296 VERA DANCHAKOFF 



There were repeatedly described cases of myeloid metaplasis, 

 in which the chief character was represented by a development of 

 granuloblastic tissue and a consequent suppressing of lymphoid 

 tissue. For the true understanding of similar conditions one 

 may remember that granulocytoblasts only might have under- 

 gone a stimulation. Granulocytoblasts are specifically differ- 

 entiated cells, the proliferation faculty of which may be aroused 

 by specific agents, which could leave inert the other offspring 

 of the common stem cells and the stem cells themselves. 



The general proliferative reaction of the younger undifferen- 

 tiated cells to the stimulation observed in the present experiments, 

 no matter where these stem cells are localized^ — whether in the 

 pulpa or in the follicle — point again to a similarity of these cells 

 in their simultaneous reaction to the same factor. It seems, 

 therefore, that to morphological and histogenetic data, new 

 data of uniform biological reaction may be added as evidence for 

 the uniformity of the hemocytoblastic cell group. This bio- 

 logical reaction consists in an intense heteroplastic and homo- 

 plastic multiplication as response to the stimulus. Isomorphism, 

 isogenesis and isodynamism under equal conditions, evidently 

 associate in the existence of the lymphoid hemocytoblasts. 



C. CONCLUSIONS 



On the basis of observations and experiments described in the 

 present paper some data may be won concerning (1) the histo- 

 genesis of the blood cells in the spleen, (2) the cell differentiation, 

 and (3) the general meaning of the myeloid metaplasis. 



The data concerning the histogenesis of the spleen cells were 

 recapitulated at the end of every section, therefore, I may here 

 merely outline the general conclusions. 



The chief results of the study of normal spleen development 

 is the statement of a regular and unalterable relation between 

 differentiation of certain kinds of blood cells and structural 

 environmental conditions. 



These results have been conf rmed by the experimental part 

 of the work. Moreover it has been shown experimentally that 



