I CYTOPLASM 177 



as are found in fibrous proteins, which may give rise to a meshwork 

 or a plaitwork (Fig. 51b, p. 66). 



The first type of framework must produce gels with a higher 

 percentage dry weight than the second, which we can picture as being 

 made up of submicroscopic or amicroscopic strands. If the cytoplasm 

 appears homogeneous in the electron microscope, the structural ele- 

 ments (globules or threads) must be amicroscopic, i.e. they must have 

 micromolecular diameters (< 50 A). It is difficult to decide which 

 type is really present, because the structure easily changes in character 

 owing to the denaturation of proteins in the fixation and drying 

 processes. The inner structure of the globules and microfibrils is 

 governed by the junction principles discussed on p. 145. If these sub- 

 microscopic elements aggregate to form a gel, another type of junction 

 is involved, caused by long-range forces (p. 158). The nature of these 

 forces is not well known but in forming gels they act morphologically 

 disjunctions in the submicroscopic domain in very much the same way 

 as the chemical forces do in the amicroscopic range. According to 

 OsTER (195 1) there is no real difference between short-range forces 

 and long-range forces. 



Assuming that there is such a gel, all the cytoplasmic properties, 

 strange as they may be, can be accounted for. 



The high water content of the cytoplasm (70 to 80% or more) is 

 caused by the considerable width of the meshes of the framework. 

 In addition, there is hydration water inside the submicroscopic strands 

 and beaded chains. The water content is liable to be so great that 

 many of the water dipoles are not fixed by the framework and have 

 freedom of movement. In this case excretion of water from the cj^to- 

 plasts and hence vacuolization becomes possible. As a rule, however, 

 all the water is loosely bound by main chains or side chains and takes 

 part in establishing the maximum state of swelling. 



The transition of protoplasm to a resting state is accompanied by 

 a gradual diminution in the amount of water brought about by a 

 narrowing of the submicroscopic interfibrillar and intramolecular 

 interstitial meshes. The water is perhaps partly replaced by lipids, as 

 hydrophilic groups are screened off by phosphatides, sterines and the 

 like. The determinant structure and the organization of the framework 

 which governs the processes of life can thus sometimes be preserved 

 for years (spores, seeds). Evidently this natural deh3"dration cannot 



