Scientia Sinica

No. 1 MA: FORMATION OF NEW EPIDERMAL CELLS DURING WOUND-HEALING 119

The new epidermis can cross the whole cartilageous plate in no more than 30 hours and grow into considerable thickness. Figure 1 of Plate VI is a photomicrograph of a specimen taken after 90 hours, and figure 2 of Plate VI after 104 hours from the same animal. On both specimens not a single mitotic figure is found in the new epidermis, and so ‘is the result on all serial sections. When the growing epidermis reaches the cartilage, leucocytes have already penetrated into the cartilage along the course of growth (Plate VI, figs. 3 and 4). The cartilage is destroyed at the place of penetration and the new epidermis is formed where the cartilage decomposés. The sequence of events is described as follows:

1. Leucocytes penetrate into the cartilage in the direction of the growing epidermis. Figure 3 of Plate VI is a photomicrograph of a complete view of the wound after 136 hours’ and figure 4 on the same Plate is a higher magnification of the rectangular area in fig. 3. On both sides of the cartilage leucocytes accumulate at the tip of the advancing epidermis and infiltrate the cartilage, more on the right side and less on the left. The leucocytes after entering the cartilage show a tendency to cross it. This indicates that the direction of the migrating leucoytes is. definite and along the same course, through which the epidermis is going to pass.

2. Leucocytes destroy the cartilageous tissue immediately after their penetration (Plate VII, figs. 1 and 2). At the same time they themselves disintegrate and mix together with the disintegrating cartilageous tissue. This is clearly shown in the second figure. .

3. New epidermis is formed at the place where the cartilage is under destruction. For a complete view the following specimens were sectioned perpendicularly to the wound and parallelly to the cartilageous plate. Figure

I of Plate III is a higher magnification of the rectangular area in fig. 4 of

Plate V. The upper purple part is the new epidermis, and the lower blue part is the cartilage. Between the epidermis and the cartilage are the disintegrating cartilageous tissue (blue fragments) and the disintegrating leucocytes (purple) mixed together (Plate III, fig. 1, A). Among the fragments there are groups of young cell nuclei (same figure, B) which form a network with the remaining cartilageous matrix, and are in close connection with the new epidermis.

Young cell nuclei further develop into young cells, continuous with the pre-existing epidermal cells and adding to the thickness of the new epidermis. In the same way, the disintegrating substances in front of them continue to form young cell nuclei, which, in turn, further develop into cells. Thus the epidermis increases in thickness, sometimes even reaching the cartilage (Plate III, Figs. 3 & 4), or entering the destroyed cartilage lacunae (Plate III, fig.5). Figure 4 of Plate III shows that the cartilageous tissue is disintegrating between the processes of new epidermal cells (Plate Ill, fig. 4, A). The cartilageous matrix has broken but still retains the normal stainability, and

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