RESORPTION WITHOUT OSTEOCLASTS (OSTEOLYSIS) 553 



(Frost, 1960) indicates that osteolysis is the result of a vital func- 

 tion of the mature, hypertrophic osteocyte. 



The Mechanism of Osteohjsis 



The facts reported here most hkely reveal only a small part of the 

 mechanism of osteolysis. It appears that this property of bone, not 

 clearly defined as yet, occurs through changes which take place 

 primarihj in the organic matrix. These changes lead to a loss of den- 

 sity, partly explained by the secretion of acid mucopolysaccharides. 

 The loss of salt follows the modification of the organic substrate. 



Although it was not within the realm of the present enterprise 

 to demonstrate this fact, it is highly probable that collagen as well 

 as the mucopolysaccharides is involved in osteolysis, through a proc- 

 ess of enzymic degradation generated by the hypertrophic osteo- 

 cytes. Rutishauser and Majno (1951) have already reported that 

 alkaline phosphatase activity which was present in osteoblasts, and 

 which had temporarily disappeared in the small osteocytes, reap- 

 pears in the large osteocytes. More recently, Lipp (1959) has ob- 

 served the occurrence of leucine aminopeptidase in "osteoclasts, 

 osteoblasts and osteocytes . . . only those which reveal resorption 

 within their lacunae." Finally, the removal of hydroxyproline from 

 bones after peritoneal lavage has just been reported by Talmage 

 ( 1962 ) . This author states that hydroxyproline removal follows a 

 pattern quite similar to that of the mineral components previously 

 studied. 



Summary 



In the older regions of cancellous and compact bone from chick, 

 rat, dog, and man, large osteocytes which secrete acid mucopoly- 

 saccharides were observed. 



Their cytoplasm, the capsule of their lacuna, and the adjacent 

 matrix were positive to different histochemical stains for acid muco- 

 polysaccharides. 



These cells were located in areas which showed low density in 

 x-ray microradiographs of mineralized sections and in alpharadio- 



