28 MYELOID METAPLASIA OF THE EMBRYONIC MESENCHYME. 



a syncytium, assume a spherical form as soon as the clot disappears and they remain 

 in a liquid medium. In this case, however, the trypsin may have attacked the thin 

 cytoplasmic processes and concurred in the isolation of cells. 



The syncytial connections of the cells seem to secure a common metabolism 

 for them and to hinder their further differentiation. The isolation of cells evidently 

 facilitates a direct interaction of the cells with the environment, and changes 

 ensue as a result of the interaction of the physico-chemical constituents of the cell 

 and of the environment. 



Suggestions were made by me as to the nature of the factors determining the 

 particular line of the hemopoietic differentiation of a mesenchymal cell after it has 

 been detached from the common syncytium (1908, 1916a, 1918a). The erythro- 

 poietic differentiation of a hemoblast seems to be closely associated with its intra- 

 vascular situation. The factors for the other lines of the hemopoietic differen- 

 tiation can at this time hardly be formulated with any degree of certainty. These 

 factors undoubtedly must be of a very definite nature, since now it is evident that 

 the same polyvalent hemoblast is the starting-point for the various lines of hemo- 

 poietic differentiation. 



The results of tissue culture, though very definite regarding the unlimited 

 proliferative ability of adult connective-tissue cells, so far has not demonstrated a 

 differentiative power in them. This is, of course, not an argument for a definitive 

 loss of such a power. The differentiating factors not being definitely determined, 

 we can not at will introduce them into our culture methods. To determine the 

 degree of the differentiative ability of a common adult connective-tissue cell is the 

 task of the future. A granuloblasts capacity of the adult reticular cell of the spleen 

 has been established by Danchakoff in grafts of adult splenic tissue on the allantois 

 (19186). A generalized granulopoietic differentiative power of the loose mesen- 

 chyme at 7 to 9 days of incubation is, I hope, established by the work which forms 

 the basis of this paper. Not only in the regions of the embryonic body, in which 

 normally some of the cells of the mesenchyme show a granuloblastic differentiation 

 at an earlier stage, could the mesenchyme be stimulated anew, but stimulation to 

 such activity could be effected in parts of the organism in which the mesenchyme 

 has never before shown such potency nor would, under normal conditions, ever 

 have exhibited it. On the basis of the present experiments and observations both 

 the intensity of the various lines of hemopoietic activity of the mesenchyme and 

 the process itself seem to be dependent, relative, provoques. 1 



The hemopoietic, in this case the granulopoietic, activity, being established as 

 a dependent differentiation (differentiatio relative/,, Roux; differentiation provoquee, 

 Brachet), the next step would be to determine the factors which may incite it. 

 However, a great uncertainty prevails as soon as we try to formulate more definitely 

 the causes of the development of the intensive granulopoiesis after grafts of adult 



1 I should like to arid a note which, though irrelevant to the present subject, is based upon the results of the present 

 work. The study of the history of the mesenchymal differentiation seems to add some probability to the opinion that immor- 

 tality and differentiation of living matter are phenomena usually excluding each other. A mesenchymal cell is immortal 

 as Ion;; as it remains as such; that is to say, as long as it retains its characteristic metabolism. Its di Eferentiation presupposes 

 a change in its constitution, a change which in the case of the hemopoietic differentiation of the mesenchyme finally leads 

 to a loss of its proliferative and assimilative powers — that is to say, to its death. 



