EVOLUTION OF COLLOIDS 141 



matter without solvent. This di-phasic 

 separation is very interesting because it 

 illustrates so many of the origins of the 

 structures shown by the microscope in cells, 

 and in colloidal solutions and suspensions 

 in general. If the greater part consists of 

 the fluid phase when separation occurs, then 

 the particulate part may either gather into 

 little spherules so widely apart that they 

 do not touch, then an emulsion is the result ; 

 or there may be just such proportions, that 

 the concentrated phase forms a meshwork 

 between small spheres of the dilute phase. 

 In this way a foam or a reticulum may be 

 formed, and the meshwork according to 

 circumstances of physical and chemical en- 

 vironment may take many forms. Again, the 

 more concentrated phase may predominate, 

 surrounded by a lacunar setting of fluid, 

 when a granular network results, coarsely or 

 finely granular, according to the degree of 

 size of the aggregate of semi-solid material. 

 These varieties may all be recognized 

 by the histologist, when examining the 

 microscopical appearances of cells. From 

 such causes, differences in staining with 

 histological reagents and in the appearances 

 with polarized or reflected light arise, and 

 these are indispensable aids in differentiating 



