326 LESLIE B. AREY 



Sometimes osteoclasts are seen which are in continuity by 

 fine processes with the marrow connective tissue (figs. 14 and 15). 

 The general appearance of such cells does not indicate advanced 

 degeneration, hence it may be thought that they have arisen 

 by coalescence of connective-tissue elements. A case illus- 

 trative of this is seen in the rather thick section shown in figure 

 15. Such osteoclasts which seemingly lie free in the marrow 

 tissue usually prove to be in contact with the bone when 

 recourse is made to serial sections. It is possible, however, 

 that even in these later stages of bone resorption some osteo- 

 clasts are formed from the marrow reticulum, similar to the 

 origin described by Jackson ('04), Danchakoff ('09), and Maxi- 

 mow ('10), and that this is an illustrative stage of such a process. 

 Indeed, from what is known of tooth resorption and of the 

 genesis of foreign-body and other giant-cells it seems reasonable 

 that the osteoclast has no single source of origin. An elabora- 

 tion of this topic will be found on pages 328 and 329 of the 

 discussion. 



Finally, the fate of the osteoclasts demands attention. That 

 these cells may be resolved ultimately into osteoblasts and 

 again resume bone formation seems improbable. Kolliker, who 

 championed this view, was unable to produce direct evidence 

 in its support. My preparations show nothing in favor of such 

 a cycle, whereas pictures of degeneration in varying degrees 

 are abundant. 



A vacuolated cytoplasm is a common characteristic of many 

 osteoclasts. The degree of vacuolization appears to be fairly 

 closely correlated with the extent of degeneration (figs. 16, 17, 

 18, 19, and 6). In other cells granular degeneration of the cyto- 

 plasm occurs (figs. 7 and 20) . Nuclei may show varying degrees 

 of pyknosis while the cytoplasm still appears to be in good con- 

 dition (figs. 2 and 5) ; on the other hand, the nuclei of cells 

 otherwise exhibiting extreme degenerative changes appear to 

 be constantly pyknotic. Through stages of increasing vacuoli- 

 zation and pyknosis conditions are reached such as are depicted 

 in figures 6, 17 and 19. In an osteoclast like figure 6 both nuclei 

 and cytoplasm are far from normal; the nuclei are highly pyk- 



