In electron micrographs of the molecular layer of the mouse cerebellum frozen within 30 sec of circulatory arrest and subsequently dried at -79 °C an appreciable extracellular space was found between the axons of the granular cells. Tight junctions were regularly observed between pre- and postsynaptic structures and the enveloping glia cells. In micrographs of cerebellum frozen 8 min after decapitation the space between the axons was absent and tight junctions between the nerve fibres were almost exclusively encountered. The extracellular space of asphyxiated and non-asphyxiated tissue in electron micrographs of frozen-dried material is similar to the space in comparable tissues treated by freeze-substitution. These observations suggest that there is an appreciable amount of extracellular material in oxygenated, living tissue which is taken up by cellular elements during asphyxiation
