LAMELLAR SYSTEMS 115 



microscope examination of osmium-fixed specimens (Feinandez- 

 Moian and Brown, 1958; Porter, 1957). Although this type of prep- 

 aration has ah'eady yielded much valuable information, it is com- 

 monly acknowledged that we are merely disclosing the refractory 

 macromolecular framework of a far more intricate dynamic system. 

 Thus, the concentric array of dense bands and light interspaces 

 revealed by electron microscopy in the nerve myelin sheath repre- 

 sents merely the "osmium-stabilized skeleton" (Fernandez-Moran, 

 1957), or the pattern of selective deposition of osmium at certain 

 sites, without permitting identification of specific regions containing 

 lipids, lipoproteins, or protein constituents (Fernandez-Moran and 

 Finean, 1957). Within this altered matrix, deprived of the funda- 

 mental water component, there is scant possibility of localizing or 

 even detecting the numerous enzymes, electrolytes, trace metals, 

 and other important constituents associated with the myelin sheath 

 (Fernandez-Moran, 1959b; Lumsden, 1957). 



The shortcomings of our present preparation techniques are more 

 acutely felt now that modern electron microscopes consistently 

 achieve resolutions of the order of 7 to 10 A, and are thus inherently 

 capable of directly visualizing molecular structures in the size range 

 of certain enzymes and hydrated lipid-protein complexes, particu- 

 larly when these are incorporated in the periodic multilayer arrange- 

 ment characteristic of lamellar systems. The development of ade- 

 quate preparation methods is therefore a major problem which must 

 be solved before high-resolution electron microscopy can be more 

 effectively applied in the study of biological systems during growth 

 and function. 



Low-temperature preparation techniques provide one of the most 

 promising approaches, since rapid freezing of biological specimens 

 suspends all physiological activity, immobilizing and preserving 

 tissue constituents (Harris, 1954). That coohng to temperatures 

 close to absolute zero does not appreciably impair critical life 

 processes has now been amply demonstrated by the survival of a 

 wide variety of living organisms, including bacteria, spermatozoa, 

 and many other sensitive cells and tissues, which are first treated 

 protectively with glycerol, then frozen with liquid nitrogen or liquid 

 helium, and subsequently thawed in a controlled manner (Harris, 

 1954;' Lovelock, 1953; Parkes, 1951 ) . By ultrarapid cooling to low 

 enough temperatures, it may be feasible to preserve the original 

 position and relationship of the main organic and inorganic con- 



