Scientia Sinica

No. 1 MA: FORMATION OF NEW EPIDERMAL. CELLS DURING WOUND-HEALING 125

cells are able to move, then they can migrate forward and become epidermal cells.

We have observed that the new epidermis is much thicker than the original, and the original epidermis has never changed its normal thickness and number of mitotic figures, and furthermore there is no sign of cellular movement in the epidermal cells. We can not agree with Holmes, because the evidences on which we formulate our theory, strongly prove against his explanation. We consider that the cellular movements observed by Holmes are possible. The question is what kind of cells he observed is able to move. Holmes worked with fresh and living material, on which it is very difficult to distinguish whether these active cells are epidermal cells or cells of other categories. In our fixed and stained specimens various cells can be easily recognized. We have seen many leucocytes and macrophages in the vicinity of the new epidermis on our specimens. These cells are able to make active movements. The leucocytes are arranged longitudinally before the growth of new epidermis (Plate I, fig. 1), but when the new epidermis appears, the leucocytes change their arrangement, in front of the growing epidermis, along the direction of growth of the epidermis to the position where the future epidermis should be. And before the epidermis penetrates into the cartilage, along the course of the growing epidermis a layer of leucocytes is already present in the firm tissue of the cartilage. These evidences strongly suggest that the active moving cells in front of the growing epidermis are leucocytes. On our specimens we have also observed macrophages, labelled with trypan blue, penetrating into the cartilage before the epidermis. We believe that the cells showing movement in front of the growing epidermis are leucocytes and macrophages.

(4) On the formation of new epidermal cells from cells derived from —

mesoderm,

As we have already referred to, Cameron, MacCardle and Andrew in their -papers claim that they have seen spindle-shaped cells, clear cells, or lymphocytes penetrating from dermis into epidermis and developing into epidermal cells there. They all believe that these cells penetrating from dermis are of mesodermal origin.

On our specimens we have seen conditions resembling their descriptions. But there is still another condition which should not be neglected and is of great importance. That is, in the process of wound-healing tissues in front of the growing epidermis change into disintegrating tissues. How and why these tissues disintegrate, and whether enzymes produced by the leucocyte fragments play a role in it, still remain as problems. But the fact is clear. These disintegrating tissues, as stated above, gradually develop into epidermal cells.