12 COLLOIDS IN BIOLOGY AND MEDICINE 



about by the fact that different conditions exist in the interior than 

 exist on the surface of the fluid or solid body. In two-phase 

 systems, such as colloids, in which the interfaces reach enormous 

 dimensions, surface and capillary phenomena become most promi- 

 nent; in fact, they are in many ways the most characteristic phe- 

 nomena of colloids. Two fluids which do not mix are described as 

 two fluid "phases"; it is possible also to speak of a fluid, of a solid 

 and of a gaseous phase. In order to give expression to the great 

 surface development in a sol or gel, WOLFGANG OSTWALD introduced 

 the very happy expression dispersed phase. In a silver sol, silver 

 is the solid dispersed phase; in an oil emulsion, oil is the fluid dis- 

 persed phase; in both, water is the dispersing medium. Colloidal 

 solutions and gels are all dispersed systems. 



[Of interest in this connection is the work of G. H. A. Clowes and 

 Martin H. Fischer. Tr.] 



