BOXE MARROW 



203 



not evident (Fig. 191). A large number of centrosome granules (over 

 one hundred) have been found, and pluripolar mitoses have been observed. 

 A phagocytic function has been ascribed to these giant cells, but it has 

 also been denied. Their origin is unknown, but is said to be from the 

 leucocyte series of cells. Their important function of producing blood 

 plates has already been described (p. 200). 



Premyelocytes are cells with large round vesicular nuclei containing 

 one or two coarse chromatin masses, and surrounded by basic protoplasm 

 free from specific granules (Figs. 190 and 191). These cells are parents of 



Neutrophile. Lymphocytes. Giant cell. 



Premyelocytes. 

 Mast cell. Erythroblast. Border of a fat cell. 



FIG. 191. ELEMENTS OF HUMAN BONE MARROW. 



A, From the femur at 10 years; B, from a cervical vertebra at 19 years; C, from the femur at 77 years; 



D, from a rib at 59 years. 



myelocytes, and are sometimes called "myeloblasts" a poor term, since 

 they do not produce marrow. Stohr refers to those in Fig. 191 as "plasma 

 cells"; others describe them as primitive wandering cells. Apparently 

 they are set free from the reticular tissue and they may produce not only 

 myelocytes but also erythroblasts. 



Myelocytes are cells larger than polymorphonuclear leucocytes, having 

 round or crescentic nuclei and protoplasm containing a varying quantity 

 of specific granules, either neutrophilic, basophilic, or eosinophilic. 

 The young cells have round nuclei and few granules. The oldest become 

 the granular leucocytes ready to enter the blood vessels. Several genera- 

 tions, derived by mitosis, intervene between the young myelocytes and the 

 mature leucocytes. Most of the myelocytes are finely granular and neu- 



