l8 THE CELL AS A PHYSICO-CHEMICAL UNIT 



lar molecules, such as proteins, within living cells will 

 markedly raise the dielectric constant of the interior of 

 a cell, by comparison with the dielectric constant of the 

 external media. This increase in dielectric constant (as 

 measured by relatively low frequency alternating cur- 

 rent) is thought likely, by some workers, to have im- 

 portant consequences for the cell. But very little as yet 

 is known about these factors. 



Membrane Properties. Extremely little is known of the 

 physico-chemical properties of the nuclear membrane, 

 but much is known about the properties of the plasma 

 membrane of the cell. The most striking properties for 

 our present purposes are i. its selective permeability, 

 2. its polarised condition, 3. its asymmetry and 4. the 

 "active patches" present within it. 



In a later chapter the permeability of the cell mem- 

 brane will be dealt with in more detail. It is sufficient 

 for the moment to know that whereas diffusion is rapid 

 through the cytoplasm and through the nuclear sap, 

 permeation of the cell membrane can be a very slow 

 process, and it is possible that this is also true of the 

 nuclear membrane. 



The polarised condition of certain cells, such as those 

 of nerve and muscle, is at present difficult to understand 

 in relation to the energy supplying systems which main- 

 tain this state of polarisation. But the development of 

 further understanding of this is of vital importance for 



