Mature thrombocyte.— The mature definitive throm- 

 bocyte has an ovoid shape and is slightly smaller than 

 the mature erythrocyte. The cytosome takes on a pale 

 blue color with most blood stains. The intensity of 

 color is varied by the presence of vaguely defined rare- 

 fied areas. 



The nucleus is usually round rather than elongated 

 as in the mature erythrocytes. The chromatin is 

 clum])ed and the clumps are closely packed, which 

 gives to the nucleus an effect of density equal to or 

 greater than that of the small lymphocyte. 



One or more specific granules, having a weak affin- 

 ity for acidophilic dyes, are visible in most mature 

 thrombocytes. These granules usually lie at one end 

 of the cell. 



LYMPHOCYTE SERIES 



Lymphoblast.— This is a large round cell with a 

 narrow rim of cytoplasm that stains dark blue but may 

 contain colorless spaces. The chromatin forms a deli- 

 cate reticular pattern. No nucleolus is visible. 



Immature lymphocyte. — General appearance the 

 same as in the blast stage, except that the chromatin 

 of the nucleus shows clumping and the cell is smaller. 



Mature lymphocvte.—KucleoceW ratio is similar to 

 that of the' blast cell. The chromatin of the nucleus 

 is definitely clumped but not always in massive blocks 

 even in the small mature lymphocyte. The separation 

 of size into "medium" and "small" is purely arbitrary. 



MONOCYTE SERIES 



Monoblast.— Thus far the monoblast stage has not 

 been definitely identified. 



Early immature monocyte. — The cytoplasm of this 

 cell stains a clear blue color with or without basophilic 

 granules. Azurophilic granules may be present. The 

 nucleus has a granularity on a reticulum quite similar 

 to that of the mature cell. The cytosome is large rela- 

 tive to the nucleus. 



Late immature monocyte. — The cytoplasm often 

 shows a basophilic granulation, or reticulum, and 

 azurophilic bodies may be present. The nucleus is 

 round and has an eccentric position in the cell and 

 a Hof may be present. 



Mature monocyte. — The cytosome is large relative 

 to the nucleus. The cytoplasm has a reticular struc- 

 ture and contains azurophilic substances, either on the 

 reticulum or as discrete granules. The nucleus usually 

 is indented and adjacent to it is a Hof area with spheres 

 faintly stained an orange color present in the vacuoles. 

 The chromatin is usually a delicate reticulum but may 

 be composed of coarse blocks. 



HETEROPHIL SERIES 



Granuloblast. — A large round cell with a narrow rim 

 of cytoplasm around the nucleus. The cytosome stains 

 an intense blue color and is only slighdy interrupted 

 by light-staining areas. The chromatin forms a reticu- 

 lum more delicate than for any other blast cell. The 

 smear method would indicate that a nucleolus is absent. 

 The morphology of the granuloblast is the same for 

 heterophils, eosinophils, and basophils. 



Metagranuloblast. — The cytoplasm on the side op- 

 posite the eccentrically placed nucleus is vacuolated 

 with spaces of approximately equal size. The nuclear 

 chromatin may be aggregated slightly, but more often 

 the chromatin remains in the form of a delicate reticu- 

 lum, and the boundary between the nucleus and cyto- 

 plasm becomes indistinct. At this stage no granules 

 characteristic of this cell line have appeared. 



Promyelocyte. — This stage also precedes the appear- 

 ance of specific granules. The boundary of the nucleus 

 often becomes indistinct and in the cytosome there ap- 

 pear dark-stained magenta granules and rings. The 

 magenta bodies are highly characteristic for the hetero- 

 phil but are not specific for it. Orange-stained spheres 

 are present in the vacuolated cytoplasm and these are 

 the precursors of the definitive rods. 



Mesomyelocyte. — From the precursor orange spheres 

 come the definitive rods. Cells with less than half the 

 number of definitive rods are included in this stage. 

 Magenta rings and granules may still be present. The 

 nuclear boundary often is still vague. In some cells 

 there is evidence of nuclear condensation. 



Metamyelocyte. — This cell usually is smaller than the 

 preceding one. The cytosome contains more than half 

 the normal complement of rods. The chromatin of 

 the nucleus is condensed and in older stages the nucleus 

 may have a bean shape. The nucleus begins to show 

 staining refractiveness characteristic of adult cells. 



Mature heterophil. — The cell contains a full comple- 

 ment of rods and the nuclear lobes may vary from 1 

 to 5 or more. The chromatin of the nucleus is aggre- 

 gated into clumps. 



EOSINOPHIL SERIES 



Granuloblast. — Morphologically this cell is the same 

 as described for the heterophil series. 



Metagranuloblast. — The nucleus is eccentric and this 

 position produces a crescent of cytoplasm at one side. 

 The vacuoles are more uniform and more sharply de- 

 fined than in the heterophil at this stage. The nuclear 

 structure is more definite than in the heterophil, and 

 chromatin clumps are larger. 



Promyelocyte. — This stage is defined as the one in 

 which only precursor substance that produces the de- 



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