14 THE CELL AS A PHYSICO-CHEMICAL UNIT 



closer resemblance to gelatin gels in which the indivi- 

 dual molecules appear to be dispersed more or less at 



random. 



When the lipoid molecules of the cell are also con- 

 sidered, we have units of structure of a fresh type aris- 

 ing, based on the micelle and on bimolecular leaflets of 

 fatty molecules. These types of structure are also shown 

 in Fig. 2. The stability of these structures is based on 

 the fact that the hydrocarbon parts of the molecules 

 concerned are in effect squeezed out of solution because 

 water attracts water more strongly than it attracts hy- 

 drocarbon. The polar groups of the molecules become 

 anchored in the interfaces between the hydrocarbon 

 parts of the molecules and the water. Owing to the very 

 high surface activity of protein molecules, the surfaces 

 of lipoid micelles and bimolecular leaflets must, under 

 biological conditions, always have adsorbed upon them 

 a monolayer of denatured protein. Under most circum- 

 stances there will also be adsorbed upon this primary 

 layer of denatured protein a secondary layer of globular 

 protein molecules. Thus a very complex structure may 

 arise simply as a result of the operation of adsorption 

 forces. 



So far, the structure of the cytoplasmic granules found 

 in the cell has not been made sufficiently clear for de- 

 tailed discussion. Nor is it clear what part the diiferent 

 nucleic acids play in determining the structure of the 

 chromosomes and other bodies in which they are found. 



