Histogenesis of the Blood Platelets. 267 



the blood platelets are stained by this method and that the blood 

 platelets are all of the same nature or kind. 



Fixation in methyl alcohol or in corrosive sublimate produces 

 in the plasma a more or less abundant precipitate in the form of 

 granules of a size and shape closely resembling the blood platelets 

 and which cannot be distinguished from blood platelets in prepar- 

 ations stained by the usual methods. This granular precipitate 

 has doubtless been confounded with blood platelets by observers 

 who have found an apparent increase of blood platelets in doubly- 

 ligated vessels and in stagnant blood, or apparent blood platelet 

 thrombus formation after cauterization of the vessel wall, because 

 they did not use a specific staining method for the blood platelets 

 in their experiments. 



In sections of the blood forming organs the blood platelets 

 may be very small in number because the blood has flowed out 

 of them, taking with it the blood platelets, and because, with the 

 stopping of the circulation, the platelets become irregularly 

 distributed throughout the vessels. They are very numerous in 

 the spleen, which is readily accounted for by the consideration 

 that the structure of that organ favors the accumulation of 

 various kinds of cells and blood corpuscles within it and prevents 

 their escape from small pieces cut from it. 



The giant cells or megakaryocytes in sections of the blood- 

 forming organs present the following peculiarities which are of 

 importance for the subject of this paper. 



In the cytoplasm of the megakaryocytes or the giant cells are 

 imbedded more or less numerous red to purple staining granules 

 identical in appearance and staining with the granules in the blood 

 platelets. Also in the cytoplasm small vacuole-like unstained 

 areas may be seen like those in the blood platelets. In preparation 

 fixed by methyl alcohol the granules may be arranged in more or 

 less definite parallel rows or Hues coursing in various directions. 



The cytoplasm of a minority of the megakaryocytes is prolonged 

 into pseudopod-like processes of varying size, shape and number. 

 These processes, which will hereafter be referred to as pseudopods, 

 often occur as bud-like projections of the size of a blood platelet 

 or as strands, of a width corresponding to that of a platelet, which 



