256 VERA DANCHAKOFF 



decade. One is naturally inclined to doubt, whether the small 

 variations in the innumerable schemes are as important, as 

 they are represented in the deductions of different workers. 



The fundamental problems of hematology have a close bear- 

 ing upon practical medicine as well as on the general problems 

 of biology. Wilson and Conklin (6) especially, and many other 

 biologists established as a fact the gradual segregation of differ- 

 ent chemical materials collected in the egg. This is accomplished 

 by a range of cleavages beginning in certain eggs at the first 

 cleavage, in others delayed to later stages. As a result there 

 appear groups of cells, different in their constitution and there- 

 fore possessing different potencies for differentiation. These 

 cell groups proliferate and give tissues, which in their own differ- 

 entiation may exhibit a great complexity. The diversity in the 

 products of differentiation may be due either to differences in 

 the physico-chemical constitution of the cells, or to differences 

 in environmental conditions. One of the important questions 

 of biology consists in determining the limit to which each of the 

 agents cited has an active role. Does the segregation lead to 

 a production of a definite number of uninterchangeable blood 

 stem cells, of which the differences in the chemical structure imply 

 a definite metabolism and their further specific development? 

 Or does the process of segregation lead to a production of one 

 group of numerous homogeneous primitive blood cells, which 

 under different conditions in the embryo, as well as in the adult 

 organism, split off variously differentiated cells? This problem 

 was differently conceived by the monophyletic and polyphyletic 

 schools. 



The importance of a true conception of this fundamental 

 problem of hematology for practical medicine is obvious'. The 

 uninterrupted, everyday destruction of the blood elements is 

 too often accompanied by a failure of regeneration in the organ- 

 ism. A whole range of stimulating agents for blood regener- 

 ation was found empirically. Still the success of interventions 

 in similar cases as well as of interventions in various other 

 deviations from the normal course of hematopoiesis (leukaemias) 

 depends greatly upon a clear understanding of the action of the 



