No. I.] GIANT CELLS OF TILE MARROW. 123 



complete, but the cells still adherent to each other (Figs. 2 

 and 3). Similar appearances have been seen and figured by 

 Werner (5). In none of the cases of division observed by me 

 was there any indication of karyokinetic figures; hence it is fair 

 to conclude that this form of cell multiplies by direct division. 

 The clear proof furnished by these observations that it does 

 increase by division is also another indication that the mega- 

 karyocyte is a definite cell form, and not one stage in the 

 formation of the multinucleated giant cell. 



What now is the origin and function of this cell ">. Believing 

 that the megakaryocyte has no genetic connection with the 

 polykaryocyte, the theories of the origin of the latter have no 

 bearing upon the former. My sections, especially those made 

 through the femur of a foetal cat, 9 cms., at a time when the 

 marrow was just beginning to form, gave me a number of 

 apparently transitional forms between typical megakaryocytes 

 and the small marrow or embryonic cells. A series of draw- 

 ings, showing apparently the gradual development of the small 

 cell into the giant cell, is given in the Fig. 4. The drawings 

 were made from different portions of the section, and the 

 theory they suggest is that the small cell enlarges, the increase 

 affecting both the nucleus and the cell substance, and, after 

 reaching a certain size, indentations of the periphery of the 

 nucleus appear, or in many cases ingrowths of the peripheral 

 chromatin, which give the incompletely segmented appearance 

 to the nucleus that is so characteristic, and which has given 

 to them the name of giant cells with budding nuclei. The 

 megakaryocyte is not formed, then, by the fusion of a number 

 of smaller lymphoid cells, nor from a single cell which increases 

 in size by engulfing other similar cells. Both these theories 

 might apply to the polykaryocytes, but certainly not to the 

 megakaryocytes. These latter are developed by the steady 

 growth in size of a smaller lymphoid cell, and the curious 

 structure of the nucleus follows after it has reached a certain 

 size in consequence of partial constrictions or divisions, which 

 are never carried so far, however, as to lead to a complete 

 separation. 



With reference to the function of these cells, several differ- 

 ent views have been proposed. Arnold and others, who believe 

 that the megakaryocyte becomes ultimately a multinucleated 



