288 VERA DANCHAKOFF 



cytoplasm. Numerous spleens of embryos, which were grafted 

 in early stages were transformed 4 to 5 days after grafting into 

 a tissue, similar to that represented on the figure 20. 



The ameboid cells appear here pressed closely together, are 

 often of polygonal form and fill up all the interstices between 

 the few sinuses. This uniform wdde-spread conversion of the 

 spleen anlage into a hemogranuloblastic tissue offers some 

 points of general interest. These changes show first, that the 

 action of the stimulus applied is intense and imperative. Prod- 

 ucts of metabolism appear in the blood current from the growing 

 graft cells. These substances incite an intense proliferation 

 of the mesenchymal cells in the spleen anlage and swiftly trans- 

 form the syncj^tial Plasmodium of the anlage into an accumu- 

 lation of ameboid cells, which proliferate and differentiate fur- 

 ther. The results may remind one of the experiments of Rous,'* 

 in which connective tissue cells became spherical under the action 

 of trypsin. 



As mentioned above the transformation of the mesenchymal 

 cells into lymphoid hemocytoblasts in the spleen anlage may be 

 universal, if stimulation is applied in early stages and merely a 

 few mesenchymal cells may remain undifferentiated, while in 

 normal development numerous mesenchymal cells persist and give 

 in course of time the reticulum tissue. MolUer (28, '11) describes 

 this tissue as a cellular syncytium with a fibrous net adjusted 

 to the cells. The changes in the experiments reported are so 

 intense (fig. 20), that it may be right to assume that numerous 

 cells, which under normal conditions would have passed into 

 the reticulum tissue, now become hemocytoblasts and differenti- 

 ate further into granulocytoblasts. This result can be taken 

 as a corroborative proof for the polyvalency of the mesen- 

 chymal cells, which may either differentiate into . granular leu- 

 cocytes or become a constituent part of the reticular tissue. 

 The general granuloblastic differentiation of the mesenchymal 

 spleen anlage is observed in embryos to which the stimulation was 

 applied before a development of vascularization has taken place. 



^ Personal communication. 



