92 



HUMAN ANATOMY. 



acteristic of the red marrow ; these are : (i) the inart'ow- cells, (2) the eosinophile 

 cells, (3) xhe. giant cells, and (4) the. mccleated j'ed blood-cells. 



The marrow-cells, or myelocytes, resemble the large lymphocytes of the 

 blood, but may difTer from the latter in their slightly larger size and in the possession 

 of a relatively large round or oval nucleus which contains comparatively little 

 chromatin; the presence of neutrophile granules within the cytoplasm of the marrow- 

 cells affords an additional differential characteristic when compared with the large 

 lymphocytes in which these granules are absent. 



The eosinophile cells occur in considerable numbers within the red marrow, 

 and appear in varying stages of growth, as evidenced by their round nio7io7i7cclear, 

 the indented transitioyial ■AXi<\ segmented polymorpliofi2iclear condition ; the cells con- 

 taining the latter form of nucleus are most abundant and represent, probably, the 

 mature elements. 



The giant cells, or myehplaxes, are huge elements of irregular oval form, and 

 contain simple or polymorphous nuclei. They represent specialized myelocytes, 



Fig. 123. 



f#-r1//ir-^? 



Marrow-cells- 



Young red blood-cells 







Giant cell 





Gifnt cell 



Blood-vessel 



Section of red marrow from epiphysis of young femur. X 300. 



and during the processes resulting in the removal of osseous tissue they are the 

 osteoclasts which are actively engaged in effecting the absorption of the bony 

 matrix. Ordinarily the giant cells occupy the central portions of the marrow ; 

 when, however, they enter upon the role of bone-destroyers, they lie on the sur- 

 face of the osseous trabeculae within the depressions known as Howship' s lactoice 

 (Fig. 128). 



The nucleated red blood-cells within the red marrow are concerned in the 

 important function of renewing the colored cells of the blood, the red marrow being 

 the chief seat in which this process takes place after birth ; hence the red marrow is 

 classed as a blood-formhig organ. The nucleated red blood-cells exist within the 

 marrow in two forms, an older and a younger. The genetically older cells, the 

 normoblasts, are the descendants of the embryonal nucleated blood- cells on the one 

 hand and the indirect parents of the younger blood-elements on the other. The 

 normoblasts possess relatively large nuclei, with chromatin reticulum and cytoplasm 

 tinged with heemoglobin ; they are frequently observed during mitosis, since they gave 

 rise to the second generation of nucleated red blood-cells. The latter, the erythro- 



