorvall MT2B ultramicrotome and cryoattachment.

The Sorvall MT2B ultramicrotome and cryoattachment were modified to extent the duration of cutting and to overcome problems in tissue preparation. Microtome and cryochamber were encased and surrounded by an atmosphere of dry nitrogen gas at room temperature. A specially designed cold block sited within the box close to the microtome enabled tissues to be trimmed at low temperatures in the dry environment. Tissues could be readily visualized both on the trimming block and in the chamber with the existing microscope modified to improve its working distance and lighting system. During transfer from storage in liquid nitrogen, through the trimming procedure, to arrival in the cryochamber, the temperature of tissues as determined using thermocouples embedded in PVP on a stub, never exceeded 140 K. Although there was a considerable standing temperature gradient within the cryochamber, the cutting environment, specimen and edge of the knife were thermally stable. Sections could be routinely cut dry and freeze-dried within the chamber, if desired.