Histogenesis of the Blood Platelets. 271 



brings out the same appearances in the megakaryocytes and blood 

 platelets of man as in those of animals. 



This conception of the histogenesis of the blood platelets de- 

 rives additional support from the following considerations: 



1. The observation by me, with the aid of Deetjen's method, 

 of protoplasmic movements of identical character both in the 

 hyaline marginal zone of the megakaryocytes and in the hyaline 

 marginal zone of the blood platelets. These movements have 

 been described by H. Deetjen and others for the blood platelets. 

 I have seen the hyaline marginal zone of the megakaryocytes and 

 of the blood platelets constantly changing its outline, sending out 

 and withdrawing short processes of various shapes. This so-called 

 amoeboid movement of the blood platelets is not surprising, be- 

 cause it is known that detached fragments of living protoplasm 

 may exhibit movement. 



In this connection I may state that I have seen a few mega- 

 karyocytes change their form very markedly, sending out and 

 withdrawing pseudopods, such as are seen in the sections. This 

 seems to show that the presence of pseudopods and protoplasmic 

 prolongations of megakaryocytes in blood vessels, as I have seen 

 in the sections, is not a passive act, due to local conditions of 

 pressure in the tissue, but is a manifestiaton of vital activity. 

 Amoeboid activity on the part of the megakaryocytes was sus- 

 pected by J. Arnold, and has been affirmed by M. Askanazy. 



2. A comparison of the numbers of blood platelets per cubic 

 millimeter of blood in certain diseases, as estimated by various 

 observers, with the histological findings in the bone marrow in 

 the same diseases, suggests a relationship between the blood 

 platelets and the megakaryocytes. Thus in pernicious anemia 

 and lymphatic leukemia the blood has been found to contain 

 abnormally few platelets, while the marrow in typical cases of 

 these diseases as far as can be inferred from the reports in medical 

 literature and from my own observations, undergoes profound 

 changes in the character of its cellular constituents with marked 

 diminution in the number of the megakaryocytes. On the other 

 hand, in post-hemorrhagic and secondary anemia the blood 

 platelets are increased in number and there is also increase in the 



