Regeneration of Epithclhun of Cornea, Hair, Hoof. 243 



The advancing margin of the epiderm may be seen as a bluish 

 white wavy zone, sometimes with a rosy tint from the hypersemic 

 substructures showing through. Sometimes in addition to the epi- 

 dermal growth at the margins of the lesion, islands of epithelium 

 may be observed in the midst of the new surface. These may origi- 

 nate from the remnants of the ducts of sweat glands or hair folli- 

 cles (the cells of which are practically identical with those of the 

 surface) which were left intact because of the superficial extent 

 of tlie loss of substance ; or may arise from epithelial cells separated 

 from the border and caused to adhere to the surface of the wound 

 by the application of a bandage. 



The proliferation of the epithelium does not stop until the free 

 surface of the lesion is completely covered. Epithelial scars are for 

 a long time devoid of pigment and in a dark skin the cicatrix is 

 conspicuous because of its whiteness. 



The corneal epithelium is ver}- quickly reformed after destruc- 

 tion, a circular loss of three millimeters diameter being perhaps re- 

 placed in the course of from thirty-six to forty-eight hours. The 

 cells at the margin, moving in by amoeboid power and flattening out 

 to form at first a protective single celled layer, spread out over the 

 surface ; these multiply, showing mitotic figures and multinuclear 

 examples, and build up the layers of corneal epithelium ; the cells 

 assume a cuboidal shape and the lesion is completely repaired. In 

 case of wounds of deeper extent or those perforating the whole 

 thickness of the cornea and involving the corneal connective tissue 

 and Descemet's membrane, the lesion is at first filled up by fibrin 

 (from tlie aqueous humor). The rapidly growing epithelium ex- 

 tends over this and forces itself into the depth of the wound like 

 a plug. The connective tissue is formed subsequently, and on the 

 posterior surface the endothelium of Descemet's membrane regen- 

 erates its single layer of cubical cells. A milk white spot remains 

 at the site, the result of cicatricial production by the newly formed 

 connective tissue. 



(Regeneration of the cornea has been exhaustively studied, especially 

 from an experimental standpoint, in animals; for details cf. Marchand.) 



Regeneration of hair can occur only in case the hair follicles 

 or portions of them remain. In all deep cutaneous lesions the cica- 

 trix is permanently smooth and devoid of hair. 



Regeneration of horny tissue of the hoof. After injuries to the 

 keratous envelope or after it has been ruptured from suppurations 

 of the corium the horny layer may be regenerated by proliferation 



