Histogenesis of the Blood Platelets. 269 



masses of granules in the blood platelets and may also contain 

 vacuole-like unstained areas like those in the blood platelets. 

 Such a small mass of granules is commonly found in a small bud- 

 like pseudopod and the appearance is thus produced of a platelet, 

 the hyaline ground substance of which is continuous with the 

 hyaline cytoplasm of the megakaryocyte or a larger pseudopod. 

 The granular material in some slender pseudopods may be more 

 or less completely segmented into these rounded masses and such 

 a pseudopod may present the appearance of being composed of a 

 chain of blood platelets united by the continuity of their hyaline 

 ground substance, which in turn, is continuous with the hyaline 

 cytoplasm of the megakaryocyte. The same appearance may be 

 shown by undoubted pseudopods not connected with megakary- 

 ocytes and lying in blood channels, and also in the cytoplasm of 

 cells in process of losing their cytoplasm. 



The identity in appearance of the small portions of cytoplasm 

 containing the separate groups of granules, and of the small 

 pseudopods, with the various forms of blood platelets in every 

 respect except that they are in continuity with the megakaryocyte, 

 and the occurrence of such separate groups of granules in giant 

 cells in process of losing their cytoplasm, have led me to the con- 

 clusion that such small portions of giant cell cytoplasm, and also 

 the small pseudopods, by separation from the cell, become the 

 blood platelets. 



Bodies identical in appearance with blood platelets are com- 

 monly found near pseudopods, but only rarely are aggregations 

 of free blood platelet-like bodies found associated with a cell in 

 active pseudopod formation. The infrequency of the occurrence 

 of such aggregations of platelets is easily explained by the con- 

 sideration that by reason of the projection of the pseudopods 

 into blood channels, and because of the close relations of the giant 

 cells to the blood stream in the marrow, the platelets are usually 

 swept into the circulation as soon as separated from the megakary- 

 ocytes or their pseudopods. That the megakaryocytes and their 

 fragments have ready access to the blood stream is shown by the 

 occurrence of detached pseudopods in the blood channels and by 

 the well-known fact, first clearly pointed out by L. Aschoff, of 



