64 



MACROMOLECULAR COMPLEXES 



and from the fact that a precise stereochemical configuration of a 

 number of amino acid side-chains was necessary to form a nucleus, 

 it was reasonable to expect that there should be a limited number 

 of such preferred centers and that they should occur periodicalh' 

 both laterally and longitudinally along the axial repeat structure of 



NATIVE TISSUES 



(DECALCIFIED BONE) 



calcification: 



CALCIFICATION 



LOSS OF LONG-RANGE 

 Fl BRI LLAR ORDER 



CALCIFICATION 



Fig. 7. Some of the experiments which demonstrated the specificity of the 

 macromoleculor aggregation state of collagen in in vitro calcification, diagram- 

 matically illustrated. (From Glimcher, 1958.) 



the collagen fibrils. Confirmation of the existence of such discrete 

 nucleation centers has come from a time-study of the nucleation 

 process, both by electron microscopy and by low-angle x-ray diffrac- 

 tion. Using the former technique, we haye been able to visualize 

 the initial stages of mineralization in vitro. These appear yery 

 similar to the initial stages of mineralization in embryonic bone 

 (Figs. 8, 9, 10), and emphasize the regularity of the initial crystal- 



