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L. J. MULLINS 



Size of Site 

 Fig. 4. The three curves at the top show the number of molecules that fit an inter- 

 space within ±0.25 standard deviation (black bar) and the number of molecules that 

 are too small for fit (shading) for a small molecule (A), a medium sized molecule (B), 

 and a large molecule (C). Below, the total number of sites available to molecules of 

 various sizes is shown by curve N; if narcosis requires 4% of all sites to be occupied, 

 the line at 2 standard deviations represents the upper limit in size for narcotics. The 

 curve E represents the ratio of the number of sites that fit a molecule corresponding to 

 a particular site size, to the total number of sites that can be occupied. Curve E is a 

 measure of the excitatory potential of a molecule. 



by a local crystallization or phase transformation taking place in the membrane 

 as a result of the strong interaction between the CI atoms of the y isomer and 

 the surrounding membrane molecules (Mullins, 1955b). Such a local trans- 

 formation of a small part of the membrane cannot readily be compensated for 

 because rearrangement of nonaffected membrane molecules cannot restore the 

 original interspace distribution without creating further disturbances. The 

 change involved appears to be of a totally different order of magnitude from 

 that produced by filling interspaces with K+, and is in the nature of a marked 

 enlargement of the surrounding interspaces. It appears consistent for the change 

 to result in the leakage of (Na+) 2 of radius 6.4 A. The general instability at the 

 site of insertion of 7-BHC appears such that the membrane will be undergoing 

 random fluctuations in permeability to all ions, e.g. an electrical short circuit 

 will develop from time to time. From steric considerations it can be shown that 



