102 



FINE-STRUCTURE OF PROTOPLASM 



ir 



wall (Fig. 112a). For this reason, when measuring the time of fall of 

 crystals traversing the cell sap, one must always observe the time 

 needed to detach the particle from the phase boundary (Weber, 1921). 

 In certain cases the cell sap solidifies on fixation, as shown in Fig. 

 112 b in the pathological giant cells of the fungus Aspergillus niger 

 (Frey, 1927a). Here the difference between the colloid systems of the 

 cell sap and the protoplasm is evident. In the cytoplasm the framework 



Fig. 112. Vacuoles, a) Sedimentation of gypsum crystals in terminal vacuoles of Closterium 



(from Frey 1926c); b) pathologic giant cells of Aspergillus niger fixed with Flemming. 



Cytoplasm 2 and nucleus k have not changed much; in the cell sap, however, a voluminous 



precipitate is formed (from Frey, 1927a). 



structure prevents a separation of the different components, whereas 

 in the cell sap precipitation occurs. The coagulated vacuole of Fig. 

 112b betrays a coarse structure of fibrous, entangled bodies. From 

 this we may conclude that the colloids in the cell sap do not possess 

 a structure comparable with the cytoplasm, but represent sols with 

 movable particles without definite mutual positions. Here coagulation 

 actually results in an orderless "pile", indicating an unordered state 

 before the precipitation. The end groups of the organic compounds 

 which are the constituents of vacuolar colloids are not screened off as 

 in the cytoplasm and are consequently reactive. This is made use of 

 in the vital staining of the vacuoles. Their colloids, which evidently 

 carry acid groups, are usually readily coloured by basic dyes. In the 

 cytoplasm, the cell nucleus (Becker, 1956) and the living, still growing 



