LAMELLAR SYSTEMS 



125 



Fig. 5. Specimen chamber for cryofixation preparations, consisting of Teflon 

 gasket bounded by thin Plexiglas sheets sealed between aluminum plates. 

 Polymerized specimens are easily removed and mounted for ultrathin sectioning 

 (arrow). 



final low-temperature photopolvmerization with ultraviolet light, 

 using benzoin in 0.3 per cent concentration as a catalyst. 



The control preparations included standard osmium-fixed and 

 araldite-embedded nerve fibers and retinas, as well as specimens 

 fixed in situ with osmium, iodine, or bromine vapors and embedded 

 at low temperatures. Serial ultrathin sections of 100 to 300 A were 

 prepared with a Moran-Leitz ultramicrotome equipped with a dia- 

 mond knife (Fernandez-Moran, 1953). The sections of "unfixed" 

 retinas were collected on the cold liquid surfaces of certain fluorine 

 compounds (e.g., Freon 11) to avoid contact with water. These 

 sections were examined with an electron microbeam of very low in- 

 tensity, using the double condenser of the Siemens Elmiskop I 

 operating at 40 to 80 kv. A Siemens-Liesegang liquid nitrogen cool- 

 ing device with modified shielding apertures was used in conjunc- 

 tion with multiple-objective apertures for low-temperature electron 

 microscopy (Fernandez-Moran, 1959c). 



