48 



Cellular Structure and Activity 



thousand Angstrom units. The fibrils, in chain. Figure 1, taken from Bear ('52), illus- 

 turn, are composed of still finer arrays which trates this fibrous hierarchy. Long axial re- 

 may be called filaments and which may be peat periods demonstrated by small-angle 

 of the order of 100 A in width, or smaller. x-ray studies have been observed in the EM 

 The ultimate fibrous array is the polypeptide in the form of cross-striations consisting of 



Microscopic Level 



ground substance 



fibroblost 



collagen primitive fiber 



T.0 



elastic fiber 



Ul f romicroscopic Level 



I 



ectron Optical Level 



b^, axial period 



2000 A 



filament 



X-Ray Diffraction Level 



I 



protofibril 



Fig. 1. 



