30 MYELOID METAPLASIA OF THE EMBRYONIC MESENCHYME. 



a production of granular leucocytes in the bone-marrow. During infection, appear- 

 ance in the organism of both homologous and heterologous proteins takes place. 

 This never occurs under normal conditions, amino-acids only being conveyed to the 

 different tissues of the organism. It is difficult in this case to determine whether 

 the stimulation of granulopoiesis is in some way connected with one of the two 

 factors, or with both of them. Furthermore, the appearance in the organism of 

 proteins or of phases of their digestion not completely reduced to their "building- 

 stones," the amino-acids, necessarily calls forth, as shown by Abderhalden, a 

 liberation of enzymes into the circulation, their presence here being easily deter- 

 mined by the dialyzation method. Not only can the appearance of proteins directly 

 stimulate the mesenchyme, but, what is even more probable, the isolation of the 

 mesenchymal syncytium into separate cells can be effected by a partial digestion 

 of the thin cytoplasmic processes by the action of circulating enzymes. Support 

 to such a view may be found in the work of Rous, in which it is shown that a tryptic 

 action of short duration will digest the clot of the medium and probably the thin 

 syncytial processes of the cells growing in it, but not the cells themselves. How 

 much probability such explanation has in itself future work will show. It is sug- 

 gestive, however, that myeloid metaplasia, different as its etiology may appear, 

 is always preceded by destruction inside of the organism of living material—/, e., 

 by the appearance in the organism of dead cells, or particles of unsplit protein, and 

 therefore (according to Abderhalden) by liberation of enzymes. 



If now we return to the analysis of factors involved in the production of the 

 extensive myeloid metaplasia in my embryonic material, we always find the graft 

 of adult splenic tissue to be not only the center of growth of living material, but 

 also to include smaller or larger blocks of necrotic masses — i. c, of masses of unsplit 

 protein. It seems, even, that the larger these accumulations of necrotic tissues 

 are the more intensive becomes the dissolution of the syncytial connections of the 

 mesenchyme in the embryonic body and its subsequent extravascular granulopoie- 

 sis. In numerous cases its action may become a vicious circle, the intensive granu- 

 lopoiesis itself leading to the appearance of new necrotic centers (spleen, muscles, 

 loose connective tissue, etc.), thus strengthening the initial stimulation. 



Effects upon the embryonic mesenchyme of grafts of different tissue will be 

 discussed in a special paper. It is, however, remarkable that only grafts of those 

 tissues will produce an extensive stimulation of the embryonic mesenchyme which 

 for a certain length of time include centers of necrotic tissue. 



There remains but little probability that factors for the mesenchymal stimula- 

 tion in the embryo may be found in the various processes constituting the growth 

 of adult splenic tissue in the graft. The proliferating mesenchyme of the grafted 

 splenic tissue itself undergoes granuloblasts transformation; it is, therefore, itself 

 under the control of the factors governing the granuloblast^ differentiation of the 

 embryonic mesenchyme. 



January 1918. 



