EQUIVALENCE OF HEMATOPOIETIC ANLAGES. I. SPLEEN 267 



poietic organs in the embryo all contain elements, which react 

 in analogous manner to the appearance of these substances. 

 The fact that the proliferating cells exhibit a more homogene- 

 ous differentiation in the various embryonic organs than in 

 adult organism may be accounted for by absence of specific 

 structural environmental conditions in the embryonic organs. 

 Though chiefly concerned in histogenesis of the blood cells, the 

 present paper may have a close bearing on the immunity 

 problem in establishing a connection between introduction of 

 heterogeneous substances and reactions exhibited by hemato- 

 poietic tissue. 



The grafting of an adult spleen on the allantois of the embryo 

 produces changes similar to those described in myeloid meta- 

 plasis, and in principle are similar in different hematopoietic 

 organs. However, these changes seem to be differently ex- 

 hibited in hematopoietic organs at different stages of embryonic 

 development. The stimulating agent may differently influence 

 various cell groups in the hematopoietic organs at different 

 stages of their development and leads often to the appearance 

 of peculiar pathological processes. There appear in different 

 organs characteristic changes depending upon their structural 

 peculiarities which will be studied and described consecu- 

 tively. As the most conspicuous phenomenon is the appear- 

 ance of an enormous hypertrophy of the spleen, therefore a 

 study of this organ will give a basis for further investigation 

 of the changes undergone by other hematopoietic organs, in- 

 cluding the mesenchyme of different parenchymal organs. A 

 study of changes in the circulating blood of the embryo, as well 

 as a study of the growth and differentiation of the grafts them- 

 selves will follow. 



2. METHODS OF INVESTIGATION AND TERMINOLOGY 



It has been shown in the introduction that the usual methods 

 of investigations applied to the problem of the origin and the 

 mutual relationship of blood cells failed in the attempt of solving 

 them. There must be found new methods for the elucidation 



