LAMELLAR SYSTEMS 153 



Our criteria for preservation of biological systems must therefore 

 be considerably extended to take into account the new range of 

 phenomena being revealed by refined physicochemical techniques. 

 From a hypothetical point of view, the "ideal" preparation tech- 

 nique for electron microscopy of biological systems would first have 

 to achieve complete immobilization of all tissue constituents in their 

 natural position by rapid freezing to temperatures close to absolute 

 zero, so that even free radicals and other transient intermediates 

 are trapped in an inert matrix and stored under conditions restrict- 

 ing diffusion and radical recombination. Once the submicroscopic 

 organization of the tissue has been "frozen in" to this characteristic 

 "solid state," a critical transformation must then be effected at the 

 molecular level in order to change the metastable equilibrium, 

 which was essentially determined by the water matrix, into a new, 

 more stable phase. This induced phase transfoiTnation, which can 

 be likened to a process of precisely controlled, heterogeneous nucle- 

 ation, would ensure adequate preservation of the tissue ultrastruc- 

 ture over a wide enough range of temperature and other physical 

 conditions to permit adequate manipulation during subsequent ul- 

 trathin sectioning and electron microscope examination. Such a 

 highly idealized form of preservation does not appear to be un- 

 attainable in principle, and eventually it may be possible to make 

 use of recent advances in polymer chemistry involving addition 

 polymerization reactions with certain ionic catalysts for this type 

 of controlled synthesis of ordered polymers fitted specifically within 

 the tissue matrix at low temperature. In order to obtain the re- 

 quired fundamental data on the hydration state and properties of 

 water in lamellar systems, combined application of nuclear mag- 

 netic-resonance spectrometry ( Denis et al., 1957; Fernandez-Moran, 

 1957), low-temperature electron microscopy (Fernandez-Moran, 

 1959d), and neutron diffraction analysis may prove to be essential. 

 Of immediate interest in connection with the potentialities of cryo- 

 fixation techniques (Fernandez-Moran, 1959a, 1959c, 1959d) would 

 be an attempt to arrest sequentially the different states of activity 

 in nerve and photoreceptors (Katz, 1959; Kropf and Hubbard, 

 1958). As already shown by the pioneering work of von Muralt 

 (1946, 1958), rapid freezing of excited nerve fixes the chemical 

 status 'and produces an accumulation of excitation waves. The re- 

 cent investigations by Hill and his associates (Abbott et al., 1958) 

 on heat production in nerve demonstrated a complex cycle of posi- 



