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



6. Conclusions 



At this point we would like to propose the following conclusions: 



(1) Normal adult bone is a constantly renewed tissue in which resorption is 

 equally matched by accretion. 



(2) Intimate resorption (osteolysis), taking place away from the bone surfaces 

 seems to occur. The mature osteocytes are probably responsible for this phenomenon. 

 One of the factors involved is the production by these cells, of a protease possibly 

 linked to lysosome activity. 



(3) The mature osteocytes seem to respond readily (within a few hours) to endo- 

 genous parathyroid stimulation. The role of these cells in the maintenance of calcium 

 homeostasis, is perhaps more important than previously realized. 



(4) Osteoclasia appears as a specialized response to the presence of abnormal 

 skeletal material, either of general or local origin. The osteoclasts which probably 

 originate from primitive cells, may be akin to the giant multinucleated cells of 

 connective tissue. Like those, their major role may be to take part in the maintenance 

 of the integrity of the body. 



Acknowledgements 



The authors are indebted to Mrs. L. F. Belanger for skilled technique; also to 

 the Medical Research Council of Canada, to the Canada Department of Agriculture 

 and to the U.S. Atomic Energy Commission (Contract No. AT(30-l)-2779) for 

 financial assistance. Para-Thormone was graciously supplied by Eli Lilly and Co. 

 (Canada) Ltd., Toronto. 



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