258 VERA DANCHAKOPF 



contradictory conclusions regarding the structure of the blood 

 tissue were made on the basis of this method. 



The embryo-genetic method may give more definite results 

 if used exhaustively. The gradual appearance of the different 

 blood cells becomes a reliable criterion for the judgment of the 

 mutual relationship of the blood cells. The discovery of young- 

 er cells, which first develop in the embryo and the study of 

 their gradual differentiation may be of great help in the identifi- 

 cation of the blood cells in the more complex structure of the 

 hematopoietic organs in the adult organism. However, the 

 demand for strict exhaustiveness is often disregarded and leads 

 to gaps, which are filled by a number of more or less keen inter- 

 pretations of the investigator. The omission of the study of 

 the first stages in the development of blood cells led investigators 

 to an admission of specific stem cells for various differentiation 

 products— Denys, (8), Bizzezero (3), and others. How- 

 ever, the recent histogenetic studies made by different investi- 

 gators on various animals gave similar results. Bryce (2), 

 Danchakoff (9), Maximow (25), Mollier (28), Haff .(18), all 

 admitted that the different blood cells are derived from mesen- 

 chyme of mesodermal origin, and that the various blood-forming 

 organs developed autochthonously at the expense of mesen- 

 chymal cells of which the various differentiation may depend 

 upon external physico-chemical agents. 



Studies of pathological changes in hematopoietic organs did 

 not contribute greatly to the solution of the problems of hemat- 

 ology. The complexity in the mutual relationship of the blood 

 cells was recognized and led many pathologists to take re- 

 course to embryo-genetic studies, (Fischer (16,) Schridde (38), 

 Schmidt (39) and others) . The conclusions drawn from studies 

 made by these methods were based upon the existence of 

 morphological similarities and differences between various blood 

 cells. They lead to more or less plausible probabilities but do 

 not determine irrefutably the functional dynamics of the various 

 blood cells in different hematopoietic organs. 



