284 H. E. JORDAN 



ess here to be described is purely erythropoietic, the primitive 

 cell is nevertheless properly termed 'haemoblast.' 



The haemoblast is in its youngest form a relatively small cell, 

 ranging from about half to approximately the full size of the 

 definitive normoblast, with a larger nucleus and much less cyto- 

 plasm (figs. 1, 2 and 3). It has a relatively enormous nucleus, 

 which is enveloped by a narrow shell of cytoplasm generally 

 wider at one point over an area of from less than a quarter to 

 more than a half of the surface (fig. 1 a). The cytoplasm is 

 finely granular and deeply basophilic. The nucleus is vesicular 

 with one or several spheroidal chromatic masses (nucleoli), 

 scattered irregularly through a wide-meshed, delicate, fre- 

 quently granular reticulum containing larger chromatin granules 

 peripherally on the nuclear membrane. In Giemsa-stained prep- 

 arations the nucleoli are colored lilac, the nuclear sap bluish 

 pink, the cytoplasm deep blue. The haemoblast may show several 

 blunt pseudopods indicating amoeboid capacity (figs. 2 and 

 27). The young haemoblasts are more generally peripherally 

 placed in the blood vessels, the later differentiation stages more 

 centrally. 



The haemoblasts show a very wide range of size variations and 

 nuclear forms, while at the same time adhering to a very close 

 structural similarity both nuclear and cytoplasmic (figs. 1, 2, 3 

 and 7). By growth the primitive haemoblast may become very 

 large; this growth may be chiefly nuclear (fig. 34) or chiefly 

 cytoplasmic (fig. 7). It does not seem possible to draw a sharp 

 line between large haemoblasts and certain so-called 'giant 

 cells,' to be described below. Their essential nuclear and cyto- 

 plasmic features are very similar. 



By division a larger haemoblast gives rise to smaller, structu- 

 rally identical, haemoblasts. The mode of division may be 

 mitotic, and apparently also amitotic (figs. 3, c, d, and e, and 22). 

 Cytoplasmic division frequently does not directly follow nuclear 

 division, thus giving rise to binucleated cells (fig. 3 d and e). 

 Similarly, tripolar spindles may produce trinucleated cells (fig. 

 21), or the same may be probably produced also by direct di- 

 vision (figs. 11 and 12). Multinuclear cells are probably simi- 



