THE WHITE BONE CELLS 209 



by great increase of nuclear and cytoplasmic constituents, gives rise to 

 the so-called GIANT CELLS. These are of two sorts, depending upon 

 whether the nucleus is single or multiple, the megakaryocyte and the 

 polykaryocyte. The latter represents a modification of the former, and 

 must not be confused with the osteoclasts of developing bone. 



Megakaryocytes are practically limited to bone-marrow. They fre- 

 quently show long and numerous pseudopodia. These, as also the cell- 

 body proper, show a differentiation of the cytoplasm into a superficial 

 hyaline layer and a central basophilic granular core. According to 

 Wright, constriction and segmentation of these IMII^M 



pseudopods give rise to the BLOOD-PLATELETS 

 (plates ; plaques) . These commonly hold positions 

 at the center of masses of converging fibrin fibrils 

 in blood clots, in consequence of which they are 

 supposed to be the essential elements, probably FIG. 224. GROUP OF 



liberating 'thrombin', in clotting, hence their JHREE SMALL AND 

 ^, . . Two LARGE BLOOD 



synonym, thrombocyte. This term, however, is ill- PLATELETS. X2000. 



chosen, for these elements contain no nucleus. 



What simulates a nucleus is the central spheroidal mass of basophilic 

 granules. Blood-platelets are capable of ameboid motility. They vary 

 in diameter from 2 to 4 microns, and in number per cubic millimeter 

 from 200,000 to 800,000. Analogous elements of avian, reptilian and 

 ichthyoid bloods are nucleated spindle cells, or true thrombocytes. 

 Wright's observations on mammalian megakaryocytes furnish at present 

 the best data for the genetic interpretation of blood-platelets. How- 

 ever, almost every conceivable mode of origin, notably from extruded 

 nuclei of erythrocytes, and fragmenting leukocytes have had, and still 

 claim, prominent supporters. 



Granulocytes., The granulocytes comprise three varieties distin- 

 guished on the basis of their cytoplasmic granules: (1) neutrophils; (2) 

 eosinophils (oxyphils) and (3) basophils, or mast leukocytes. The nu- 

 cleus is of the polymorph type, perhaps occasionally, polynuclear. This 

 nuclear condition consists in a commonly crescentic chain of nuclear 

 masses connected by frequently extremely delicate nuclear strands. 



The NEUTROPHILS are characterized by their fine cytoplasmic gran- 

 ules, having a neutrophil staining reaction (lilac color) in mixtures of 

 acid (eosin) and basic (methylene blue) dyes. They range in size 

 from 7.5 //, to 10 /* in diameter. They are predominantly phagocytic. 

 They constitute in normal adult life about 70 per cent, of the total white- 

 cell blood content. 



