EPITHELIALIZATION 



68 I 



one another in any species, they fuse and movement ceases. This piienomenon 

 does not depend upon the mere presence of an obstruction. Chiakulas (1952) has 

 demonstrated that in amphibians, migration ceases only when homologous cell 

 contact is made. Epithelium from the intestinal tract, for example, fails to fuse 

 with that of the skin. There is either a piling up of cells at this junction or else 

 they migrate past one another. The presence of dead epithelium likewise fails to 

 inhibit migration (Lash, 1956). These findings are in complete accord with the 

 coaptation theory of Weiss (1950, 1955). No experiments have been done to test 

 this concept in mammals, however, clinical observations tend to support it. A 

 mechanical obstruction such as fine-mesh gauze on a granulating surface, fails to 

 block epithelial movement, and furthermore, epidermal cells are capable of 



.•>.2S^ 



Fig. 6. Photomicrograph showing a typical junction area of abdominal skin and colon 

 mucosa in an old colostomy. There is no true fusion and the abdominal epithelium is 

 thickened indicating a state of instability. Sk — skin; Muc — mucosa ;Jun — junction. 



(Hematoxylin and eosin, x 16). 



moving under an obstruction of dead cells such as a burn eschar. The extent of 

 migration is dependent not only upon the lack of proper contact for the peripheral 

 cells, but also upon an inherent limit beyond which epithelivim, for reasons still 

 obscure, fails to advance. Whether or not a homologous cell is the only type 

 which will produce cessation of migration in mammals is a matter for conjecture. 

 Although this specific point has not been investigated, there are many reports 

 in the literature indicating that mammalian epithelium reacts in a manner 

 identical with that of amphibians. A colostomy would seem to be one instance 

 where fusion of two entirely different epithelial cell types can occur; however, 

 histological examination of 35 colostomy stumps has failed to reveal a true 

 junction such as seen at the anal area (Washburn, 1957). Intestinal segments 

 transferred as a flap, and anastomosed to the urinary bladder exhibit overgrowth 

 by the transitional bladder epithelium at the line of junction (McLean and Pais, 



Lileralure p. 703 



