334 LESLIE B. AREY 



inference, there is the most carbon dioxide." From these and 

 other considerations Wells concludes: "It is indeed probable 

 that it is the C0 2 which accomplishes the resorption of dead bone 

 in the living body, and perhaps also the normal resorption of 

 bone in the various conditions in which this process takes place." 

 It is, perhaps, difficult to imagine the mechanism of the local- 

 ization of carbon dioxide ( or the stronger lactic acid?) in sufficient 

 concentrations to effect the selective erosion of small areas, or to 

 account for the frequent directional polarization of the resorptive 

 wave. However this may be, there is, of course, no basis for 

 suspecting the osteoclast of special carbon dioxide production. 

 On the contrary, if it is indeed a degenerating cell, its carbon di- 

 oxide output is presumably low. The conception of Wells adds 

 to the objections already enumerated against the osteoclast as 

 a specific osteolytic agent. 



SUMMARY 



The multinucleate giant-cells known as 'osteoclasts' probably 

 include several morphologically similar but development ally 

 distinct elements. 



In the earliest stages of bone development, and to a certain 

 extent in later stages, osteoclasts apparently arise from the con- 

 fluence of the mesenchymal cells and connective tissue of the 

 marrow. 



The chief source of osteoclasts, however, is from old osteoblasts 

 and bone cells. 



Depleted, basophilic osteoblasts coalesce to form multinucleate 

 masses. These syncytial elements become typical osteoclasts 

 when their cytoplasm assumes an oxyphilic stainability. All 

 intermediate tinctorial stages are demonstrable. 



True oxyphilic osteoclasts also exist in cytoplasmic continuity 

 with basophilic osteoblasts. Increase in size and nuclear con- 

 tent results from the engulfing of osteoblasts met in the path of 

 resorption and from bone cells which are ingested as the bone 

 matrix is resorbed. 



Osteoclasts undergo retrograde changes and ultimately dis- 

 appear through extreme degeneration. 



