THE WHITE BLOOD CELLS 209 



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

 the so-called <;I\\T CELLS. These are of two sorts, depending upon 

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

 polyknryoi-ylt'. The latter are thought by some to be identical 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 

 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 p u; 2 24 A GROUP 



supposed to be the essential elements, probably OF BLOOD PLATE- 

 liberating 'thrombin', in clotting, hence their LETS, FROM THE Hu- 



.7. Z. . m-i i -11 MAN BLOOD. 



synonym, thrombocyte. Ihis term, however, is ill- 



\ery highly magni- 

 chosen, for these elements contain no nucleus. ec j (After Eisen.) 



What simulates a nucleus is the central spheroidal 



mass of basophilic granules. Blood-platelets are capable of ameboid mo- 

 tility. 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 throm- 

 bocytes. AYright's observations on mammalian megakaryocytes furnish 

 at present the best data for the genetic interpretation of blood-platelets. 

 However, almost every conceivable mode of origin, notably from ex- 

 truded 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) 

 eosinoplnls (o.rypliils) and (3) basopliils, 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 /u. to 10 /u, in diameter. They are predominantly phagocytic. 

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

 cell blood content. 



