An ultrastructural study of initial changes in epithelium damaged by surface freezing.

The changes seen in frozen thawed epithelium have been compared with pathological changes occurring under other circumstances. The intact cell membranes, invaginated cells, and varying densities of cell cytoplasm are all compatible with osmotic changes occurring after alteration in cell membrane permeability as is the development of bullae under these conditions. It is suggested, therefore, that this constitutes the major mechanism of cryosurgical attack at these temperatures. The finding that ultrastructural damage was evident very shortly after thawing, implicates changes directly due to freezing and thawing but does not necessarily rule out later additional cell damage occurring in an ischaemic situation.