270 James Homer Wright. 



the lodgement of them and of their more or less naked nuclei 

 in the blood vessels of the lung. 



The appearances observed are summarized and interpreted as 

 follows : 



All of the blood platelets are detached portions or fragments 

 of the cytoplasm of the megakaryocytes, which are in such rela- 

 tion to the blood channels in the marrow that detached portions 

 of their cytoplasm are quickly carried by the blood current into 

 the circulation. The breaking up of the cytoplasm into the 

 platelets occurs only in cells which have reached a certain stage 

 of growth and development, and is probably rapidly completed 

 when once begun. It takes place in various ways but usually by 

 the pinching off of small rounded projections or pseudopods from 

 the cell body or from larger pseudopods, or by the segmentation 

 of slender pseudopods, or by the pinching off of longer or shorter 

 pseudopods which may or may not undergo segmentation later. 

 All or most of the cytoplasm of the giant cell is given off to the 

 blood stream and the nucleus degenerates. The more or less naked 

 nucleus is often carried by the blood stream to the lungs where it 

 lodges in the capillaries. Before the separation of a platelet takes 

 place the red to purple staining granules in that portion of the 

 cytoplasm which is to form the platelet are separated from the 

 rest by a zone of hyaline cytoplasm and arranged in a more or 

 less sharply outlined, rounded or oval mass. The line of cleavage 

 is through this zone of hyaline cytoplasm and this sharply out- 

 lined mass of granules becomes the central granular mass of the 

 blood platelet which has been regarded by some observers as a 

 nucleus. 



These observations and conclusions concerning the origin and 

 nature of the blood platelets have been confirmed by C. H. 

 Bunting for the rabbit. On the other hand, H. Schridde, who also 

 devised a method of staining the granules in the cytoplasm of 

 the megakaryocytes, could not confirm them for the blood plate- 

 lets of man, because the blood platelets in his preparations did 

 not show the characteristically staining granules. This must be 

 due to a defect in his staining method, for my method clearly 



