GIANT-CELLS OF BONE-MARROW 119 



nuclei, and the hemogenic giant-cells include also cells with 

 many nuclei, that is, polykaryocytes. Prenant apparently con- 

 siders all multinucleated giant-cells of marrow as osteoclasts, 

 and he describes their mitochondria as consisting of three mor- 

 phologic varieties: granules, rodlets, and vesicles. These three 

 varieties I can demonstrate also in the hemogenic giant-cells, 

 polymorphonucleated as well as multinucleated. 



In two other recent important contributions the results are 

 likewise vitiated by failure to make a distinction between osteo- 

 lytic and hemogenic giant-cells. Perroncito ('20) speaks of the 

 predominant function of the giant-cells of red bone-marrow as 

 one of phagocytosis, especially for bacteria, erythrocytes, and 

 leucocytes. Pianese ('20), while correctly interpreting the 

 polykaryocyte (of the hemogenic series) as an advanced stage 

 of development of the mononucleated giant-cells ('megakaryo- 

 cytes'), holds erroneously that it can function also as an osteo- 

 clast. Both Perroncito and Pianese hesitate to accept Wright's 

 conclusion that blood platelets are fragments of giant-cell (hemo- 

 genic) cytoplasm, but they are unable to furnish any conflicting 

 evidence. 



In view of the prevailing confusion with regard to the giant- 

 cells of red bone-marrow in growing and mature bones, it seems 

 desirable to summarize in this connection my general conclusions, 

 based upon an extensive study of osteolytic and hemopoietic 

 foci, regarding two types of giant-cells. 



Giant-cells of bone-marrow belong to two ontogenetically, 

 cytologically, and functionally distinct categories: the hemo- 

 genic and the osteolytic (Jordan, '18, '21). The former develop, 

 both in red bone-marrow and in the yolk sac, from mononu- 

 cleated, lymphocyte-like cells, the hemoblasts (Jordan, '18, 

 '19 a). They may exist as giant mononucleated cells (giant 

 hemoblasts), and as such are properly called megakaryocytes. 

 They may suffer a nuclear modification, leading to a complex 

 polylobulated 'basket' nucleus, and at such a stage are more 

 correctly designated polymorphokaryocytes. This polymor- 

 phous nuclear condition indicates a stage in amitotic nuclear 

 division, and leads to a multinucleated condition, when the cell 



