tions. Thus, there may be found a complete 

 range of color from a basophilic cytoplasm with 

 a trace of hemoglobin (fig. 11) to a cell that 

 has a high hemoglobin content and only a trace 

 of basophilia (figs. 16-18). The early poly- 

 chromatic erythrocyte is characterized by a blue 

 cytosome, tlie mid-polychromatic erythrocyte by 

 a gray coloration, and the late stage by various 

 tints of orange. A mixture of blue and orange 

 produces gray, and in some cases the yellow por- 

 tion of eosin mixed with blue adds a slightly 

 greenish tinge. With a shift from a predomi- 

 nantly basophilic to predominantly acidophilic 

 cytoplasm there is an accompanying progres- 

 sion of changes involving cytoplasmic texture, 

 nuclear structure, nucleocytoplasmic ratio, and 

 cell shape. Each cell passes through an infinite 

 number of steps, but for purposes of communi- 

 cation we arbitrarily break up a continuous series 

 into segments ; three seems to be the most work- 

 able number, and these, as already indicated, are 

 called, early, mid-, and late. 



The color of the cytoplasm serves as the pri- 

 mary criterion in identifying each of these three 

 phases. Figures 11 and 12 are examples of 

 early polychromatic erythrocytes, as has already 

 been mentioned. An important nuclear change 

 is an increase in the amount of chromatin clump- 

 ing beyond that obsei-ved in the erythroblast. 

 The cytoplasm has taken on some of the homo- 

 geneous textural characteristics found in the ma- 

 ture erythrocyte. This is variable, as shown in 

 these two figures, and is not veiy closely synchro- 

 nized with the degree of basophilia. The size of 

 nucleus in comparison with the size of cytoplasm 

 usually shows a definite decrease in the shift 

 from erythroblast to early polychromatic erythro- 

 cyte, but this, also, is not constant. In general, 

 this cell is somewhat smaller than the erythro- 

 blast but size in itself is not a reliable criterion 

 for separating the two stages of development. 

 These points are examples of the lack of close 

 synchronism between different parts of the cell 

 during development. Actually the cell in figure 

 11 is relatively rare, even in bone marrow. Its 

 homogeneous cytosome combined with strong 

 basophilia is not typical. Figure 12 is more typ- 

 ical in that there is some evidence of mitochon- 

 drial spaces and of irregularities in cytoplasmic 

 structure. These may persist even up through 

 the mid-polychromatic erythrocyte stage of de- 

 velopment (figs. 13 and 14). 



The classification of stages in the development 

 of erythrocytes on the basis of hemoglobin con- 

 tent has not found general acceptance by hemo- 

 tologists working on human blood, and the point 

 is illustrated by Osgood's (1938) statement (p. 

 67), "However, it seems to the author unjusti- 

 fiable to use die amount of hemoglobin in the 

 cytoplasm as the criterion of the age of the indi- 

 vidual cell since many polychromatophilic akary- 

 ocytes (nonnucleated red cells) are seen which 

 contain practically no hemoglobin and these must 

 certainly be more mature than nucleated red 

 cells which contain much hemoglobin. If one 

 uses the nucleus alone, however, as the criterion 

 of the maturity of the cell, one can arrange a 

 continuous series, each one differing from the 

 neighboring cell by an almost imperceptible de- 

 gree, from the most immature karyoblast (mega- 

 loblast) to the most mature metakaryocyte (nor- 

 moblast) which is just losing its nucleus." This 

 point of view is probably entirely justified for 

 erythrogenesis of mammalian blood, but in avian 

 blood where the red cells do not lose their nuclei, 

 the color changes withhi the cytosome seem to 

 be a much more reliable criterion of progressive 

 cellular differentiation than the alternate ones 

 suggested by Osgood for man. It is agreed that 

 hemoglobin uptake and structural differentiation 

 are not always synchronized. 



Dantschakoff ( 1908b) faced the same problem 

 in her use of the term "polychromatic." Her 

 comments (p. 519) are interesting. 



"Da die jungen, eben erst aus den farblosen 

 Elementen entstandenen primitiven Erythro- 

 blasten noch sehr wenig Hamoglobin enthalten, 

 erscheint ihr Protoplasma nach D-, EA- und G- 

 Farbung in einem Mischton von blau und rosa 

 tingiert, weil es eben seine urspriingliche Baso- 

 philic nur noch zum kleinsten Teil eingebiisst 

 hat. Hamoglobinfiihrende Zellen mit ahnlich 

 reagierendem Protoplasma werden bekanntlich 

 bei verschiedenen Tieren und auch beim Men- 

 schen im erwachsenen Korper bei verschiedenen 

 Kranklieitszustanden im Blute gefunden and sie 

 erhielten in der Pathologic den Namen 'poly- 

 chromatophile Erythrocyten resp. Erythro- 

 blasten'. Das Wesen dieser sogen. Polychroma- 

 tophilie wurde von verschiedenen Autoren sehr 

 verschieden aufgefasst. Ehrlich (15 u. 16) 

 betrachtet sie als Folge anamischer Degenera- 

 tion, wobei die Erythrocyten den Blutfarbstoff 

 ins Plasma diffundieren lassen; einen ahnlichen 



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