30 INTRODUCTION TO CYTOLOGY 



These films not only prevent the coalescence of the droplets, but also, 

 through alterations in surface tension, influence the transposition or 

 inversion of phases which occurs under certain conditions, whereby the 

 suspended phase becomes the medium of dispersion and vice versa (Fig. 

 8). Such inversion probably plays an important role in many cases of 

 transformation of sol into gel and of gel into sol. 



FIG. 8. Diagram of a colloidal emulsion, illustrating transformation of emulsion of oil 



in water to emulsion of water in oil. 



A, aqueous phase. B, oil or other non-aqueous phase. C, surface film of soap or other 

 dispersing agent. (After Clowes, 1916.) 



The properties and behavior of colloidal substances in general appear 

 to be due primarily to the enormous extent of the reacting surface be- 

 tween the constituent phases which results from the finely divided state 

 of one or more of them. In the accompanying table is shown the amount 

 of surface which a given mass of matter may expose when subdivided 

 into successively smaller particles. 



TABLE SHOWING THE INCREASE OF SURFACE WITH THE SUBDIVISION OF 1 c.c. OF 

 MATTER IN THE FORM OF A CUBE (DATA PARTLY FROM HATSCHEK, 1919.) 



Length of edge of cube 



Number of cubes 



Total surface exposed 



The evidence at hand supports the view that protoplasm is essentially 

 a colloidal solution of the emulsion type. It consists of at least three 

 principal phases: a water phase, containing a number of dissolved compo- 



