Freeze fracture electron microscopy of a suspension of human sperm cryopreseved in a straw (0.25ml capacity). The cryoprotectant used was glycerol/egg yolk. Ice was nucleated within the straw at -7°C. The sample was then cooled at 10°C per minute to -100°C and then transferred to liquid nitrogen. A cross fracture of the straw followed by deep etching reveals the structure of ice (etched areas) and of the freeze concentrated material (non-etched material). Sperm cells have migrated into the freeze concentrated material during solidification: spermatozoa were not entrapped within ice crystals. However, some sperm tails are evident extending from the freeze concentrated material into the regions previously occupied by ice crystals. No other cellular structures are evident. Detail from a cross fracture of a whole straw
