EQUIVALENCE OF HEMATOPOIETIC ANLAGES. I. SPLEEN 257 



agent on the processes underlying a definite symptom complex. 

 An expenditure implies a complete knowledge of the reserve 

 stock, the reserve being represented in the particular case by 

 the group of cells, which by their uninterrupted reproduction 

 and differentiation may supply the deficiencies. 



The reserve stock is differently appraised by the monophyletic 

 and polyphyletic schools. According to the polyphyletic school 

 these reserves are formed by a number of specifically differenti- 

 ated cell groups, which may multiply and ripen into still more 

 specialized cells. The monophyletic school, on the contrary, 

 finds in the organism along the various intermediate stages of 

 differentiation also the young, undifferentiated polyvalent cells, 

 which in the embryo have been the source of the various lines of 

 blood cell differentiation. The monophyletic school admits a 

 greater amplitude in the regeneration, and hence a wider sphere 

 of influence upon the blood tissue. These common stem cells 

 were identified by Pappenheim (31) as the large lymphocytes, 

 by Dominici (10) as the small lymphocytes, by Weidenreich (44) 

 and Downey (11, 12) as reticular cells. 



However great the differences between the mono- and poly- 

 phyletic schools may seem, both groups of hematologists admit 

 in the adult organism the existence of younger and riper cells 

 and of their gradual differentiation products. The difference 

 between them consists chiefly in the value of the amplitude of 

 the differentiation process in the adult organism, in other words 

 in the admission of different degrees of segregation, which may 

 preserve or dissolve the common stem cells for various blood 

 elements. 



Various methods were applied for the elucidation of the funda- 

 mental problems of hematology, as well as for the understanding 

 of the mutual relationship of the various .blood-cells and of the 

 structure of the hematopoietic organs. As expected, the his- 

 tological study of normal preparations of hematopoietic organs 

 in adult organism was unable to solve the problem. The mere 

 statement of coexisting cells in the hematopoietic organs offers 

 a wide field for personal interpretation. Therefore the most 



