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phones increases in the pericellular fluid, the regeneration 

 of tissue cells begins. 



These facts help us to understand better the mechanism 

 of repair in the organism. From numerous experiments C a r- 

 rel has shown, that an aseptic wound made on an adult 

 animal begins to cicatrize after two or three days. 



If regeneration is a direct consequence of the loss of 

 tissue, the healing of a wound, perfectly protected against 

 irritation from outside, should take place normally. Sucli 

 wounds were found by Carrel not to heal. The regenerative 

 stimulus does not depend upon the tissue tension according 

 to Ribbert. If the wound, instead of being protected 

 against external irritation, was covered with a slightly ir- 

 ritating dressing, such as turpentine, a few staphylococci or 

 dry gauze, cicatrization commenced within the two days. 

 The action of the irritants is explained by C a r r e 1 in the 

 following way, that it brings about the invasion of leucocytes. 

 The healing of the wound is therefore due to the trephones 

 secreted by the invaded leucocytes. The irritant does not 

 act on the tissue cells themselves as Y i r c h o w believed in 

 his assumption of the initiation of cicatrization from an 

 inflammatory irritant, but causes the embryonic substances 

 of the organism to be brought to the wound in the form of 

 leucocytes. 



C arret mentioned that regeneration in lower organisms 

 may also be determined by certain cell secretions. L o e b '"o) 

 has observed that in t u b u 1 a r i a, endodermic cells gather' 

 at the end where a new polypus is about to form, and pro- 

 bably set free substances necessary for the proliferation of 

 the cells. As mentioned before H a b e r 1 a n d t -^^) has ob- 

 served that substances secreted by the leptom cells in 

 certain plant tissues initiates the cell division of the plant 

 cells. He calls these substances -wound-hormones". 



From these experiments w^e have learned about proces- 

 ses which play an important role for the cicatrization, re- 

 generation, transplantation and related phenomena. We have 



