BONE DESTRUCTION BY MULTINUCLEATED GIANT CELLS 527 



considerable activity. They commented that this high activity might 

 be characteristic of multinucleated cells in general, since osteoclasts 

 also had these enzymes. Incidentally, this high activity disposes of 

 the views expressed by some writers that multinucleated cells are 

 a degenerate and dying form. More recently, Cabrini et al. (1962) 

 compared the histoenzymologic activity of osteoclasts with that of 

 giant cells of foreign body granulomata and found intense activity 

 of the following: acid phosphatase, succinic dehydrogenase, phos- 

 phoamidase, and yS-glucuronidase in both types of cells. They com- 

 mented that there was a high degree of metabolic activity in these 

 cells and also that a similar enzymic pattern was needed for the 

 absorption of different substances. 



In the present experiments, cells were investigated that were 

 actually attacking bone, either calcified or decalcified. The tech- 

 nique we used had the advantage that histological procedure could 

 be kept to a minimum, and in particular histological decalcification 

 was not required. The results showed that, when compared with 

 "official" osteoclasts, our giant cells showed a close enzyme corre- 

 spondence, differing qualitatively only in a somewhat lower acid 

 phosphatase content. Though the evidence is circumstantial, pre- 

 sumably the mechanics of implant destruction and the enzymes 

 involved are similar to those of osteoclasts found around bone. It is 

 on this basis that we believe that our implants can be used as a model 

 for the study of bone resorption, and that the giant cells are osteo- 

 clasts. 



These osteoclasts obviouslv arose from the cells surrounding the 

 implant and were observed in areas of cellular reaction. It is too 

 early to say, in these investigations, what their precursors might be. 

 Multinucleated cells seemed to spring into existence with remarkable 

 rapidity, and cells with 2 or 3 nuclei were not commonly seen. Work 

 using markers such as tritiated thymidine is planned in an endeavor 

 to pin down the parents of the cells we are studying. A recent studv 

 (Fischman and Hay, 1962) offers convincing evidence that such 

 cells, at least in the newt, may arise from blood cells. It would seem 

 that the osteoclasts, which lack the ability to ingest trypan blue, are 

 not part of the reticulo-endothelial system. It is possible that the 

 intense initial mononuclear cell reaction may be related to the sub- 



