262 VERA DANCHAKOFF 



tissue cells for Fischer (16) and Klein (22) and finally reticulum 

 cells for Klein (22) . iVn attempt was made to explain the mye- 

 loid metaplasis, not only by attributing potencies, characteris- 

 tic for embryonic cells to cell-groups in adult hematopoietic 

 organs, but also by assuming the existence of a mysterious proc- 

 ess of dedifferentiation of already differentiated cells, Schridde 

 (38), Fischer (16), Nageli (31). 



Among the investigators who studied the myeloid metaplasis 

 only a few admitted the existence of a common stem-cell for 

 various blood-cells in the adult organism. Pappenheim (32), 

 Werzberg (46), later Dominici (10) and Blumenthal (4) became 

 supporters of the monophjdetic interpretation of the myeloid 

 metaplasis. They pointed out that the localization of the new 

 myeloid tissue during myeloid metaplasis is not as strict as the 

 dualists admit. Moreover, the separate localization of the mye- 

 loid and the lymphatic tissues, where it exists, may become the 

 differentiating factor for a common stem cell, which of course 

 could not develop under equal conditions into different products. 

 The monophjdetic interpretation of the myeloid metaplasis 

 was corroborated to a great extent by embryogenetic studies, 

 Bryce (2), Danchakoff (9), Maximow (25), Moliier (28), Haff (18) 

 and by histological studies (Weidenreich (44), Downey (11, 12), 

 Ferrata (33). 



The study of myeloid metaplasis of lymphatic tissue has been 

 mr.de in adult organs, in which at least a temporary embryonic 

 or even a permanent partial granuloblastic differentiation existed. 

 Therefore a possibility of persistence of specific granuloblastic 

 stem cells in such organs could not be denied and a differenti- 

 ation of specific cells could be explained by the specific consti- 

 tution of their stem cells. Under definite stimulation, these 

 specific stem cells might intensely proliferate. On the other 

 hand, the hematopoietic organs could also preserve young 

 specifically undifferentiated cells, polj^valent in their potencies. 

 Their partial and local differentiation into myeloid tissue might 

 have been caused by specific conditions of their environment. 



