266 VERA DANCHAKOFF 



lysins stimulate the hematopoietic organs and induce intense 

 proliferation of their cells. 



Antibodies are regarded as being specific and may influence 

 only cells in which they find adequate receptors. Dr. Flexner (17) 

 has shown an apparent lack of specificity both of certain kinds 

 of leucolytic sera to different hematopoietic organs and of differ- 

 ent leucolytic sera to one definite hematopoietic organ. The 

 spleno- lympho and marrow-lytic toxins, each of them acted in 

 a stimulating manner upon all the hematopoietic organs, — hence 

 the antibodies of the leucolytic sera evidently found cells with 

 adequate receptors in all hematopoietic organs. These cells 

 under the influence of certain amboceptors responded by com- 

 mon proliferation in different hematopoietic organs. 



The results of the experiments cited offer a further corro- 

 boration of the monogenetic conception of blood development. 

 The histological studies established in all the hematopoietic 

 organs — the presence of cells, of which the morphological struc- 

 ture seemed to indicate a great potency for differentiation and 

 proliferation. The embryogenetic studies pointed out these 

 cells, as the true stem cells, common to all the hematopoietic 

 organs and endowed with faculty to intense polyvalent differen- 

 tiation. Finally, studies on stimulation of the hematopoietic 

 organs by agents, which were supposed to be specific, seemed 

 to indicate in all the hematopoietic organs the presence of 

 cells, which respond to each of these stimuli by a common 

 proliferation. 



The experiments used in the present work are closely related 

 to the experiments referred to above. The present study, 

 however, is connected exclusively with the stage of antibody 

 production. The requirement of heterogenicity of tissues might 

 be found in the differences of the tissues in the adult organism 

 and the embryo. (Even the morphological structure of the same 

 kind of cells, for example the hemocytoblasts, changes some- 

 what with age, the cells undergoing an ontogenetic development.) 



The intense proliferation, exhibited after the appearance 

 in the embryo of heterogeneous substances by all the embryonic 

 hematopoietic organs seems to indicate that different hemato- 



