LAMELLAR SYSTEMS 151 



"holes" on the other. According to the proposed scheme (Calvin, 

 1959a), "the exciton is converted into conductive carriers, these into 

 chemical radicals, and the chemical radicals lead to stable chem- 

 icals" (p. 161). Direct experimental evidence for the existence of 

 trapped electrons and holes has been provided bv recording elec- 

 tron-spin resonance signals from illuminated whole chloroplasts at 

 temperatures as low as —150° C (Calvin, 1959a, 1959b). 



Electron-spin resonance techniques are being extensivelv applied 

 to detect the presence of free radicals in enzymatic reactions, and of 

 other intermediates with unpaired electron-spin in biological sys- 

 tems. However, these techniques lack the necessary sensitivity for 

 adequate detection of the small, steady-state concentrations of free 

 radicals in many biological processes, and for a specific localization 

 within the complex lamellar systems. As pointed out earlier, the 

 possibility of trapping and detecting free radicals within highly 

 organized tissue components by rapid freezing with liquid helium II 

 represents one of the major justifications for the use of extremely 

 low temperatures in ultrastructure research. 



It has been suggested that lamellar systems might have many 

 properties in common with semiconductors (Fernandez-Moran, 

 1957; Szent-Gyorgyi, 1957), although the concepts of solid-state 

 physics are not directly applicable to the fluid-crystalline state 

 (Fernandez-Moran, 1954, 1959b). Recent physicochemical studies 

 of water and ice by Eigen and his associates indicate that "The 

 ('excess' and 'defect') proton-conducting H-bond systems (which 

 are also of biological interest) show certain parallels to electronic 

 semiconductors" (Eigen and DeMaever, 1959, p. 84). The semi- 

 conductor concept is now introduced from the unexpected quarter 

 of water, the very constituent which had previously restricted the 

 solid-state analogy. Attention is thus focused on a novel aspect of 

 this fundamental "matrix of life" as Szent-Gyorgyi ( 1957 ) has so 

 aptly designated water. 



The Role of Hydration Water In Lamellar Systems. Water is a 

 major component of all lamellar complexes, constituting, for example, 

 at least 35 per cent of the myelin sheath. The water layers at the 

 aqueous interfaces of the fundamental repeating unit in the compact 

 myelin are considered to be about 12 to 15 A thick (Schmitt, 1959). 

 It has 'been shown (Robertson, 1959; Schmitt, 1959) that, under 

 certain experimental conditions, much larger amounts of water can 

 be incorporated between these aqueous interfaces, leading to con- 



