28 GEORGE T. HARGITT 



In cultures of skeletal muscle of chick embryos, Lewis ('17) 

 observed the growth of the cut ends of the muscle into em- 

 bryonic tissue without striations. Streeter ('17) observed a 

 de-differentiation of cartilage cells in the normal development 

 of the ear in human embryos, the cartilage of the membranous 

 labyrinth undergoing a despecialization and a return to the 

 condition of embryonic connective tissue. From experiments 

 with muscle, kidney, eye, thyreoid, and other organs, Champy 

 ('14) observes a characteristic behavior of the cells of the edge 

 of the culture where they receive abundant air and food. These 

 cells form such an indifferent mass as to resemble cells of a young 

 blastoderm; and this is true for all tissues, irrespective of their 

 source or the culture medium. Such a de-differentiation takes 

 place from explanted adult tissues as well as from embryonic 

 tissues. 



Danchakoff ('18) mashes adult spleen and grafts it upon the 

 allantois of embryos. The spleen tissue forms a syncytium of 

 embryonic character, and the cells forming the mass contain 

 endothehal cells of blood-vessels as well as reticular tissue of the 

 spleen. The syncytial mass develops and forms cells of a dif- 

 ferent sort than those which composed it. Danchakoff inter- 

 prets this, not as a de-differentiation, but as an expression of an 

 inherent capacity of the original cells to undergo a further 

 differentiation. Her point of view is as follows (p. 161) : 



The changes undergone by the living matter during development 

 are not always specific. They may lead to a specialization of tissue 

 without differentiating them specifically. The difference between 

 these two processes consists in that specialization does not imply a 

 limitation of potencies in the cell, wliile specific differentiation is a 

 process, by which the constitution of a cell is changed irrevocably and 

 its potencies to development are narrowed. The distinction between 

 the two processes would make it unnecessary to introduce a new 

 concept of dedifferentiation in order to understand certain phenomena. 



I am not comdnced that this view is simpler or more nearly 

 interprets the phenomena observed than the view of regressive 

 changes in the tissues and a later differentiation of these. Nor 

 does this opinion take into consideration the fact that de- 

 differentiation has actually been observed to take place; that is, 



