4 L. F. Belanger, T. Semba, S. Tolnai, D. H. Copp, L. Krook, C. Gries 



of the disodium salt of ethylene-diamine tetra-acetic acid (EDTA) at pH 7.4. Sec- 

 tions of ca. 800 A were cut in epoxy resin and submitted to electron microscopy. 



The low power pictures obtained so far have revealed that the ovoid cells (osteo- 

 blasts) located at the immediate outer border of the peripheral trabeculae contained 

 mitochondriae and an extensive endoplasmic reticulum network, as already described 

 elsewhere in mammalian tissue (Dudley and Spiro, 1961; Cameron et al., 1963). 



Young osteocytes located immediately inside the bone matrix (Fig. 1) revealed 

 similar features of the cytoplasma. These cells generally filled the lacunae in which 

 they were contained. Osteocytes located further away from the border, inside larger 

 lacunae (Fig. 2) showed apart from the above features, some osmiophilic vesicles of 

 different sizes, which might well be lysosomes. This observation is of interest in view 

 of the previous histochemical demonstration of protease activity over the more 

 mature osteocytes (Belanger and Migicovsky, 1963 a). 



3. The effects of acute parathyroid stimulation 



Parathyroid stimulation by perfusion of dogs and sheep with EDTA, over periods 

 of a few hours only, such as performed by D. H. Copp at the University of British 

 Columbia (Copp, 1963) has produced effects in cancellous bone particularly visible in 

 alpharadiographs (Belanger, in press). The number of enlarged osteocytes was 

 increased in the parietal bone after 4 hrs. Moreover, the surrounding matrix displayed 

 already at this early stage, a remarkable loss of density. 



4. The effects of prolonged parathyroid stimulation 



We were highly privileged during the years 1964 — 65 to be associated with Drs. 

 Lennart Krook and Christian Cries from the Veterinary College of Cornell 

 University in studies involving horses which were fed a diet containing an optimum 



Hi ••P ^i^- ^ • '^ ; ' h -^ ' ..^ 



"■■■ ■ *J^;j-V.W -•: ,; ■ 



Figs. 3, 4, 5, 6 represent alpharadiographs (X75) of lamina dura dentis from horses on high P diet: Fig. 3, 4 weeks, 



Fig. 4, 7 weeks; Fig. 5, 12 weeks; Fig. 6, 30 weeks. Osteolysis at first intense (Fig. 3); newly-formed tissue 



decreasing (Fig. 4, larger canals); compact bone replaced by spongy bone (Fig. 5); becoming more and more 



immature and abnormal (Fig. 6) 



