STRUCTURE-FUNCTION RELATIONSHIPS IN OSTEOCLAST 505 



study (Hancox and Boothroyd, 1961), collagen fibrils completely or 

 partially ( Fig. 5 ) denuded of their apatite crystals occur constantly. 

 This strongly suggests that the primary change is the removal of 

 crystals, collagen disappearing subsequently. The reasons for this 

 interesting discrepancy are not clear. Naturally the question of arti- 

 fact has to be reviewed carefully v^ith respect to the possibility of 

 loss of crystals during specimen preparation or in the electron beam. 

 It is unlikely, however, that they would be removed from collagen 

 in this way while persisting in near-by channels and vacuoles. All 

 the same, this point merits further study, and Boothroyd is currently 

 working on it. Another possibility is that a species difference is in- 

 volved. Scott and Pease (1956) worked with kitten tissue; Gonzales 

 and Karnovsky (1961) used rat tissue; Dudley and Spiro (1961) 

 studied material from man and 10-week-old chickens, but give no 

 indication in their paper of the species of the osteoclasts illustrated. 



If crystals indeed leave the fibril first, then presumably the forces 

 which anchor them must be weakened or abolished. What the forces 

 are, and how they can be affected, remains obscure. It is difficult to 

 see how acid decalcification ( Kolliker, 1873 ) or chelation ( McLean 

 and Urist, 1955) can be involved; these should lead to disappear- 

 ance of the crystals rather than their shift from matrix to cell. 



At all events, it would follow that as demineralization proceeds, 

 the underlying fibrils will be exposed. Those which protrude from 

 the resorbing edge seem to become gathered up by folds in the 

 ruffled border, and their fate, presumably, is to be digested away 

 by enzyme action as erosion of the matrix deepens. 



No solid formed bodies are seen in the osteoclast cytoplasm which 

 might be the carriers of enzymes. Dense bodies, such as have been 



Fig. 5. Edge of bone matrix runs vertically downward just beyond left- 

 hand margin. The field is occupied by ruffled border of zone A. Channels, some 

 wide and pinocytotic, and others finer, lead (horizontally) from matrix into 

 cytoplasm. A demineralized collagen fibril (horizontal arrow) can be seen 

 toward top; another (vertical arrow) still appears to have a few crystals at- 

 tached. (X 30,000.) 



Fig. 6. Zone C. Bone matrix runs vertically down left side of figure. The 

 typical "inert-looking" cytoplasm fills rest of field. There are several short, 

 blunt cytoplasmic channels (arrows) apparently containing free bone salt 

 crystals. (X 70,000.) 



