182 VICTOR E. EMMEL 



morphological elements of mammalian blood. A well substan- 

 tiated conclusion is that of Wright's ('10), that ''all of the blood 

 platelets are detached portions or fragments of the cytoplasm of 

 the megakaryocytes" (p. 8). Weidenreich ('12) observed the 

 pinching off of portions of the cytoplasm of lymphocytes in the 

 human thymus, which he describes as follows: ''Zweitens kommen 

 Partien in der Rinde vor in denen die Rindenzellen grossere oder 

 kleinere Telle ihres Protoplasmaleibes abschnuren, die dann als 

 basophile blutplattchenahnliche Gebilde frei zwischen den Zellen 

 liegend angetroffen werden" (p. 2602). Pappenheimer ('13) in his 

 study of cultures of thymic tissues, found in the thymic cells a 



separation of portions of proplasm, which gradually l^ecome constricted 

 off and are set free in the plasma. The separated portions contain fat 

 drops and granules. The process resembles curiously the formation of 

 blood platelets from megakaryocytes, as first described by H. Wright. 

 Its significance here is uncertain; it may be found in cells which show no 

 -other degenerative changes (p. 313). 



Weidenreich and Goldmann ('12, p. 61) found similar changes 

 occurring in plasma cells.*' Downey and Weidenreich ('12) de- 

 scribe the same process for lymphocytes in normal lymph glands. 

 In a recent investigation Downey ('13) further "found that the 

 lymphocytes of the germ centers and pulp of the spleen were fully 

 as active in the cutting off particles of their cytoplasm as were those 

 of the lymph glands" (p. 40), and, moreover, after careful study 

 draws the important conclusion, "that the hyalin bodies which 

 are constricted off from the protoplasm of lymphocytes and mono- 

 nuclears, especially in the rabbit, are in no way related to blood 

 platelets, as was claimed by Dominici and others" (p. 52). 



We have then what appears to be convincing evidence that 

 megakaryocytes, plasma cells and lymphocytes, and thymic cells 

 (i.e., if the latter are to be regarded as distinct from lymphocytes) 

 contribute at least two important non-nucleated morphological 

 elements to the mammalian blood, and that they do this by con- 



^ Compare also a recent paper by Brown ('13) for the constriction off of parts 

 of the cytoi)hism from "hyperplastic endothelial cells in the marrow, and mono- 

 nuclear and transitional cells (premegakaryocytes) in the inarrow, spleen, and 

 blood." (p. 286). 



