Ultracryotomy: a technique for cutting ultrathin sections of unfixed frozen biological tissues for electron microscopy

An apparatus is described which facilitates the sectioning of unfixed and unembedded biological tissues for electron microscopy. The specimen is maintained at the temperature of boiling liquid nitrogen; the knife temperature may be controlled between -50 and -150 degrees C. Under the worst operating conditions specimen drift with respect to the knife is about 5 nm/sec, and suggestions are made on how this drift may be further reduced. We propose to call the apparatus an 'ultracryotome'. Electron micrographs of a variety of unfixed, unembedded and unstained tissues are shown and commented on. Some developments of experimental electron microscopy which may be expected to develop from use of the ultracryotome are listed.