Leo Loeb and E. M. Strong 279 



and it seems unlikely that such failures in regeneration were due entirely 

 to infection by micro-organisms. Those connective-tissue cells that ad- 

 vance into the fibrin quite frequently degenerate; they swell up and 

 their nuclei are destroyed by chromatolysis. 



In the case where the cutis did not heal, masses of leucocytes were 

 found in the epidermis at some places. It has not been possible to decide 

 whether this condition was due to an invasion of leucocytes into the 

 epithelium after which a destruction of epithelial cells followed, or 

 whether on the contrary a degeneration of the epithelial covering, caiised 

 by imperfect healing of the connective tissue, was the primary factor, 

 resulting, secondarily, in an immigrating of leucocytes. 



A number of small gland tubules were seen under the regenerating 

 epidermis in three wounds, at the end of the third week in two cases, and, 

 after 3-1 days, the third one had gland cells dividing mitotically. In 

 these cases only the most superficial portion of the cutis had been removed 

 with the epidermis. In the skin adjoining the wound, typical large 

 glands were present. It seems likely that we have here a regeneration 

 of gl'ands, but, as in these cases only a small part of the cutis had been 

 removed with the epidermis, it has been impossible to determine whether 

 or not such glandular regeneration starts from gland cells left in that 

 part of the cutis not removed, or in the epidermis itself. 



The Chromatopliores of the Regenerated Tissue. — There has been no 

 unanimity of opinion concerning the origin of chromatophores, or 

 pigment-bearing cells with ramifying processes, in the epidermis. The 

 earlier views, that they are immigrated leucocytes, or common connec- 

 tive-tissue cells that have invaded the epidermis, have been more or less 

 generally abandoned. At present two views are held, either (1) that all 

 chromatophores of the body are of common mesodermic origin, or (3) 

 that the chromatophores of the epidermis are simply modified epithelial 

 cells. This latter view has been held l)y a number of writers, including 

 Kodis, Jarisch, Post, Kromayer, and ourselves, Loeb, 97, Strong, 02. 

 According to the first view, all chromatophores, at a certain stage of 

 embryonic development, are differentiated from ordinary connective- 

 tissue cells, and a part of them grow secondarily into the epidermis. 

 These are called melanoblasts by Ehrmann, 96, the main exponent of 

 this idea. Eibbert, 01, holding the same opinion, believes that the pig- 

 mented tumors, arising from pigmented naevi of the skin, are composed 

 entirely of such cells, and accordingly calls them Melanomata to designate 

 their genetic difference from other tumors. 



One of the aims of our studies was to compare the behavior of the 

 chromatophores and the pigmentation of the regenerating frog skin with 

 the pigmented skin of the guinea-pig during regeneration. 



