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HOWELL. [Vol. IV. 



a division of the chromatin occurs, leading to a more or less 

 diffused coloration of the nucleus. 2. The periphery of the 

 nucleus becomes indented, and in many cases there is such an 

 important increase in the diffused chromatin substance that the 

 filaments can no longer be distinguished. The indentations of 

 the periphery of the nucleus occur at many points and advance 

 toward the middle, forming the complicated nuclear figures 

 so characteristic of these cells. 3. The chromatin substance 

 becomes concentrated at different points, forming small, dark- 

 colored nuclear bodies which are united by colorless bands. 

 By a continuation of these changes a number of entirely in- 

 dependent nuclei are formed. 4. The protoplasm segments 

 round the newly formed nuclei, either endogenously or by 

 constriction from the periphery. This makes up the process 

 designated by Arnold as "indirect fragmentation," and it is, 

 according to him, the normal method of development or multi- 

 plication of the giant cells. He admits in addition, and quotes 

 from Martin and Waldstein to support the statement, that the 

 multinuclear giant cells may reproduce also by true mitotic 

 division of the nucleus, but thinks that this method of division 

 is very rare. I have never myself seen any indication what- 

 ever that the nucleus of the giant cells divides by karyokinesis, 

 though I have examined many sections of marrow from cats of 

 all ages, normal, bled, and starved, so that with this animal at 

 least it must be an exceedingly rare occurrence. Moreover, 

 my observations upon the giant cells have never given me any 

 evidence of the correctness of Arnold's view that these cells 

 normally undergo indirect fragmentation. Foa and Salvioli 

 also thought that the megakaryocytes break up by segmenta- 

 tion to form a number of colorless or hyaline cells, which in 

 turn develop into nucleated red corpuscles, and I shall speak 

 further of their theory in discussing the function of this form 

 of giant cell. 



On the other hand, that the megakaryocytes multiply by 

 division, like other cells, giving rise to two daughter giant cells, 

 has been clearly proved by my sections. In quite a number of 

 cases the sections have shown me megakaryocytes with two 

 large nuclei at the ends of the cells, and a constriction begin- 

 ning between them, or, more frequently, two megakaryocytes 

 lying side by side with the line of demarcation between them 



