ORIGIN AND FATE OF OSTEOCLASTS 327 



notic while the cytoplasm takes the eosin poorly and is riddled 

 with vacuoles which at the edges produce a ragged, laced appear- 

 ance. In short, the optical appearance is such as one normally 

 associates with extreme degeneration. 



As the resorption of local areas of bone is completed, the 

 accompanying osteoclasts become left behind, stranded in the 

 marrow tissue. Thus, one occasionally finds a small portion of 

 bone enclosed by an osteoclastic mass (fig. 17). Only when 

 serial sections are available is one certain that a paratangential 

 section of a spicule-tip had not produced a deceptive appearance 

 of an isolated bone fragment and enclosing osteoclast. 



Left behind in regions where resorption has apparently finished 

 its course are sometimes found also nests of large osteoclasts 

 (figs. 19 and 22). Such a stage as figure 21 apparently shows 

 in its inception how these masses become thus isolated, for this 

 particular giant-cell is at the rear of an area of bone dissolution 

 that is almost completed locally. Some of these stranded 

 elements show excessive degenerative changes. Illustrations 

 show but poorly the pale, reticulate or fragmented cytoplasm 

 and the shrunken and distorted, pyknotic nuclei. 



Jackson ('04) and Maximow ('10), in particular, have upheld 

 the fragmentation of osteoclasts into detached cells which 

 become indistinguishable from the reticulum of the marrow 

 (compare p. 327). I have seen several stages which show 

 stellate portions of the osteoclast being cut off by vacuolization 

 (fig. 18). That these moieties, some of which may even lack 

 nuclei, persist as elements indistinguishable from the reticulum 

 is doubtful; on the contrary, the general appearance of such 

 osteoclasts seems rather to point to ultimate degeneration. 

 If my interpretation of the osteoclasts be correct, the entire 

 course from the time of osteoblastic coalescence is one of pro- 

 gressive decline (see foot-note 6, p. 320). To return to a healthy, 

 active state, the fragmentation products of such osteoclasts 

 would seemingly have to undergo extensive rejuvenation both 

 as regards nucleus and cytoplasm. 



Large osteoclasts were observed within the blood-vessels of 

 the marrow (figs. 7 and 20) . That such gain admittance and 



