STRUCTURE-FUNCTION RELATIONSHIPS IN OSTEOCLAST 503 



Loose, detached crystals have been described within cytoplasmic 

 channels in the ruffled border and its vacuoles in all previous pub- 

 lished reports on the electron microscopy of the osteoclast ( Scott and 

 Pease, 1956; Cameron and Robinson, 1958; Gonzales and Karnovsky, 

 1961; Hancox and Boothroyd, 1961; Dudley and Spiro, 1961). Their 

 strict confinement to these sites and their constant occurrence seem 

 to rule out any question of mechanical shift by the knife edge dur- 

 ing sectioning, and one can conclude that loose crystals genuinely 

 occur in such areas as zones A and B. 



Concerning zone C, however, the question of artifact has to be 

 considered carefully. Here again, however, artifact seems unlikely; 

 the tissue samples, of course, were supported bv and permeated with 

 hard plastic, and if the crystals had been translocated by the knife 

 edge one would expect to find telltale scars or tears in the Araldite, 

 but these are not seen. In zone C, free crystals are encountered be- 

 low what seems to be inert cvtoplasm. It is very interesting that 

 similar loose crystals can be distinguished in Dudley and Spiro's 

 Fig. 13 ( 1961 ) , where they are present below the inert-looking cyto- 

 plasm of an "endosteal lining cell." This observation suggests that 

 crystals can be detached from the surface of normal bone, or, rather, 

 that the osteoclast is not required for the detachment of ciystals, 

 and of course it raises the whole question of the nature of the forces 

 which normally bind crvstals to collagen, and what is normal bone. 



Passing from zone C through B to A, more crystals can be seen to 

 have been shifted and over longer distances. How the crystals are 

 detached is uncertain. Other workers, of course, have proposed that 

 the primarv change is solution of the collagen; if it is removed first, 

 it would, of course, leave the crystals free. This view of the sequence 

 of events is based chieflv on failure to detect demineralized collagen 

 fibrils in the subjacent matrix ( Scott and Pease, 1956; Gonzales and 

 Karnovsky, 1961; Dudlev and Spiro, 1961). However, both with 

 Araldite in the present work and with methacrylate in our previous 



Fig. 4. Bone matrix runs vertically down the left margin, and osteoclast 

 cytoplasm occupies rest of field. At top, zone C is indicated. There is a tran- 

 sition to zone B features below; arrows indicate its short cytoplasmic channels, 

 containing bone salt crystals. Note innumerable cytoplasmic vesicles and mito- 

 chondria. (X 35,000.) 



