278 Regeneration of the Skin of tlie Frog 



in cases where the connective tissue underlying the hypertrophied epithe- 

 lium has regenerated perfectly. These degenerations are accompanied 

 by cell-inclusions, which are sometimes almost indistinguishable from 

 red blood corpuscles. It was found by L. Loeb, 02, that epithelial 

 cells in regenerating mammalian skin do actually take up blood cor- 

 puscles and other solid particles. 



In one case, 14 days after the operation, a development of epithelial 

 pearls had taken place in the regenerating and hypertrophied epithelium 

 of a frog which had been kept in a solution of atropine. Epithelial 

 pearls could also occasionally be seen in the guinea-pig epithelium which 

 was growing in agar. We believe that these morphological changes do 

 not indicate a tendency of this epithelium to assume a carcinomatous 

 character, an interpretation which has been given to similar formations 

 by certain investigators. 



It Avas not imcommon to find processes of the regenerating epithelium 

 penetrating the coagulum beneath the wound. They may advance in 

 different directions, either in one layer or in several layers of cells. 

 Often the fibrin fibers are merely bent inwards by the advancing epithe- 

 lial cells, but they are sometimes actually perforated by the epithelium. 



This penetration of the fibrin may occur within twenty-four hours 

 after the operation, and processes in the epithelium may be observed 

 in the fibrin as late as ten days. The cells in these processes multiply 

 mitotically, and mitosis occurs in the epithelium lying directly on the 

 coagulum, also, just as was the case in the experiments of Loeb for epithe- 

 lium penerating coagulated blood-serum and agar. 



Regeneration of the Cutis. — Though regeneration in the epidermis be- 

 gins within a few hours after the operation, it does not appear in the 

 cutis until the fifth day. When once started, however, the regeneration 

 is frequently rapid. After six days, or a day or so from the beginning 

 of regeneration in the cutis, a small defect may be entirely filled by con- 

 nective tissue and capillaries; at later periods it was sometimes impos- 

 sible to detect the wound. The position of the former wound was recog- 

 nized in one case at the end of three weeks only through the presence of 

 small mononuclear cells (lymphocytes?) in the connective tissue. In 

 another case, taken thirty-four days after the operation, masses of small 

 round cells in the cutis indicated the previous existence of a wound; the 

 connective tissue had not regained its typical structure. 



In a number of cases where the defect in the cutis was comparatively 

 large there was either no regeneration of connective tissue or it was more 

 or less incomplete. Though, in many cases, a variable number of leuco- 

 cytes were frequently present in the fibrin, this was not always the ease, 



