Scientia Sinica

No. 1 MA: FORMATION OF NEW EPIDERMAL CELLS DURING WOUND-HEALING: 115

tinguished: the upper is scab tissue, and the lower is normal tissue. The scab is again divided into two regions, with blood clot lying above and granulation tissue below. In the granulation tissue it can be observed that

the collagenous fibres are arranged parallel to the surface of the cartilage, and ~

are continuous with those from the normal tissue. Leucocytes, mostly neutrophils, migrating from the normal tissue below, fill in columns between the bundles of collagenous fibres in the scab to indicate the direction of their migration. At the same time their shape has changed from the original roundness into narrow and. slender rectangles, as they go into the space between the bundles of collagenous fibres in the scab. They crowd here in a large number and in close contact; consequently they form a long column of leucocyte-chain between the longitudinally disposed collagenous fibres. The latter arrangement is of particular interest, for after the appearance of new epidermis their arrangement changes from the longitudinal direction into one of growth of new epidermal cells. The change of arrangement indicates that the migration of the leucocytes has changed its course.

2. The process of formation of new epidermal cells under scab

(1) A general survey of the regenerating epidermis. Around 24 hours after the cutting, new epidermis grows under the surface of the scab. The growth of the new epidermis is considerably rapid’ and as a result of it, sometimes the growing epidermis is much thicker than the original, but mitotic cell division has never been found in the region of the newly formed epidermis, save only a few mitotic figures observable in the basal and spinous layers of the pre-existing epidermis.

On the specimen taken off from the wound after 36 hours, (Plate IV, fig. 1), the newly formed epidermis grows from A and B towards the centre: Figure 2 on Plate IV is a highly magnified photomicrograph of area A in figure 1. It shows that the newly formed epidermis consists of more layers of cells than the original, and no mitotic figure can be observed. Serial sections have been traced forwards and backwards, giving, however, the same results.

Another unique event goes along with the advancement of the growing new epidermis, 1.e., the transection of the longitudinally disposed collagenous fibres running from the scab to the normal tissues by the advancing new epidermis. The details of this change are described under (3).

(2) Changes due to the infiltration of leucocytes under the scab. Leucocytes undergo two kinds of changes in front of the growing epidermis, one being the change of direction of their arrangement and the other their disintegration. In the-early stage (13 hours, Plate I, fig. 1) leucocytes migrate towards the wound and are arranged longitudinally, but later (32 hours, Plate IV, fig. 4), when the new epidermis, D, grows from right to left, the leucocytes in front of the newly-formed epidermis begin to appear, in the direction of