Scientia Sinica

122 SCIENTIA SINICA Vol. V

he attributes the source of new cells chiefly to amitotic divisions, for under favourable dietary conditions cells under amitotic division can be observed around the margin of the growing epidermis.

(3) Holmes’! considers that there is no mitosis in the early growing stage of epidermis. He has found cells in the growing epidermis migrating from the original epidermis. He mentions in his paper that he has directly observed amceboid movement in some of epidermal cells near the growing epidermis in larval and adult amphibians. This shows that the new epidermal cells are migrating from the pre-existing epidermal cells by cellular moyement. Besides, many other authors give the same explanation, though they have never witnessed any amceboid movement of the cells.

The ability of cells to move was first described in 1875 by Kleb®” and Peters’), and later proved by Arey” and Herrick”). Others try to prove it with experiments. For instance, Poynter! made a wound on chick ectoderm. While healing, he observed cells along the margin of the wound changing to undifferentiated cells. He claimed that the undifferentiated cells were capable of making amceboid movement during the healing of the epidermis. He mentioned mitosis appearing in the later stage of wound-healing. Born”? considered that in wound-healing on the epidermis of amphibians the number of the cells produced from mitosis could not reach that of the newly formed epidermal cells. The newly formed epidermis is a thin membrane of squamous cells which migrate from the pre-existing epidermal cells by amoeboid movement. Hartwell! also mentions that the layer of squamous cells covering the surface of surgical wounds is formed by amcboid movement of cells from the spinous layer of the original epidermis. Mitosis can only be found after these cells have formed the new epithelium and further differentiated into epidermis.

(4) Besides, there is another school of investigators who are not satisfied with the evidences that the new epidermal cells come from the pre-existing epidermal cells and give other explanations.

In normal and irradiated epidermis of the frog, Cameron”” has observed spindle-shaped mesodermal cells entering the epidermis and being converted into epidermal cells. MacCardle, Engman and Engman', in studying neurodermatitis, have discovered that during recovery, there are many clear cells in close relation with the new epidermal cells. When a wound just heals up, there are many poorly stained cells in the basal and spinous layers undergoing mitotic divisions. Many clear cells penetrate into the basal layer but they are also found in the dermis. They emphasize that the clear cells are rather related to the function of regeneration of the epidermis than the formation of pigment cells. Clear cells are derived from the dermis.

_ W. Andrew and N. V. Andrew!!! have examined the epidermis of men and rats. The results make them believe that mitosis can not make up the