8i FUNDAMENTALS OF SUBMICROSCOPI C MORPHOLOGY E 



§ 4. Studies in Gels 



The colloid chemical methods of investigation which have proved so- 

 successful in the elucidation of the nature of sols have only a limited 

 applicability to gels (compare the discussion of Table X, p. 75). Gels 

 must therefore be investigated by different means. Of these we shall 

 only discuss those which are of special importance to the investigation 

 of cytological objects, leaving others, such as are of interest, e.g., in 

 the technical testing of gels, out of account. For lack of space the 

 methods of investigation will not be treated in great detail ; we shall 

 only deal with the principles of these methods and the problems which 

 they can solve. 



a. Polarisation Microscopy 



Theory of composite bodies. The texture of gels can be explored by 

 optical means if two conditions are fulfilled. In the first place the 



"//="/ 



i"//="< 



ni-n,f_ 



nj, = n^ 



Fig. 60. a) Rodlet composite body, ny big, 



Ha small refractive index, b) Layer or platelet 



composite body, Oy big, Hq small refractive 



index. 



strands of the framework must be separated from the intermicellar 

 space by definite phase boundaries, and secondly they may not be 

 oriented at random but must show a certain tendency to orientation 

 in a given direction in space, Wiener (191 2) has calculated theoretic- 



