Effect of fixation on cell membrane of early embryonic material as observed on freeze-fracture replicas.

Some cell membranes of chemically fixed, cryoprotected and freeze-fractured chick embryonic material are characterized by 150-250 nm diameter circular smooth blebs. No such blebs are observed, however, on cryoprotected, rapidly frozen but not chemically fixed samples. It is concluded, therefore, that fixation with buffered glutaraldehyde and not cryoprotection with glycerol is mainly responsible for the appearance of the blebs. The suggestion that blebs represent a budding virus is not tenable, since blebs are present in material obtained from virus free embryos.