ERYTHROBLASTS IN THE PIG EMBRYO 155 



natives. On the contrary the non-nucleated elements were found 

 to arise by a process apparently fundamentally different. 



The best results were obtained with autoplastic cultures made 

 from blood taken directly from the heart. Selecting a successful 

 culture in which the erythrocytes present a normal appearance, 

 a careful examination of the erythroblasts, especially of those with 

 the more eccentric, pyknotic nuclei, an occasional blood cell 

 will be found exhibiting a cytoplasmic activity distinguishing it 

 from the surrounding cells. This activity in its earlier stages 

 manifests itself in a modification of the rounded contour of 

 the cell (as seen in a surface view) of such a character as 

 to result in a somewhat pear-shaped elongation of the cell 

 (figs. 13-17, a), with the nucleus at one pole of the long axis, 

 and the greater bulk of the cytoplasm tending to segregate itself 

 at the other. The cytoplasm at the latter pole of the erythro- 

 blast is observed to be in a state of more or less quivering activity, 

 accompanied at varying intervals by slight elongation and subse- 

 quent retraction of the cell body. In other respects such an eryth- 

 roblast may appear perfectly normal its nuclear, cytoplasmic, 

 and hemoglobin elements apparently differing in no material way 

 from that of the adjacent quiescent, normal nucleated and non- 

 nucleated erythrocytes. The further behavior, which in a favor- 

 able case may now be observed in the erythroblast under consider- 

 ation, is illustrated by the successive stages shown in figure 14. 

 This preparation was a 20-hour blood culture from a 30 mm. pig 

 embryo. The erythroblast to be described was characterized by 

 the slightly elongated form and cytoplasmic activity of the type 

 just described. This active cell was brought into the field of the 

 microscope at 11.40 a.m. and observed continuously until 12.15 

 p.m. A constriction in the cytoplasm of the erythroblast soon 

 became evident, which within four minutes had assumed the 

 characteristics shown in figure 14, h. Gradually this cytoplas- 

 mic constriction became more marked (c), and within twenty 

 minutes after the observation had been begun the process of 

 constriction was completed {d) , at which stage the parent erythro- 

 blast had now become divided into two parts, the one still contain- 

 ing the original nucleus, the other a non-nucleated hemoglobin- 



