The Osteon Calcification as Revealed by the Electron Microscope 



143 



a way as to obtain respectively ultrathin sections, (a) tangentially orientated as 

 regards the lamellae, (b) running radially and (c) cross-orientated in respect to the 

 osteon. 



Fig. 1. Two dissected specimens showing 



top a longuudinal por 

 scope. X 75 



The osteons were sectioned with a Porter-Blum microtome fitted with a diamond 

 knife. A Siemens Elmiskop I electron microscope was used to examine the sections. 



For particular purposes the specimens were decalcified by EDTA before em- 

 bedding. Decalcification was also carried out on ultra-thin sections, using phospho- 

 tungstic acid, which also gives good staining of the collagen fibrils. 



Results 



In osteons at the initial stage of calcification, the calcium salts show two different 

 features at the level of the lamellae (Fig. 2). The first is a series of parallel bands 

 which are separated by clear interbands and run almost perpendicular to the osteon 

 axis. The bands have an average width of 400 A and the interbands reach 250 A. 

 These values indicate that the parallel banding identifies the broad bands at the 

 major collagen periods. Fiere small spots appear measuring no more than 10 A across. 

 These spots which apparently represent foci of crystal inception or centers of 

 nucleation (see Glimcher, 1959) fuse in linear or needleshaped crystallites which 

 span the band regions, reaching a maximum width of 40 — 45 A. 



The second feature met in the lamellae of the osteons during the initial stage of 

 calcification are bundles of needle-shaped crystallites considerably longer than those 

 at the level of the broad band. Generally they have a longitudinal orientation as 

 regards the osteon axis. Owing to their length the crystallites can cover two or many 

 major collagen periods. The thickness averages 40 — 45 A. 



