COMPLEX COACERVATES AND PROTOPLASM 315 



rather high degree of structural viscosity or, when the solu- 

 tion is highly saturated, even elasticity and mechanical 

 resistance to deformation ; in the presence of such rigid 

 layers the stability of disperse systems may be extremely 

 great. 



It is very significant that proteins themselves should 

 be among those substances which give rise to differentiated 

 surface layers. The transformation of protein molecules in 

 the surface layers into a laminar state with an increase in 

 their mechanical rigidity is well known ; it has been studied 

 in detail, particularly by A. Trapeznikov. However, although 

 in coacervates of simple liquids the elastic surface layers 

 can only arise by the admixture of a third substance, in 

 coacervates of proteins they can arise directly from parts of 

 the protein molecules themselves or other substances associ- 

 ated with them such as lipids, polysaccharides, etc., which 

 migrate to the boundary layer and form molecular layers at the 

 interface, or perhaps only a single layer with changed struc- 

 tural and mechanical properties. This seems to be just the 

 sort of phenomenon which lies at the basis of the formation 

 by protein coacervates and protoplasm (after disintegration 

 of the cell with water) of sharply defined surface films with 

 fairly rigid mechanical properties. This has nothing to do 

 with surface tension or with the fact that the protoplasm 

 forms a separate phase, but is due to the transformation 

 of the protein molecules and their associated groups in the 

 surface layer into a different structural state. 



At the interfaces between the drops of a complex coacervate 

 and its equilibrium liquid, or between a vacuole and the 

 coacervate in which it lies or, finally, between the drops of 

 one coacervate and another in which it is included, one 

 may certainly demonstrate the presence of colloidal films 

 made up of oriented colloidal particles of whichever com- 

 ponent is present to excess in the coacervate-equilibrium 

 liquid system. Such films are formed especially readily in 

 protein-lipid coacervates. In particular, Bungenberg de 

 Jong" and his colleagues have recently studied coacervates 

 of gelatin and potassium oleate and concluded that they 

 contain micellar films in the form of a sandwich, molecules 



