270 ON GKOWTH AND OVERGROWTH 



must contain elements of an embryonal character, or at least 

 such elements as can take on that character." And again, in 

 the same article : " These cells then are dependent upon the 

 same law as, in the embryo, is the formation of organs." 1 



But in the general portion of his great Handbuch der Gewebe- 

 lehre des Menschen, published in 1889, I cannot find that he 

 again refers to this principle, hence it would appear that he did 

 not realize its wide application. 



Thus, although the law when once grasped is simple, almost 

 to the verge of being a truism, it merits being stated for once in 

 as clear terms as possible that its high importance may be fully 

 recognized. 



Regeneration 



Applying now these considerations to certain pathological 

 conditions, it is in the first place necessary to say but little 

 concerning pathological regeneration and repair, for I have 

 already applied some of the facts gained from a study of such 

 regeneration in the development of my argument. This much, 

 however, may be said, that the more we study the regeneration 

 of various tissues, the more we see that the phenomena of the 

 process fall into place in consonance with the law above laid 

 down. The cells of a regenerated tissue are derived from the 

 pre-existing cells (and mother cells) of that particular tissue, 

 and the more highly differentiated the tissue the less is its capacity 

 for regeneration. 



Of all cells, those which are the most highly differentiated, 

 namely the nerve cells, show the least capacity for proliferative 

 regeneration ; there is a remarkable lack of evidence of fully 

 developed nerve cells having been observed in the process of 

 mitosis, and, corresponding with this lack, when we consider the 

 histological basis of motor, sensory, and mental acts, it is a 

 priori hard, if not impossible, to conceive a given cell in any of 

 the higher nerve centres undergoing proliferation without there 



1 Kolliker : " In alien Fallen, in denen ein Organ oder ein Gewebe filing 

 ist aich wieder zu erzeugen, muss dasselbe Elemente von embryonalem Charakter 

 enthalten oder wenigstens solohe, die diesen Charakter anzunehmen im Stande 

 sind." " Diese Zellen bedingen dann nach denselben Gesetzen, wie beim 

 Embryo, die Organgeetaltung " (" Die Bedeutung der Zellenkerne fur die 

 Vorgange der Vererbung," Zeitschrift f. wise. Zool. vol. xlii., 1885, quoted 

 by Barfurth " Zur Regeneration der Gewebe," Arch. f. mikrosk. Anal, xxxvii., 

 1891, p. 424). 



