130 ir.NDAMEKTALS OF SUBMI C RO SCOPI C MORPHOLOGY 1 



of tunicin are left. The chitin of fungi cell walls has been prepared in a 

 similar way. Only after repeated boiling of the objects in io% KOH 

 is the texture of the gel disclosed as in Fig. 86c, where two different 

 textures (parallel texture and dispersed texture, see p. 95) are portrayed 

 side by side. If such methods are not used, many of the biological gels 

 furnish the picture of a homogeneous film, because the incrusting 

 substances have the same electron-optical behaviour as those of the 

 gel framework. Clear-cut micrographs of gels can only be obtained if 

 all incrusting substances are carefully removed. This is a handicap in 

 the electron microscopy of protoplasm, as its frame substances are 

 far less resistent to chemical agents used in purifying the framework 

 of gels than are cellulose and chitin. 



e. Summary 



Gels with reticular structure are characterized by the existence of a 

 framework whose constituent parts occupy definite mutual positions. 

 The frame strands have either submicroscopic or amicroscopic dia- 

 meters. In the first case they can be detected by electron microscopy 

 and the submicroscopic morphology of such gels is thus accessible ta 

 detailed direct investigation (Fig. 86). 



In the second case the framework is formed by chain molecules 

 which cannot be solvated completely and maintain c^txAn junctions. 

 If these junctions are released, the network character is lost. In this 

 case the reticular gel, which originally showed only limited swelling, 

 can change into the sol state via the gel solution. As will be obvious 

 from this definition, there exists a transitional state between the 

 reticular and the corpuscular dispersed state. It will require further 

 studies to elucidate the morphological properties of such gel frames 

 and the nature of the bonds in the junctions, which may be quite 

 different in character (see p. 145). 



