296 CELLS, TISSUES, AND ORGANISMS 



ous particles into the epithelium in various vertebrates, including 

 mammals. Bostroem (1928) believed that the cells were converted 

 into epithelial cells, a view shared by Levander (1950). The notion 

 in literature that epidermal cells might arise by transformation from 

 subepidermal elements during epidermal regeneration has been 

 touched upon by Naville (1924) for amphibian regeneration. And the 

 review of Fraisse (1885, pp. 44 and 45) shows that this idea appeared 

 in the earliest histological studies and received some support from 

 Virchow, Cohnheim, and Recklinghausen, among other well-known 

 histopathologists. Fraisse believed that the invading phagocytes re- 

 move intercellular debris and nourish the epidermal cells with the 

 products of digestion. He depicted these cells as then falling apart and 

 the fragments condensing to form new nuclei in the general plasm of 

 the epidermis. Ide-Rozas (1936) described intercellular bridges 

 formed with epidermal cells by invading lymphocytes in tadpole tail 

 regeneration. Andrew and Andrew (1949) reported the transformation 

 of infiltrating lymphocytes into epidermal cells and reviewed the in- 

 formation available then on wandering cells within the epidermis. 

 Andreasen (1952) reported, however, that invading lymphocytes de- 

 generate within the epithelium, and he suggested, among other possi- 

 bilities, that epithelium may serve as an organ of disposal of lym- 

 phocytes. Pinkus (1954) described the movement of particulate mat- 

 ter into the epidermis and noted: "The life-cycle of the epidermal cells, 

 which moves newly formed cells gradually outward, also causes any 

 extraneous matter that enters the epidermis from below to be moved 

 to the surface." He also presented a photograph (p. 598) showing 

 "elastic fibers incorporated in various layers of the epidermis over an 

 old scar, and . . . assumed that they are being eliminated in this man- 

 ner." Moreover, he also recorded the movement of granules of melanin, 

 absorbed by basal epidermal cells from subepidermal melanocytes and 

 carried thence to the surface. Freudenthal ( 1930 ) reported the move- 

 ment of amyloid and blood cells into epitheliomata. The growing epi- 

 thelium at first surrounded the amyloid-containing connective tissue; 

 then the connective tissue was dissolved, leaving the more resistant 

 amyloid, clumps of which were caught in the epithelium. The clumps 

 of amyloid were found always between the cells in all layers of the 

 epidermis including the outermost horny ones; they appeared to be 

 carried along in the movement of epidermal cells from the basal layers 

 to the surface. 



In one of our experiments we inserted carbon particles into the 

 blastema. Within a few days large concentrations appeared among the 

 epidermal cells. As histological sections showed, much of the carbon 

 accumulated in intercellular lacunae. Some was scattered among and 

 within the cells; the rest was located in the blastema. The movement 



