Scientia Sinica

124 SCIENTIA SINICA Vol, V

epidermis has passed through tissues of different consistencies and healed to considerable thickness. In early stages, ie., 32 hours after the wound-making (Plate IV, fig. 1), though the new epidermis is very thick and grows very rapidly, there is no mitosis. At the same time, the original epidermis does not change to any extent its thickness and the number of mitosis. In later stages, when the healed epidermis has increased in thickness, it remains in the same conditions. For instance, when the healed epidermis reaches 3 or 4 times its normal thickness 120 hours after the wound-making, the pre-existing epidermis remains in its normal thickness without any increase of the number of mitosis. In the new epidermis, mitosis is occasionally found along the margin of the early formed epidermis and its number is scanty. In the epidermis just formed, there is no mitosis.

_ To sum up the conclusions of the investigations of the previous workers and our own observations, it is questionable to say that the new epidermis is formed by means of mitosis of pre-existing epidermal cells. If the new epidermis of such thickness were formed in a short time interval from mitotic cell divisions, there would be much more mitotic figures in the original or newly formed epidermis. But this can not be proved on our specimens.

(2) New epidermal cells do not come from the pre-existing epidermal cells by means of amitosis.

Since the theory of mitosis as the source of supply of new epidermal cells has met with difficulty, many investigators try to explain their origin in the light of amitosis. But these explanations are not readily acceptable either.

Thuringer'! concludes that the amitotic division of the cells below the granular layer is responsible for replacing the dead desquamated cells. This theory is not very sound, for these cells are approaching senility and death, have decreased their ability of multiplication, and are not capable of adding to the thickness of the spinous layer.

Patzelt’s conclusion based on the amitotic division of cells along the margin of the newly formed epidermis does not fit to our observations. On our specimens there are many young cell nuclei in the periphery of the growing epidermis (Plate II, Figs. 1, 2, & 4). From these young nuclei, the epidermal cells are formed. These young nuclei usually accumulate in groups (Plate Il, fig..1, B). When cytoplasm develops around these nuclei and before they separate into individual cells, they appear as binucleated or multinucleated cells. Therefore these binucleated or multinucleated cells do not represent stages of amitosis, but rather stages of development from disintegrating tissues.

(3) Further discussion on the migration theory of the origin of the new epidermal cells.

Holmes gives witness to the migration of the epidermal cells around the new epidermis. This evidence is easily acceptable, if the original epidermal