MYELOID METAPLASIA OF THE EMBRYONIC MESENCHYME 



IN RELATION TO CELL POTENTIALITIES AND 



DIFFERENTIAL FACTORS. 



y 



By Vera Danchakoff. 



INTRODUCTION-POLYVALENT STRUCTURES-FACTORS OF THEIR FURTHER 



DEVELOPMENT. 



The gradual development of diversity in ontogeny can be brought about in 

 two different ways. It may result from merely a conversion of hidden diversities 

 into visible ones and be determined by factors found in the physico-chemical con- 

 stitution of the living matter itself. The environment in this case furnishes only 

 the necessary conditions for the realization of the already existing diversity. Ac- 

 cording to Roux, a similar process can be called self-differentiation ( "different i:iti<> 

 sui," Roux; "differentiation spontanee," Brachet). Structures, anlages, or cells 

 developing in this manner are specific; that is to say, under any non-injurious con- 

 ditions they will transform into definite products in a predetermined way. Such 

 structures are univalent or unipotent and possess narrow and well-limited potencies 

 which they fully realize in their development. 



On the other hand, the diversity appearing during ontogeny may be deter- 

 mined by factors lying partly or fully outside of the developing structures. Such 

 changes or differentiations are called by Roux dependent differentiation ("differ- 

 entiatio relativa," Roux; "differentiation provoquee," Brachet). In this case the 

 changes in the living matter may be considered as reactions, the results of which 

 will depend upon external agents . They will be different in compliance with different 

 environmental factors. The structures, primordia, or cells are in this case poly- 

 valent, because they may develop along different lines. The living matter in this 

 case may become a starting-point for various lines of development; the determining 

 factors of the actual line of its development, however, lie outside of it, in the environ- 

 ment. In this case the actual line of development realized by the living matter 

 is merely a part of its total potencies. It is to similar structures that the following 

 words of Brachet can be so well applied: "Apres que le naturaliste a constate ce 

 qu'un animal est et fait, il lui faut rechercher ce qu'il est en outre capable d'etre et 



de faire." 



Researches along these lines have taught us that not all of the typical develop- 

 ment in the organism is a spontaneous differentiation, but that it may be determined 

 by environment including the correlations of its organs. These correlations may 

 inhibit some or even the greater part of the potencies of a structure or directly 

 determine its actual line of development, which might be a fraction only of what it is 



