222 ' BLOOD 



2. Lymphocytes. These include larger and smaller varieties. They 

 are similar to, and in part identical with, the ahove-described cells, the 

 myeloblasts. They include both cells differentiated from marrow and 

 cells transported by the blood stream. They are indistinguishable from 

 the osteoblast. In short, these several cells of similar characteristics may 

 be identical in their capacity to function as progenitors of blood-cells, 

 and may represent the parent blood-cell. 



3. Large Mononuclear Leukocytes. These cells are distinguished 

 from the myeloblasts and lymphocytes only by their slightly modified 

 nucleus, and by the occasional presence of a small number of fine neu- 

 trophilic granules. The nucleus is oval or bean-shaped. It represents 

 a transition phase between the less differentiated lymphocyte stage and 

 the granulocytes. It contains a centrosome located usually in that por- 

 tion of the cytoplasm lying in the concavity -of the bent nucleus. This 

 cell may proliferate extensively. 



4. Polymorphonuclear Neutrophil Granulocytes. These include 

 a graded series of stages from the standpoint of shape of nucleus, and 

 amount of granular content. The younger stages contain a less com- 

 plicated nucleus, generally bean-shaped with centrosome and relatively 

 fewer (some basophilic, 'unripe') granules; these have a slight prolifera- 

 tive capacity. Older stages have progressively more complicated nuclei, 

 characterized by a lobulated chain (with from two to five segments) of 

 dense chromatin, and are no longer capable of mitotic division. 



5. Eosinophil Granulocytes. These cells resemble the neutrophils 

 in their graded series of nuclear forms, ending in a lobulated poly- 

 morphous nucleus ; but differ in the matter of size and staining capacity 

 of the cytoplasmic granules. These granules are of fairly uniform size 

 and of spherical shape, but much larger than the neutrophilic granules, 

 and are strongly acidophilic, showing special affinity for the cytoplasmic 

 stain, eosin. In the younger forms the granules are basophilic. The 

 older types are identical with those of the blood. Again, only the less 

 differentiated, that is, those with oval nucleus and a centrosome, may 

 divide mitotically. 



The commonly accepted view of the origin of neutrophilic and oxy- 

 philic cytoplasmic granules is that they arise intracellularly under nuclear 

 influence, perhaps from less differentiated nuclear extrusions or chro- 

 midia. Originally these granules are basophilic ('unripe'). However, 

 Weidenreich regards the eosinophil granules as the ingested hemoglobin 

 particles of degenerating and fragmenting erythroplastids. Their con- 

 siderable presence in red marrow and spleen where blood-cell disintegra- 



