364 • WILLIAM H. COLE 



The artificial cultivation of epithelial cells (Loeb, '02; Harrison, 

 '10, '14; Holmes, '13, '14; Oppel, '13; Uhlenhuth, '14; Osowski, 

 '14; Hooker, '14 b, and Matsumoto, '18) has shown the migration 

 to be ameboid in character and demonstrated that the cells are 

 stereotropic. The presence of some solid body along which they 

 may migrate is necessary. Loeb ('20 b) interprets the reactions 

 seen in wound healing as essentially reactions to foreign bodies. 

 The stimulus of the foreign body causes surface changes in the 

 cells, leading to ameboid movement. Holmes ('14) had these 

 reactions in mind when he said, page 292, that ''cells of the epider- 

 mis have an inordinate tendency to lateral spreading." The time 

 necessary to restore the epidermis depends upon the size of the 

 wound. According to Loeb and Strong, a small wound in the 

 skin of the frog will be covered within two or three days. No 

 distinct increase in mitoses is seen until after the second day. 

 Experiments with wounds in tadpoles' skin show conditions simi- 

 lar to those found in the frog. The regeneration of the dermis, 

 on the other hand, is a much slower process. It proceeds first 

 by migration, and later by proliferation of cells, and requires 

 weeks for completion. Even after three months the boundaries 

 of the old wound can be distinguished. 



When an autotransplant is fitted into an area denuded of 

 integument, the migration of epidermal cells is reduced to a 

 minimum. In such cases the cells move centripetally from the 

 edges of the wound, and centrifugall}^ from the edges of the trans- 

 plant, until by fusion they form a connecting layer. The epi- 

 dermis of the graft and the host becomes continuous within three 

 hours. After several days the line of union is marked by an 

 hypertrophy of epidermal cells, forming a wedge-shaped mass 

 extending down towards the dermis. Figure 11 shows such a 

 formation, although of different origin. By the time the dermal 

 layers of the two regions have united, between three and four 

 weeks after the operation, this formation has disappeared, and 

 the normal thickness of the epidermis is restored. Subsequent 

 behavior of the graft depends upon its kind and its source, and 

 will be described later. 



