phil, and 5 for the basopliil. Each of the 3 

 granulocytes reveals the characteristics of each 

 of the 6 steps in development; but in the eosino- 

 phils and basophils, 2 of the stages have been 

 telescoped and the name chosen for the combina- 

 tion is the last one in the series.' 



The granuloblast is identified !)y its large nu- 

 cleus surrounded by a narrow rim of cytoplasm 

 densely stained. Relatively few cytoplasmic 

 spaces are in the cytoplasm (figs. 366 and 367), 

 and these lie adjacent to the nucleus. 



The intensely colored narrow rim of violet- 

 stained cytoplasm, comljined with the delicately 

 stained nuclear reticulum and lack of visible 

 nucleolus, makes the granuloblast readily recog- 

 nizable even under relatively low magnification. 

 Figure 366 is the largest granuloblast observed, 

 and figure 367 represents the size usually seen. 

 These cells resemble very closely the lympho- 

 blast, but are different from the thromboblast and 

 the erythroblast. 



The scheme presented in talkie 2 has been 

 written under the assumption that the granulo- 

 blast has equal potentialities to produce a hetero- 

 phil, eosinophil, or basophil. Early in this study 

 it was thought that the stem cell for each type of 

 granulocyte had a different appearance, but it has 

 since been decided that these were either meta- 

 granuloblasts or promyelocyte stages. Hamre 



' Six subdivisions of the sranulocyte series are suggested in 

 the First Report of the Committee for Clarification of the 

 Nomenclature of Cells and Diseases of the Blood and Blood- 

 Forming Organs (1948), and Dr. L. W. Diggs states (personal 

 communication), ". . . it is my opinion that terminologies 

 used in human hematology and widely accepted and under- 

 stood, should he used for lower animals when applicable." 

 This is a commendable point of view; unfortunately it has been 

 necessary to depart in some cases from the terminology pro- 

 posed by the Committee because the definitions associated with 

 certain terms used in studies on blood of mammals do not ade- 

 quately cover the ol)servations made on birds. As pointed out 

 by Jones (1949), zoologists, embryologists, and physiologists 

 all have a stake in these problems. 



"Myelo" is an inappropriate term for immature stages of 

 granulocyte development because it means "marrow," and in 

 the birds granulocytes develop in many organs other than the 

 hone marrow. To have substituted the term ''granulocyte" for 

 "myelocyte" would have been acceptable as far as the de- 

 velopmental stages are concerned but would have conflicted with 

 the term almost universally accepted for the adult cell. It 

 seems confusing to use the term "myeloblast" for the earliest 

 stage and "progranulocyte" for the next stage and then follow 

 with two myelocyte stages. Therefore, for this study on avian 

 hematology these terms have been changed to "granuloblasl" 

 Ian old term) and "metagranuloblast," respectively; these are 

 followed by the pro-, meso-, and meta- stages of the myelocyte, 

 and these are followed by the mature cell. The prefix "meso" 

 uas used so that each of these phases of developTiient could be 

 identified without confusion, and so that the term "myelocyte" 

 without any prefix could be used as a general tenn signifying 

 the full range of development from the metagranuloblast up In 

 the mature cell. Metagranuloblast is a new term. 



has prepared a colored plate showing granu- 

 lopoiesis; it was based on the use of a different 

 stain but in the sequence of stages (Hamre, 1952 I 

 there was nearly complete similarity with the 

 data given here. The privilege of examining 

 his data before publication has been helpful in 

 this complex problem. He did not set apart as 

 a separate stage what has been given here as the 

 metagranuloblast. 



The metagranuloblast is derived from the 

 granulo])last Ijy a great expansion in the cyto- 

 plasm at one side of the nucleus, and by an in- 

 crease in the vacuolization of this portion of the 

 cytosome. Often the remainder of the cytosome 

 is unchanged from the condition characteristic of 

 the granuloblast — that is, it stains an intense vio- 

 let color. This was the case in figure 368 but not 

 in 369. At this stage the nucleus may remain 

 round (fig. 368) or it may be partially collapsed 

 ( fig. 369 ) . The reticular pattern of the nucleus 

 may be just as finely patterned and delicately 

 stained as in the granuloblast stage, or it may 

 show clumping. The nucleus collapses or be- 

 comes irregular in shape more readily in the 

 heterophil metagranulolilast than in either tlie 

 eosinophil metagranulojjlast or the basophil 

 pi'omyelocyte. Also, the chromatin condensation 

 is greater in the last two cells. The metagranulo- 

 blast stage of the heterophil and of the eosinophil 

 can be readily separated. The difference is ap- 

 parent when a comparison is made lietween figure 

 368 and 378. In the heterophil, the boundaries 

 of the vacuoles are rather indefinite and they 

 appear oftentimes as spaces in a reticulum, but 

 in the eosinophil they are round areas with clean- 

 cut boundaries. This difference was the chief 

 factor in calling cell ii of figure 330 an eosino- 

 phil metagranulol)last rather than a heterophil of 

 the same stage. 



One group of hematologists (Anonymous, 

 1949) gives only the term "myelocyte" to cover 

 the entire span of specific granule production. 

 In avian blood for the heterophil at least, there 

 is a definite stage of development between the 

 ntetagranuloblast and the stage where specific 

 granules first appear. Microscopically, it is one 

 of the most conspicuous of the entire progression 

 and it would be awkward not to have a name for 

 it. Its two outstanding characteristics are the 

 presence of (1) cytoplasmic rings and gramiles 

 that take the same intense magenta stain as the ] 



194 



