EQUIVALENCE OF HEMATOPOIETIC ANLAGES. I. SPLEEN 299 



Lymphocyten, die sich ja sicherlich auch in gleichen aussern 

 Exist enzbedingungen befinden, doch zu verschiedenen Endpro- 

 dukten entwickeln." Maximow rightly points out, that the 

 problem of the differentiation of blood cells forms merely a par- 

 tial question of the general problem of differentiation of an egg 

 in a multicellular organism. The observation that cells begin 

 their granuloblastic differentiation soon after completion of 

 mitosis, led Maximow to connect differentiation with mitosis. 

 The differentiation factor is conceived by Maximow as "eine 

 tiefe Gleichgewichtsstorung" which occurs during cell division 

 is not reversible, and concerns both daughter cells. It leads to 

 specific qualitative changes, — to the development in the cytoplasm 

 of hemoglobine or granules — ''Warum aus einem sich teilenden 

 Lymphocyt in dem einen Fall ein Paar junger Myelozyten, in 

 einem anderen ein Paar junger Erythroblastenu.s.w.hervorgeht, 

 hangt wahrscheinlich vom Zufall ab. " It is, however, not deter- 

 mined how the chance can lead to definite and well pronounced 

 differences in the development of two identical cells which seem 

 to be submitted to equal surrounding conditions. Maximow' s 

 hypothesis attributes the differentiation to 'Gleichgewichtsstor- 

 ung,' which depends upon chance. It seems to me that the factor 

 of differentiation which so evidently appears in birds and reptiles, 

 and consists here in definite structural conditions, cannot be es- 

 sentially different in maimnals. However, these conditions are 

 more difficult to trace in mammals. 



The proliferation, of the mesenchyme and lymphoid hemo- 

 cytoblasts — and perhaps the development of lymphoid hemo- 

 cytoblasts at the expense of mesenchymal cells — ^seems to depend 

 upon stimulation by enzyme-like substances, which appear in 

 the organism of the embryo from the growing graft cells. 

 The circulating substances call forth an enormous production 

 of lymphoid hemocytoblasts through the whole spleen tissue. 

 In early stages, when the spleen tissue is homogenous and the 

 conditions correspond to those which are required for granu- 

 lopoiesis, only granular leucocytes are developed, and the dif- 

 ferentiation of small lymphocytes does not appear until struc- 

 tural conditions develop in the spleen under which normally 



