218 BLOOD 



The primitive blood-cell may by slight differentiation become a leuko- 

 l>last; according to whether the cytoplasm elaborates neutrophilic, acido- 

 philic, or basophilic granules, it becomes a polymorphonuclear neutrophil, 

 eosinophil, or basophil ('mast-cell') leukocyte. The transition stage, from 



FIG. 231. DIAGRAMMATIC ILLUSTRATIONS OF SUCCESSIVE STAGES IN THE TRANS- 

 FORMATION OF THE MAMMALIAN ERYTHROCYTE (a) TO FORM THE EUYTHRO- 

 PLASTID (/). 



b and c, by extrusion of the nucleus as a whole; d and e, by extrusion of the frag- 

 mented nucleus. 



the standpoint of the nucleus, between the leucoblast with spherical nucleus 

 and the granulocyte with polymorphous nucleus, is the large mononuclear 

 leukocyte (transitional leukocyte). According to Kyes (1915), certain large 

 mononuclear leukocytes are derived from the reticulum of lymph nodes. Both 

 the reticular cells and their leukocyte derivatives are said to be phagocytic. 

 Giant cells are derived from the leukoblast, or perhaps primitive blood- 

 cell, along a separate line of differentiation, characterized by absence of cy- 



FIG. 232. SUCCESSIVE STAGES IN THE ELIMINATION OF THE ERYTHROBLAST NU- 

 CLEUS, FROM HOMOPLASTIC CULTURES OF BLOOD OF A 32 MM. PlG EMBRYO. 



This is regarded by Emmel as a 'somewhat imperfect case of constriction,' but 

 it illustrates the fundamental similarity between erythroplastid formation by ex- 

 trusion of nucleus (Howell) and by cytoplasmic constriction. (After Emmel, Amer. 

 Jour. Anat., 16, 2, 1914.) 



toplasmic division, excessive growth, and giant or multiple nucleus. The 

 multinucleate condition is attained apparently by both mitotic and amitotic 

 division of the nucleus. From the megakaryocyte pseudopodia are derived 

 the blood-platelets as explained above. Blood development in marrow passes 

 through the same phases, the hemoblast stage here being generally known as 

 the myeloblast, and characterized by a considerable finely granular neutro- 

 philic cytoplasmic content. The above is given in outline in the following 

 scheme, adapted largely from the work of Maximow on hemapoiesis in the 

 rabbit embryo. (Arch. mikr. Anat., Bd. 73, 1909.) 



