268 VERA DANCHAKOFF 



of the problems so unsuccessfully discussed year after year. 

 Such a new method for study of hematological and other biologi- 

 cal problems may be offered by the study of transplantations of 

 tissues on the allantois of an embryo and also in the study of the 

 changes, which occur in the tissues of the host after grafting. 

 The influence of identical environment upon different hemato- 

 poietic organs may be easily tested by this method. Trans- 

 plantations on the allantois of embryos were used by Murphy 

 and Rous (30) in their studies of transplantability of tissues to 

 the embryo and by Murphy (29) in his study of the factors of 

 resistance to heteroplastic tissue-grafting. Transplantations of 

 adult spleen and bone-marrow seemed to supply the embryo 

 with a refractory mechanism against heteroplastic grafting, 

 which in a normal embryo is lacking. These transplantations 

 as told are followed b}^ a considerable enlargement of the host 

 spleen. 



Every theory is a deduction of a limited number of facts, 

 but if the theory is true, it must apply to all analogous cases. 

 The enlargement of the embryonic spleen, mentioned above, 

 which soon was discovered to be a true hypertrophy, could not 

 be explained from the standpoint of the monophyletic school 

 as an isolated process. The monophyletic school, if true, had 

 to assume that changes in the embryonic spleen were accompanied 

 by analogous changes in other hematopoietic organs. Since 

 the hyperthrophy of the embryonic spleen has been involved 

 by a considerable proliferation of the stem cells, stem cells 

 in other hematopoietic organs admitted by the monophy- 

 letic school equal for all, must have been affected also and must 

 have proliferated. Since the structural environmental con- 

 ditions in the embrj^o are less differentiated than in the adult 

 organism, the reactions in the different embryonic hematopoietic 

 organs may be expected to be more homogeneous. As will be 

 seen later, this assumption, resulting from the premises of the 

 monogenetic conception of the blood origin, has been fully con- 

 firmed by the results of the experiments. 



In principle similar to the tissue cultures the grafting method 

 has a. great advantage over them. The allantois offers for the 



